Glucose and Glycolysis Flashcards
What is the function of glycolysis?
To convert glucose to pyruvate
To convert 2ADP to 2ATP
To reduce 2 molecules of NAD+ to NADH
Where does glycolysis take place?
In the cytosol
What is the net reaction of glycolysis?
Glucose + 2ADP + 2Pi –> 2 Pyruvate + 2 ATP + 2 NADH + 2H + 2H20.
What are the two stages of glycolysis?
- Hexose/Energy input.
2. Triose/Energy payout.
How many molecules of ATP are formed in the triose stage?
4 ATP
How many molecules of ATP are consumed in the hexose stage?
2 ATP.
What step does hexose become two triose molecules?
Step 4.
Which steps of glycolysis are coupled to the utilization of ATP?
Steps 1 and 3; drive the reaction forward.
What is step 6 coupled to?
The synthesis of reducing agents NADH
What occurs in the first step of glycolysis?
ATP phosphoryl group is transferred to the oxygen atom of glucose, producing G6P and ADP.
PHOSPHORYLATION.
What enzyme catalyzes step one?
Hexokinase.
Is step one reversible? why/why not?
No, hexokinase quickly phosphorylates glucose to prevent glucose from diffusing back out of the reaction.
What occurs in the second step of glycolysis?
G6P is converted into F6P, a keto-isomer.
ISOMERIZATION.
Is step two reversible?
Yes, the free energy change is near zero so it is a near-equilibrium reaction.
What occurs in the third step of glycolysis?
A phosphoryl group of ATP is transferred to F6P, producing F-1,6-P.
PHOSPHORYLATION
What enzyme is active in step three.
PFK-1.
What step in glycolysis is the rate-determining step?
Step three (PFK-1).
Is step three reversible?
No, it is metabolically irreversible. There is a large negative free energy change.
What occurs during step four of glycolysis?
F-1,6-P is cleaved into GAP and DHAP.
Is step four reversible?
Yes, the free energy change is near zero.
What occurs in step five of glycolysis?
DHAP molecule is converted to GAP
ISOMERIZATION.
Is step five reversible?
Yes, the free energy change is near zero.
What occurs in step six of glycolysis?
GAP is oxidized and phosphorylated to produce 1,3-BPG.
OXIDATION, PHOSPHATE ADDITION.
What are the products of step six?
1 NADH
1,3-BPG
What step is of glycolysis produces the most energy?
Step 6; formation of NADH.
What is the free energy change of step 6?
Oxidation: very negative.
Phosphorylation: very positive.
In total, near zero but driven forward by formation of NADH and coupling with next reaction.
What occurs in step seven of glycolysis?
A phosphoryl transfer from 1,3-BPG to ADP creates 3-PPG and ATP.
What is substrate level phosphorylation?
The formation of ATP by the transfer of a phosphoryl group from a ‘high energy’ compound to ADP.
Is step 7 reversible?
Yes.
What occurs in step eight of glycolysis?
3-PPG is converted into 2-PPG.
ISOMERIZATION.
Is step 8 reversible?
Yes.
What occurs in step nine of glycolysis?
2-PPG is dehydrated to PEP.
What enzyme is activated in step nine?
Enolase.
What are the products of step nine?
Phosphoenolpyruvate and water.
What does enolase require to operate?
Magnesium ions (2).
Is step nine reversible?
Yes.
What occurs in step ten?
SBL of ADP, phosphoryl transfer from PEP to ADP to form pyruvate.
PHOSPHORYLATION
What enzyme is active in step ten?
Pyruvate kinase.
Is step ten reversible?
No; pyruvate kinase is heavily regulated.
What net free energy change is essential for glycolysis to operate? Is this requirement satisfied? Which particular reactions play the biggest role?
Negative.
Yes, net negative energy change.
Steps 1, 3, and 10 have the largest negative energy change.
What is hexokinase regulated by?
Product inhibition via G6P.
What is PFK-1 regulated by?
Inhibited via feedback inhibited by ATP/Citrate
Activated by AMP and F-2,6-BP. Feedback inhibition by PEP.
What is pyruvate kinase regulated by?
Feed-forward activated by F-1,6BP
Inhibited by ATP via product inhibition.
Can glycolysis operate under anaerobic conditions?
Yes.
What is 2ADP equal to?
1 AMP and 1 ATP
What step is the dehydration step?
Step 9: 2-PPG to PEP.
What does glycogen require to break glycosidic bonds?
Inorganic phosphate, NOT ATP.
What is glycogen synthesized from?
G6P
What five routes can pyruvate take?
- Enter the CAC as acetyl-CoA.
- Carboxylated to oxaloacetate, CAC intermediate.
- Reduction to ethanol.
- Reduction to lactate.
- Converted to alanine.
What fates of pyruvate require oxygen?
Carboxylation to oxaloacetate and conversion to Acetyl-CoA for CAC.
What fates of pyruvate occur in anaerobic conditions?
Reduction to ethanol and lactate.
How is pyruvate reduced to ethanol?
- Decarboxylated to acetaldehyde.
2. Reduced to ethanol via alcohol dehydrogenase; coupled to oxidation of NADH.
What is fermentation?
A process where electrons from glycolysis in the form of NADH are passed to organic molecules such as ethanol/lactate.
How is pyruvate reduced to lactate?
- Transfer of a hydride ion from NADH produces Lactace and NAD+.
Is pyruvate reduction to lactate reversible?
Yes.
What is the net effect of lactate formation?
To maintain the flux of the glycolytic pathway and the production of ATP. ONLY IN OXIDATIVE ENVIRONMENT.
What effect does lactate have on the blood after excretion from muscle?
Lowers pH, inducing T-state and increasing oxygen unbinding.
What kind of transporter moves lactate out of muscles?
Proton-lactate symporter.
What are the pros of lactate formation?
Increased oxygen unloading in muscles.
Metabolic fuel for cardiac tissues in aerobic conditions.
What is the main substrate of CAC?
Acetyl-CoA
What converts pyruvate to acetyl-CoA?
Pyruvate Dehydrogenase Complex PDC/PDH
What are the products of PDH?
Acety-CoA, NADH, and CO2
Where does the pyruvate dehydrogenase reaction occur?
Inside the mitochondrial matrix.
How is pyruvate transferred to the matrix?
Pyruvate translocase (Proton symport)
Explain the pyruvate dehydrogenase reaction:
Pyruvate is decarboxylated, the acetyl group is transferred to SH-CoA to form a thioester (high energy) bond.
The carboxyl group is reformed at CO2 and a hydrogen from the SH-CoA reduces NAD+
What is coenzyme A?
Derivative of vitamin B attached to adenosine nucleotide, contains a reactive thiol (SH) group.
Is the formation of acetyl-CoA reversible?
No, it is a significant committed step in carbohydrate metabolism.
What are the three main cofactors involved in pyruvate dehydrogenase reaction?
Coenzyme A, NAD+ and FAD.
What are the advantages of multienzyme complexes?
- Faster reaction times.
- Limits side reactions.
- Controlled as a single unit.
How is PDH regulated?
NADH inhibits PDH (product inhibition)
Acetyl-CoA inhibits PDH (product inhibition)
Calcium activates PDH.
Activated by NAD+ and Coenzyme-A
How does protein kinase regulate PDH?
Protein kinase is activated by NADH and Acetyl-CoA; phosphorylates and shuts ‘off’ PDH.
How does protein phosphatase regulate PDH?
Activated by Calcium, activated PDH via dephosphorylation.
