Cell and it's organelles

INTRODUCTION

CELL

All the living  things are composed  of cells.  A  single  cell is the smallest unit that has all the characteristics of life.

Cell  is  defined  as  the  structural  and functional  unit  of  the living body.

General Characteristics of Cell Each cell in the body:

1. Needs nutrition and oxygen

2.  Produces its  own energy necessary for  its  growth, repair and other activities

3.  Eliminates carbon dioxide and other metabolic wastes

4.  Maintains  the medium, i.e. the environment  for its survival survival.

5.

6.  Shows immediate response to the entry of invaders like bacteria or toxic substances into the body Reproduces  by division.  There  are some exceptions like neuron, which do not reproduce.


TISSUE

This  is  defined  as  the  group  of  cells  having  similar function.

There are many types of tissues in the body.
All the  tissues  are  classified  into  four  major  types  which  are called the primary tissues.
The primary tissues include:

1. Muscle tissue (skeletal  muscle, smooth muscle and cardiac muscle)

2. Nervous tissue (neurons and supporting cells)

3. Epithelial  tissue (squamous, columnar and cuboidal epithelial cells)

4. Connective  tissue  (connective tissue proper, cartilage, bone and blood).

ORGAN

An organ is defined as the structure that is formed by two or more primary types of tissues, which execute the functions of the organ. Some organs are composed of all the four types of primary tissues.

The organs are of two types, namely tubular or hollow organs and compact or parenchymal organs.

Some of the organs in the body are brain, heart, lungs, stomach, intestine, liver, gallbladder, pancreas, kidneys, endocrine glands, etc.

SYSTEM

The organ system is defined as group of organs that work together to carry out specific functions of the body.
Each system performs a specific function.

Digestive system is concerned with digestion of food particles.

Excretory system eliminates unwanted substances.

Cardiovascular system is responsible for transport of substances between the organs.

Respiratory system is concerned with the supply of oxygen and removal of carbon dioxide.

Reproductive system is involved in the reproduction of species.

Endocrine system is concerned with growth of the body and regulation and maintenance of normal life.

Musculoskeletal system is responsible for stability and move ments of the body.

Nervous system controls the locomotion and other activities including the intellectual functions.

STRUCTURE OF THE CELL

Each cell is formed by a cell body and a membrane covering the cell body called the cell membrane.
Cell body has two parts, namely nucleus and cytoplasm surrounding the nucleus.
Thus, the structure of the cell is studied under three headings:

1. Cell membrane
2. Cytoplasm
3. Nucleus

 CELL MEMBRANE

Cell membrane is a protective sheath, enveloping the cell body.
It is also known as plasma membrane or plasmalemma.

This membrane separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF).
The cell membrane is a semipermeable membrane. So, there is free exchange of certain substances between ECF and ICF. Thickness of the cell membrane varies from 75 to 111Å.


COMPOSITION OF CELL MEMBRANE

Cell membrane is composed of three types of substances:

1.Proteins (55%)
2.Lipids (40%)
3.Carbohydrates (5%).


STRUCTURE OF CELL MEMBRANE

On the basis of structure, cell membrane is called a unit membrane or a three-layered membrane.

The electron microscopic study reveals three layers of cell membrane, namely;

» one central electron-lucent layer and
» two elec-tron-dense layers.

The two electron-dense layers are placed one on either side of the central layer.

The central layer is a lipid layer formed by lipid substances.

The other two layers are protein layers formed by proteins.
Cell membrane contains some carbohydrate molecules also.

FUNCTIONS OF CELL MEMBRANE

1. Protective function: Cell membrane protects the cytoplasm and the organelles present in the cyto-plasm

2.  Selective permeability: Cell membrane acts as a semipermeable membrane, which allows only some substances to pass through it and acts as a barrier for other substances

3.  Absorptive function: Nutrients are absorbed into the cell through the cell membrane

4.  Excretory function: Metabolites and other waste products from the cell are excreted out through the cell membrane

5.  Exchange of gases: Oxygen enters the cell from the blood and carbon dioxide leaves the cell and enters the blood through the cell membrane

6.  Maintenance of shape and size of the cell: Cell mem-brane is responsible for the maintenance of shape and size of the cell.

CYTOPLASM

Cytoplasm of the cell is the jellylike material formed by 80% of water. It contains a clear liquid portion called cytosol and various particles of different shape and size.
These particles are proteins, carbohydrates, lipids or electrolytes in nature.
Cytoplasm also contains many organelles with distinct structure and function.

Cytoplasm is made up of two zones:

1.Ectoplasm: Peripheral part of cytoplasm, situated just beneath the cell membrane

2.Endoplasm: Inner part of cytoplasm, interposed bet ween the ectoplasm and the nucleus.

ORGANELLES IN CYTOPLASM

Cytoplasmic organelles are the cellular structures embedded in the cytoplasm. Organelles are considered as small organs of the cell. Some organelles are bound by limiting membrane and others do not have limiting membrane.

Each organelle is having a definite structure and specific functions.

ORGANELLES WITH/WITHOUT LIMITING MEMBRANE

ENDOPLASMIC RETICULUM

Endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are interconnect-ed with one another. It is covered by a limiting membrane which is formed by proteins and bilayered lipids. The lumen contains a fluid medium called the endoplasmic matrix and it's about 700Angstrons in diameter. The membrane of the endoplasmic reticulum is continuous with that of the nucleus. Thus there is a relative communication between the two by the interconnected membranes.

Types of Endoplasmic

ReticulumEndoplasmic reticulum is of two types, namely;

» Rough endoplasmic reticulum and
» Smooth endoplasmic reti-culum.

