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
Where does Fructose 1,6bisphosphatase act on?
Converts Fructose 1,6busphosphate into Fructose 6-phosphate
Where does Glucose-6-phosphates act on?
Glucose 6-phosphate into glucose
What is the function of the hormone glucagon in gluceoneogensis?
Acts on PEPCK, increases the amount and stimulates the effects on gluconeogensis
What is the function of the hormone cortisol in gluceoneogensis
Increases the amount and activity of Fructose 1,6 bisphosphatase and stimulates gluconeogensis
What is the effects of the hormone insulin in gluconeogensis?
- Acts on PEPCK, decreases amount- inhibits gluceoneogensis
- Acts on Fructose 1,6 phosphatase- decreases amount and activity- inhibits
What is the synthesis and hydrolysis of triacylglycerol What is the function of the hormone glucagon in
Synthesised from glycerol and fatty acids into triacylglycerol via esterification
Degradation- Lipolysis
Benefits of triacylglycerol
Compact
Hydrophobic
What are the two types of adipocytes
Unilocular (white)
Multinocular (brown)
TAG metabolism process
TAG is hydrolysed by pancreatic lipase to fatty acids and glycerol
Which these two diffuse into intestinal epithelial cell
Converts back into TAG and binds to chylomicrons
Goes through lymph and blood
It has two places it can go: Storage or directly utilised as tissue (fatty acid oxidation)
What effects are there on hormone sensitive lipase in adipose?
Glucagon and Adrenaline causes a positive effect on Hormone sensitive lipase which causes more mobilisation
Insulin causes a negative effects on Hormone sensitive lipase which causes less mobilisation
