Glycolysis for WSU Biochem Test 4
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What is glycolysis?
a central sequence of reactions in biochemistry that converts glucose into two molecules of pyruvate.
What happens to pyruvate?
It is taken into the mitochondria and burned to produce CO2 and several NADH and FADH2.
What is this?
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What is this?
isomerization of a ketose into and isomer aldose or vise versa
adds a carbon in the form of CO2 to a molecule (Usually requires a biotin coenzyme)
aldol cleavage (splits a C6 into two C3, one is always and aldose and the other a ketose)
Oxidize alcohols and other molecules (FAD+ and NAD+ coenzymes)
What is reaction #1 of glycolysis and what is the enzyme? What kind of reaction is this? How is it made favorable?
- Glucose + ATP ---> G6P + ADP + H+ via hexokinase.
- A Phosphoryl transfer.
- Equilibrium is skewed to the right by coupling with ATP hydrolysis.
What are the requirements of hexokinase?
- Hexokinase requires ATP and Mg2+ or Mn2+.
- Mg or Mn complex with negative charges on ATP phosphates
What is reaction #2 of glycolysis? What kind of reaction is this? How is it controlled?
- G6P <-----> F6P via phosphoglucoisomerase.
- Isomerization (general acid/base) aldose to ketose.
- Mass action
What is reaction #3 of glycolysis? What kind of reaction is this? How is it controlled?
- F6P + ATP ---> F-1,6BP via phosphofructokinase.
- A phosphoryl transfer.
- Allosterically controlled
How is PFK allosterically regulated?
- Taught form = lower affinity for F6P, promoted by high levels of ATP (prevents too much lactic acid)
- Relaxed form = higher affinity, promoted by high levels of ADP.
- Inhibited by citrate.
What is reaction #4 of glycolysis? What kind of reaction is this? How is it controlled?
- F-1,6BP <---> DHAP + G3P via aldolase.
- Reverse of an aldol condensation.
- Controlled by mass action
Which carbons in glucose form DHAP and G3P?
- G3P from carbons 4,5,6.
- DHAP from 1,2,3.
What is reaction #5 of glycolysis? What kind of reaction is this? How is it regulated?
- DHAP <---> G3P via Triosephosphate isomerase.
- Isomerization (ketose to aldose) reaction.
- Mass action, G3P is pulled away for metabolic processes.
What is reaction #6 of glycolysis. what kind of reaction is this? How is it regulated?
- G3P + NAD+ + Pi <---> 1,3BPG + NADH via G3P dehydrogenase.
- Substrate level phosphorylation.
What is substrate level phosphorylation?
Unfavorable Phosphorylation is coupled with favorable oxidation (no ATP required)
How is the mechanism for reaction #6 different?
- The rxn is unfavorable under standard conditions. Synthesis of 1,3BPG is coupled with favorable oxidation of the aldehyde to an acid.
- Aldehyde + NAD + H2O ---> acid + NADH + 2H + +
What is reaction #7 of glycolysis? What kind of reaction is this? How is it regulated?
- 1,3BPG + ADP <---> 3PG + ATP via phosphoglycerate kinase.
- Reverse of a kinase reaction.
- High energy transfer potential of the phosphoanhydride bond found in 1,3BPG favors or couples the unfavorable synthesis of ATP
Which reaction of glycolysis is the break even point? How many moles of ATP/mole glucose?
- 1,3 BPG + ADP <---> 3PG + ATP.
- 2mol ATP and 2 NADH/glucose
How does arsenate uncouple ATP synthesis?
- Arsenate (a poison) is very similar to phosphate and can act as the nucleophile in place of inorganic phosphate (Pi) which uncouples the formation of ATP in reactions 6 and 7.
- Phosphate and arsenate are chemically similar. However the arsenate bond is water labile and is easily hydrolyzed in the presence of water without an enzyme.
