Eukaryotic Chromosome Organization

Eukaryotic Chromosomal Organization:

Ø      Fundamental difference between prokaryotic and Eukaryotic genome organization is prokaryotes have a single type of chromosome but Eukaryotes have two sets of chromosomes making the cell has diploid.

Ø      To know the structure of Eukaryotic chromosome, Metaphase chromosome is preferred.

Ø      They are easily observed under microscope after staining.

Ø      The number of human chromosomes is 46 and the length of human genome is 5.5X10⁹ base pairs.

Ø      When compared with prokaryotic cell, Eukaryotic cell is having the large amount of DNA in its nucleus.

Ø      The DNA is found associated with proteins.

Ø      Chromatin is the complex basis of DNA and protein that makes up chromosomes consists of Linear unbroken double stranded DNA. Chromatin is of two types

a.     Euchromatin, and

b.     Heterochromatin

a. Euchromatin

·        Euchromatin is a type of chromatin which is genetically active. It consists of all functional genes which are expressive.

·        This type of chromatin stains very lightly.

b. Heterochromatin:

·        It is genetically inactive, the genes are not expressive. Heterochromatin stains darkly because the chromatin region here is highly condensed.

·        Histones are the chief protein components of chromatin they act as spools around which DNA winds and play a role gene regulation.

Ø      Five major histone classes are present which are associated with eukaryotic genome i.e., H₁, H₂A, H₂B, H₃ & H₄.

Ø      These are basic proteins which have a positive charge at normal pH which facilitates the binding of negatively charged DNA

Nucleosome:

Ø      The simplest level of packing of DNA which is found winding around Histones is known as Nucleosome.

Ø      There are two molecules of each of four types of Histones namely H₂A, H₂B, H₃ & H₄. this give rise to a complex of 6 proteins named as “Histone octomer”

Ø      This Histone octomer is flattened cylindrical particle of about 11 nm and thickness of nucleosome is 5.7nm.

Ø      The H1 protein is present only in single set. These nucleosomes are attached to each other by means of a thin naked DNA which is known as Linker DNA (the H₁ is associated with Linker DNA)

Ø      Higher order organization is seen further where this nucleofilament has the appearance of beats on a string at 11 nm

Ø      The complexity in the organization may be represented further by the packing of chromosomes in a highly compact fashion giving rise to 30 nm, then 300 nm, 700 nm and finally 1400 nms in thickness which are able to see as rod like chromosome at metaphase of cell division.

      

Dialysis

Dialysis:

Purpose:
       Dialysis is the separation of small solute molecules (or) ions (Ex: Glucose,Na+, Cl) from macromolecules ( Ex: Starch)

Principle:
Dialysis works on the principles of Diffusion of solutes and Ultra filtration of fluid across a semi permeable membrane.

a. Diffusion:
· Diffusion is the process by which atoms, molecules, and other particles move from an area where they are in high concentration to an area where they are in low concentration
· Diffusion is the random movement of molecules from an area of higher concentration to those molecules of an area of lower concentration.
· Diffusion can occur in solids, gases, or liquids, such as blood. Energy for the movement comes from the molecules themselves, and does not depend on outside forces
· In the body, substances move into and out of cells by diffusion through the cell membranes.
· In dialysis, diffusion occurs across an artificial semipermeable membrane. This is how wastes and fluid are removed from the patient’s blood, and electrolytes are balanced.

For example, if one opened a bottle of Hydrogen sulphate (H2S has the odour of rotten egg) in one corner of a room, it would not be long before some one in the opposite corner would also recognize the smell of rotten egg.

b. Osmosis:
· In diffusion, solutes move but in osmosis, the solvent moves across the membrane.
· Osmosis is movement of a solvent through a semipermeable membrane from an area of lower solute concentration toward an area of higher solute concentration.
· The difference in concentration is called an osmotic pressure gradient.
· In both diffusion and osmosis, movement goes on until the concentration of molecules equilibrates (becomes equal) on both sides of the membrane.
Ø The best studied example is the dialysis of blood.
Ø Blood perform essential functions of bringing nutrients and oxygen to the cells of the body and also carrying waste materials away from those cells.
Ø Blood contains particles of many different sizes and types, including cells, proteins, dissolved ions and organic waste products.
Ø Some of these products such as urea (waste product from protein metabolism), must be removed otherwise it accumulates and interferes with normal metabolic process.
Ø Kidney acts like dialysis unit for blood, in which nephron the functional unit which performs this is functioning, if the kidney becomes diseased or ceases functioning, the blood gets poisoned and the patient dies.
Ø The only way to deal with kidney failure is either to transplant a healthy kidney (which is obtained from either living or just dead person) or to remove the impurities from the blood artificially.
Ø So the patients come to dialysis with wastes in their blood, extra fluid between their cells and in their blood vessels, and often with electrolyte imbalances. The main tasks of dialysis are to remove wastes and excess
fluid, and balance electrolytes.
Ø Blood itself is a solution. Water is the solvent, and electrolytes, glucose, and many other substances are the solutes. Blood also has many particles, such as red and white blood cells.

Procedure:Dialysis can be done in 2 methods, they are
                          1. Haemo Dialysis, and
                          2. Peritoneal Dialysis

1. In Haemodialysis, the patient’s blood is pumped through the blood compartment of a Dialyzer, exposing it to a semipermeable membrane. The cleaned blood is then returned back to the body.

2. In Peritoneal dialysis, a sterile solution containing minerals & Glucose is run through a tube into the peritoneal cavity, the abdominal body cavity around the intestine, where the peritoneal membrane acts as a semi permeable membrane.

HaemoDialysis:
1. There are 3 essential components present in HaemoDialysis, they are a Dialyzer, the composition and delivery of the dialysate and the blood delivery system.
2. First, the blood from an Artery in the arm or leg is drawn into a dialysis machine (Dialyzer). This is controlled through the blood pump and arterial pressure pump.
3. Before passing blood into the Dialyzer, Heparin (an anticoagulant) is added in order to prevent the clotting of blood.
4. In Dialyzer, blood flows by one side of a semi permeable membrane, and dialysate are fluid flows by the opposite side.
5. The concentrations of undesired solutes (eg: urea) are high in the blood, but low or absent in the dialysis solution and constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this die of the membrane.
6. The clean blood is then returned via venous pressure pump back to the body.

Applications
1. Removing wastes from the blood
2. Removing excess fluid from the blood
3. Keeping electrolytes (electrically charged particles) in balance