Glycolysis Flashcards
What are the stages of glycolysis? What is the net reaction?
2 stages - energy investment and energy producing
Glycolytic Pathway: D-Glucose + 2ADP + 2Pi + 2NAD+
YIELDS
2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
How is energy captured in glycolysis?
As 2 ATP and 2 NADH
How many reactions are involved in glycolysis? How many are irreversible?
10 are involved; 3 are irreversible (1,3,10–this is where glycolysis is regulated).
Irreversible often = large decrease in deltaG
Most reactions are reversible and used in gluconeogenesis?
Steps of glycolysis?
1) IRREVERSIBLE: glucose to glucose-6-phosphate, via hexokinase. Occurs as soon as glucose enters cell, to prevent it from leaving.
2) Glucose-6-phosphate to fructose-6-phosphate, via phosphoglucoisomerase
3) IRREVERSIBLE: F6P to F-1,6-bisphosphate, via phosphofructokinase-1 (PFK-1). Glucose is now committed to the glycolytic pathway. Irreversible due to large decrease in deltaG.
4 and 5) F-1,6-BP to Glyceraldehyde-3-P, via aldolase and triose phosphare isomerase
6) G3P to glycerate-1,3-BP, via G3P dehydrogenase
7) glycerate-1,3-BP to glycerate-3-P, via phosphoglycerate kinase. Substrate level phosphorylation occurs, producing ATP from ADP
8) Glycerate-3-P to glycerate-2-P, via phosphoglycerate mutase
9) Glycerate-2-P to phosphoenolpyruvate, via enolase, releasing H20
10) IRREVERSIBLE: Phosphoenolpyruvate to pyruvate, via pyruvate kinase. Substrate level phosphorylation produces ATP from ADP
What happens to pyruvate under aerobic conditions?
Under aerobic conditions, pyruvate is converted to acetyl-CoA for use in the citric acid cycle and electron transport chain.
What is gluconeogenesis? What is its relationship to glycolysis?
Gluconeogenesis is the formation of glucose from pyruvate. It is antiparallel to glycolysis.
What happens to pyruvate under anaerobic conditions in muscle?
Lactic acid fermentation. 1 lactate produced from 1 pyruvate.
NAD+ regenerated so that glycolysis can continue.
What happens to pyruvate under anaerobic conditions in yeast?
Alcoholic fermentation.
1) Pyruvate -> Acetaldehyde
2a) Acetaldehyde -> Ethanol
2b) Acetaldehyde -> Acetyl CoA (via other intermediates).
What enzymes are involved in glycolysis regulation? What type of regulation is this?
Hexokinases I, II, III, IV. PFK-1. Pyruvate kinase.
Do some of these sound familiar? Irreversible reactions…
This is allosteric regulation. Regulated locally by effector molecules.
What peptide hormones regulate glycolysis?
Glucagon and insulin
How do hexokinases I, II, and III regulate glycolysis? Where do they work?
Work in many tissues.
High affinity for glucose. Inhibited by G6P (produced in which step of glycolysis…?)
When blood glucose is low, G6P is also low, allowing cells to use available glucose. When blood glucose is high, G6P rises and inhibits hexokinase I, II, and III so that cells only phosphorylate the amount of glucose they need.
How does hexokinase IV work? Where does it work?
Works mostly in liver. To a very small degree in pancreas, intestine, and brain.
Low affinity for glucose. NOT inhibited by G6P.
When glucose is high, hexokinase IV is active and converts it to G6P, so that it can be converted into glycogen and stored.
Sensitive to small changes in glucose concentration = glucose sensor
What is the major role of the liver?
Regulating blood glucose.
When blood glucose is high, convert it into glycogen. When glucose is low, catabolize glycogen to glucose (glycogenolysis)
How does pyruvate kinase work?
Activated by high levels of cAMP and accumulation of fructose-1,6,-bisphosphate (which step of glycolysis…?)
Causes a “feed-forward” loop
How does PFK-1 work?
Activated by fructose-2,6-bisphosphate, which is produced by hormone induced covalent modification of PFK-2
