RED &WHITE BLOOD CELLS DR AMINA TARIQ BIOCHEMISTRY

RED &WHITE BLOOD CELLSDR AMINA TARIQ

BIOCHEMISTRY

Blood has two distinct parts to it. Plasma, the fluid part of the blood, takes up

about 55% of the blood volume. Plasma is 91% water with various other materials in solution and suspension, such as dissolved proteins, nutrients, electrolytes, hormones, and metabolic wastes.

The cellular portion of blood normally makes up about 45% of the blood volume.

It consists primarily of white blood cells (WBCs), platelets, and red blood cells (RBCs). The white blood cells are the mobile elements of the body's defense system. Platelets are small cell fragments which play an important part in blood clotting

RED BLOOD CELLS

Biomedical Importance Structure of Hb Function of Hb Porphyrias Jaundice Iron metabolism Anemias

STRUCTURE OF RBC

A very simple cell. Major function is to transport oxygen to the

tissues . And disposal of carbon dioxide and protons

formed by the tissue metabolism. Is composed of a membrane surrounding the

hemoglobin. Hb forms about 95% of the intracellular

protein of the red cell.

There are no intracellular organelles, such as mitochondria, lysosomes or golgi apparatus.

Non- nucleated. Metabolically is active. Biconcave shape increases the surface to

volume ratio of RBC, thus facilitating the gas exchange.

Contain cytoskeletal components that play an important role in determining its shape.

RBC contains certain enzymes of nucleotide metabolism.

At the end of their life span, globin is degraded to amino acids which are reutilized in the body. Iron is released from heme and also reutilized, and porphyrins are converted to bilirubin.

Life span of RBC is 120 days. Production of red cells is regulated by

erythropoeitin.

Erythropoeitin: It is a glycoprotein of 166 amino acids. It is a major regulator of human

erythropoiesis. It is synthesized mainly in the kidney. Is released in response to hypoxia into the

blood stream, and travel to bone marrow. There it interacts with the progenitor of red

cells -Burst forming unit-erythroid (BFU-E). Recombinant DNA (anemia of renal failure)

MEMBRANE OF RED CELL

Membrane is a lipid bilayer.50% lipids and 50% proteins.

Major lipids are phospholipids and cholesterol.

Major phospholipids are: PC, PE,PS and sphingomyelin.

Choline containing phospholipids are in the outer leaflet(PC, Sph).

Amino containing phospholoipids are in the inner leaflet (PE, PS).

Glycosphingolipids constitute about 5-10%. These constitute neutral GSLs, gangliosides

and complex species, including ABO blood group substances.

10 major proteins and 100 minor species. Major proteins include: spectrin,

ankyrin,anion exchange proteins, actin and band 4.1.

Many of the proteins are glycoproteins.

ASPECTS OF RBC METABOLISM

Glucose dependent (glucose transporters). Anaerobic glycolysis for ATP production. No mitochondria, no oxidative

phosphorylation. Transporters on the membrane. Production of 2,3 BPG. Pentose Phosphate pathway. Methemoglobin reductase. Synthesis of glycogen, fatty acids, proteins

and nucleic acids does not occur in the RBC.

Glucose Transporter – GLUT 1 is present on RBC. It is an example of facilitated transport. Not dependent on insulin. It generates a gated pore in the membrane and to permit the passage of glucose.

Transporters maintain the ionic and water balance. It involves the movement of Cl⁻ and HCO3( anion exchange protein). In RBC it is called band 3. It is important in adjusting the levels of RBC HCO3 ⁻ concentration in arterial and venous blood.

DISORDERS AFFECTING RBCS

Iron deficiency anemia Methemoglobinemia Sickle cell anemia Thalassemias Megaloblastic anemias ( B12 , folic acid) Hereditary spherocytosis G6PD deficiency Pyruvate kinase deficiency Paroxysmal nocturnal hemoglobinemia

G6PD deficiency- It is an inherited disorder. Characterized by the hemolytic anemia. Caused by the inability to detoxify oxidizing

agents. It is the most common disease producing

enzyme deficiency in the world. It is X-linked disorder.