Both the types are interconnected and continuous with one another. Depending upon the activities of the cells, the rough endoplasmic reticulum changes to smooth endoplasmic reticulum and vice versa.


Rough Endoplasmic Reticulum

It is the endoplasmic reticulum with rough, bumpy or bead-like appearance. Rough appearance is due to the attachment of granular ribosomes to its outer surface. Hence, it is also called the granular endoplasmic reticulum.

Rough endoplasmic reticulum is vesicular or tubular in structure.


Functions of Rough Endoplasmic Reticulum

1. Synthesis of proteins

Rough endoplasmic reticulum is concerned with the synthesis of proteins in the cell. It is involved with the synthesis of mainly those proteins which are secreted from the cells such as insulin from βcells of islets of Langerhans in pancreas and antibodies from B lymphocytes. Ribosomes arrange the amino acids into small units of proteins and transport them into the rough endoplasmic reticulum. Here, the carbohydrates are added to the protein units forming the glycosylated proteins or glycoproteins, which are arranged in the form of reticular vesicles. These vesicles are transported mainly to Golgi apparatus for further modification and processing. Few vesicles are transported to other cyto-plasmic organelles.

2. Degradation of worn-out organelles

Rough endoplasmic reticulum also plays an important role in the degradation of worn-out cytoplasmic orga-nelles like mitochondria. It wraps itself around the worn-out organelles and forms a vacuole which is often called the autophagosome. Autophagosome is digested by lysosomal enzymes.

Smooth Endoplasmic Reticulum

It is the endoplasmic reticulum with smooth appearance. It is also called agranular reticulum. It is formed by many interconnected tubules. So, it is also called tubular endoplasmic reticulum.

Functions of Smooth Endoplasmic Reticulum

1. Synthesis of non-protein substance Smooth endoplasmic reticulum is responsible for synthesis of non-protein substances such as cholesterol and steroid.
This type of endoplasmic reticulum is abundant in cells that are involved in the synthesis of lipids, phospholipids, lipoprotein substances, steroid hormones, sebum, etc. In most of the other cells, smooth endoplasmic reticulum is less extensive than the rough endoplasmic reticulum.

2. Role in cellular metabolism
Outer surface of smooth endoplasmic reticulum contains many enzymes which are involved in various metabolic processes of the cell.

3. Storage and metabolism of calcium

Smooth endoplasmic reticulum is the major site of storage and metabolism of calcium. In skeletal muscle fibers, it releases calcium which is necessary to trigger the muscle contraction.

4.Catabolism and detoxification

Smooth endoplasmic reticulum is also concerned with catabolism and detoxification of toxic substances like some drugs and carcinogens (cancer-producing substances) in the liver.


GOLGI APPARATUS

Golgi apparatus or Golgi body or Golgi complex is a membrane-bound organelle, involved in the processing of proteins.
It is present in all the cells except red blood cells. It is named after the discoverer Camillo Golgi.

Usually, each cell has one Golgi apparatus. Some of the cells may have more than one Golgi apparatus.

Each Golgi apparatus consists of 5 to 8 flattened membranous sacs called the cisternae.
Golgi apparatus is situated near the nucleus.

It has two ends or faces, namely;

» cis face and
» trans face.

The cis face is positioned near the endoplasmic reticulum.

Reticular vesicles from endoplasmic reticulum enter the Golgi apparatus through cis face.

The trans face is situated near the cell membrane. The processed substances make their exit from Golgi apparatus through trans face.


Functions of Golgi Apparatus

Major functions of Golgi apparatus are processing, packing, labeling and delivery of proteins and other molecules like lipids to different parts of the cell.

1. Processing of materials Vesicles containing glycoproteins and lipids are transported into Golgi apparatus. Here, the glycoproteins and lipids are modified and processed.

2. Packaging of materials

All the processed materials are packed in the form of secretory granules, secretory vesicles and lysosomes, which are transported either out of the cell or to another part of the cell.
Because of this, Golgi apparatus is called the ‘post office of the cell’.

3. Labeling and delivery of materials

Finally, the Golgi apparatus sorts out the processed and packed materials and labels them (such as phosphate group), depending upon the chemical content for delivery (distribution) to their proper destinations.
Hence, the Golgi apparatus is called ‘shipping department of the cell’.

LYSOSOMES

Lysosomes are the membrane-bound vesicular organelles found throughout the cytoplasm. The lyso-somes are formed by Golgi apparatus. The enzymes synthesized in rough endoplasmic reticulum are processed and packed in the form of small vesicles in the Golgi apparatus. Then, these vesicles are pinched off from Golgi apparatus and become the lysosomes. Among the organelles of the cytoplasm, the lysosomes have the thickest covering membrane. The membrane is formed by a bilayered lipid material. It has many small granules which contain hydrolytic enzymes.


Types of Lysosomes

Lysosomes are of two types:

1.Primary lysosome, which is pinched off from Golgi apparatus. It is inactive in spite of having hydrolytic enzymes

2.Secondary lysosome, which is the active lyso some. It is formed by the fusion of a primary lyso some with phagosome or endosome (see below).

Functions of Lysosomes

Lysosomes are often called ‘garbage system’ of the cell because of their degradation activity. About 50 different hydrolytic enzymes, known as acid hydroxylases are present in the lysosomes, through which lysosomes exe cute their functions.Important lysosomal enzymes

1.Proteases, which hydrolyze the proteins into amino acids

2.Lipases, which hydrolyze the lipids into fatty acids and glycerides

3.Amylases, which hydrolyze the polysaccharides into glucose

4.Nucleases, which hydrolyze the nucleic acids into mononucleotides.


