Glycolysis Flashcards
Define glycolysis.
Catabolism of glucose to yield two molecules of pyruvate.
Glucose + _______ + _______ + 2Pi
_______ + 2NADH + _______ + _______ + 2H+
Glucose + 2NAD+ + 2ADP + 2Pi
2 pyruvate + 2NADH + 2ATP + 2H2O + 2H+
Where does glycolysis take place?
In the cytosol.
How many reaction stages are there in glycolysis?
10.
What is reaction stage 1 and 2 known as?
Energy investment phase.
What is reaction stage 3 known as?
Energy harvesting phase.
What tissue does GLUT1 and GLUT3 diffuse across?
All mammalian tissues.
What tissue does GLUT2 diffuse across?
Liver and pancreatic cells.
What tissue does GLUT4 diffuse across?
Muscle and fat cells.
What tissue does GLUT5 diffuse across?
Small intestine.
In regards to glucose transport into cells, define isoform specificity.
Different affinities for glucose.
How many molecules of ATP are used in glycolysis?
Two.
State the three chemical reactions that take place in reaction stage 1 of glycolysis.
- Glucose —> Glucose-6-phosphate.
- Glucose-6-phosphate —> Fructose-6-phosphate.
- Fructose-6-phosphate —> Fructose-1,6-bisphosphate.
State the two chemical reactions that take place in reaction stage 2 of glycolysis.
- Fructose-1,6-bisphosphate —> Glyceraldehyde 3-phosphate + Dihydroxyacetone phosphate.
- Dihydroxyacetone phosphate —> Glyceraldehyde 3-phosphate.
Define preparatory phase.
Phosphorylation of glucose and its conversion to glyceraldehyde 3-phosphate.
What enzyme is used for the conversion of glucose to glucose-6-phosphate?
Glucokinase.
State the coupled reaction of glucose to glucose-6-phosphate.
Glucose + ATP —> Glucose-6-phosphate + ADP
State the process that occurs in reaction stage 1 of glycolysis.
There is a transfer of phosphoryl group from ATP to glucose. Hexokinase is used but requires Mg2+ ATP complex.
What complex does hexokinase require for essential kinase activity?
Mg2+ ATP complex.
What effect does glucose have upon hexokinase?
It induces a conformational change in hexokinase by placing ATP close to group C6 in glucose and excludes water from the active site.
What type of group transfer does hexokinase permit?
Phosphoryl group transfer.
What is the purpose of glucokinase?
Localisation.
What are two advantages of phosphorylating glucose?
- Retention in the cell (glucose-6-phosphate cannot easily cross the plasma membrane).
- Glucose-6-phosphate is the branch point for several metabolic pathways.
State the process that occurs in reaction stage 2 of glycolysis.
Glucose-6-phosphate is converted to fructose-6-phosphate by phosphoglucose isomerase. The isomerisation is of an aldose to a ketose and is a readily reversible reaction.
State the process that occurs in reaction stage 3 of glycolysis.
Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate. Phosphofructokinase (PFK) catalyses this reaction and requires Mg2+ ATP complex.
What is the purpose of phosphofructokinase (PFK)?
It is the central role in the control of glycolysis (rate determining step).
What is reaction stage 4 of glycolysis catalysed by?
Aldolase.
State the process that occurs in reaction stage 4 of glycolysis.
The cleavage of fructose-1,6-bisphosphate forms 2 trioses.
What 2 trioses are formed in reaction stage 4 of glycolysis?
- Glyceraldehyde-3-phosphate (GA3P).
2. Dihydroxyacetone phosphate (DHAP).
Out of the 2 trioses formed in reaction stage of glycolysis, which one continues along the glycolytic pathway? What is this known as?
Glyceraldehyde-3-phosphate (GA3P). It is known as the suction effect.
State the process that occurs in reaction stage 5 of glycolysis.
Glyceraldehyde-3-phosphate (GA3P) and dihydroxyacetone phosphate (DHAP) are interconverted by triose phosphate isomerase. Under steady state, as GA3P is consumed, more DHAP is converted into GA3P.
What are two outcomes of reaction stages 1 to 5 of glycolysis?
- Glucose is phosphorylated, consuming 2 ATP.
2. 2x glyceraldehyde-3-phosphate (GA3P) are produced.
State the chemical reaction that takes place in reaction stage 6 of glycolysis.
Glyceraldehyde-3-phosphate —> 1,3-bisphosphoglycerate
State the chemical reaction that takes place in reaction stage 7 of glycolysis.
1,3-bisphosphoglycerate —> 3-phosphoglycerate
State the chemical reaction that takes place in reaction stage 8 of glycolysis.
3-phosphoglycerate —> 2-phosphoglycerate
State the chemical reaction that takes place in reaction stage 9 of glycolysis.
2-phosphoglycerate —> phosphoenolpyruvate
State the chemical reaction that takes place in reaction stage 10 of glycolysis.
Phosphoenolpyruvate —> pyruvate
What products are produced at the end of glycolysis?
2x pyruvate, 2ATP (4ATP are made but 2ATP are consumed) and 2NADH.
State the process that occurs in reaction stage 6 of glycolysis.
Glyceraldehyde-3-phosphate is oxidised and phosphorylated. It requires co-enzyme NAD+ and Pi, which is catalysed by GAPDH. 1,3-bisphosphoglycerate is produced.
What reaction stage in glycolysis is the first high energy intermediate?
Reaction stage 6.
What does NAD stand for?
Nicotinamide adenine dinucleotide.
State the process that occurs in reaction stage 7 of glycolysis.
3-phosphoglycerate is produced by the catalysation of phosphoglycerate kinase. The first ATP is generated.
What reaction stage in glycolysis produces the initial 2 ATP?
Reaction stage 7.
State the process that occurs in reaction stage 8 of glycolysis.
Phosphoglycerate mutase interconverts 3-phosphoglycerate and 2-phosphoglycerate. Mutase forms a 3PG-phosphoenzyme complex which decomposes to form 2PG and regenerate free mutase.
State the process that occurs in reaction stage 9 of glycolysis.
Enolase forms the second high energy intermediate, phosphoenolpyruvate (PEP). 2PG is dehydrated to PEP by enolase.
State the process that occurs in reaction stage 10 of glycolysis.
Pyruvate kinase generates the second lot of 2ATP by coupling PEP cleavage to ATP synthesis. Pyruvate kinase requires Mg2+ and K+.
Why can glycolysis occur under anaerobic conditions?
Because ATP is produced by substrate-level phosphorylation.
What are the three irreversible reaction stages of glycolysis.
1, 3 and 10.
Low ATP levels initiate glycolysis by stimulating what molecule?
Phosphofructokinase (PFK).
Glucose-6-phosphate can only be made and used in what pathway?
The pentose phosphate pathway.
What is the effect of glucose-6-phosphatase upon glucose-6-phosphate in the liver and kidneys?
It removes the phosphate group, liberating free glucose into the blood.
