Storage Flashcards
How is glycogen stored in muscles?
As intra- and intermyofibrillar glycogen granules
How is glycogen stored in the liver?
As granules within hepatocytes
Which glycosidic bonds form the branches in glycogen?
alpha -1,6 glycosidic bonds
Where do the glycogen chains originate from?
The dimer of the protein glycogenin.
How often do branch points occur in glycogen?
Every 8-10 residues
Which molecule is needed to begin glycogenesis?
Glucose-6-phosphate
What is the sequence of molecules for glycogenesis?
Glucose -> glucose-6-phosphate -> glucose-1-phosphate -> UDP-glucose -> glycogen
What is the role of phosphoglucomutase?
Conversion of glucose-6-phosphate to glucose-1-phosphate at the beginning to glycogenesis.
What are the main enzymes required for glycogenesis?
Glycogen synthase
Branching enzyme
What are the main enzymes required for glycogenolysis?
Glycogen phosphorylase
Debranching enzyme
Can phosphoglucomutase be used reversibly?
Yes
It is used in glycogenesis and glycogenolysis.
What is the end point of glycogenolysis in muscle and liver?
Glucose-6-phosphate is created in both circumstances but in the muscles G6P is immediately used for glycolysis whereas in the liver it is converted back to glucose.
What is the effect of glucagon on glycogen?
liver: activates glycogen breakdown by increases phosphorylation by glycogen phosphorylase
muscle: glucagon has no effect
What is the effect of insulin on glycogen?
Activates glycogen synthesis by increasing dephosphorylation by glycogen synthase.
Does AMP activate glycogen phosphorylase?
Yes
but only in the muscle not in the liver.
What is the difference between the glycogen phosphorylase of the liver and the one of the muscle?
They are coded for by different genes
What is Von Gierke’s disease?
glucose-6-phosphatase deficiency
glycogen storage disease
What is McArdle disease?
muscle glycogen phosphorylase deficiency
glycogen storage disease
When does gluconeogenesis begin?
Beyond 8 hours of fasting
What are the precursors of gluconeogenesis?
lactate, glycerol and glucogenic amino acids
What is the Cori Cycle?
The conversion of glucose to lactate in muscle which is then reversed in the liver.
What are the key enzymes of gluconeogenesis?
PEPCK
Fructose-1,6-bisphosphatase
Glucose-6-phosphatase
What is the role of PEPCK?
PEPCK is the enzyme used to reverse step 10 of glycolysis through the production of oxaloacetate. This is because the enzyme of step 10 is irreversible.
What does fructose-1,6-bisphosphatase do?
the opposite of phosphofructokinase
reversal of step 3 of glycolysis
What kind of reaction synthesises TAG?
esterification
How is TAG stored?
In anhydrous form as it is hydrophobic.
Within adipocytes.
What is hyperplasia?
An increase in cell number
Where does fatty acid synthesis occur?
Liver
Why is acetyl coA converted to citrate during fatty acid synthesis?
Acetyl-CoA is too big to leave the mitochondria so must be converted to citrate first. Citrate is then cleaved in the cytoplasm.
What is the role of acetylcoA carboxylase?
Prodution of malonyl coA from acetyl coA
What is the role of the fatty acid synthase complex?
Building fatty acids by the sequential addition of 2 carbon units.
Requires ATP and NADH.
What increases the activity of the fatty acid synthase complex?
Insulin and citrate
What decreases the activity of the fatty acid synthase complex?
Glucagon
Adrenaline
AMP
By which mechanism do hormones change the activity of enzymes?
Covalent modification
By which mechanism do citrate and AMP alter enzyme activity?
Allosteric
Which tissues have an absolute requirement for glucose?
erythrocytes, leukocytes, testes, kidney medulla and lens and cornea of eye