Mechanism of lysosomal function

Lysosomal functions involve two mechanisms:

1.Heterophagy: Digestion of extracellular materials engulfed by the cell via endocytosis

2.Autophagy: Digestion of intracellular materials such as worn-out cytoplasmic organelles.

Specific functions of lysosomes

1. Degradation of macromolecules Macromolecules are engulfed by the cell by means of endocytosis (phagocytosis, pinocytosis or receptor-mediated endocytosis.

The macromolecules such as bacteria, engulfed by the cell via phagocytosis are called phagosomes or vacuoles. The other macromolecules taken inside via pinocytosis or receptor-mediated endocytosis are called endosomes.

The primary lysosome fuses with the phagosome or endosome to form the secondary lysosome. The pH in the secondary lysosome becomes acidic and the lysosomal enzymes are activated. The bacteria and the other macromolecules are digested and degraded by these enzymes.

The secondary lysosome containing these degraded waste products moves through cytoplasm andfuses with cell membrane. Now the waste products are eliminated by exocytosis.

2. Degradation of worn-out organellesThe rough endoplasmic reticulum wraps itself around the worn-out organelles like mitochondria and form the vacuoles called autophagosomes.
One primary lysosome fuses with one autophagosome to form the secondary lysosome. The enzymes in the secondary lysosome are activated. Now, these enzymes digest the contents of autophagosome.

3. Removal of excess secretory products in the cells

Lysosomes in the cells of the secretory glands remove the excess secretory products by degrading the secretory granules.

4. Secretory function – secretory lysosomes

Recently, lysosomes having secretory function called secretory lysosomes are found in some of the cells, particularly in the cells of immune system.
The conventional lysosomes are modified into secretory lysosomes by combining with secretory granules (which contain the particular secretory product of the cell).

Examples of secretory lysosomes:

i. Lysosomes in the cytotoxic T lymphocytes and natural killer (NK) cells secrete perforin and granzymes, which destroy both viral-infected cells and tumor cells. Perforin is a pore-forming protein that initiates cell death.

Granzymes belong to the family of serine proteases (enzymes that dislodge the peptide bonds of the proteins) and cause the cell death by apoptosis

ii. Secretory lysosomes of melanocytes secrete melanin

iii.Secretory lysosomes of mast cells secrete serotonin, which is a vasoconstrictor substance and inflammatory mediator.


PEROXISOMES

Peroxisomes or microbodies are the membrane limited vesicles like the lysosomes. Unlike lysosomes, peroxisomes are pinched off from endoplasmic reticulum and not from the Golgi apparatus.
Peroxisomes contain some oxidative enzymes such as catalase, urate oxidase and Damino acid oxidase.

Functions of Peroxisomes

i. Breakdown the fatty acids by means of a process called betaoxidation: This is the major function of peroxisomes

ii. Degrade the toxic substances such as hydrogen peroxide and other metabolic products by means of detoxification.

A large number of peroxisomes are present in the cells of liver, which is the major organ for detoxification. Hydrogen peroxide is formed from poisons or alcohol, which enter the cell. Whenever hydrogen peroxide is produced in the cell, the peroxisomes are ruptured and the oxidative enzymes are released. These oxidases destroy hydrogen peroxide and the enzymes which are necessary for the production of hydrogen peroxide

iii. Form the major site of oxygen utilization in the cells

iv. Accelerate gluconeogenesis from fats

v. Degrade purine to uric acid

vi. Participate in the formation of myelin

vii. Play a role in the formation of bile acids.


CENTROSOME AND CENTRIOLES

Centrosome is the membrane-bound cellular organelle situated almost in the center of cell, close to nucleus. It consists of two cylindrical structures called centrioles which are made up of proteins. Centrioles are responsible for the movement of chromosomes during cell division.

SECRETORY VESICLES

Secretory vesicles are the organelles with limiting membrane and contain the secretory substances. These vesicles are formed in the endoplasmic reticulum and are processed and packed in Golgi apparatus. Secretory vesicles are present throughout the cytoplasm. When necessary, these vesicles are ruptured and secretory substances are released into the cytoplasm.


MITOCHONDRION

Mitochondrion (plural = mitochondria) is a membrane-bound cytoplasmic organelle concerned with production of energy. It is a rod-shaped or oval-shaped structure with a diameter of 0.5 to 1 μ. It is covered by a bilayered membrane.

The outer membrane is smooth and encloses the contents of mitochondrion. This membrane contains various enzymes such as acetyl-CoA synthetase and glycerolphosphate acetyltransferase. The inner membrane is folded in the form of shelf-like inward projections called cristae and it covers the inner matrix space.

Cristae contain many enzymes and other protein molecules which are involved in respiration and synthesis of adenosine triphosphate (ATP). Because of these functions, the enzymes and other protein moleculesn cristae are collectively known as respiratory chain or electron transport system.

Enzymes and other proteins of respiratory chain

i.Succinic dehydrogenase

ii. Dihydronicotinamide adenine dinucleotide (NADH) dehydrogenase

iii. Cytochrome oxidase

iv. Cytochrome C

v. ATP synthase. Inner cavity of mitochondrion is filled with matrix which contains many enzymes. Mitochondrion moves freely in the cytoplasm of the cell. It is capable of reproducing itself. Mitochondrion contains its own deoxyribonucleic acid (DNA), which is responsible for many enzymatic actions. In fact, mitochondrion is the only organelle other than nucleus, which has its own DNA.

