Glucose and Glycogen metabolism
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Give 3 structural differences between glucose and glycogen
Glucose is a monosaccharide and glycogen is a polysaccharide. Glucose is osmotically active and glycogen is low osmolarity. Glucose is an immediate energy store and glycogen is ` medium term energy store.
What is the role of the liver in terms of glycogen?
It is a site of storage. It acts to maintain blood glucose under the control of insulin and glucagon.
What intermediate molecule can we use instead of glucose in the liver?
glucose - 6 - phosphate
What is the name of the enzyme involved in glycogen synthesis? What molecule is needed to be an activated intermediate in this reaction?
Glycogen synthase UDP glucose
What enzyme is needed for glycogenolysis? What ends as the final product in the liver? skeletal muscle?
Glycogen phosphorylase glucose glucose - 6 - phosphate
What is the purpose of the synthesis and breakdown not being a direct reversal?
Independent regulation. Speeding up one process does not speed up the other.
What are the 2 steps involved in glycogen synthesis?
• Glucose is converted to UDP glucose. - add a phosphate to glucose forming glucose - 6 - phosphate - enzyme called phosphoglucomutase to form glucose - 1 - phosphate - Add UTP and make UDP glucose • Glycogen synthase enzyme used. It takes the UDP glucose and adds it to the glycogen chain. Different enzyme will be needed to add a branching glucose to position 6
What is the 2 steps for glycogen breakdown?
• Phosphorolysis - the phosphate bonds with the glucose leaving the glycogen chain and glucose - 1 - phosphate Phosphoglucomutase is then used to move the phosphate to position 6 making glucose - 6 - phosphate. Water and glucose - 6 - phosphatase (only found in liver and kidney) is added to remove the phosphate to form glucose.
What are 3 sources of glucose to be used in glycolysis?
Sugars and starch from fat Breakdown of stored glycogen from the liver Recycled glucose from lactic acid or amino acids or glycerol
What are the 4 ‘stages’ of glycolysis?
1 = activation (using up ATP) 2 = splitting the 6 sugar into half 3 = oxidation (removing 2H atoms) 4 = synthesis of ATP
Outline the first 3 reactions of the glycolytic pathway
1 = glucose to glucose - 6 - phosphate (done for diffusion purposes). Glucokinase enzyme catalyses this in the liver and hexakinase in the muscle 2 = glucose - 6 - phoshate to fructose - 6 - phosphate 3 = fructose - 6 phosphate to fructose 1,6 - bisphosphate
What is the purpose of reactions 4 and 5?
Splitting the 6C sugar in 3C sugar
Explain reactions 4 and 5
4 = aldolase is added to fructose 1, 6 - bisphopshate 5 = This either froms glyceraldehyde 3 - phosphate or dyhydroxacetone phosphate. More of the first one gets used up so more of this is produced.
What step is the oxidation step?
6
What occurs in reaction 6?
Glyceraldehyde 3 - phosphate is converted to 1,3 - bisphosphoglycerate by the addition of phosphate and NAD+. Aldehyde is becoming a carboxylic acid
Summarise reactions 7 - 10 which are the ATP synthesis stages
7 = substrate - level phosphorylation. Makes ATP from ADP and Pi. 3 - phosphoglycerate is made 8 = Movement of phosphate group to form 2 - phosphoglycerate 9 = Dehydration reaction as water is removed. Forms phosphoenol pyruvate 10 = substrate level phosphorylation as pyruvate is formed. Removal of phosphate to turn ADP to ATP
Explain the anaerobic process
Glycolysis occurs and pyravte is not converted to C02 and H20. It is converted into lactate in order to convert NADP to NAD+. This is catalysed by lactate dehydrogenase.
How are hormonal control and allosteric regulation relevant?
Hormonal control - hormone bind to cell surface receptor and activates internal signalling pathway. This activates kinase. Allosteric regulation - alteration of the activity of an enzyme by means of a conformational change induced by a different molecule
• The metabolism of glucose to pyruvate: a) can only occur in anaerobic conditions. b) involves six irreversible reactions c) is the main source of ATP in red blood cells. d) occurs in the mitochondrial matrix. e) requires the cofactor FAD.
C
• When glycogen is broken down in skeletal muscle cells: A. glucose is produced by hydrolysis of glucose-1-phosphate. B. glucose is produced by hydrolysis of glucose-6-phosphate. C. glucose is produced by hydrolysis of glucose-1-6-bisphosphate D. glucose-1-phosphate is produced via glucose-6-phosphate. E. glucose-6-phosphate is produced via glucose-1-phosphate.
E