Question

4. Describe each cycle/transport system (compounds, compartments, tissues) and explain its purpose:

            A. malate/aspartate shuttle

            B. citrate transport system

            C. Cori cycle

            D. glucose/alanine cycle

Answer 1

4. Describe each cycle/transport system (compounds, compartments, tissues) and explain its purpose:

            A. malate/aspartate shuttle =

compartment -cytoplasm and mitochondrial matrix.

compounds = NADH & NAD+.

is the principal mechanism for the movement of reducing equivalents (in the form of NADH ) from the cytoplasm into the mitochondrial matrix . the electron are carried into the mitochondrial matrix in the form of malate . cytoplasmic malate dehydrogenase (MDH) reduces oxaloacetate to malate while oxidizing NADH to NAD+ . malate then enters the mitochondrial matrix where the reverse reaction is carried out by mitochondrial MAD and regeneration of NADH occurs .

            B. citrate transport system = citrate and pyruvate can cross the mitochondrial membrane via specific transport proteins.

compartment = matrix and cytosol

compounds = citrate ,pyruvate.

            C. Cori cycle =the cori cycle refers to the metabolic pathway which lactate produced by anaerobic glycolysis in the muscle move via the blood stream to the liver where it is converted into blood glucose and glycogen .

it is cycle in which - glycogen in the muscle is degraded to produce lactic acid - blood-liver-where it is changed back into glycogen .

Purpose= when needed the glycogen is broken down into glucose and the blood carries the glucose to the muscle .

lactate produced by the muscles is converted to glucose .

glucose is converted by liver ,and fed back to the muscles.

liver shares in the metabolic stress created by vigorous exercise.

D. glucose/alanine cycle = it cosists of series of steps through which extrahepatic tissues,for example skeletal muscle ,export pyruvate and amino groups as alanine to the liver,and receive glucose from the liver via the bloodstream.

compartment =

compounds = L-alanine

tissues = muscle & tissues ,liver

purpose of Glucose-alanine cycle- it transports nitrogen in a non toxic form from peripheral tissues to liver.

-it transports pyruvate,a gluconeogenic substrate,to the liver.

- It removes pyruvate from peripheral tissues this leads to higher production of ATP from glucose in these tissues.

-It allows to maintain a relatively high conc.of alanine in hepatocytes,sufficient to inhibit protein degradation.

Tissues =