Metabolism Flashcards
what’s are difference between hexokinase and glucokinase, in terms of tissue distribution?
Hexokinase is present in most tissues. glucosekinase is present only in hepatocytes (liver cells) and pancreatic B-islet cells
What’s the difference between hexokinase and glucokinase, in terms of Km and Vmax?
Hexokinase has a low Km and low Vmax (reaches max velocity at low [glucose] - zero order kinetics)
glucosekinase has a high Km and a high Vmax (rate adjusts according to [glucose] - first order kinetics)
What’s the difference between GLUT 2 and GLUT 4 in terms of tissue distribution? What is their function?
GLUT 2 and GLUT 4 are glucose transporters. GLUT 2, like glucokinase, is present in hepatocytes (liver cells) and pancreatic cells. GLUT 4 is present if adipocytes and muscle cells.
In terms of Km and Vmax, what’s the difference between GLUT 2 and GLUT 4?
GLUT 2, like glucokinase, has a high Km and high Vmax (first-order kinetics). GLUT4, like hexokinase, has a low Km and a low Vmax (zero-order kinetics)
What is hexokinase inhibited by?
glucose 6-phosphate (feedback inhibition)
what is glucokinase activated by?
insulin in hepatocytes
what is the rate-limiting enzyme of glycolysis?
phosphofructokinase 1 (PFK-1)
In the catabolism of galactose, what does galactokinase and galactose 1-phosphate uridyltransferase do?
galactokinase: phosphorylates galactose to keep it in cell
galactose 1-phosphate uridyltransferase: converts galactose 1-phosphate to glucose 1-phosphate
If galactose builds up due to deficiency in galactokinase, what can happen?
galactose is turned into galactitol and cataracts form
In the catabolism of fructose, what does fructokinase and aldolase B do?
fructokinase: phosphorylates fructose (fructose 1-P) to keep it in cell
aldolase B: forms dihydroxyacetone phosphate (DHAP) and glyceraldehyde
What are three functions of NADPH?
- biosynthesis (fatty acids, cholesterol)
- immune system (bleach in white blood cells)
- antioxidant (forms reduces glutathione)
what is reduced glutathione used for in the cell?
reverse oxygen free radical formation (especially formation of free radicals from hydrogen peroxide produced from ETC)
what is a phosphorylase?
enzyme that breaks a bond using inorganic phosphate, rather than water (hydrolase)
what’s the difference between a synthase and a synthetase?
synthases form covalent bonds without needing much energy input, whereas synthetases form covalent bonds with energy input.
(think citrate synthase vs. succinate-CoA synthatase)
what are cytochromes?
proteins with heme groups in which Fe3+ is reduced to Fe2+.
