Glycolysis Flashcards
What is the storage form of glucose?
Glycogen
What type of pathway is the citric acid pathway?
Catabolic
What is the first stage of catabolism in the presence of oxygen?
In glucose, fatty acids and amino acids (least 10) all converge to make simple 2C Acetyl-CoA
What metabolite feeds into the citric acid cycle?
Acetyl-CoA
What is an example of a sugar that is a major fuel for most organisms and has a central position in metabolism?
D-Glucose
- Major source of metabolic energy in brain, erythrocytes, renal medulla, sperm.
Complete oxidation of one D-glucose gives what after the 3 stages of catabolism?
CO2, H2O and gives mega-energy: DeltaG’0 = -2840kJ/mol
What is the major source of energy in the brain?
D-glucose.
What does E.coli rely on for energy and biomolecular synthesis?
D-glucose
What is the product of oxidation of glucose via glycolysis?
Pyruvate.
What pathway is responsible for the largest flux of C in cells?
Glycolysis
How many enzymes are used in the glycolysis of D-glucose to pyruvate?
10
What do the 10 enzymes in glycolysis allow for?
They allow for specific thermodynamically favourable molecular processes that keep all cells alive.
Is glycolysis regulated?
Highly regulated and is only catabolized with cells need energy.
What cells rely on glucose as a major source of energy?
Sperm, erythrocytes, brain, renal medulla
What can E.coli synthesis from glucose?
C skeletons for every amino acid, nucleotide, coenzyme, fatty acid and other intermediates it needs for growth and function from glucose.
What diseases have altered glycolysis?
Diabetes, cancer, neurodegeneration, infection and more.
What are the major pathways of glucose utilization?
- synthesis of structural polymers
- storage
- oxidation via glycolysis
- oxidation via pentose phosphate pathway.
How was glycolysis discovered?
It was the first metabolic pathway elucidated in yeast and muscle cells.
How many carbons does pyruvate have?
3C
What biochemical processes in the cell were discovered as a result of studies on glycolysis?
The role of ATP and phosphorylates compounds in cell biology discovered by research which discovered glycolysis.
How does elevated glucose levels affect SARS-Cov-1 infection?
Diabetes - elevated glucose favor SARS-Cov-1 infection and monocyte response through a glycolysis dependent axis.
What is the first enzyme in the prep phase (P.1). Glucose is phosphorylated on pos.6.
What donates a phosphate?
Hexokinase - ATP donates a phosphate
It is a regulatory enzyme.
The phosphorylation of glucose by HK ‘traps’ glucose inside cells for metabolism.
What are kinases?
These are a large family that add phosphoryl groups to substrates.
Mostly need magnesium
Describe the hexokinase induced fit?
Has a U-shaped clamp like structure.
Conformational change induced by binding of D-glucose.
Irreversible enzymes are often?
Regulatory
What is the second enzyme in the prep phase which isomerize glucose 6 - phosphate to fructose 6-phosphate.
Phosphohexose Isomerase (PHI)
- reversible reaction (aldose to ketose)
- small change in standard free energy
- shuffles atoms to move carbonyl from C1 to C2
- His residue in active site of enzyme opens ring structure to achieve this.
What does phosphohexose isomerase (PHI) do?
Glucose 6-phosphate isomerized to fructose 6-phosphate.
What is the 3rd enzyme in the prep phase which phosphorylated fructose?
Phosphofructokinase-1 (PFK-1)
Bacterial form has 4 subunits, human form can be more complex
What does phosphofructokinase-1 do?
‘committed step’ - highly regulated
Phosphorylates fructose 6- phosphate to fructose 1-6- bisphosphate (2 phosphates either end)
- priming irreversible reaction.
- major regulatory enzyme for glycolysis
- decided time is right to be o/off
What is the 4th enzyme in the prep phase of glycolysis?
Enzyme Aldolase - hexose is split to form two trioses = 2 x3C sugar phosphates.
- reversible
- near-equilibrium
produces DHAP and GAP -3
What is the 5th enzyme in the prep phase of glycolysis?
Triose phosphate isomerase (TPI)
What does triose phosphate isomerase (TPI) do?
It isomerases DHAP to GAP-3, maintains a steady state
- near equilibrium reaction
- TPI ‘pulls’ a H off one carbon and replaces it on another carbon
- perfect enzyme
- speeds isomerisation 1 billion times faster than that would happen.
What is the main energy molecule that goes on in glycolysis after the prepatory phase?
Glyceraldehyde 3-phosphate.
What are the 5th and 6th step/enzyme of glycolysis, in the pay off phase?
Glyceraldehyde 3- phosphate dehydrogenase (removal of electrons to an acceptor NAD)2x
What is the 6th step glyceraldehyde 3-phosphate dehydrogenase?
Oxidation (loss) + phosphorylation.
What donates energy in step 6?
An inorganic phosphate, on the glyceraldehyde 3- phosphate.
What is the oxidation equation in step 6?
oxidation transfers electrons from 2XG3P to 2NAD
What is the final product of step 6 in the pay off phase?
1,-3 bisphosphate - has a very high energy of hydrolysis = -49kJ/mol.
This molecule gives energy to produce 2ATP X2 in reaction 7 &8
What is the enzyme in step 7?
Phosphoglycerate kinase
What happens at step 7?
