Glycolysis Flashcards
Which steps of glycolysis require input of ATP and which enzymes are involved?
Conversion of glucose into glucose-6-phosphate, catalyzed by hexokinase or glucokinase and conversion of Fructose-6-phosphate into fructose 1,6-phosphate, catalyzed by phosphofructokinase-1, (PFK-1.)
What happens to glycolysis products when a cell is under anaerobic conditions (such as contracting muscle cells).
NADH that is produced by glycolysis has to be converted into NAD+ so that build-up does not inhibit glycolysis. Pyruvate is converted into lactate, which builds up in the muscle.
Which steps in glycolysis are irreversible and regulated?
Step 1: conversion of glucose into glucose-6-phosphate, catalyzed by hexokinase or glucokinase.
Step 3: Fructose-6-phosphate into fructose 1,6-bisphosphate, catalyzed by phosphofructokinase-1, (PFK-1.)
Step 10: conversion of phosphophenolpyruvate (PEP) into pyruvate by pyruvate kinase.
How are the activity of hexokinase/glucokinase, PFK-1, and pyruvate kinase regulated?
by the energy status of the cell - ratio of ATP to ADP/AMP. As well as build-up or deficiency of the products of the reactions they catalyze.
How is glycolysis regulated on a systemic level?
by hormones - ratio of glucagon to insulin in the liver, and insulin/epinephrine in the muscles.
Why is glucokinase used in liver cells and hexokinase used in other cells?
Glucokinase has a high Km and therefor low affinity for glucose, restricting its ability to start glycolysis in the liver to times when blood glucose is in excess (after a meal), so the liver is not taking glucose and storing it when other tissues need it. Hexokinase has a low Km and therefore high affinity for glucose, making it active in times of low blood glucose.
What are the respective functions of insulin and glucagon?
Insulin tells the liver to obtain and store glucose, and glucagon tells the liver to release glucose into the bloodstream.
