Glycolysis Flashcards
What happens in the fourth step of glycolysis?
Step 4: 6 carbon fructose is split into 2 x 3 carbon units
- Fructose-1,6-bisphosphate binds to aldose (lyase; splits one molecule into 2)
- Yields products : dihydroxyacetone (DHAP) and glyceraldehyde-3-phosphate (G3P)
which enzyme converts 3-phosphoglycerate into 2-phosphoglycerate
Enzyme 8: phosphoglycerate mutase
What happens in the fifth step of glycolysis?
Step 5: Interconversion of the triose phosphates
- dihydroxyacetone phosphate becomes glyceraldehyde-3-phosphate
- DHAP is immeidately isomerized into G3P
- catalysed by triose phosphate isomerase
Note: every step after this; EVERYTHING IS DOUBLED
which enzyme converts PEP into pyruvate
Enzyme 10: pyruvate kinase
Describe the Cori cycle
Liver recycles lactate by converting it back to glucose via gluconeogensis
*uses ATP
What happens in step 8 of glycolysis?
Step 8: conversion of 3-phosphoglycerate to 2-phosphoglycerate
- 8th enzyme of glycolysis is phosphoglycerate mutase
- mutases catalyze rxns where a functional group is moved between different positions in a molecule
How does pyruvate move from the cytosol to the mitochondria? What happens after?
*Pyruvate dehydrogenase complex (link between glycolysis and TCA)
A special transport protein; once in the mitochondria pyruvate is converted to acetyl CoA by pyruvate dehrydrogenase.
Acetyl CoA can then enter the TCA cycle to get completely metabolized to CO2.
- requries 5 coenzymes: NAD+, FAD, CoA (all derived from vitamin B), TPP, and lipoate
which enzyme converts G3P + Pi into 1,3-bisphosphoglycerate
Enzyme 6: glyceraldehyde 3-phosphate dehydrogenase
How do animals balance redox in anaerobic condition?
Redu pyruvate to lactate regenerating NAD+ needed by G3P dehydrogenase
- Glycolysis uses pyruvate to reoxidize NADH
- Accomplished by pyruvate reducing into L-lactate via lactate dehydrogenase
Which enzyme converts glucose into glucose-6-phosphate
Enzyme 1: hexokinase
which enzyme converts fructose-6-phosphate into fructose-1,6-bisphosphate
Enzyme 3: phosphofructokinase (PK-1)
What is the malate-aspartate shuttle?
Method of crossing IMM for reducing equivalents ;
liver kidney and heart
- relies on redox interconversions of malate to oxaloacetate
- NADH reduces oxaloacetate to malate and malate is transported into the mitochondria
- Malate then reduces NAD+ into NADH, regenerating oxaloacetate
- then transamination occurs
- Malate/oxaloacetate interconversions are catalysed by malate dehydrogenase
What happens in the third step of glycolysis?
Step 3: the second phosphorylation
- Fructose-6-phosphate becomes fructose-1,6-bisphosphate
- catalyzed by phosphofructokinase (PK-1)
- rxn is ATP driven/the source of the phosphate
- irreversible
Note: bisphosphate is meant to indicate that there are 2 phosphates on the same molecules but different positions
How is glucose transported into cells
- highly polar cannoy enter via passive diffusion
- transporter proteins called GLUTs residing in cell membrane catalyze glucose transport
which enzyme converts DHAP into G3P
Enzyme 5: triose phosphate isomerase
What happens in the seventh step of glycolysis?
Step 7: Phosphoryl transfer from 1,3-BPG to ADP
>the first substrate level phosphorylation
- Converts 1,3-Bisphosphoglycerate into 3-phosphoglycerate
- 1,3-Bisphosphate transfers its phosphoryl group to ADP converting it to ATP
- product is 3-Phosphoglycerate
- catalysed by phosphoglycerate kinase
- rxn generates 2 ATP/glucose (recall: everything doubled)
Which enzyme converts 1,3-Bisphosphoglycerate into 3-phosphoglycerate
Enzyme 7: phosphoglycerate kinase
What happens in the second step of glycolysis?
