BMP: TCA cycle and ETC

Question 1

1. What are alternative names to the TCA cycle?
2. Where does this process occur?
3. What is utilised and where does this come from

Answer 1

1. Krebs or citric acid
2. Mtocondria of eukaroytes and cytosol of prokaryotes
3. Utilises acetyl coA - the immediate precurosr of acetyl coA from carbohydrate metabolism is pyruvate

Question 2

How does pyruvate enter the mitocondria?

What happens to it?

Answer 2

Under aerobic conditions pyruvate enters via a specific H+ transporter and undergoes further oxidation to CO2 and H20

Question 3

1. What happens to acetyl coA
2. What is the outcomes of the TCA?

Answer 3

1. IT is completely oxidised
2. At the end of the cycle, 2 Carbons from the 6 carbons of citrate leave as CO2 to ultimately yield the 4 carbon oxaloacetate, which is used again in the first step of the next cycle

Question 4

What does every molecule of acetyl coA produce?

Answer 4

• 3 NADH
• 1 FADH2 (flavin adenine dinucleotide)
• 1GTP (ATP equivalent)
• Co2

But remeber 1 glucose = 2 pyruvaye = 2 acetyl coenzyme A (therefore this will be doubled)

Question 5

What molecules are required for TCA?

Answer 5

• Acetyl (in the form of acetyl coA)
• Citrate
  
  • consumed and then regenerated
• Coenzymes
  
  • FAD and NAP+
• GDP
• H2O

Question 6

What are products of TCA?

Answer 6

• GTP (ATP equivalent)
• CO2 (waste product)
• CoA
• Reduced coenzymes
  
  • later undergo oxidative phosphorylation (ETC)

Question 7

Before the TCA cycle can begin, pyruvate must be converted to the intermediate acetyl coA for TCA.

1. How does this happen?

Answer 7

• Pyruvate under goes oxidative metabolism to acetyl coA via oxidative decarboxylation
• This is catalysed by pyruvate dehydrogenase complex (PDC)

(NAD+ is also converted to NADH)

Question 8

What regulates the activity of PDC?

Answer 8

• PDC kinase (conversion to inactive form)
• PDC phosphatase (conversion to active form)

Question 9

What is the first step of TCA cycle?

Answer 9

• Condensation
• Transfer of a 2-carbon acetyl group from acetyl CoA to the 4-carbon oxaloacetate to form a 6-carbon compound (citrate)
• This is catalysed by Citrate synthase

Question 10

What is the 2nd step?

Answer 10

• Isomerisation
• The citrate is dehydrated to cis-aconitase via the enzyme aconitase
• It is then rehydrated by the same enzyme to form isocitrate
• This isomerisim is reversible

Question 11

What is the 3rd step?

Answer 11

Isocitrate dehydrogenase catalayses the oxidation of isocitrate to oxalosuccinate. NADH is also produced

Question 12

What is the 4th step?

Answer 12

• Decarboxylation
• Decarboxylation of oxalosuccinate to a-ketoglutartate (5C) by oxalosuccinate decarboxylase
• This is the rate limiting step and is irreversible

Question 13

What is the 5th step?

Answer 13

• Oxidative decarboxylation
• Oxadative decarboxylation of a-ketoglutartate by a-ketoglutartate to succinyl-coA (4C) and one molecule of NADH.
• This step is irreversible

Question 14

What is step 6?

Answer 14

• Hydrolysis/ GTP synthase
• Hydrolysis of succiny-CoA to succinate via succinyl-CoA synthase and producing one moleculr of GTP
• –GTP generation driven by hydrolysis of high energy thioester bond
• •Condensation of GDP + Pi

Question 15

What happens in stage 7?

Answer 15

Oxidation of Succinate by succinic dehydrogenase to fumarate and one molecule of FADH2

FAD —> FADH2 genertes equivalent of 2ATP

Question 16

What happens in stage 8?

Answer 16

• Hydration
• Hydration of fumarate to malate by fumarase

Question 17

What happens in stage 9?

Answer 17

Oxidation of malate by malate dehydrogenase to oxaloaxetate and one molecule of NADH

Question 18

Describe sources of energy from TCA

Answer 18

• •TCA cycle produces
  
  • Reduced co-enzymes (NADH or FADH2) generated by action of four dehydrogenase enzymes
  • GTP produced by one thiokinase enzyme
    
    • Used to produce ATP (GTP + ADP → GDP + ATP)
• Energy produced per molecule pyruvate
  
  • 3 NADH
  • 1 FADH2
  • 1 GTP

Question 19

What is the net reaction for TCA cycle?

What is the energy yield per cycle?

Answer 19

Question 20

What is the ATP count so far?

Answer 20

• •Per molecule of glucose
• –2 ATP from glycolysis
• –2 ATP from TCA cycle
• •Life requires far more than 4 ATP!!!

Question 21

What is the electron transport chain?

Answer 21

Couples electron transfer between an electon donor (NADH) and an electron acceptor (O2) with the transfer of a H+ (Proton)

Series of molecules build into the inner mitocondrial membrane

Question 22

How much energy is produced?

Answer 22

34 ATP from 1 glucose

Question 23

What coditions are required?

Answer 23

aerobic - O2

Question 24

What is the purpose of ETC?

Answer 24

To create an protein gradient between the inside and outside of the innermitocondiral membrane which ATP synthase uses to create ATP

Question 25

What is the process by which the mitocondria produces ATP?

Answer 25

Oxidative phosphorylation "The generation of ATP from ADP through the oxidation of metabolic products (food) to CO2"

Question 26

What happens to energy during biological oxidation

Answer 26

Not just released - transducted to a more useful form - ATP

Question 27

What does protein complex 1 do?

Answer 27

Protons from NADH associate with proton complex I. Complex I (NADH dehydrogenase) removes 2 electrons from NADH and transferred to the lipid soluble carrier protein ubiquinone. Complex I translocates 4 protons across the innermembrane producing a proton gradient. Complex 1 is a major site of premature electron leakage to O2 occurs

Question 28

What happens in complex II?

Answer 28

Electrons carried as FADH2 are passed to complex II. Complex II (succinate dehydrogenase) is a parellel electron transport pw to complex 1, but unlike complex 1 doesnt transport protons into the intermembrane space. This means it contributes less energy overall to the ETC process

Question 29

What does complex III do?

Answer 29

Hydrogen ions are transolcated into the intermembrane space by interaction with complex III (cytochrome bc1 complex) and, simulataneouly, an electron is passed to complex III

Question 30

What happens in complex IV?

Answer 30

In complex IV (Cytochrome c ocidase) four electrons are removed from 4 molecules of cytochrome c and transferred to molecular oxygen to produce 2 molecules of water

Question 31

What is the final electron acceptor?

Answer 31

Oxygen

Question 32

What inhibits complex IV?

Answer 32

Potassium cyanide

Question 33

How is ATP finally produced?

Answer 33

The proton gradient created from transferring protons across the IMM to the intermembrane space increases membrane potential and drives ATP synthase (therefore ATP production) as the built up H+ rushes back into the matrix

Question 34

What is the complete equation for cellular resperation?

Answer 34

6C₆H₁₂O₆ + 6O₂ ---\> 6H₂O + 6CO₂ + ~38 ATP

Question 35

Why migth actual ATP be less?

Answer 35

Premature leakage of e-s to O2