Carbohydrate Metabolism Flashcards
Where is glycogen found?
Found in liver + muscle
What is role of liver?
Supplier and store of glycogen
Muscle is source…..
Source of energy and net user
What are symptoms of hypoglycaemia?
Muscle weakness, loss of coordination, muscle confusion, sweating, hypoglycaemic coma + death
What are symptoms of hyperglycaemia?
Non enzymatic modification of proteins: cataracts, lipoproteins important in atherosclerosis:hyperosmolar coma
What processes are involved with excess blood glucose?
Glycogen synthesis
Pentode phosphate pathway
Fatty acid synthesis
What processes involved with lack of blood glucose ?
Glycogen breakdown
Gluconeogensis
Describe the structure of glycogen?
Large branched molecule
Branches are essentially glucose residues which are linked together by a1-4 + a1-6 links
Alpha 1-6 links=> branched part of molecule
Alpha 1-4 links=> linear part of molecule
Consists of molecule called glycogenin
Glycogenin is essential component of glycogen as without it glycogen cannot be formed
What is name of enzyme that makes a1-6 links?
Branching enzyme
Glucose 6 phosphate to glucose 1 phosphate
Is catalysed by….
Phosphoglucomutase
What enzyme catalyses the reaction glucose 6 phosphate to UDP glucose?
UDP glucose pyrophosphorylase
What does glycogen synthase do?
It adds glucose residues + will attach them in a1-4 configuration => there is continuation of this addition until it gets 11 length of residues
Why use glycogen instead of glucose?
Cannot store glucose as it’s osmotically active
Glycogen is heavily branched so can be broken down => many residues can be released
Glucose can be metabolised in absence of oxygen
What are 2 activities Debranching enzyme is associated with it?
It takes all but last residue + transfer it to end of neighbouring a1-4 chain
It remove branch group + breaks a1-6 links + glucose is generated
What are enzymes involved in glycogen breakdown?
Debranching enzyme Transferase/translocase Phosphorylase Phosphoglucomutase Glucose 6 phosphatase
Describe the structure of glycogen phosphorylase and what it is involved in?
Key enzyme for glycogenolysis + its activity forms glucose 1 phosphate
Large multi subunit enzyme
Is an example of allosteric enzyme one that sites away from active site that control its activity by inducing shape changes in protein
Phosphorylase b is converted by active form called phosphorylase a by enzyme called
Phosphorylase b kinase
It transfers phosphate from ATP to one serine residue on each phosphorylase subunit
It also adds phosphates to phosphorylase b to form phosphorylase a
Hormone regulation of glycogenolysis
Adrenaline stimulates cAMP
cAMP activates protein kinase A
Protein kinase A phosphorylate phosphorylase kinase
Phosphorylase kinase phosphorylates phosphorylase kinase b
Phosphorylase kinase a generates glucose 1 phosphate
Protein kinase A phosphorylates glycogen synthase a to give glycogen synthase b => phosphorylationun glycogen synthase activates it
Describe the control of glycogen phosphorylase
In muscle, glycogen phosphorylase b can be activated by 5’ AMP which binds to another allosteric site without being phosphorylated
ATP binds to same site +blocks activation
Glucose 6 phosphate blocks 5’AMP activation
In liver, activated phosphorylase a is inhibited by glucose
Activation of phosphorylase b kinase by Ca2+
Ca2+ ions activate phosphorylase b kinase=> in muscle, mediating glycogenolysis during muscle contraction
Only get max activity with Ca2+ and phosphorylation=> in liver, a-adrenergic activation stimulates Ca2+ release
Glycogen synthesis and degradation is ….
.. regulated
Reciprocal regulation
Glycogen synthase is activated by…
Activated in times of plenty of glucose
Activated by ATP +GTP
Activated by dephosphorylation by protein phosphatase 1)
Glycogen synthase is inactivated ……
Phosphorylation by protein kinase A
Glycogen phosphorylase is activated by….
Activated when glucose is in short supply
Activated by phosphorylation by phosphorylase b kinase