Decreased G6PD activity impairs the ability of the cell to form NADPH.

Which is responsible for the maintenance of reduced glutathione.

Glutathione also helps maintain the reduced states of sulfhydryl groups in proteins including Hb.

When these proteins are oxidized it leads to the denaturation of these proteins.

That form insoluble masses called Heinz Bodies.

These bodies attach to the red cell membrane.

Membranes become rigid and deformable. G6PD deficiency occurs in all the cells , but is

most severe in RBCs. Because other cells are able to produce

NADPH by alternate pathway(NADP dependent malate dehydrogenase).

Precipitating Factors: Oxidant drugs(AAA- antibiotics, antimalarials

and antipyretics). Favism. Infection. Neonatal jaundice

Caused by Missense point mutations. Variant forms:1. G6PD A⁻ - Moderate form of disease.2. G6PD Mediterranean – Severe form of disease.

PROTECTION OF RBC

Several powerful oxidants are produced in the course of metabolism, in both blood cells and other cells of the body.

These include superoxide, hydrogen peroxide, peroxyl radicals and hydroxyl radicals.

These are known as reactive oxygen species. Superoxide dismutase, Catalase and

Glutathione protect red cell from these ROS.

SOD convert O⁻2 into H2O2.

Catalase detoxify H2O2 to H2O. Glutathione also does the same.

NEUTROPHILS

BIOCHEMICAL FEATURES

Active glycolysis Active pentose phosphate pathway Moderate oxidative phosphorylation Rich in lysosomes. Unique enzymes and proteins. E.g.

myeloperoxidase , NADPH oxidase, Contain CD 11/ CD 18 integrins in plasma

membrane.

IMPORTANT ENZYMES & PROTEINS

Myeloperoxidase- responsible for the green color of the pus. Deficiency causes chronic infections.

NADPH oxidase- responsible for the respiratory burst.

Lysosomes- Abundant in macrophages. Defensins- Antibiotic peptide, kills bacteria

by causing membrane damage.

Lactoferrin- It is an iron binding protein, inhibits growth of certain bacteria by binding iron.

CD 11/ CD 18- Adhesion molecules. Receptors for the Fc fragment of IgGs- bind

Fc fragment of IgG molecule. Vasoactive biomolecules (plate activating

factor, eicosanoids).

PROTEINASES

Elastase Collagenase Gelatinase Cathepsin G Plasminogen activator

ANTIPROTEINASES

α-1 antitrypsin α-2 macroglobulin Secretory leukoproteinase inihibitor α-1antichymotrypsin Plasminogen activator inhibitor-1 Tissue inhibitor of metalloproteinase.

ACTIVATION OF NEUTROPHILS

They are activated by specific receptors. By interaction with bacteria, chemotactic

factors, antigen-antibody complexes. Intracellular calcium rises and activates

protein kinase C.

RESPIRATORY BURST

It involves NADPH oxidase and helps kill bacteria.

There are two mechanisms – oxygen dependent and oxygen independent for killing bacteria.

Oxygen independent mechanism: These involve pH changes in phagolysosmes And Lysosomal enzymes to kill bacteria.

Oxygen dependent mechanism: It includes myeloperoxidase system(MPO)

and NADPH oxidase system. It is the most potent bactericidal mechanism. Microorganism is internalized. NADPH oxidase converts molecular O2 into

superoxide radical. This rapid conversion is called respiratory

burst.

Then superoxide is spontaneously converted into hydrogen peroxide.

This product is then neutralized by catalase or glutathione peroxidase.

In the presence of Myeloperoxidase which is a lysosomal enzyme, Hydrogen peroxide plus chloride ions are converted to hypochlorous acid.

This kills the bacteria. Hypochlorous acid is the major component

of household bleach.

Mutations in the genes encoding NADPH oxidase leads to a disease called chronic granulomatosis.

In which severe chronic pyogenic infections occur.

LEARNING RESOURCES

Harpers Biochemistry Lippincott's Biochemistry