Session 2- Energy Storage And Lipid Transport Flashcards
Describe the energy stores in a 70kg man
Glycogen stored in skeletal muscle and liver- Alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds. Alpha 1,5 bonds are branch points. This allows it to be compact, branched allows many sites for addition/ removal hence rapid synthesis and degradation and osmotically inert
Triaglycerols
Muscle protein
Describe, in outline, the reactions involved in glycogen synthesis
Starts from glucose+ ATP which forms glucose 6-P and ADP. Enzyme that does this is hexokinase but glucokinase in the liver.
Step 2: Glucose 6-P to glucose 1-P via phosphoglucomutase and is reversible
Step 3: Glucose 1-P+UTP+H20 to UDP-Glucose and 2pi (Pyrophosphate) Enzyme: G1P Uridyl transferase
Step 4: Glycogen ( n residues) + UDP-glucose to Glycogen (n+ 1 residues) + UDP
Enzymes: Glycogen synthase
Branching enzyme
Which enzyme catalyses the reaction from glucose to glucose 6 phosphate?
Hexokinase
Liner: Glucokinase
Which enzyme catalyses the reversible reaction Glucose 6-Phosphate to Glucose1-Phosphate?
Phosphoglucomutase
What catalyses the reaction from Glucose1-Phosphate to UDP-glucose?
G1P-Uridyl transferase
Which enzymes acts on the alpha 1,4 glycosidic bonds to create glycogen.
Glycogen synthase
Which enzymes acts on the Alpha 1,6 glycosidic bonds to convert into glycogen?
Branching enzyme
Describe the process of Glycogen degradation
Happens in skeletal muscle
Step 1:Glycogen (n residues)+ inorganic phosphate into glucose 1-phosphate + glycogen (n-1) via glycogen phosphorylase
Step 2: Glucose 1-phosphate converts into glucose 6-phosphate via phosphoglucomutase
Function of glycogen store in the liver
Glucose 6-phosphate is converted into glucose via glucose 6-phosphotase. Glucose is released into blood stream.
It’s a buffer of blood glucose levels
Function of glycogen stores in the muscle
G6P enters glycolysis.
Regulation of liver-glycogen metabolism
What does the glycogen phosphorylase?
It targets the 1,4 glycosidic bonds but not the 1,6 glycosidic bonds
De-branching enzymes works on the 1,6 glycosidic bonds
What’s the rate limiting enzyme for glycogen synthesis? (Regulation)
Glycogen synthase
What’s the rate limiting enzyme for glycogen degradation? (Regulation)
Glycogen phosphorylase
Function of glucagon hormone
Acts on the enzyme glycogen synthase
Mechanism phosphorylation
Decreases the enzyme activity
Function of adrenaline
Acts on the enzyme glycogen phosphorylase
Mechanism phosphorylation
Increases the enzyme activity
Function of insulin
Acts on the enzyme glycogen synthase
Mechanism de-phosphorylation
Increases the enzyme activity
Acts on the enzyme glycogen phosphorylase
Mechanism de-phosphorylation
Decreases the enzyme activity
Does glucagon have an effect on muscle glycogen stores
No
The skeletal muscle doesn’t have glucagon receptors
The liver-glycogen storage function is to buffer the blood glucose levels
Whereas muscles are for energy and contraction
Glycogen storage diseases
Inborn errors of metabolism (deficiency/ dysfunction of the enzymes in glucose metabolism)
What is Von Gierke’s disease?
Glucose 6-phosphatase deficiency
What is Mcardle disease?
Muscle glycogen phosphorylase deficiency
When does Gluconeogenesis occur?
8-10 hours fasting
Liver
What are the 3 major precursors of gluceoneogensis?
Lactate: From anaerobic glycolysis in exercising muscle and muscle blood cells (Cori cycle)
Glycerol: Released from adipose tissue breakdown of triglycerides
Amino acids: Mainly alanine
What are the key enzymes in gluconeogensis?
PEPCK
Fructose 1,6-biphosphatase
Glucose-6-phosphatase
Where does PEPCK act on?
It catalyses the reaction from oxaloacetate into phosphoenolpyruvate