Functions of Mitochondrion

1. Production of energy

Mitochondrion is called the ‘power house’ or ‘power plant’ of the cell because it produces the energy required for cellular functions. The energy is produced during the oxidation of digested food particles like proteins, carbo-hydrates and lipids by the oxidative enzymes in cristae. During the oxidative process, water and carbon dioxide are produced with release of energy. The released ener-gy is stored in mitochondria and used later for synthesis of ATP.

2. Synthesis of ATPThe components of respiratory chain in mitochondrion are responsible for the synthesis of ATP by utilizing the energy by oxidative phosphorylation. ATP molecules diffuse throughout the cell from mitochondrion. Whenever energy is needed for cellular activity, the ATP molecules are broken down.

3. Apoptosis

Cytochrome C and second mitochondria-derived activator of caspases (SMAC)/diablo secreted in mito chondria are involved in apoptosis.

Could it be your gut is keeping you awake at night

When we lie awake at night, unable to sleep, we usually blame stress, depression, anxiety, adrenaline or the memory of something stupid we said in 2003. But what if our guts were actually the culprit? What if the trillions of microbes sitting in our small intestines – known collectively as the microbiome or microbiota – were actually affecting our mood, digestion, overall health and ability to get a full eight hours’ shut-eye? Scientists are beginning to suspect there is a strong, if as yet unproven, link between gut health – the diversity and wellbeing of bacteria in the stomach, small and large intestines – and sleep health.

“This is an embryonic field right now in the annals of sleep research,” says Matt Walker, the author of Why We Sleep and the director of the Center for Human Sleep Science at the University of California, Berkeley. “We know an enormous amount about the relationship between a lack of sleep and appetite, obesity and weight gain, as well as aspects of insulin resistance and glucose regulation. What we don’t fully understand yet is the role of the microbiome in sleep.”

We know that sleep deprivation increases our chances of obesity and affects the way we control food intake. Lack of sleep results in a decrease in leptin, the hormone that makes us feel full, and a surge in ghrelin, which stops us feeling satisfied with the food we do eat. That means we keep eating – sometimes as much as an extra 300 calories a day. Lack of sleep also affects the parts of our brain responsible for impulse control, leaving us with very little chance of eating healthily and taking care of that gut ecosystem. Poor sleep, then, can certainly affect our gut. The question is, could our gut affect our sleep?

“Is improving gut health a possible new sleep therapy? That is one of our least understood but most exciting possibilities,” says Walker.

Dr Michael Breus, a clinical psychologist and fellow of the American Academy of Sleep Medicine, agrees that this is a possibility worth pursuing. “There is no question in my mind that gut health is linked to sleep health, although we do not have the studies to prove it yet. Scientists investigating the relationship between sleep and the microbiome are finding that the microbial ecosystem may affect sleep and sleep-related physiological functions in a number of different ways: shifting circadian rhythms, altering the body’s sleep-wake cycle, affecting hormones that regulate sleep and wakefulness. ”

While we wait for the definitive science, Breus suggests taking probiotics (a type of live bacteria) and prebiotics (non-digestible carbohydrates, mainly fibre) to feed the good bacteria in our guts. The benefits of probiotics for the gut are well documented. A recent study from scientists at the University of Colorado, published in Frontiers of Behavioural Neuroscience, suggests that prebiotics could have a significant effect on the quality of non-REM and REM sleep. This is something insomniac Dr Michael Mosley tested out with some success in a recent BBC documentary – he took prebiotics for five days and saw improvement in his sleep. The day before the experiment, Mosley spent 21% of his time in 

Eating berries, along with nuts, 70% dark chocolate, seeds and decaffeinated coffee could help improve gut health, and as a result, your sleep. Photograph: Alamy Stock Photo

Tim Spector, professor of genetic epidemiology at King’s College London and the author of The Diet Myth, agrees that a healthy gut could promote good sleep. Like Walker and Breus, he also believes gut health is linked to our moods. That is particularly interesting for someone like me, who suffers from both depression and insomnia. I live with bipolar disorder; my moods affect my sleep, and, traditionally, I would expect my brain to be in charge of that. But it turns out it is not that simple.

“We know that people who live with depression and people who sleep poorly both have abnormal microbes in the gut, which would suggest there is a very real connection here between all three,” says Spector. “I’ve always found that if you help someone sleep, it improves their depression, and vice versa. If we can also look after the gut, this may have an impact on both sleep disturbances and mood disorders.” It has long been known that there is a reciprocal relationship between depression and sleep, in that most depressed people sleep poorly and many insomniacs develop depressive symptoms.

Spector is convinced that you can improve sleep disturbance with diet. “That was dismissed until recently by psychiatrists and sleep therapists, but if we eat badly, we sleep badly,” he says. “If you wanted to improve sleep, you could try a gut-friendly regime by eating a broad and inclusive diet with real food, not processed. Everyone is going to be different. You could try being vegetarian for a month and see if it helps. Double your fibre intake and eat fermented foods every day, such as full-fat yoghurt and good-quality cheeses. Increase the range of foods in your diet.

Eat berries, green tea, 70% dark chocolate, decaffeinated coffee, nuts and seeds. Don’t eat just before you go to bed, but equally, don’t go hungry. Avoid snacking before bedtime. I don’t want to be too prescriptive but really, if you want richer microbes, you’ll eat more of a range of foods and that will induce chemicals that will calm you.”

