Energy Storage Flashcards
Write the four steps in glycogenesis
Glucose + ATP —> G6P + ADP (hexokinase/glucokinase) G6P G1P (phosphoglucomutase) G1P + UTP +H2O —> UDP-glucose + 2Pi Glycogen(n residues) + UDP-glucose —> glycogen(n residues + 1) + UDP (glycogen synthase and branching enzymes)
Write the overall equation for glycogenolysis
Glycogen(n residues) + nPi —> 0.9n G6P + 0.1n glucose
Write the three steps in gycogenolysis
Glycogen(n) + Pi —> G1P + glycogen(n+1) (glycogen phosphorylase/branching enzymes) G1P G6P (phosphoglucomutase) G6P + H2O —> glucose + Pi
Which bonds do glycogen phosphorylase and de-branching enzymes affect?
Glycogen phosphorylase - glycosidic 1,4 bonds - phosphorolysis therefore produces G1P De-branching enzyme - glycosidic 1,6 bonds - produces free glucose
What is the difference between liver and muscle glycogen?
Liver - glucose store for all tissues of the body. Muscle - G6P store, only for muscles
Which two main enzymes are used in glycogen metabolism?
Glycogen synthase and glycogen phosphorylase
What inhibits glycogen synthase?
Phosphorylation (de phosphorylation activates glycogen synthase)
Which three enzyme defects can lead to abnormal glycogen metabolism?
Glycogen phosphorylase, phosphoglucomutase and glucose-6-phosphatase (liver)
What is the main site of gluconeogenesis?
Liver
What are possible substrates for gluconeogenesis?
Pyruvate, lactate and glycerol can be converted to glucose. Essential and non-essential amino acids whose metabolism involves pyruvate.
What is the overall equation for gluconeogenesis?
2 pyruvate + 4 ATP + 2 GTP + 2 NADH –> glucose + 2 NAD+ + 4 ADP + 2 GDP + 6Pi + 2H+
What stimulates glycogen phosphorylase?
De-phosphorylation (inhibited by phosphorylation)
How are the irreversible steps of glycolysis by-passed in gluconeogenesis?
1 & 3 - thermodynamically spontaneous reactions (glucose 6-phosphatase and fructose 1,6-bisphosphatase) 10 - ATP and GTP-driven hydrolysis (pyrivate carboxylase and PEPCK)
What are the major control sites for gluconeogenesis?
PEPCK and fructose 1,6-phosphatase
What stimulates PEPCK and fructose 1,6-phosphatase?
High glucagon, low insulin therefore insulin:anti-insulin ratio is important
How are TAGs usually stored?
In an anhydrous form in adipose.
What is the function of TAGs?
Store of fuel molecules for prolonged aerobic exercise.
How is storage of TAGs controlled?
Hormonally: promoted by insulin, depletion activated by glucagon, cortisol, adrenaline, growth hormone and thyroxine
How are TAGs transported to adipose tissue?
In chylomicrons
Describe how fatty acid synthesis differs from fatty acid degradation (beta oxidation)
Which enzyme(s) are necessary for lipogenesis?
Fatty acid synthase complexes
What role does acetyl co A carboxylase play in fatty acid synthesis?
Controls the rate of fatty acid synthesis. Can be regulated by: allosteric regulation, regulation by covalent modification of protein structure. Insulin activates by promoting dephosphorylation and glucagon/adrenaline inhibit the enzyme by promoting phosphorylation
