Energy Storage Flashcards
What happens once glycogen stores have been depleted? (After 8-12 hours)
Gluconeogenesis
What are the main energy stores in a 70kg man?
Triacylglycerols - 15kg
Glycogen - 0.4kg
Muscle proteins - 6kg
Which two types of glycosidic bonds are present in glycogen?
Alpha 1-4 and a1-6
Which bonds are the branch points in glycogen?
Alpha 1-6
What does the highly branched structure of glycogen allow?
Many sites to which glucose residues can be added/removed, allowing rapid synthesis/degradation of glycogen
Where is glycogen stored?
Granules in liver and skeletal muscle
Why is there a limit to how much glycogen can be stored?
A highly polar molecule so attracts lots of water
No specialised storage tissue so has to be stored in tissues with other important functions
What is glycogenesis?
Synthesis of glycogen
Name the six enzymes needed for glycogenesis
Hexokinase / glucokinase in liver
Phosphoglucomutase
Glycogen synthase
Branching enzyme
When is glycogen degraded?
In skeletal muscle - exercise
In liver - during fasting, stress response
Glycogen degradation is not a reversal of the synthetic pathway. What does this allow for?
Greater metabolic flexibility
Independent control
What does glycogen phosphorylase do?
Involved in glycogen degradation
Attacks alpha 1-4 bonds by phosphorolysis
This releases glucose residues as glucose 1P
What does debranching enzyme do in glycogen degradation?
Breaks down alpha 1-6 bonds and releases free glucose.
What does glucose 6-phosphatase do?
Converts glucose 6-P releases from glycogen degradation into glucose in the liver.
Which two enzymes are regulated in glycogen synthesis/degradation?
Glycogen synthase
Glycogen phosphorylase
How are the enzymes activated/inhibited in glycogen regulation?
Synthase - inhibited by phosphorylation and activated by dephosphorylation
Phosphorylase - inhibited by dephosphorylation and activated by phosphorylation
Regulated by glucagon and insulin
How does insulin and glucagon regulate the enzymes of glucagon synthesis/degradation?
Insulin promotes dephosphorylation
Glucagon promotes phosphorylation
What are consequences of glycogen storage diseases?
Too much/little glycogen can cause
- tissue damage if excessive
- fasting hypoglycaemia
- poor exercise tolerance
What can be used in gluconeogenesis?
Lactate, pyruvate, amino acids and glycerol
Which reactions is gluconeogenesis from pyruvate similar to?
Glycolysis
Which enzymes are involved in gluconeogenesis from pyruvate?
Glucose 6-phosphatase
Fructose 1,6-bisphosphatase
Pyruvate carboxylase
PEPCK
Which two enzymes are controlled in gluconeogenesis and how?
PEPCK and fructose 1,6-bisphosphatase
Activity is increased by glucagon and cortisol and decreased by insulin
When does gluconeogenesis occur?
When all of the glycogen has been used up after 8-10hrs of fasting
What is the overall equation of gluconeogenesis?
2 pyruvate + 4ATP + 2GTP + 2NADH
——-> glucose + 2NAD+ + 4ADP + 2GDP + 6Pi + 2H+
List the enzymes which reduce storage of triacylglycerols.
Glucagon
Cortisol
Thyroxine
Growth hormone
What is lipogenesis?
Fatty acid synthesis
What are fatty acids synthesised from and where does it occur?
Acetyl CoA
Cytoplasm
What does fatty acid synthesis require and where do they come from?
NADPH - from the pentose phosphate pathway
Acetyl CoA - comes from the mitochondria as citrate
Citrate -> oxaloacetate + acetyl CoA
ATP
Where does FA synthesis occur?
Cytoplasm
Describe the process of FA synthesis
Carried out by FA synthase complex
C2 added as malonyl CoA (a C3 molecule) in each turn of the cycle to the growing FA chain with a subsequent loss of carbon dioxide
How is malonyl CoA produced?
From acetyl CoA
Done by the enzyme acetyl CoA carboxylase.
How is acetyl CoA carboxylase regulated?
Allosteric regulation - citrate activates and AMP inhibits
Covalent modification - insulin activates by promoting its dephosphorylation and glucagon inhibits by phosphorylation
Why are TAGs an efficient way of storing energy
Can be stored in bulk in an anhydrous form
