Carbohydrate metabolism Flashcards
What is the critical blood glucose concentration? [1 mark]
2.5mM
What is the usual blood glucose concentration? [1 mark]
5mM
Symptoms of hypoglycaemia [5 marks]
- muscle weakness
- loss of coordination
- mental confusion
- sweating
- hypoglycaemic coma or death
Symptoms of hyperglycaemia [4 marks]
- Non enzymatic modification of proteins (glucose is reactive)
- cataracts
- artheriosclerosis
- hyperosmolar coma
How does the body deal with excess glucose? [3 marks]
- Glycogen synthesis
- Pentose phosphate pathway
- fatty acid synthesis
How does the body deal with a lack of glucose?
- Glycogen breakdown
- Gluconeogenesis
Glycogen structure [3 marks]
- large
- branched with alpha-1,4 (linear) and alpha-1,6 (branched) links
- glycogenin helps molecule form
What reaction does UDP-glucose-pyrophorylase catalyse? [1 mark]
Glucose-1-phosphate → UDP-glucose
What does UDP-glucose-pyrophorylase do to glucose? [1 mark]
Activates it to make it more available for reaction with glucogenin
When does glycogen synthase stop adding glucose residues? [1 mark]
When it reaches ~11 residues
What stimulates branching enzyme? [1 mark]
11 residue length of glycogen
WHy is glycogen a suitable storage molecule? [4 marks]
- Glycogen is osmotically inactive
- Glycogen is compact
- It’s broken down quickly
- it can be used in short bursts of energy
What does phosphorylase do to glycogen? [2 marks]
- Alpha-1,4 links are broken
- glucose-1-phosphate is produced
What are the two activities associated with debranching enzyme and what are their functions? [4 marks]
- transferase
which transfers all but last residue to neighbouring alpha-1,4 chain - alpha-1,6 glucosidase
breaks alpha-1,6 link
Why is glucose mobilised in muscles? [1 mark]
To maintain contraction
How is blood sugar maintained with glucose-6-phosphate?
- G6P is dephosphorylated
- G6P is secreted into the blood
What does the activity of glycogen phosphorylase form? [1 mark]
Glucose-1-phosphate
Glycogen phosphorylase structure [3 marks]
- Large multi subunit enzyme
- allosteric enzyme
- Many phosphorylase molecules are bound to each glycogen particle
What is phosphorylase activated by? [2 marks]
- Phosphorylation
- but it’s modulated by other factors
Forms of phosphorylase? [2 marks]
- Phosphorylase a (active)
- phosphorylase b (inactive)
What is phosphorylase b kinase and how does it work? [2 marks]
- it regulates phosphorylation of phosphorylase b
- transfer Pi from ATP to a serine residue on each subunit
What inhibits glycogenolysis? [1 mark]
Insulin
What stimulates glycogenolysis in the liver?
Glucagon
What stimulates glycogenolysis in the muscles? [1 mark]
Adrenaline
What is a weak stimulator of glycogenolysis? [1 mark]
Cortisol
Enzymes involved in glycogenolysis [4 marks]
- adenylate cyclase
- protein kinase A
- phosphorylase kinase
- phosphorylase a
What does protein kinase A phosphorylate? [2 marks]
- phosphorylase kinase (activation)
- Glycogen synthase (inactivation)
What does 5’-AMP do?
- binds to glycogen phosphorylase b (without phosphorylation)
- happens when ATP is depleted
What blocks activation via 5’-AMP [2 marks]
- ATP
- G6P
What is phosphorylase a inhibited by in the liver? [1 mark]
Glucose
What do calcium ions activate?
Phosphorylase b kinase
