Steps 1-4
What is a rate-limiting step? And which step (out of 1-4) is the rate-limiting step?
A rate-limiting step is the slowest step of a reaction which will determine the overall rate of the reaction. Step 1 is the rate-limiting step.
True or False: The hydration of fumarate converts it to malate in step 7 of the Krebs cycle.
True!
How many cycles do we have to undergo to produce the per glucose yield?
2 cycles
What are three ways that the Krebs cycle is regulated?
- regulation at thermodynamically favorable steps
- PDC (pyruvate dehydrogenase complex)
- Regulation of oxaloacetate
Where does the acetyl CoA and OAA come from in step 1?
Which step generates the final third NADH in this reaction (steps 5-8)?
Step 8 (malate --> OAA)
How to calculate the per glucose yield?
Multiply the products produced in one cycle by 2.
Which process generates oxaloacetate?
Gluconeogenesis.
What is an isomerization reaction? And which step undergoes this reaction?
An isomerization reaction is a chemical process that turns a reactant into one of their isomeric alternatives. Step 2 undergoes an isomerization reaction with an intermediate of cis-aconitase
If a reaction uses ATP to link two molecules together, what type of enzyme is being used? Which step involves this type of enzyme (from steps 5-8)?
Synthetase. Step 5 (succinylcholine CoA --> succinate)
Where is ATP and GTP generated?
ATP in skeletal muscle; GTP in liver
How does the presence of either low or high acetyl CoA affect the Krebs cycle?
Low acetyl CoA activates PDC to convert pyruvate into acetyl CoA.
High acetyl CoA activates pyruvate carboxylase to convert pyruvate to OAA to initiate Krebs cycle.
Name all the enzymes involved in steps 1-4.
Step 1 - citrate synthase
Step 2 - aconitase
Step 3 - isocitrate dehydrogenase
Step 4 - alpha ketoglutarate dehydrogenase complex
Name all enzymes in involved in each step (5-8).
Step 5 - succinyl CoA synthetase
Step 6 - succinate dehydrogenase
Step 7 - fumarase
Step 8 - malate dehydrogenase
How much NADH would be produced from one glucose molecule?
6 NADH
What is PDC activated and inhibited by?
Activated: NAD+, AMP (ADP), substrate (pyruvate)
Inhibited: NADH, ATP, product (acetyl CoA)
If a reaction was driven by the reduction of NAD+ --> NADH, but the overall reaction led to an oxidation reaction (from reactants to products). What is the type of enzyme involved?
Dehydrogenase.
What does thioester hydrolysis do and which step in the reaction is it present in?
Breaking of thioester bond in succinyl CoA via hydrolysis. Present in step 5.
List the final products after two cycles of Krebs cycle (one glucose molecule).
2 ATP/GTP
6 NADH
2 FADH2
4 CO2
What are the enzymes that are regulate the Krebs cycle at thermodynamically favorable steps?
- isocitrate dehydrogenase in step 3
- alpha ketoglutarate dehydrogenase in step 4