Energy Storage Flashcards
Which tissues have an absolute requirement for glucose?
Red blood cells, neutrophils, innermost cells of kidney medulla, lens of the eye
What is glucose stored in the form of?
Glycogen
Below what level of blood glucose would a patient experience confusion?
2.8mmol/L and below
Below what level of blood glucose would a patient experience weakness and nausea?
1.7mmol/L and below
Below what level of blood glucose would a patient experience muscle cramps?
1.1mmol/L and below
Below what level of blood glucose would cause brain damage/death?
0.6mmol/L
Which two cell types store glycogen?
Muscle and liver
What is the difference between muscle and liver glycogen?
Muscle glycogen just supplies muscle while liver glycogen can supply the rest of the body
What is glycogen?
A polymer consisting of chains of glucose residues
Which type of bonds join chains in glycogen?
Alpha 1-4 glycosidic bonds
Which bond types form branch points in glycogen?
Alpha 1-6 glycosidic bonds
Where do the branches in glycogen originate?
From a dimmer of the protein glycogenin
How frequent are the branch points in glycogen?
Every 8-10 residues
Does synthesis of glycogen require energy???
Yes
What are the four steps of glycogenesis?
1) Glucose to Glucose-6-phosphate
2) Glucose-6-phosphate to Glucose-1-phosphate
3) Glucose-1-Phosphate to UDP glucose + PPi
4) UDP glucose + Glycogen(n residues) to Glycogen(n+1 residues) + UDP
Which enzyme converts glucose into glucose-6-phosphate in the first step of glycogenesis?
Hexokinase or glucokinase (in liver)
Which enzyme converts glucose-6-phosphate into glucose-1-phosphate in the 2nd step of glycogenesis?
Phosphoglucomutase
Which enzyme converts glucose-1-phosphate into UDP-glucose in the 3rd step of glycogenesis?
G1P uridylyltransferase
What is the equation for the 3rd step of glycogenesis?
Glucose-1-phosphate + UTP + H2O —> UDP-glucose + PPi
Which enzyme catalyses the final step of glycogenesis?
Glycogen synthase
Which enzyme is responsible for the branching of glycogen?
Glycogen branching enzyme
What are the overall equations for glycogenolysis?
Glycogen(n residues) + Pi —> Glucose-1-phosphate + glycogen (n-1 residues)
Glucose-1-phosphate glucose-6-phosphate
What enzymes are involved in the first step of glycogenolysis where glycogen goes to glucose-1-phosphate?
Glycogen Phosphorylase or de-branching enzyme
What enzyme is involved in the conversion of glucose-6-phosphate to glucose-1-phosphate?
Phosphoglucomutase
What happens to glucose-6-phosphate in glycogenolysis?
Muscle - glycolysis - used by energy production
Liver - glucose - released by liver into blood for use by other tissues
Why does glycogen stay in the muscle to be used there?
Muscle lacks glucose-6-phosphatase so G6P enters glycolysis for energy production
What is the rate limiting enzyme in glycogen synthesis?
Glycogen synthase
What is the rate limiting enzyme in glycogen degradation?
Glycogen phosphorylase
What effect does glucagon and adrenaline have on the activity of glycogen synthase?
Decreases the activity
What effect does glucagon and adrenaline have on the activity of glycogen phosphorylase?
Increases the activity
What effect does insulin have on the activity of glycogen synthase?
Increases the activity
What effect does insulin have on the activity of glycogen phosphorylase?
Decreases the activity
Why does glucagon have no effect on muscle glycogen stores?
Muscle cells do not have glucagon receptors
What is an allosteric activator of muscle glycogen phosphorylase?
AMP
What do glycogen storage diseases arise from?
Deficiency or dysfunction of enzymes of glycogen metabolism
What are some examples of glycogen storage diseases?
McArdle disease, von Gierke’s disease
What is the enzyme deficient is von Gierke’s disease?
Glucose 6-phosphatase
What is often seen in von Gierke’s disease?
Enlarged liver
What enzyme is deficient in McArdle disease?
Muscle glycogen phosphorylase
At how many hours of fasting do liver glycogen stores start to deplete?
After 8 hours
Where does gluconeogenesis occur?
Liver and to lesser extent in kidney cortex
What are the 3 major precursors to glucose for gluconeogenesis?
Lactate, glycerol, amino acids (mainly alanine)
What is the cori cycle?
Metabolic process in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is metabolised back to lactate
True or False:
Acetyl-CoA can be converted into pyruvate
False
Acetyl-CoA cannot be converted into pyruvate as the pyruvate dehydrogenase reaction is irreversible so there is no net synthesis of glucose from acetyl coA
What are the key enzymes in gluconeogenesis?
1) Phosphoenolpyruvate carboxykinase (PEPCK)
2) Fructose 1,6 bisphosphatase
3) Glucose-6-phosphatase
What does PEPCK convert?
Converts oxaloacetate into phosphoenolpyruvate and CO2
What does Fructose 1,6-bisphosphatase convert?
Fructose 1,6 bisphosphate into Fructose-6-phosphate
What does glucose-6-phosphatase convert?
Glucose-6-phosphate into glucose
Which are the two key enzymes regulated by hormones that regulate gluconeogenesis?
PEPCK and Fructose 1,6-bisphosphatase
What is the effect of glucagon and cortisol on PEPCK?
Increases the amount so stimulates gluconeogenesis
What is the effect of glucagon and cortisol on Fructose 1,6-bisphosphatase?
Increases amount and activity so stimulates gluconeogenesis
What is the effect of insulin on PEPCK?
Decreases the amount so inhibits gluconeogenesis
What is the effect of insulin on Fructose 1,6-bisphosphatase?
Decreases amount and activity so inhibits gluconeogenesis
After feeding, when does gluconeogenesis occur?
8-10 hours after
What are lipids stored as?
Triglycerides
Describe adipocytes
Contain large lipid droplet, cytoplasm and organelles pushed to edge
How much can adipocytes increase in size on weight gain before dividing and increasing total number of fat cells?
About fourfold
What transports dietary fat?
Chylomicrons
Where do chylomicrons travelling in the lymph enter the blood?
Left subclavian vein
Which enzyme produces malonyl-coA from acetyl-coA?
Acetyl-CoA carboxylase
How many carbons does malonyl-CoA have?
3
What builds fatty acids by sequential addition of 2 carbons provided by malonyl-CoA and what is required?
Fatty acid synthase complex
Requires ATP and NADPH
What increases the activity of acetyl-coA carboxylase?
Insulin and citrate
What decreases the activity of acetyl-coA carboxylase?
Glucagon, adrenaline and AMP
What is produced when malate is converted to pyruvate?
NADPH
How is malonyl coA produced for use with fatty acid synthase complex to produce fatty acids?
Citrate from TCA forms acetyl coA which is acted upon by acetyl-coA carboxylase to make malonyl coA
What does VLDL stand for?
Very low density lipoproteins
Where does fatty acid synthesis occur within the cell?
Cytoplasm (whereas fatty acid oxidation occurs in mitochondria)
Is fatty acid synthesis an oxidative or reductive process?
Reductive - requires NADPH
What is fatty acid synthesis regulated by?
Activity of acetyl-coA carboxylase
What stimulates fatty acid synthesis?
Insulin
What inhibits fatty acid synthesis?
Glucagon and adrenaline
What effect does glucagon and adrenaline have on hormone sensitive lipase (HSL)?
Leads to phosphorylation and activation of HSL
What effect does insulin have on hormone sensitive lipase (HSL)?
De-phosphorylation and inhibition of HSL
