Ls4203_class test_2017 please answer only question no.7. (5 marks) Class Test, L

Question

Ls4203_class test_2017
please answer only question no.7. (5 marks)

Class Test, LS4203, Full marks: 15, Time: 3:05 PM to 3:50 PM, Answer any three Liver contain both Hexokinase and Glucokinase: catalyze reaction (ie, glucose + ATP glucose-6-phosphate ADP). Describe how glucokinase and hexokinase regulate blood glucose homeostasis? How activity of hexokinase and glucokinase is regulated? 3+2 5 6. If only three protons are required to power the FoF ATP synthase to produce one molecule of ATP, explain why does the text book say that four protons are required for the synthesis of one molecule of ATP? Explain how dinitrophenol functions as a chemical uncoupler of the electron transport chain and oxidative phosphorylation. Discuss the possibility for dinitrophenol, can be used as a drug for weight loss. 2+1+2-5 7. Discuss catabolism of lactose in aerobic condition. What is the function of Phosphprylase? How its activity is regulated? 2+1+2-5 8. Discuss the fates of pyruvate in yeast under anaerobic condition. What are the roles of 0 mitochondria in gluneogenesis? What are the roles of fermentation in aerobic organisms? 2+1 +2=5

Explanation / Answer

Lactose is composed of one unit of galactose and one unit of glucose. It gets degraded into its two components by the action of the enzyme lactase also called -galactosidase, encoded by the lac operon. This cleavage occurs at the brush border of small intestine, from where the monosaccharide units are absorbed at transported to the liver. The galactose is converted into glucose-6-phosphate in the liver via the Leloir pathway and then enters the anaerobic glycolysis along with glucose and then to aerobic Krebs cycle finally making way into the electron transport chain. One molecule of lactose thus generates (2x38)=72 ATPs.

Phosphorylase enzymes catalyse phosphate group addition from inorganic phosphate to any acceptor/substrate molecule (A-B + H-OP= {displaystyle ightleftharpoons } A-OP + H-B). for example, glycogen phosphorylase.

Phosphorylase enzymes are regulated by allosteric interactions and reversible phosphorylation.

For example muscle glycogen phosphorylase exists in tow interconvertible forms: phosphorylase a ehich is active state and phosphorylase b that is inactive. Both phosphorylase b and phosphorylase a exist as equilibria between an active R state and a less-active T state. Phosphorylase b is usually inactive because the equilibrium favors the T state. Phosphorylase a is usually active because the equilibrium favors the R state. the b form gets converted into the a by a single phosphorylation of serine residue at position 14 by phosphorylase kinase.   

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