1,-3 phosphoglycerate is dephosphorylated at pos 1 to yield 2x3-phosphoglycerate & 2ATP.
- induced fit (2 lobes))
Which two enzymes in glycolysis have an induced fit?
Hexokinase
Phosphoglycerate kinase
What do steps 8 and 9 consist of?
Moving things around to make them more favourable for donating the final phosphate to an ATP in the last reaction
What is the enzyme in step 8?
Phosphoglucomutase - reversible
changing from 2x3 phosphoglycerate to 2x2 phosphoglycerate
What is the enzyme in step 9?
Enolase - the 2x2 phosphoglycerate is dehydrated to yield 2 x phosphoenolpyruvate and 2xH2O
= puts phosphate in uncomfortable reaction to encourage it to move.
- high energy
What is the 10th enzyme?
Pyruvate kinase (4 flexible subunits)
2x phosphoenolpyruvate to dephosphorylated to yield 2x pyruvate & 2ATP.
- irreversible
- 2nd substrate level phosphorylation (like 7)
- allosteric - can be turned on/off, senses
What are the 3 sensory enzymes?
Regulatory enzymes
phosphofructokinase (3)
hexokinase (1)
Pyruvate kinase (10)
What is the standard free energy available after glycolysis? (anaerobic)
-85kj/mol - pyruvate contains most of the chemical potential energy of glucose extracted in aerobic conditions in stage 2/3 catabolism.
Where does glycolysis occur in the cell?
Cytosol
What is the difference between the 2 phases in terms of energy?
Prep - 2ATP produced
Pay off - 4 ATP and 2NADH produced.
Where is NADH produced in glycolysis and how?
In step 6 - when oxidation involves the transfer of electrons from 2- F3P to 2NAD –> 2NADH = energy
What is a substrate level phosphorylation?
The phosphate comes from a substrate onto ATP rather than be made by ATP synthase in the mitochondria.
What is the overall energy equation?
glucose + 2 NAD+ + 2ADP +2pi —-> 2 pyruvate + 2NADH+ +2TP + 2H20
What are the 3 fates of pyruvate in the presence and absence of O2?
Anaerobic : Ethanol (x2 + 2CO2) or lactate (2x)
Aerobic: 2 Acetyl Co-A (stage 2 and 3 of catabolism ) - more energy rich
When oxygen happens where does the product cycle of
glycolysis occur?
In the mitochondria.
Decarboxylation occurs on the pyruvate to make the 2 acetyl CoA and the 2CO2.
For one glucose = ~2850kj energy produced for aerobic oxidation.
What are the 2 fates of pyruvate in the absence of oxygen?
- reduced to lactate (lactate dehydrogenase)
- reduced to ethanol (alcohol dehydrogenase)
- produces 5% of energy (85kh/mkl compared to aerobic.
Which produces more energy aerobic or anaerobic ?
Aerobic: 2850kj energy
Anaerobic:85kj energy.
Why is the anaerobic phase of glycolysis important?
As it keeps recycling rapidly to produce 2ATP per glucose & to regenerate essential NAD+ for step 6 of glycolysis.
is pyruvate decarboxylase present in vertebrates ?
It is absent and lactic acid bacteria so impossible to convert pyruvate to ethanol.
When is lactate produced in the body from pyruvate?
- erythroblasts, retina, brain cells produce lactate when O2 present, responsible for at least 10% of overall glucose breakdown.
- very active skeletal muscle uses anaerobic pyruvate - lactic acid
- cancer cells and immune cells can have very active aerobic glucose catabolism even in the presence of O2.
Where is lactate produced?
Made from broken down muscle glycogen stores - > glucose -> pyruvate -> lactate for energy
Lactate is produced in the blood -> liver
Lactate synthesised in liver glucose goes from liver -> blood -> muscle replenished glycogen.
Who discovered the role of anaerobic glycolysis and cancer?
Discovered by Otto Warburg in the 20s
Cancerous cells/tissues can have very active anaerobic glucose catabolism to lactate even in the presence of O2.
This is due to ‘re-wiring’ of glycolysis and metabolism to allow energy production to maximize proliferation.
What and why is a PET scan used in cancer patients?
Used as levels of many glycolytic enzymes increase and use different isoforms of certain glycolytic enzymes occurs.
2F-Deoxyglucose is used - shows ip the glucose intake in cancer cells and the increased glycolysis and glucose metabolism in cancer cells.
What types of enzymes are increased in cancer cells?
Glycolytic enzymes
Different isoforms of these enzymes can occur including
- Pyruvate kinase PKM2 rather than PKM1
- PKM” has a reduced cat activity
- This allows cancer cells to keep using anaerobic glycolysis.
Uses as a two way system, cat and ana. Can promote proliferation.
How does anaerobic glycolysis affect the cells of the immune system?
Immune cells ‘rewire’ metabolism to use aerobic glycolysis: Glucose —> Lactate even when O2 is present.
Hijack the system to produce more cytokines.
They use the glucose - pyruvate - lactate.
Glycolytic switch can be good and bad (inflammation - cytokine storm) regulation = immunometabolism
Is pyruvate oxidised or reduced when it is converted to lactate/ethanol?
Reduced
Does NAD+ get regenerated for step 6 of glycolysis in the conversion of pyruvate -> lactate and ethanol?
Yes it does