- The placement of arsenate onto G3P as it is converted to 1,3PG � Arsenate uncouples the synthesis of an ATP
What is reaction #8 of glycolysis? What kind of reaction is this? How is it regulated?
- 3PG <---> 2 PG via phosphoglycerate mutase.
- Phosphoryl transfer reaction - high energy molecule constructed from low energy bond by removing -OH group.
- Mass action.
What is reaction #9 of glycolysis? What kind of reaction is this? How is it regulated?
- 2PG <---> PEP via enolase.
- Formation of a double bond via elimination rxn.
Which biomolecule has the highest transfer potential of any molecule?
What is reaction #10 of glycolysis? What kind of reaction is this? How is it regulated?
- PEP + ADP ----> pyruvate + ATP via pyruvate kinase.
- Reverse of a kinase rxn.
- Allosterically regulated
What is the net production per mole of glucose for glycolysis?
2 atp and 2 NADH/mole glucose
How is pyruvate kinase allosterically regulated?
The enzyme is basically regulated by phosphorylation through a signal initiated by the peptide hormones, glucagon and insulin.
What does insulin do for pyruvate kinase?
- When blood sugar levels are high insulin is released from the pancrease and signals the fed state. Insulin initiates a series of events which cause the cells to take in additional glucose
- as part of this process P-PK (phosphorylated PK) is dephosphorylated and the enzyme changes to an open active conformation (higher binding affinity) ----> PK
What does glucagon do for pyruvate kinase?
- When blood sugar levels are low, glucagon is released from the pancrease and signals the fasting state. In this state sugar is reserved for the brain and muscle.
- The signal sent by glucagon activates a kinase which phosphorylates PK to P-PK conformation. The P-PK conformation is a taught conformation with low binding affinity for PEP.
- Net result � the glycolytic path is slowed way down in liver and other fuels are used to actually drive the synthesis of glucose and release it into the blood stream
what happens to pyruvate when oxygen is limiting?
It is converted to lactic acid
What is the purpose of a lactate/alcohol shunt?
Buy time for survival - NADH produced in glycolysis is sacrificed to produce as much ATP as possible with limiting O2.
What is the mechanism by which pyruvate is converted to lactate?
Pyruvate + NADH <---> Lactate + NAD+ via lactate dehydrogenase
Why is there no net production of NADH during glycolysis under anaerobic conditions?
NADH is sacrificed so that production of ATP can continue when O2 is limiting
How does the alcohol shunt (bacteria) work?
- Pyruvate <---> Acetaldehyde + CO2 via pyruvate decarboxylase
- Acetaldehyde +NADH ---> Ethanol + NAD+ via alcohol dehydrogenase
What does the liver do with metabolic waste products such as lactate and alcohol?
It converts them into useful materials.
What happens to fructose and galactose in the liver?
- It is almost completely filtered by the liver and processed before release into the blood stream.
- If not needed for energy, F6P is converted into glucose for storage or release into the blood stream.
How is fructose prepped for glycolysis in the liver cells?
- Fructose + ATP ----> F1P + ADP via fructokinase.
- F1P is then split by alsolase into DHA and Glyceraldehyde.
- DHA is phosphorylated into DHAP and converted to G3P.
- Glyceraldehyde + ATP ---> G3P + ADP via glyceraldehyde kinase.
How is galactose prepped for glycolysis in the liver?
- Galactose + ATP ---> Gal-1P + ADP.
- UDP-Glucose + Gal-1P <---> UDP-Galactose + Glu-1P via Gal-1p Uridyl transferase.
- UDP-Gal <---> UDP-Glu via UDP galactose epimerase.
- UDP-Glu is recycled to part 3 and the cycle continues until Gal levels drop.
- Glu-1P is then converted to Glu-6P and sent through glycolysis.
What causes the hereditary disorder galactosemia?
Problems with the uridyl transferase.
how many ATP does it take to prime glucose, fructose and galactose for ATP production in glycolysis?
What is the relationship of galactose to glucose?
They are epimers
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