Energy Storage Flashcards
What are the three major energy stores? (70KG man)
Triacyclglycerols (15KG)- Stored in adipose tissue.
Glycogen (0.4KG) - Stored in the liver.
Muscle Proteins (6KG) - Only used during starvation.
Outline the reactions involved in glycogen synthesis:
Glucose is phosphorylated to form Glucose 6-phosphate by hexokinase.
Glucose 6P is converted to Glucose 1P
Glucose 1P reacts with UTP to form UDP-glucose - an inorganic phosphate molecule is released.
UDP-glucose then reacts with glycogen. The glucose monomer is added to the glycogen polymer. UDP is released and reforms UTP with a phosphate molecule.
Which enzymes are used to catalyse the addition of glucose from UDP-Glucose to glycogen?
Glycogen Synthase (a1-4 glycosidic bond) Branching enzyme. (a1-6 glyosidic bond)
Remember that glycogen is a branched molecule (which means lots of glucose monomers can be broken off at once). Branching enzyme adds glucose via bonds which produce those branches.
Outline glycogen breakdown:
Either glycogen phosphorylase or de-branching enzyme cleave a molecule of glucose 1-P from glycogen. A molecule of phosphate is needed as a substrate.
Glucose 1-P is converted to glucose 6-P which can be used metabolically.
How does the functions of liver and muscle glycogen vary?
In both Glucose 6-P is produced from glycogenolysis.
In muscle Glucose 6-P is used for glycolysis to produce energy.
In the liver Glucose6-P is converted back to glucose by glucose-6-phosphatase and released into the blood for use in other tissues.
In the liver what are the rate-limiting enzymes for glycogen synthesis and glycogenolysis?
Glycogen synthesis - Glycogen synthase
Glycogenolysis - Glycogen Phosphorylase
How do glucagon and adrenaline regulate glycogen metabolism?
Remember glucagon and adrenaline are produced to trigger a ‘fight or flight’ response.
They stimulate glycogen phosphorylase so that more energy is released.
They inhibit glycogen synthase to limit the amount of energy put into storage.
How does insulin regulate glycogen metabolism?
Remember insulin is produced as a hormone to begin ‘rest and digest’ responses.
It stimulates glycogen synthase to put more energy into storage.
It inhibits glycogen phosphorylase to limit the blood glucose levels.
Name two glycogen storage diseases:
Von Gierke’s disease -
Glucose 6-phosphatase deficiecy.
(Inefficiency of the liver to convert G6P to glucose for transport around the body)
McArdle Disease -
Muscle glycogen phosphorylase deficiency.
(Inefficiency in glycogen mobilisation)
What are the clinical consequences of glycogen storage diseases?
Can affect either the liver or muscle.
Excess glycogen can lead to tissue damage.
Diminished glycogen stores can lead to hypoglycaemia.
When does gluconeogenesis occur?
Beyond 8 hours of fasting the liver’s glycogen storage is depleted.
It therefore starts to produce glucose from non-carbohydrate sources.
Where does gluconeogenesis occur?
Mainly in the liver but also in the kidney cortex.
What precursors can be used for gluconeogenesis?
Lactate (Produced from anaerobic glycolysis)
Glycerol (Released from adipose tissue)
Glucogenic Amino Acids (Mostly alanine)
Outline gluconeogenesis:
Lactate and glucogenic amino acids are converted into oxaloacetate.
Oxaloacetate is fed into a chain of reactions by the enzyme PEPCK.
Eventually Fructose 1,6-bis phosphate is produced as an intermediate.
This is converted to fructose 6P by fructose 1,6-bis phosphatase.
Fructose 6P is converted to Glucose 6P and then from that to glucose by Glucose-6-phosphatase.
What are the key regulatory enzymes in gluconeogenesis?
PEPCK (Converts oxaloacetate into an intermediate)
Fructose 1,6-bis phosphotase (Converts fructose 1,6-bids phosphotase into Fructose 6P)
