Lecture 4 Flashcards
Hemeproteins
Specialized proteins that contains heme as a prosthetic group.
Heme function
- Reversibly binds oxygen, each heme group contains an iron atom.
- Electron carrier in cytochrome.
- Catalyzes the breakdown of hydrogen peroxide.
Myoglobin
- Function
- Consists of
- Type of amino acids
- Reservoir for oxygen and as an oxygen carrier.
- A single polypeptide chain.
- Non- polar AA.
- Charged AA are located on the surface.
Hemoglobin
- Found in
- Function
- Composed of
- Red blood cells.
- Transport oxygen from the lungs to the capillaries.
- 4 polypeptide chains: 2 alpha and 2 beta chains.
Why myoglobin affinity for oxygen is higher than hemoglobin?
Because it has a proximal histidine group that helps it bind oxygen.
T and R forms of hemoglobin
T form: less affinity for O2, tense state, deoxyhemoglobin, weak ionic and H bonds.
R form: relaxed state, oxyhemoglobin, ionic and H bonds are broken.
Allosteric effects
Binding O2 to one of the subunits is affected by its interactions with other subunits.
- pO2
- pH of the environment
- pCO2
Bohr effect
An acidic environment reduces the oxygen affinity of Hb
-Protons are released from Hb when O2 binds
Effect of CO2
CO2 reduces the oxygen affinity of hemoglobin by covalent binding to the terminal amino groups of the alpha and B chains
Effect of 2,3- bisphosphoglycerate on Oxygen Affinity
- Binds to the T conformation
- BPG decreases the oxygen- binding affinity.
- Enhances the unloading of oxygen in the tissues.
Binding of CO
- It has a much higher affinity to iron than O2.
- CO and O2 compete for the same binding site.
Fetal Hemoglobin (Hb F)
- Major Hb found in newborns.
- Higher affinity to O2, because it binds weakly to 2,3- BPG.
- Higher affinity facilitates the transfer for oxygen from the maternal circulation across the placenta.
Hemoglobinopathies
Disorders caused by the production of abnormal hemoglobin molecule or synthesis of insufficient quantities of normal hemoglobin.
- Sickle cell anemia
2. Hemoglobin C disease
- Glutamic acid is replaced by Valine.
2. Glutamic acid is replaced by Lysine.
- B- Thalassemias
2. A- Thalassemias
- B- globin chains is decreased or absent.
2. A- globin chains is decreased or absent.
Fibrous proteins
- 3 different structures
- Alpha helix cross-linked by disulfide bonds.
- Beta conformation
- Collagen triple helix
Collagen
- Characteristics
- Types
- Most abundant protein in the human body.
- Left- handed helix.
- 3 AA residues per turn.
-Fibril- forming (type I, II, III), Network- forming (IV, VIII), Fibril- associated (IX, XIII).
Collagen structure
- Triple helix
- Alpha chains (left handed helix)
- Rich in proline and glycine
- Glycine is found IN EVERY THIRD POSITION
- Stabilized by hydrogen bonds
Gly- X- Y
X: proline
Y: hydroxyproline.
Osteogenesis imperfecta
- Brittle bone syndrome.
- Collagen related disease.
- Gly is replaced by bulky side chains (big)
Plasma Proteins - Blood
-Composition
Composed of an aqueous solution containing molecules of varying sizes and a number of cellular elements.
Plasma vs. Serum
Plasma: treated with anticoagulant, contains clotting proteins
Serum: it is allowed to clot, absence of fibrinogen.
Major functions of blood
Respiration: transport of O2 from the lungs to the tissues.
Regulation of body temperature.
Excretion transport of metabolic wastes to the kidneys and intestines for removal.
Transport: of hormones, metabolites..
Coagulation
Plasma consists of:
Water Proteins Electrolytes Metabolites Nutrients
Oncotic pressure
Hydrostatic pressure
- Pressure created by water moving across a membrane due to osmosis (from the outside, to the inside).
- From inside to the outside.