As for the bedtime routine, Christine Hansen, author of Sleep Like a Boss, has some further tips. “My general advice is to eat low-glycaemic index foods before bed because they’ll release the energy more slowly. If you do eat high-GI foods, like a dessert or sugar or something refined, pair it with some protein or fibre. For example, if you have white bread, have it with cream cheese and banana or eggs. If you want crackers, go for wholegrain. You probably don’t want to eat food before bed that’s difficult to digest – fried food or heavy meats, for example. Go for fish or chicken rather than sitting down for a big steak, and try to indulge at lunchtime rather than dinner to give yours

Many things are wrongly associated with Obesity 

From the 16th century to the 19th, scurvy killed around 2 million sailors, more than warfare, shipwrecks and syphilis combined. It was an ugly, smelly death, too, beginning with rattling teeth and ending with a body so rotted out from the inside that its victims could literally be startled to death by a loud noise. Just as horrifying as the disease itself, though, is that for most of those 300 years, medical experts knew how to prevent it and simply failed to.

In the 1600s, some sea captains distributed lemons, limes and oranges to sailors, driven by the belief that a daily dose of citrus fruit would stave off scurvy’s progress. The British Navy, wary of the cost of expanding the treatment, turned to malt wort, a mashed and cooked byproduct of barley which had the advantage of being cheaper but the disadvantage of doing nothing whatsoever to cure scurvy. In 1747, a British doctor named James Lind conducted an experiment where he gave one group of sailors citrus slices and the others vinegar or seawater or cider. The results couldn’t have been clearer. The crewmen who ate fruit improved so quickly that they were able to help care for the others as they languished. Lind published his findings, but died before anyone got around to implementing them nearly 50 years later.

This kind of myopia repeats throughout history. Seat belts were invented long before the automobile but weren’t mandatory in cars until the 1960s. The first confirmed death from asbestos exposure was recorded in 1906, but the U.S. didn’t start banning the substance until 1973. Every discovery in public health, no matter how significant, must compete with the traditions, assumptions and financial incentives of the society implementing it.

Which brings us to one of the largest gaps between science and practice in our own time. Years from now, we will look back in horror at the counterproductive ways we addressed the obesity epidemic and the barbaric ways we treated fat people—long after we knew there was a better path.
I have never written a story where so many of my sources cried during interviews, where they shook with anger describing their interactions with doctors and strangers and their own families.

About 40 years ago, Americans started getting much larger. According to the Centers for Disease Control and Prevention, nearly 80 percent of adults and about one-third of children now meet the clinical definition of overweight or obese. More Americans live with “extreme obesity“ than with breast cancer, Parkinson’s, Alzheimer’s and HIV put together.

And the medical community’s primary response to this shift has been to blame fat people for being fat. Obesity, we are told, is a personal failing that strains our health care system, shrinks our GDP and saps our military strength. It is also an excuse to bully fat people in one sentence and then inform them in the next that you are doing it for their own good. That’s why the fear of becoming fat, or staying that way, drives Americans to spend more on dieting every year than we spend on video games or movies. Forty-five percent of adults say they’re preoccupied with their weight some or all of the time—an 11-point rise since 1990. Nearly half of 3- to 6- year old girls say they worry about being fat.

polymerase chain reaction

Polymerase Chain Reaction

PCR means a technical and biological method of making multiple copies of a segment of a gene of interest producing many from an initial little sample.

Watch the PCR video below

How proteins and enzymes are synthesized

Protein Synthesis

Gene expression

This  is  the  process  by  which  the genetic  code  -  the  nucleotide  sequence  -  of  a gene  is  used  to  direct  protein  synthesis  and produce  the  structures  of  the  cell.  Genes  that code  for  amino  acid  sequences  are  known  as 'structural genes'. 

The  process  of  gene  expression  involves  two main stages: 

-Transcription
-Translation

Transcription:  the  production  of  messenger RNA  (mRNA)  by  the  enzyme  RNA  polymerase, and  the  processing  of  the  resulting  mRNA molecule. 

Translation:  the  use  of  mRNA  to  direct  protein synthesis, and  the  subsequent  post-translational processing of the protein molecule. Some  genes  are  responsible  for  the  production of  other  forms  of  RNA  that  play  a  role  in translation,  including  transfer  RNA  (tRNA)  and ribosomal RNA (rRNA). 

 Gene Control Sites

  Start site. A start site for transcription.   

  A promoter. A region  a few hundred nucleotides  'upstream' of the gene (toward the  5' end). It is  not transcribed into  mRNA, but plays a role in controlling the transcription  of the  gene. Transcription factors bind to  specific nucleotide sequences  in the promoter region  and assist  in the binding of RNA polymerases. 

  Enhancers. Some transcription factors (called activators) bind to  regions called 'enhancers' that increase the  rate  of transcription. These  sites may be thousands  of nucleotides from the coding sequences or within an intron. Some enhancers are conditional and only work in  the presence of other factors as  well as transcription  factors. 

  Silencers. Some transcription factors (called repressors) bind  to regions  called 'silencers' that depress the rate  of transcription. 

Note:  The  term  'gene  expression'  is  sometimes used to  refer  to  the transcription  phase alone. 

Coded RNA includes;

  Exons. Exons code for amino acids and collectively  determine the amino  acid sequence  of  the protein product. It is these  portions  of the gene that are represented  in final mature mRNA molecule.

  Introns. Introns  are  portions  of  the gene that do not  code for amino acids, and are  removed (spliced) from the mRNA molecule before  translation.


Molecular basis of gene expression

  Transcription


This  is  the  process  of  RNA  synthesis, controlled  by  the  interaction  of  promoters  and enhancers.  Several  different  types  of  RNA  are produced,  including  messenger  RNA  (mRNA), which  specifies  the  sequence  of  amino  acids  in the  protein  product,  plus  transfer  RNA  (tRNA) and  ribosomal  RNA  (rRNA),  which  play  a  role  in the translation process.

