biochem exam III

Lehninger Principles of Biochemistry

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1) Glucose is converted to glucose-6-phosphate via hexokinase IV, a.k.a. glucokinase. Hexokinase is commited only to the forward reaction to G6P because the reaction has a large – ’°G and the byproduct is CO2, which flies Δ away as a gas making it difficult to obtain in the reverse reaction. During gluconeogenisis in the liver, eleven enzymes are used to produce glucose from various beginning substrates. In the last step however, G6P is converted to glucose via hydrolysis by glucose-6-phosphotase. This is carried out in the lumen of the endoplasmic reticulum, and is then shuttled out through glucose transporters into the cytosol, and then eventually to the blood. This is important when blood-sugar levels are low, and the glucose can be used for energy by organs such as the heart. Therefor, it is true that the reverse reaction by hexokinase is irreversible, however the conversion of G6P to glucose is possible by glucose-6-phosphotase. 2) LDH is an isoenzyme that is produced in five different forms. The different isoenzymes play different roles depending on i) different metabolic patterns in different organs, ii) different locations and metabolic roles for the isoenzyme in the same cell, iii) different stages of development in embryonic and in adult tissues, and iv) different responses of isoenzymes to allosteric modulators. LDH1 and LDH2 are found in heart and blood cells. LDH4 and LDH5 are found in the liver. LDH1 is primarily found in the heart and favors rapid oxidation of lactate to pyruvate in the heart; NAD+ and pyruvate strongly inhibit the reaction of pyruvate to lactate in the heart. In the oxygen- rich organ of the heart, LDH is required to catalyze the reverse reaction (explaining ’°G=0) so that lactate from the tissues can fuel the heart. In Δ erythrocytes, LDH enables the continuous conversion of glucose to two molecules of excreted lactic acid and ATp (energy) in the anaerobic cells. The final oxidation of NADH+ to NAD in the pyruvate to lactate reaction regenerates the NAD+ that is consumed in the G3P dehydrogenase step earlier in glycolysis. The lactic acid that is excreted is circulated back to the heart for further oxidation. The energy released in red blood cells is not as high as say, in skeletal muscles that are aerobic. In muscle cells when oxygen becomes scarce, there is a high concentration of NADH. This shifts the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/17/2009 for the course CHEM 430 taught by Professor Brandt during the Winter '09 term at Rose-Hulman.

Page1 / 5

Biochem exam III - 1 Glucose is converted to glucose-6-phosphate via hexokinase IV a.k.a glucokinase Hexokinase is commited only to the forward

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online