Topic 12 - Principles of Metabolic Regulation Flashcards
Describe Glycogen
- Branched polymer of glucose
- linked by a 1-4 bonds w/ a 1-6 branches
- Serves as reservoir of glucose
- Found primarily in liver & skeletal muscle
- Catabolism of glycogen occurs when BGL <
Enzymes of Glycogen Catabolism
Describe the function of glycogen phosphorylase
- Catalyses reaction where a1-4 linkage undergoes attack by Pi
- Releases terminal glu. res. from non-reducing end as glucose 1P
- Stops when reaches a point of 4 glu. res. away from a1-6 branch point
Enzymes of Glycogen Catabolism
Describe the function of debranching enzyme
- Shifts a block of three glu. res. from branch to a nearby non-reducing end (attached by a1-4 linkage
- Cleaves last glu. res @ branch point :: introduces a1-6 linkage
Enzymes of Glycogen Catabolism
Describe the function of phosphoglucomutase
- Converts glucose 1P => glucose 6P
- Glucose 6P exclusively catabolised in glycolysis to generate e in muscle
Enzymes of Glycogen Synthesis
Describe the function of glycogen synthase
- Catalyses transfer of glu. res. from UDP-glucose to a non-reducing end of a glycogen chain
- Requires a “primer” a1-4 polyglucose chain
Enzymes of Glycogen Synthesis
Describe the function of branching enzyme
- Catalyses transfer of a terminal fragment (6-7 glu. res.) from non-reducing end of a glycogen branch to C6 hydroxyl group of a glu. res.
Draw flow chart of glycogen catabolism and synthesis.
- Endeavour to include sugar nucleotide pathway and names of enzymes
- Try to explain if you can
Reference written notes for sug. nucleotide pathway
Name, in order, the 11 enzymes of GNG
(could use flow chart?)
- Pyruvate carboxylase
- PEP carboxykinase
- Enolase
- Phosphoglycerate mutase
- Phosphoglycerate kinase
- Glyceraldehyde phosphate dehydrogenase
- Triose phosphate isomerase
- Aldolase
- Fructose 1, 6 Bisphosphatase
- Phosphohexose isomerase
- Glucose-6-phosphatase
Regulation of Glycolysis & GNG
How does it occur?
What is it based on?
What molecules signal e status of cell?
When does GNG or Glycolysis predominate?
**Think BGL levels and ATP
- Occurs by regulating enzymes that catalyse the irreversible reactions
- Based on:
-Energy status of cell:
< e (ATP) = glycolysis predominates
> e (ATP) = GNG predom.
-BG levels (occurs only in insulin responsive cells):
< BGL = GNG predom. glucagon released
>BGL = glycolysis predom. insulin released - Molecules that signal e status of cell
< e = AMP & ADP
> e = ATP; citrate; fructose 1,6BP; acetyl-CoA; long chain FA’s.
Reciprocal regulation of reaction 3
Draw the flow chart (sl 35) of RRR3 identifying:
- GNG is on or off
- Glycolysis on or off
- enzymes and energy molecules
- Which signal molecules inhibit/activate either side
Reciprocal regulation of reaction 3
Enzymes
Describe the actions of Glycogen Phosphorylase (look at diagram in book to help with understanding or sl 17)
- Catalyses breakdown of glycogen
- Activated when BGL<. Glucagon activity
- active form (a) is phosphorylated
- Inactivated when BGL>. Insulin activity
- inactive form (b) is unphosphorylated
Reciprocal regulation of reaction 3
Enzymes
Describe the actions of Glycogen Synthase (look at diagram in book to help with understanding or sl 17)
- Catalyses synthesis of glycogen
- Activated when BGL>. Insulin activity
- active form (a) is unphosphorylated
- Inactivated when BGL<. Glucagon activity
- inactive form (b) is phosphorylated
- Glycogen phosphorylase
- formation of (a1-6) linkages during glycogen synthesis
- It catalyses addition of glucose-UDP residues to the non-reducing end of a glycogen chain by formation of (a1-4) bonds
Describe the role of hormones in carbohydrate metabolism
Draw the flow chart showing the influence of insulin (High BGL)
Describe the role of hormones in carbohydrate metabolism
Draw the flow chart showing the influence of glucagon (low BGL)