Transcription involves four steps:

1.  Initiation. The DNA molecule unwinds and separates to  form a  small  open complex. RNA polymerase binds to the promoter of the  template strand.

2.  Elongation. RNA polymerase moves along  the template  strand, synthesising an mRNA molecule. In prokaryotes RNA polymerase is a holoenzyme  consisting of a number of subunits, including a sigma factor  (transcription factor)  that recognises the promoter. In eukaryotes there are three RNA polymerases:  I,  II and III. The process  includes a proofreading mechanism.

3.  Termination. In prokaryotes there are two ways in  which transcription is terminated. In  Rho-dependent termination, a protein factor called "Rho"  is responsible for  disrupting the complex involving the template strand, RNA polymerase and RNA molecule.  In Rho-independent  termination, a loop forms at the end of  the  RNA molecule, causing it to detach itself.  Termination in eukaryotes is more  complicated, involving  the  addition of additional adenine nucleotide at the 3'  of the  RNA transcript (a  process referred to  as polyadenylation). 

4.  Processing. After transcription the RNA molecule is  processed in a number of ways:  introns are removed and the exons  are  spliced together  to form a mature mRNA molecule consisting  of a single protein-coding sequence. RNA synthesis involves the normal base pairing rules, but the base thymine is replaced with the base  uracil. 

  Translation 

In  translation  the  mature  mRNA  molecule  is used  as  a  template  to  assemble  a  series  of amino  acids  to  produce  a  polypeptide  with  a specific  amino  acid  sequence.  The  complex  in the  cytoplasm  at  which  this  occurs  is  called  a ribosome.  Ribosomes  are  a  mixture  of ribosomal  proteins  and  ribosomal  RNA  (rRNA), and  consist  of  a  large  subunit  and  a  small subunit.

Translation involves four steps: 

1. Initiation. The small subunit of the ribosome binds at the 5' end of  the  mRNA molecule and  moves  in a  3' direction until it meets a start codon  (AUG). It then forms a complex with the large unit of  the ribosome complex and an initiation tRNA molecule. 

2. Elongation. Subsequent codons on the mRNA molecule  determine which tRNA molecule linked to an amino acid binds to  the mRNA. An  enzyme  peptidyl transferase links the amino acids together using peptide bonds. The process continues, producing a chain  of amino acids as  the ribosome moves along the  mRNA molecule. 

3. Termination. Translation  in terminated when the  ribosomal complex  reached one or more stop codons  (UAA, UAG, UGA).  The ribosomal complex  in eukaryotes is  larger  and more complicated than in prokaryotes. In addition, the processes  of transcription and translation are divided in  eukaryotes  between the nucleus  (transcription) and the  cytoplasm (translation), which provides more opportunities for the regulation  of gene expression.   

4.  Post-translation  processing of  the protein 

  Gene regulation

This is a label for the cellular processes that control the rate  and manner of  gene  expression.  A complex set of  interactions  between genes,  RNA molecules,  proteins (including transcription factors) and other components of  the expression system determine  when and where specific genes are activated and the amount of protein  or RNA product produced. 

  Some genes  are  expressed continuously, as they produce proteins  involved in basic metabolic functions; some genes are  expressed as part of the process of cell differentiation; and some genes are expressed as a result of  cell differentiation. Mechanisms  of gene regulation  include: 

  Regulating the rate of transcription.  This is the most economical  method of regulation. 

  Regulating the processing  of RNA molecules, including alternative splicing to produce  more than one protein product  from a single gene. 

  Regulating the stability  of mRNA molecules. 

  Regulating the rate of translation. Transcription  factors  are  proteins  that  play  a role  in  regulating  the  transcription  of  genes  by binding  to  specific  regulatory  nucleotide sequences.

A MAMMOGRAM SHOWING PROCEDURES

Breast Cancer

 Major signs of Breast Cancer

The upper and outer quadrant of breast is a frequent site of carcinoma (cancer). Several anatomical facts are of importance in diagnosis and treatment of this condition. Abscesses may also form in the breast and may require drainage. The following facts are worthyof note.

Incisions of breast are usually made radially toavoid cutting the lactiferous ducts.

1.  Cancer cells may infiltrate the suspensory ligaments. The breast then becomes fixed.Contraction of the ligaments can cause retractionor puckering (folding) of the skin.

2.  Infiltration of lactiferous ducts and their consequent fibrosis can cause retraction of the nipple.

3.  Obstruction of superficial lymph vessels by cancer cells may produce oedema of the skin giving rise to an appearance like that of the skin of an orange(peau d'orange appearance).

4.  Because of communications of the superficial lymphatics of 'the breast across the midline, cancer may spread from one breast to the other.

5.  Because of communications of the lymph vessels with those in the abdomen, cancer of the breast may spread to the liver, and cancer cells may 'drop' into the pelvis producing secondaries there.

6.  Apart from the lymphatics, cancer may spread through the segmental veins. In this connection, it is important to know that the veins draining the breast communicate with the vertebral venous plexus of veins. Through these communicationscancer can spread to the vertebrae and to the brain.


Preventive and diagnostic measures

Self examination of breast as follows;

a. Inspect: Symmetry of breasts and nipples.

b. Change in colour of skin.

c. Retraction of nipple is a sign of cancer.

d. Discharge from nipple on squeezing it.

e. Palpate all four quadrants with palm of hand.Note any palpable lump.

f. Raise the arm to feel lymph nodes in axilla.

g. Mammogram may reveal cancerous mass.

h. Fine needle aspiration cytology is safe and quick method of diagnosis of lesion of breast.