Step 2: Phosphohexase Isomerization
- Previously phosphorylated glucose (glucose-6-phosphate) is isomerized to fructose-6-phosphate
- catalyzed by enzyme phosphohexose isomerase
Note: cyclic ring structures are in equilibrium with the open-chain forms (enzyme catalyzes the opening/closing of the ring)
What is the 3 phosphate shuttle
method for chrossing mem
- in skeletal muscle and brain
- interconversion between dihydrozyacetone phosphate (DHAP) and glyclerol 3 phosphate catalyed be glycerol 3 phosphate dehydrogenase
- the mitochondiral form of the enzyme uses FAD rather than NAD+ to oxidize glycerol - phosphate
- shuttle generates mitochondiral FADH2 for each cytosolic NADH
DONT CONFUSE WITH GLYCERALDEHYDE 3 PHOSPHATE
What happens in the first step of glycolysis?
Step 1: Phosphorylation of Glucose
- Conversion of Glucose into Glucose-6-Phosphate
- ATP is the cofactor; reaction is ATP dependent
- Enzyme is hexokinase
- Irreverisble process
which enzyme converts fructose-1,6-bisphosphate into DHAP and G3P
Enzyme 4: aldolase
What is the final step of glycolysis?
Step 10: Transfer of phosphoryl group from PEP to ADP
> the second substrate level phosphorylation
- accomplished by pyruvate kinase
- Converts phosphoenolpyruvate into pyruvate
- pyruvate exists as an equilibrium mixture of keto and enol tautomers
Note: PEP is a very high energy compound (free NRG liberated by PEP is sufficient to drive ATP)
What is unique abobut glycolysis
- only pathway that can provide energy under anerobic conditions
- occurs in cytosol (anerobic organisms dont have mitochondria)
which enzyme converts glucose-6-phosphate into fructose-6-phosphate
Enzyme 2: phosphohexose isomerase
What is the sixth step of glycolysis?
Step 6: G3P dehydrogenase rxn
> 2 electron oxidation of an aldehyde to a carboxlic acid is energetically favourable
- Overall G3P becomes 1,3-bisphosphoglycerate
- G3P is bound to a cysteine residue on the enzyme (G3P dehydrogenase) and oxidized to an enzyme bound thioester
- thioester is attacked by Pi and the product is 1,3-bisphosphoglycerate
What is alcohol fermentation?
The conversion of pyruvate to ethanol and CO2
- Pyruvate decarboxylase catalyses the loss of CO2 to give acetaldehyde
- acetaldehyde is reduced to ethanol by alcohol dehydrogenase
Purpose of reaction: regenerate NAD+ in yeast/other microorganisms(equivalent to how animals operate under anaerobic conditions)
How do animals reoxidize NADH in aerobic conditions?
Electron transport chain reoxidizes NADH using O2 as the oxidant
- pyruvate is completely oxidzed to CO2 via Citric Acid Cycle
which enzyme converts 2-phosphoglycerate into phosphoenolpyruvate
Enzyme 9: enolase
How is glucose oxidized
3 stages: glycolyses, TCA, ETC
What is transamination?
Part of malate-aspartate shuttle reaction; process where oxaloacetate is converted to aspartate - occurs in mitochondria
Reverse transamination can occur in cytosol turning aspartate into oxaloacetate
What is the ninth step of glycolysis?
Step 9: dehydration of 2-phosphoglycerate
- Converts 2-phosphoglycerate to phosphoenolpyruvate (PEP)
- enzyme enolase eliminates H2O to create a double bond
Note: hydrolysis breaks a molecule into 2; hydration is when H2O is added to a molecule but it remains intact. Therefore we are removing water but not breaking the molecule
