Ill. PROTEIN FUNCTION: MYOGLOBIN AND HEMOGLOBIN 9. (6 pts) Sickle-cell anemia is
ID: 491558 • Letter: I
Question
Ill. PROTEIN FUNCTION: MYOGLOBIN AND HEMOGLOBIN 9. (6 pts) Sickle-cell anemia is a genetic blood disorder that results from a point mutation in hemoglobin. Hemoglobin is a protein made of four subunits: two alpha chains and two beta chains. A mutation in the gene for the beta subunit changes an E at amino acid position 6 to a V. This change causes the hemoglobin molecules to polymerize, forming fibers under low blood oxygen conditions. a) Explain how a single amino acid change can cause such a large effect on protein structure. b) Below is a graph of the binding curves for fetal hemoglobin and adult hemoglobin. Explain the major difference(s) between fetal and adult hemoglobin. 100 95.8 Fetal hemoglobin Adult hemoglobin 2 50 19 26.8 400 80 120 Oxygen partial pressure Gpo2. mmHg) c) List two major differences between myoglobin and hemoglobinExplanation / Answer
9.) Protein has got basically 4 kinds of structure, primary, secondary, tertiary, quarternary. Primary structure is the basic thing where it is a linear chain of aminoacids. If any change in the position of any of the aminoacid will result changes in the further structures ie, secondary, tertiary and quarternary. The folding of the primary structure leads to secondary structure. The interactions present are Wanderwaalis forces, H-bonding, disulphide bond etc. Secondary structures are of 2 types namely alpha helix and beta sheets. The further folding of secondary results in tertiary structure where the folding is done by chaperons. Further folding leads to quarternary.
a.) Each aminoacid acid has a particular R group that dofferentiate each other. It can be polar, non-polar, acidic, bacic, thiol etc. So if one aminoacid change means the chemical property, the interaction that was there is changing. The functional protein is acquired due to folding, that occurs via interaction between the aminoacids. Thus any change in the position or replacement will lead to non-functional protein as proper folding is necessary for proper functioning.
b.) In adult haemoglobin (Hb) it consist of 2 alpha and 2 beta subunits. But in Fetal Hb it consist of 2 alpha and 2 gamma subunits. This helps fetal Hb to bind more efficiently to oxygen even under low partial pressure of oxygen. Thus the graph get shifted up towards the left for fetal Hb.
c.) Haemoglobin is a protein that transports oxygen, wheras myoglobin (Mb) stores oxygen. Mb is a monomer and one unit can tranport only one molecule of oxygen whereas Hb is a tetramer and can transfer 4 molecules. When one unit get attatched to oxygen there is achange that occurs which causes the other 3 units also to take up oxygen and this effect is called co-operative effect. Mb doesn't show this. Its also found that due to this property Hb takes up oxygen at only high partial pressure but Mb takes up at lower pressure itself. The resulting graph of partial pressure of oxygen vs intake of oxygen for Hb is a sigmoid curve and Mb its a hyperbola.