Energy Storage, Glycogen & Fat Flashcards
How and where is glucogen stored?
Stored as glycogen granules in:
muscles (provide muscle with energy)
liver (provide plasma glucose)
What tissues have an absolute requirement for glucose?
RBCs = no mitochondria
neutrophils,
inner most cell of kidney medulla,
lens of eye
Briefly explain the structure of glycogen
α-1-4 glycosidic bonds form chain
α-1-6 glycosidic bonds form branch points, braches can be broken to release energy
Describe the major energy stores in a 70kg man.
TAG ~600,000,
muscle protein ~100,000
Describe, in outline, the reactions involved in glycogen synthesis: glycogenesis
Glucose –> G6P –> G1P –> UDP-glucose + glycogen residues = glycogen
Describe, in outline, the reactions involved in glycogen breakdown: glycogenolysis
Glycogen + Pi –> glycogen + G1P,
G1P to G6P used for muscle energy prod, released by liver as glucose
Compare the functions of liver and muscle glycogen
Liver = G6P to glucose, by G6Pase, to blood.
Muscle = no G6Pase, so G6P enters glycolysis for energy prod
What enzyme rate limits glycogen synthesis?
Glycogen synthase
What enzyme rate limits glycogen degradation?
Glycogen phosphorylase
What effect does insulin have on liver glycogen enzymes?
Increase synthase, decrease phosphorylase
What effect does glucagon/adrenaline have on liver glycogen enzymes?
Increase phosphorylase, decrease synthase
What effect does glucagon have on muscle glycogen stores?
It has no effect
Explain the clinical consequences of glycogen storage diseases
Excess = tissue damage.
Low stores = hypoglycaemia/poor exercise tolerance.
Von gierkes disease = G6Pase def = can’t release glycogen stores.
McArdle disease = muscle glycogen phosphorylase def = quick fatigue
Explain why and how glucose is produced from non-carbohydrate sources
Gluconeogenesis =
~8 hours, liver glycogen depletes, need alternate source of energy = lactate (anaerobic glycolysis), glycerol (adipose tissue), AA (protein)
Name the key enzymes of gluconeogenesis
1) PEPCK,
2) fructose 1,6-bisphosphatase,
3) glucose-6-phosphatase
What is gluconeogenesis?
After 8hrs, no liver glycogen = alternate source of glucose required
Met pathway resulting in generation of glucose from non-carb carbon substrates:
1) glycerol
2) lactate
3) glucogenic AA
What hormones inhibit and stim gluconeogenesis?
Insulin = inhibits.
Glucagon = stimulates
Explain why triacylglycerols can be used as efficient energy storage molecules in adipose tissue
TAG is hydrophobic = stored in anhydrous form in adipose tissue – highly efficient energy store = energy content per gram twice of carb or protein
Give an overview of dietary triacylglycerols metabolism
Intestinal epithelial cell absorb TAG to lymph to blood stored in adipose – transported to tissue on albumin = fatty acid oxidation = energy
Describe how fatty acid oxidation differs from fatty acid synthesis
Oxidation = remove C2 as acetyl-CoA, in mitochondria, oxidative: prod NADH/FADH2, needs small ATP, insulin inhibits.
Synthesis = add C2 by malonyl CoA, in cytoplasm, reductive: requires NADPH, needs large ATP, insulin stim.
What effect does insulin have on glycogen phosphorylase in muscle?
Decrease activity
Where does fatty acid synthesis occur?
Cytoplasm
What are the benefits of glycogens structure?
1) readily release glucose = breaking many diff points
2) reduce osmotic effect by storing as one molecule
What enzyme is involved in glycogenesis?
Glycogen synthase
What enzyme is involved in glycogenolysis?
Glycogen phosphorylase
What is von Gierkes Disease?
G6Pase def
Hepatomegaly = cant release glycogen stores
Outline McArdle disease
Muscle glycogen phosphorylase def
Physically exhausted as cant utilise muscle stores