 
Note worthy;
 
Retracted nipple is a sign of tumour in the breast.

Cancer of the mammary glands is the most comnon cancer in females of all ages. It is more frequently seen in postmenopausal females due to lack of oestrogen hormones.Self-examination of the mammary gland is the only way for early diagnosis and appropriate treatment.

What to study

EMBRYOLOGY 

Embryology:  It is the study of the development of an individual before birth (prenatal period). Embryo (G): (en = within; bruein= to swell or to be full); Logos = study Natal = birth; Prenatal = before birth; Postnatal = after birth 

• Embryo:  It is the developing individual during the first 2 months or 8 weeks of intrauterine life. 

• Fetus:  It is the developing individual from the 3rd month or 9th week of intrauterine life to the time of birth. 

• Development before birth is called  prenatal development, and that after birth is called  postnatal development. 

• There are three stages in prenatal development. They are  (1) preimplantation, (2) embryonic and (3) fetal periods. 

• Gonads:  They are the sex organs that produce  sex cells or  gametes. The  testis  is the male gonad  and the  ovary  is the female gonad. Male gametes are called spermatozoa. Female gametes are called  ova. 

• Gametogenesis: It  is  the  process  of  production  of  gametes  in  gonads  or  sex  organs.  In  males  it  is  known  as  spermatogenesis and in females as  oogenesis. 

• Fertilization:  It  is  the  process  of  fusion  of  male  and  female  gametes.  It  takes  place  in  the  uterine  tube  of  female  genital  tract. 

• Zygote:  It is the single cell that results from fertilization. 

• Development:  It is a process where something grows or changes and becomes more advanced. 

• Growth:  It is a quantitative change that increases the size. 

• Ontogeny:  Complete life cycle of an organism. 

• Phylogeny:  Evolutionary history of a group of organisms. 

• Differentiation:  It is a qualitative change in structure for an assigned function. 

• Organizer:  Any part of the embryo which exerts stimulus on an adjacent part. 

• Cell potency:  It is the potential to differentiate into different cell types.


Gonads and Gametes 

• Gonads are the paired sex glands that are responsible for the production of  gametes  or  sex cells  that carry out the special function of reproduction. The male sex cells (spermatozoa) are produced in the male gonads  (testes) while the female sex cells (ova) are produced in female gonads (ovaries). 

• The formation of spermatozoa in testis is called spermatogenesis, while the formation of ova in the ovary is called  oogenesis. The two are collectively referred to as  gametogenesis. 

• The development of a new individual begins at the movement when one male  gamete  (sperm  or spermatozoon) meets and fuses with one female gamete (ovum  or  oocyte). The process of  fusion of male and female gametes is called  fertilization.

• The zygote multiplies and reorganizes to form the miniature new individual called embryo that grows and matures as  fetus  in the mother’s womb and delivered at the end of term of pregnancy.

DEVELOPMENT OF A HUMAN BEING Development is a process where someone or something grows or changes and becomes more advanced. Human development is a continuous process that does not stop at birth. It continues after birth for increase in the size of the body, eruption of teeth, etc. 
Development before birth is called  prenatal development, and that after birth is called postnatal development.  
Each period is further subdivided into several stages. 

Prenatal Development There are three stages in prenatal development. They are: 

1.  Preimplantation/pre-embryonic period 
2.  Embryonic period 
3.  Fetal period. 

•  Preimplantation/Pre-embryonic Period; 

It extends from fusion of male and female gametes to form single-celled zygote to formation of primitive germ layers of developing organism. It includes 1st and 2nd weeks of intrauterine development. The following morphogenetic events take place during this period. 

1.  Fertilization: Fusion of male and female gametes resulting in the formation of zygote. 

2.  Cleavage: A series of mitotic divisions of zygote resulting in the formation of morula.

3.  Transportation of cleaving zygote, i.e. morula along the fallopian tube toward the uterus. 

4.  Blastocyst: Structural and functional specialization and reorganization of cells (blastomeres) of cleaving zygote that becomes blastocyst. 

5.  Implantation: Process of attachment of blastocyst to the uterine endometrium is called implantation.

6.  Specialization of primordial embryonic tissue: It involves specialization  of  blastomeres  to  form  embryonic structures  (embryoblast)  and supportive/nutritive structures  (trophoblast). 

7.  Differentiation of embryoblast—to form the primitive two layered (bilaminar) germ disc having ectoderm and endoderm. 

8.  Differentiation of trophoblast into  cytotrophoblast  and syncytiotrophoblast. 


•  Embryonic Period; 

It  extends  from  3rd  week  of  intrauterine  life  to  8th  week  of intrauterine  life.  The  following  morphogenetic  events  take place during this period. 

1.  Trilaminar germ disc differentiation: Formation of three layered germ disc with  the  appearance  of  mesoderm in between ectoderm and endoderm. 

2.  Early organogenesis: Formation of primordia of various organs like lungs, heart, liver, etc. 

3.  Formation of extraembryonic supportive organs and membranes: Placenta, umbilical cord, amnion, allantois. 


•  Fetal Period; 

It  extends from 9th week to 9th month. This period includes the following: 

1.  Growth of fetus in all dimensions 

2.  Specialization of various body structures.


Postnatal Period of Development

 It extends from birth of an individual to adulthood. The various stages in postnatal development are as follows: 

1.  Neonatal period: It extends from birth to 28 days after birth. These first 4 weeks are critical in the life of the  newborn/neonate  as  various  systems  especially respiratory and cardiovascular have to make adjustments with the external/extrauterine environment. 

