Energy Storage Flashcards
Which tissues have an absolute requirement for glucose?
RBC
Neutrophils
Innermost cells of kidney medulla
Lens of eye
What can hypoglycaemia lead to/cause? (ie symptoms)
Confusion
Weakness, nausea
Muscle cramps
Brain damage, death
How is glycogen stored and where?
As granules; in the liver and muscle
What is the structure of glycogen?
Highly branched polymer molecule with glucose subunit.
Chains originate from a dimer of the protein glycogenin at the centre.
Alpha-1,4 glycosidic bonds joining the chains.
Alpha-1,6 glycosidic bonds from branch points.
What is glycogenin?
The protein at the centre of glycogen from which the chains branch from.
Glycogenesis
Glycogen synthesis.
Glucose + ATP -> glucose-6-P + ADP
— hexokinase (glucokinase in liver)
Glucose-6-P -> glucose-1-P
— phosphoglucomutase
Glucose-1-P + UTP + H2O -> UDP-glucose +Pi
— G1P uridylyltransferase
Glycogen (n residues) + UDP-glucose -> glycogen (n+1 residues) + UDP
— glycogen synthase (extend chain - alpha-1,4)
— branching enzyme (form branch - alpha-1,6)
Hexokinase
(What is this in the liver?)
Catalyses glucose to glucose-6-P.
Glucokinase in liver
Phosphoglucomutase
Catalyses glucose-6-P to glucose-1-P as well as the reverse reaction.
G1P uridylyltransferase
Catalyses glucose-1-P to UDP-glucose
Glycogen synthase
Forms alpha-1,4 glycosidic bonds between glucose subunits to extend the chains in glycogen.
Branching enzyme
Forms alpha-1,6 glycosidic bonds to form branches between glucose subunits in glycogen.
Glycogenolysis
Breakdown of glycogen to produce glucose.
Glycogen phosphorylase
Glycogen (n residues) + Pi -> glucose-1-P + glycogen (n-1 residues)
Breaks alpha-1,4 bonds
De-branching enzyme
Breaks alpha-1,6 bonds
Why is the use of different enzymes in glycogenolysis and glycogenesis important?
Using different enzymes allows for the simultaneous inhibition of one pathway and the stimulation of the other.
How is glycogenolysis different in skeletal muscle to the liver?
Skeletal muscle lacks glucose-6-phosphatase, so doesn’t produce glucose and instead stops at glucose-6-P, which feeds into glycolysis.
What is the rate limiting enzyme for glycogen synthesis?
Glycogen synthase
What is the rate limiting enzyme of glycogen degradation?
Glycogen phosphorylase
Glycogen storage diseases
(No specific diseases)
Inborn errors of metabolism - inherited diseases.
Arise from deficiency or dysfunction of enzymes of glycogen metabolism.
Gluconeogenesis - what is it?
Where does it occur?
Synthesising glucose from alternative source (not glycogen).
Occurs in liver and to a lesser extent in kidney cortex.
What are the three major precursors of gluconeogenesis?
Lactate (from anaerobic glycolysis)
Glycerol (from breakdown of fats)
Amino acids (mainly alanine)
What are the three key enzymes in gluconeogenesis?
Glucose-6-phosphatase
Fructose 1,6-bisphosphatase
Phosphoenolpyruvate carboxykinase (PEPCK)
What hormones stimulate gluconeogenesis?
Glucagon, cortisol
What hormone inhibits gluconeogenesis?
Insulin
