Questions from study guide for biochem exam. Please answer as many as you can. T
ID: 205074 • Letter: Q
Question
Questions from study guide for biochem exam. Please answer as many as you can. Thank you
1. Where is glycogen found? What is the glycogen granule comprised of and what is its overall structure? What types of linkages are found in glycogen? How do they differ from cellulose?
2. What is glycogen phosphorylase? What are the two activities of the debranching enzyme? What does phosphoglucomutase do in both breakdown and synthesis of the glycogen particle? What are the two products of glycogen breakdown? In what proportion will they be found?
3. What is UDP-glucose pyrophosphorylase and what does it do? What is glycogen synthase? What is glycogenin?
4. What signals lead to the breakdown/synthesis of glycogen?
5. When is phosphorylase active/inactive? When is glycogen synthase active/inactive? What role do phosphorylase kinase, PP1c, GSK-3, and the GL or GM proteins play in regulation of glycogen synthesis/breakdown?
6. What role does Ca2+ and AMP play in the breakdown of glycogen in the skeletal muscle?
7. Based on the questions above (#4-6) you should be prepared to fully diagram the regulation of glycogen synthesis and breakdown.
Explanation / Answer
1) Glycogen is the principal storage form of glucose in animal cells. In humans, the most glycogen is found in the liver, However, relatively low amount of glycogen is also found in muscle and in certain glial cells in the brain. It is a homopolysaccharide formed by units of glucose.Glycogen is a highly branched glucose polymer that consists of small chains of 8 to 12 glucose molecules linked together with -(14) glycosidic bonds. These small chains are further linked together with an -(16) glycosidic bond. A single molecule of glycogen can be made of up to 120,000 molecules of glucose.
Glycogen differs from the cellulose due to the fact that Cellulose is a straight chain polymer consists of (14) glycosidic bonds between Glucose molecules whereas, Glycogen is branched chain polymer consisting of (14)-glycosidic bonds and (16)-glycosidic bonds. Glycogen is a storage form whereas, cellulose is a constituent of cells.
2) glycogen phosphorylase is an enzyme that releases glucose molecule from the glycogen in liver and muscle.it uses inorganic HPO42– to split glucose from the polysaccharide chains of glycogen, therefore, avail glucose-1-phosphate for glycolysis without using an ATP.
The glycogen-debranching enzyme has two independent catalytic activities, oligo-1,41,4-glucanotransferase and amylo-1,6-glucosidase. 1,4-glucanotransferase, or glucosyltransferase, transfers three glucose residues from the four-residue glycogen branch to a nearby branch, therefore, exposes a single glucose residue joined to the glucose chain through an -1,6 glycosidic linkage. Amylo-1,6-glucosidase, cleaves the remaining alpha-1,6 linkage, producing glucose and a linear chain of glycogen.
Phosphoglucomutase is an enzyme that transfers a phosphate group on a glucose monomer from the 1' to the 6' position in case of glycogen breakdown, while 6' to the 1' position in case of glycogen synthesis.
the breakdown products from glycogen are G1P and glucose. In the equilibrium state, it is found in the proportion of glucose/G1P = 3.6
3) UTP—glucose phosphorylase that is also known as glucose-1-phosphate uridylyltransferase is an enzyme, found in all three domains (bacteria, eukarya, and archaea). It is a key player in glycogenesis and cell wall synthesis that synthesizes UDP-glucose from glucose-1-phosphate and UTP.
Glycogen synthase is an enzyme that catalyzes the converts glucose into glycogen. Glycogen synthase catalyzes the transfer of glucose monomers from UDP-glucose to the terminal branch of the growing glycogen chain via the formation of (14) glycosidic bonds.
Glycogenin is a substrate that acts as a primer, by polymerizing the first few glucose molecules, after which other enzymes take over to catalyze the formation of complete glycogen molecule.
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