Glycolysis Flashcards
Glycolysis is the central pathway for what?
Carbohydrate metabolism
What are 3 examples of organisms that use glycolysis
Mammals, bacteria and plants
Is glycolysis an anaerobic or aerobic process?
It is an anaerobic process
How many phases are involved in glycolysis
There are 2 phases in glycolysis
How many carbons does glucose have?
Glucose has 6 carbons (C6)
Glycolysis involves the breakdown of glucose (C6) into what? And what is the result of this?
Breakdown of glucose into 2 molecules of pyruvate
Results in a net production of 2 ATP molecules
How many carbons does a Pyruvate molecule have?
3 carbons
Where does glycolysis occur in mammalian cells?
Glycolysis occurs in the cytosol of mammalian cells
How many reactions does glycolysis consist of?
Consists of 10 reactions
Describe what is involved in phase 1 of glycolysis
- Converts glucose to two glyceraldehyde 3-phosphate molecules
- energy requiring phase (catabolic, or energy investment)
Describe what is involved in phase 2 of glycolysis
- Generates two pyruvate molecules
- Energy producing phase (anabolic, or energy payoff)
What are the 4 products of glycolysis?
•2x Pyruvate
•4x ATP
•2x NADH
•2x H2O
What are the 3 irreversible reactions in the glycolysis pathway?
•Hexokinase
•Phosphofructokinase
•Pyruvate kinase
What happens in reaction 1 of glycolysis?
Reaction 1 = Hexokinase
- Glucose is irreversibly phosphorylated into Glucose-6-phosphate
- Powered by the hydrolysis of ATP
What is the transfer of a phosphate group from ATP onto another molecule called? And why is it important?
- Transfer of a phosphate group from ATP onto another molecule is called a phosphoryl transfer
- Important to trap Glucose inside the cells
What are the names in order of reactions 1-10 in glycolysis
1= Hexokinase
2= Phosphoglucose isomerase
3= Phosphofructokinase
4=Aldolase
5= Triose phosphate isomerase
6= Glyceraldehyde 3-phosphate dehydrogenase
7= Phosphoglycerate kinase
8= Phosphoglyceromutase
9= Enolase
10= Pyruvate kinase
What is involved in reaction 2 of ** glycolysis **
- isomerisationof glucose-6-phosphateto fructose-6-phosphate
- the reaction is the conversion of analdosesugar intoaketosesugar
- reaction 2 = Phosphoglucose isomerase
Aldose = Aldehyde group
Ketose = Ketone group
What is involved in reaction 3 of glycolysis?
- Reaction 3= Phosphofructokinase
- Fructose-6-phosphate isphosphorylatedagain to generatefructose-1,6-bisphosphate
- This is the second phosphoryl transfer reaction of glycolysis
What 2 things is Phosphofructokinase described as?
Phosphofructokinase is an isoenzyme and allosteric
Describe the term allosteric
- Enzymes that have an additional binding site for effector molecules other than the active site
-ATP is an allosteric effector - high levels inhibit the enzyme, low levels activate
Isoenzymesare a combination of what subunits?
- M4, M3, M2L2, ML3, L4
What does phosphofructokinase exit as?
- Exists as a tetramer
-The tetramer is composed of L and M subunits
What are muscles and the liver rich in?
Muscles are rich in M4; the liver is rich in L4
What is involved in reaction 4 of glycolysis?
- Fructose-1,6-bisphosphate iscleavedinto two 3-carbonfragments
- Dihydroxyacetonephosphate – aketose
- Glyceraldehyde 3-phosphate – an aldose
What is involved in reaction 5 of glycolysis?
- reaction 5= Triose phosphate isomerase
- The subsequent reaction uses only glyceraldehyde 3-phosphate
- Dihydroxyacetonephosphate (DHAP) is converted toglyceraldehyde-3-phosphate
- When glyceraldehyde 3-phosphate is used, the equilibrium isrestored by conversion of DHAP to glyceraldehyde 3-phosphate
Summarise phase 1 of glycolysis
- Phase 1= involves reactions 1 to 5
- Catabolic, energy investment phase
- 2 molecules of ATP have beenused
- Glucoseis converted to two molecules of glyceraldehyde3-phosphate
-The key intermediate in this series of reactionsis fructose-1,6-bisphosphate. The enzyme thatcatalyses this reaction, phosphofructokinase, issubject toallostericcontrol
What is involved in reaction 6 of glycolysis?
- Reaction 6= Glyceraldehyde 3-phosphate dehydrogenase
- The first reaction that begins the conversion to pyruvate
- involvesthe oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
- This reaction involves addition of an inorganic phosphate group(Pi).