Neonatology:  The branch of medicine that takes care of neonates is called  neonatology. 

Perinatology:  It is  the branch of  medicine that takes care of the  fetus  and  newborn from 28th week of intrauterine life to 6th day of extrauterine life. 

2.  Infancy: It extends from 1 month to 1 year and the newborn during this period is called  infant. 

3.  Childhood: It extends from 2nd year to 12th year of age and an individual is called a child. It is the period of rapid growth and development. This age is also called pediatric age. Pediatrics  and  pediatrician:  The  medical  branch  that deals with infants and children is called  pediatrics. The specialist who treats them is known as  pediatrician.

4.  Puberty: It extends from 12 years to 16 years. There will be  rapid  physical growth and development of secondary sex characters and it depends on the interaction of sex hormones and growth hormones. 

5.  Adolescence:  It  extends  from  17  years  to  20  years. During this period, there will be rapid physical growth and  sexual  maturation.  The  reproductive  ability  is established. 

6.  Adulthood: It extends from 21 years to 40 years. 

7.  Middle age: It extends from 40 years to 60 years. 

8.  Old age: It extends from more than 60 years to death. Ontogeny: Complete life cycle of an organism involving both prenatal and postnatal developments is called ontogeny. It is the expression of blue print of life hidden in genes. It includes progressive changes followed by retrogressive changes. It involves various processes like cell division, differentiation and growth. Phylogeny: Evolutionary/ancestral history of a group of organisms is called phylogeny. It includes developmental changes in various organs (e.g. kidney, heart) and organ systems (e.g. respiratory, skeletal) starting from fishes, amphibians, reptiles, birds and mammals. 
Ontogeny repeats phylogeny: Life cycle of an organism repeats its  ancestral  history.  This  is  observed  in  the  development  of certain organs viz. heart, lung and kidney.

HUMAN BIOLOGY SUMMARY

👉 Musician bone = Ulnar
👉 Musician nerve = Ulnar nerve
👉 Labourer nerve = Median nerve
👉 Beauty bone = Clavicle
👉 Strongest muscle = Masseter
👉 Strongest tendon = Tendocalcaneous
👉 Longest muscle = Sartorios
👉 Longest tendon = Plantaris tendon
👉 Muscle for grafting = Gracilis
👉 Bone for grafting = Fibula
👉 Bulkiest muscle = Gluteus maximus
👉 Hybrid muscles in upper limb = P. major & Flexor digitorum profundus
👉 Hybrid muscles in lower limb = Adductor Magnus & Pectineus
👉 Vein for CABG = Long saphenous vein
👉 Strongest & longest bone = Femur
👉 Number of Bones 206
👉 Number of Muscles 639
👉 Number of Kidneys 2
👉 Number of Milk Teeth 20
👉 Number of Ribs 24 (12 pair)
👉 Number of Heart Chamber 4
👉 Largest artery Aorta
👉 Normal blood pressure 120/80mmHg
👉 Ph of Blood 7.4
👉 Number of vertebrae in the Spine 33
👉 Number of vertebrae in the Neck 7
👉 Number of Bones in Middle Ear 6
👉 Number of Bones in Face 14
👉 Number of Bones in Skull 22
👉 Number of Bones in Chest 25
👉 Number of bones in upper limbs = 64
👉 Number of bones in lower limbs = 66
👉 Number of Muscles in Human Arm 72
👉 Number of Pumps in Heart 2
👉 Largest Organ Skin
👉 Largest gland Liver
👉 Biggest cell female Ovum
👉 Smallest cell male Sperm
👉 Smallest Bone Stapes
👉 First transplanted Organ Heart
👉 Average length of Small Intestine 7m
👉 Average length of Large Intestine 1.5m
👉 Average weight of new Born baby 2.6kg
👉 Pulse rate in One Minute 72 times
👉 Normal body temperature 37 C° (98.4 F°)
👉 Peripheral heart = Soleus
👉 Average Blood Volume 4 to 5 liters
👉 Life Span of RBC 120 days
👉 Life Span of WBC 13to 20 days
👉 Pregnancy Period 280 days (40 week)
👉 Number of Bones in Human Foot 33
👉 Number of Bones in Each wrist 8
👉 Number of Bones in Hand 27
👉 Largest Endocrine gland Thyroid
👉 Largest Lymphatic Organ Spleen
👉 Largest part of Brain Cerebrum
👉 Largest & Strongest Bone Femur
👉 Smallest Muscle Stapedius (Middle Ear)
👉 Number of Chromosome 46 (23 pair)
👉 Number of Bones in new Born baby 306
👉 Viscosity of Blood 4.5 to 5.5
👉 Universal Donor Blood Group O
👉 Universal Recipient Blood Group AB
👉 Largest WBC Monocyte
👉 Smallest WBC Lymphocyte
👉 Increase RBC count called Polycethemia
👉 Blood Bank in the Body is Spleen
👉 Non Nucleated Blood cell is RBC
👉 RBC produced in the Bone Marrow
👉 River of Life is Called Blood
👉 Normal Blood Cholesterol level 250mg/dl
👉 Fluid part of Blood is Plasma
👉 Normal Blood Sugar 100mg/dl

Catalog of Health Conditions.

Know your eye health conditions by mere looking.


> Conjunctivitis

> Blepharitis

> Stye

> Dry eye

> Cataracts

> Focus on vision problem
> Macular degeneration

> Glaucoma

> Uveitis

> Retinitis pigmentosa

> Ocular cancers