Session 4-Energy Storage (Glycogen And Fat) Flashcards
Which tissues have an absolute requirement for glucose as an energy source? (4)
1) red blood cells
2) neutrophils
3) innermost cells of kidney medulla
4) lens of eye
Define glycation
Addition of glucose to protein without enzymatic regulation
What is the normal blood glucose concentration?
~5mmol/L
What are the consequences of the following blood glucose concentrations: A) 2.8 mmol/L B) 1.7 mmol/L C) 1.1 mmol/L D) 0.6 mmol/L
A) confusion
B) weakness, nausea
C) muscle cramps
D) brain damage, death
What is glycogen stored as?
Granules
Glycogen is a polymer consisting of chains of which residues?
Glucose
The chains of glycogen are branched and originate from a dimer of which protein?
Glycogenin
Which reactions in glycogenesis require energy and which enzymes catalyse these reactions? (2)
1) glucose + ATP -> glucose-6-phosphate + ADP
Catalysed by hexokinase (glucokinase in liver)
2) glucose-1-phosphate + UTP + water -> UDP-glucose + PPi
Catalysed by G1P uridylyltransferase
Which enzyme catalyses the reversible reaction between glucose-6-phosphate and glucose-1-phosphate?
Phosphoglucomutase
Which enzyme/s catalyse the following reaction:
Glycogen + UDP-glucose -> glycogen + UDP
Glycogen synthase
Or
Branching enzyme
What is glycogenolysis?
Glycogen degradation
Which enzyme catalyses the following reaction:
Glycogen (n residues) + Pi -> glucose-1-phosphate + glycogen (n-1 residues)
Glycogen phosphorylase
OR
De-branching enzyme
True or false: glycogenolysis is a simple reversal of glycogenesis
FALSE - different enzymes allow inhibition of one pathway and stimulation of another
How is glucose-6-phosphate used in muscle?
Used in glycolysis for energy production
How is glucose-6-phosphate used in the liver?
Converted to glucose which is released into the blood for use by other tissues
True or false: liver glycogen is a buffer of blood glucose levels
TRUE
Which enzyme does muscle lack?
Glucose-6-phosphatase
What is the rate limiting enzyme for glycogen synthesis?
Glycogen synthase
What is the rate limiting enzyme for glycogen degradation?
Glycogen phosphorylase
What effect does glucagon and adrenaline have on:
1) glycogen synthase
2) glycogen phosphorylase
1) decreases enzyme activity
2) increases enzyme activity
What effect does insulin have on:
1) glycogen synthase
2) glycogen phosphorylase
1) increases enzyme activity
2) decreases enzyme activity
True or false: glucagon has no effect in the muscle
TRUE - no glucagon receptors in muscle
What is an allosteric activator of muscle glycogen phosphorylase but not of the liver form of the enzyme?
AMP
What can diminished glycogen stores lead to?
Hypoglycaemia and poor exercise tolerance
What is von Gierke’s disease?
Glucose-6-phosphatase deficiency
What happens to the liver in von Gierke’s disease?
Hepatomegaly
What is McArdle disease?
Muscle glycogen phosphorylase deficiency
Where does gluconeogenesis occur?
In liver and to lesser extent in kidney cortex
What are the three major precursors for gluconeogenesis?
1) lactate
2) glycerol
3) amino acids (mainly alanine)
Why is there no net synthesis of glucose from acetyl-CoA?
Acetyl-CoA cannot be converted into pyruvate because the pyruvate dehydrogenase reaction is irreversible
Which enzyme converts glucose-6-phosphate to glucose in gluconeogenesis?
Glucose-6-phosphatase
Which enzyme converts fructose 1,6-bisphosphate to fructose 6-phosphate in gluconeogenesis?
Fructose 1,6-bisphosphatase
Which enzyme converts oxaloacetate to phosphoenolpyruvate in gluconeogenesis?
PEPCK
Which two key enzymes are regulated by hormones in response to starvation/fasting, prolonged exercise and stress?
Fructose 1,6-bisphosphatase
PEPCK
What effect does glucagon and cortisol have on:
1) PEPCK
2) Fructose 1,6-bisphosphatase
3) gluconeogenesis
1) increases amount
2) increases amount and activity
3) stimulates
What effect does insulin have on:
1) PEPCK
2) Fructose 1,6-bisphosphatase
3) gluconeogenesis
1) decreases amount
2) decreases amount and activity
3) inhibits
Which receptor does insulin act through?
Tyrosine kinase receptor
Which receptor does glucagon act through?
GPCR
Which receptor does cortisol act through?
Steroid hormone nuclear receptor
How many hours after feeding does gluconeogenesis occur?
8-10 hours
What is excess energy intake converted to for storage?
Triacylglycerol (TAG)
True or false: TAGs are hydrophilic and stored in hydrous form in adipose tissue
FALSE - hydrophobic so stored in anhydrous form
True or false: TAG has an energy content that is twice that of carbohydrate or protein
TRUE
When is TAG utilised?
Prolonged exercise
Stress
Starvation
During pregnancy
Why does fatty acid oxidation not occur in the brain?
Fatty acids don’t easily pass blood-brain barrier
Where does lipogenesis occur?
Mainly in liver
Which two molecules does lipogenesis require?
ATP
NADPH
What is the key regulatory enzyme in liver lipogenesis?
Acetyl-CoA carboxylase
Describe the steps involved in lipogenesis (50
1) glucose -> pyruvate (glycolysis)
2) pyruvate enters mitochondria and forms acetyl-CoA and oxaloacetate which condense to form citrate
3) citrate -> cytoplasm and cleaved back to acetyl-CoA and oxaloacetate
4) acetyl-CoA carboxylate produces malonyl-CoA from acetyl-CoA
5) fatty acid synthase complex builds fatty acids by addition of 2 carbon units from malonyl-CoA
What does insulin and citrate do to acetyl-CoA carboxylase?
Increases activity
What does glucagon/adrenaline and AMP do to acetyl-CoA activity?
Decreases activity
Where does fatty acid oxidation occur?
Mitochondria
Where does fatty acid synthesis occur?
Cytoplasm
True or false: fatty acid oxidation is reductive
FALSE - oxidative, fatty acid synthesis is reductive
What is the term given to fat mobilisation?
Lipolysis
What do glucagon and adrenaline do to hormone sensitive lipase (HSL)?
Lead to phosphorylation and activates HSL
What does insulin do to hormone sensitive lipase (HSL)?
Leads to de-phosphorylation and inhibits HSL
Which protein transports fatty acids to muscle and other tissues?
Albumin