-NAD+is reduced to NADH
What is involved in reaction 7 of glycolysis?
- Reaction 7=Phosphoglycerate kinase
- 1,3-bisphosphoglycerate is converted to 3-phosphoglyceratebyPhosphoglyceratekinase.
-This step involves another reaction in which ATP is produced - ATP is produced by phosphorylation ofADP
-1,3-bisphosphoglycerate transfers a phosphate group to ADP. - known assubstrate-levelphosphorylation
- Reaction is catalysed byphosphoglyceratekinase and “paysoff” the ATP debt created by the priming reactions in the firstphase.
What is involved in reaction 8 of glycolysis?
- Reaction 8= Phosphoglyceromutase
- The next step involves the isomerization of 3-phosphoglycerateto 2-phosphoglycerate
- A “mutase” catalyses migration of a functional group within asubstrate.
What is involved in reaction 9 of glycolysis?
- Reaction 9= Enolase
- Enolase = Phosphopyruvate hydratase
- 2-phosphoglycerate loses one molecule of water,producingPhosphenolpyruvate
- Enolasecatalyses the reaction and requires a Mg2+cofactor
What are the 3 isoenzymes involved in reaction 9 of glycolysis and give key features of all 3
- αα or non-neuronal enolase (NNE)
- Found in a variety of tissues, including liver, brain, kidney, spleen, adipose
-Present at some level in all normal human cells - ββ or muscle-specific enolase (MSE)
- this enzyme is largely restricted to muscle
-where it is present at very high levels - γγ or neuron-specific enolase (NSE):
- Expressed at very high levels in neurons and neural tissues
- can account for as much as 3% of total soluble protein
- expressed at much lower levels in most mammalian cells.
What is involved in reaction 10 of glycolysis?
- Reaction 10= pyruvate kinase
- Phosphoenolpyruvatecontains a high energy bond
- Transfers its phosphate group toADP, producing ATP and pyruvate.
- Another example ofsubstratelevel phosphorylation
- Reaction is catalyzed by pyruvate kinase
Summarise phase 2 of glycolysis
- Phase = Reactions 6-10
- Anabolic
- energy producing phase
- Two molecules of pyruvate areproduced for each molecule of glucose that entered thepathway.
- These reactions involve the production of 2 molecules ofNADH, and the net production of 2 ATP for each molecule ofglucose.
What are the metabolic fates of NADH and pyruvate in mammals after being produced by glycolysis?
- NADHcan be recycled via aerobic or anaerobicpathways:
- In aerobic conditions (O2is available), NADH is re-oxidized in the electron transport pathway, makingATP in oxidative phosphorylation.
- 3 molecules of ATPcan be made from one molecule of NADH.
- In anaerobic conditions (O2is not available), NADH isre-oxidized bylactate dehydrogenase(LDH) whichprovides NAD+for more glycolysis.
Under anaerobic conditions: eg. Actively contracting muscle. What is the most important pathway for the regeneration of NADH+ ?
The most important pathway for the regeneration ofNAD+is reduction of pyruvate to lactate.
What is the goal of aerobic metabolism of pyruvate?
- Goal is to get pyruvate into the citric acid cycle
-where the products of glucose can becompletely oxidised, leading to the productionof many ATP molecules.
2 steps required to achieve this:
Convert pyruvate into acetyl-CoA
Put the acetyl CoA into the citricacid cycle.
What part of the cell contains the enzymes that perform glycolysis?
Cytosol
Complete the following:
In the glycolytic pathway, one molecule of the 6-carbon compound, ———- is converted into 2 molecules of the 3-carbon compound, ————-.
- glucose
- Pyruvate
Before glycolysis can occur, glucose must be trapped inside the cell. Explain how this is achieved
Glucose is phosphorylated to glucose 6-phosphate by hexokinase.
Name two glycolytic reactions that involve phosphoryl transfers.
Hexokinase and phosphofructokinase
Name one glycolytic reaction that is an example of substrate level phosphorylation.
The one catalysed by phosphoglycerate kinase or pyruvate kinase
Glyceraldehyde 3-phosphate is oxidised during glycolysis. Choose the option below which best explains what happens to the hydrogen atom and the electron that are removed during oxidation.
a. They reduce NAD+
b. They oxidise NAD+
c. They are transferred to ATP
d. They are eliminated as methane
a. They reduce NAD+
Glycolysis is a pathway which occurs:
a. Eukaryotic cells only
b. Prokaryotic cells only
c. Most muscle cells
d. Virtually all cells
d. Virtually all cells
If 1NADH yields 3ATP molecules by oxidative phosphorylation, how many ATP molecules are made from one molecule of glucose undergoing glycolysis?
8
