4. Glycogen & Fat Flashcards
By what mechanism do adrenaline and glucagon regulate the enzymes in glycogenesis/lysis?
Phosphorylation
By what mechanism does insulin regulate the enzymes in glycogenesis/lysis?
Dephosphorylation
How is the regulation of muscle glycogen stores different from liver stores?
Glucagon has no effect
AMP is an allosteric regulator
What are 2 glycogen storage diseases?
McCardle
Von Gierke’s
What enzyme is deficient in McCardle disease?
Muscle glycogen phosphorylase
What symptoms would you expect to see in McCardle disease?
Exercise intolerance, exhaustion as cannot mobilise skeletal muscle glycogen stores.
Hypoglycaemic.
What enzyme is deficient in Von Gierke’s disease?
Glucose - 6 -Phosphorylase
What changes do you see in the liver in patients with Von Gierke’s disease and why?
Hepatomegaly as the liver cannot release it’s glycogen stores.
Hypoglycaemic
What enzyme catalyses the conversion of Glucose -1P to UDP- glucose?
GTP- uridyltranferase
Which enzyme does muscle lack?
Glucose-6- phosphorylase
How long after eating do glycogen stores run out and gluconeogenesis begin?
8 hours
Where does gluconeogenesis happen?
Liver and kidney cortex
What are the 3 precursors used in gluconeogenesis?
Lactate (cori cycle)
Glycerol
Amino acids - alanine particularly
Which 3 enzymes are needed in gluconeogenesis to bypass irreversible steps in glycolysis?
- PEPCK
- Fructose-1,6-bisphosphatase
- Glucose-6-phosphatase
What reaction does PEPCK catalyse?
Oxaloacetate -> phosphoenolpyruvate
What reaction does fructose-1,6-bisphosphatase catalyse?
Fructose-1,6-bisphosphate -> Fructose-6-P
What reaction does glucose - 6-phosphatase catalyse?
Glucose-6P -> Glucose
Which 2 enzymes are more important for the regulation of gluconeogenesis?
PEPCK and Fructose-1,6-bisphosphatase
What type of receptor is the glucagon receptor?
GPCR
What type of receptor is the cortisol receptor?
Nuclear
What type of receptor is the insulin receptor?
Tyrosine kinase
Which 2 hormones increase gluconeogenesis?
Cortisol, Glucagon
What effect does insulin have on gluconeogenesis?
Inhibits both PEPCK and F-1,6-BP
What is the key regulatory enzyme in lipogenesis?
Acetyl CoA carboxylase
How is AcetylCoA carboxylase regulated?
Stimulated by insulin and citrate
Inhibited by glucagon/adrenaline and AMP
Why is Acetyl CoA carboxylase inhibited by AMP?
Low energy signal - process of lipogenesis requires ATP and NADPH so won’t happen if no energy.
Where does fatty acid synthesis occur?
Cytoplasm
What are the major energy stores and when are they used?
Glycogen- overnight fast and as part of the response to stress and exercise. (1-10 hours)
TAGs - starvation, prolonged exercise, stress
Protein - emergency during starvation
What happens to the fatty acids once they are taken up by adipose and muscle cells?
Re-esterified to triacylglycerols using glycerol phosphate derived from glucose metabolism.
Why do individuals with a defect in the enzyme LCAT produce unstable lipoproteins of abnormal structure?
The spherical shape of lipoproteins is dependent on the ratio of core:surface lipids. As the core gets depleted, LCAT converts surface lipid cholesterol to cholesterol esters, a core lipid. This maintains stability.
What is the clinical consequence of LCAT deficiency?
Lipid deposits occur in many tissues and atherosclerosis is a serious problem.
