TCA Cycle

Q1: Most multi-cellular organisms obtain energy for the synthesis of ATP during oxidative phosphorylation from

A high energy phosphate compounds

B a proton gradient across the inner mitochondrial membrane

C a proton gradient across the cell membrane

D a proton gradient across the outer mitochondrial membrane

ANS:B - a proton gradient across the inner mitochondrial membrane

During TCA, electron carriers are generated in the cell, examples of this are the conversion of NAD+ to NADH and a proton & FAD to FADH2. These electron carriers can drive the movement of protons from the mitochondrial matrix to the space between the inner and outer membranes of the mitochondria via a chain of associated complexes in the inner mitochondrial membrane, we know this as the Electron transport chain.

Because the inner membrane is not permeable to protons, a electrochemical gradient is generated. The protons may pass back into the mitochondrial matrix via embedded ATPases in the inner mitochondrial matrix. The movement of protons will cause rotation in different subunits, resulting in the conversion of ADP and an inorganic phosphate into ATP.

Q2: The FADH2 and NADH produced by the oxidation of one acetyl-CoA results in the synthesis of about-

A 3 ATPs

B 6 ATPs

C 11 ATPs

D 15 ATPs

ANS:C - 11 ATPs

The FADH2 and NADH produced by the oxidation of one acetyl-CoA results in the synthesis of about;

3 NADH are produced = 7.3 ATPs.
1 FADH2 is produced = 1.5 ATP,

Total ATPs produced = 9 ATP.

This is very different from the total number of ATPs produced in TCA which is:

3NADH + 1FADH2 + 1 ATP = 10 ATPs.

Q3: Which one is not the main protein in electron transport chain?

A NADH dehydrogenase

B Cytochrome bc1 complex

C Cytochrome oxidase

D Citrate synthease

ANS:D - Citrate synthease

No answer description is available.

Q4: How many ATPs are produced during citric acid cycle?

A 10

B 13

C 12

D 8

ANS:C - 12

The answer is 10.
TCA has eight steps.
4 of these steps are oxidative.
Which are steps 3,4,6 & 8.
They are 1 ATP that is produced at substrate level phosphorylation that is synthesized to become 1 just like that but in the 4 oxidative steps 1 step Carries FAD which translates in a 1.5 atp, then the remaining 3 NADH accounts for 2.5 each.
If you add rightfully you get 10 atp Molecules per cycle. (1)

Q5: Citric acid cycle occurs in

A cytoplasm

B mitochondria

C endoplasmic reticulum

D golgi bodies

ANS:B - mitochondria

The enzymes required for carrying cyclic chain of citric acid are located in the mitochondria as a result TCA cycle occurs in the mitochondria.

Q6: A positive redox potential means substance has

A lower affinity for electron

B higher affinity for electron

C lower affinity for proton

D higher affinity for proton

ANS:B - higher affinity for electron

I'm not clear with the given answer.

Please explain it.

Q7: The first intermediate in TCA cycle is

A succinate

B fumerate

C citrate

D malate

ANS:C - citrate

1st step of the TCA cycle is a condensation of acetyl CoA with Oxaloacetate to form Citrate by the enzyme citrate synthase. So, the citrate is the 1st intermediate product.

Q8: Which of the following is involved in energy production?

A Generation of proton gradients across membranes

B Transport of electrons on organic molecules

C Conversion of compounds with high energy to those of low energy

D All of the above

ANS:D - All of the above

No answer description is available.

Q9: How many molecules of ATPs are synthesized per NADH oxidation?

A 2

B 1

C 3

D 4

ANS:C - 3

1 NADH oxidized to give 3ATP molecules (malate-aspartate shuttle).

On the other hand, 1 NADH oxidized to give 2ATP (in glycerol phosphate shuttle).

1 FADH2 oxidized to give 2ATP molecules.

Q10: The end product of glycolysis is pyruvate, which enters the citric acid cycle after being converted to

A acetic acid

B acetyl-CoA

C acetaldehyde

D none of these

ANS:B - acetyl-CoA

The end product of glycolysis, ie Pyruvate is undergo oxidative decarboxylation to form 2C Acetyl CoA by the enzyme pyruvate dehydrogenase.

This acetyl CoA enters into the TCA cycle by condensation with Oxaloacetate to form Citrate by the enzyme citrate synthase.

Q11: The enzymes of the TCA cycle in a eukaryotic cell are located in the

A nucleus

B mitochondria

C plasma membrane

D lysosomal bodies

ANS:B - mitochondria

Mitochondria is the major source of enzymes which is involved in oxidation of Carbohydrates and fatty acids example, TCA cycle Beta oxidation.

Q12: Why is the TCA cycle the central pathway of metabolism of the cell?

A It occurs in the center of the cell

B Its intermediates are commonly used by other metabolic reactions

C All other metabolic pathways depend upon it

D None of the above

ANS:B - Its intermediates are commonly used by other metabolic reactions

There are certain reactions that can feed intermediates into the TCA cycle, these reactions are called Anaplerotic Reactions. As these intermediates are also part of other systems, it can suggest that process of TCA is flexible and will adapt to accommodate different conditions of the cell. e.g. when there is sufficient energy, TCA is less likely to take place.

Q13: The catabolism of sugars and fatty acids is similar because

A both of these compounds are funnelled through the TC A/citric acid cycle

B both of these compounds generate redox energy during catabolism

C both of these compounds generate chemical energy during catabolism

D all of the above

ANS:A - both of these compounds are funnelled through the TC A/citric acid cycle

I think the answer can be All of the above. Because Citric acid cycle is the common pathway for both carbohydrates and fats. Ultimately all biomolecules catabolize to generate chemical energy. And almost all the processes of generating chemical energy involve redox energy.

Q14: Which one of the following is not the intermediate of Kreb's cycle?

A Isocitrate

B Succinate

C Fumarate

D Stearate

ANS:D - Stearate

No answer description is available.

Q15: To stop ATP synthesis which chemical is generally used?


B 2,4 dinitrophenol


D None of the chemical can stop ATP synthesis

ANS:B - 2,4 dinitrophenol

Dinitrophenol (DNP) is an uncoupler, allowing respiration to continue without ATP synthesis.

Q16: Malate-asparatate shuttle operates in

A lungs and liver

B heart and liver

C pancreas and liver

D none of these

ANS:B - heart and liver

Someone, please explain more about this.

Q17: In what form does the product of glycolysis enter the TCA cycle?

A AcetylCoA

B Pyruvate


D Glucose

ANS:A - AcetylCoA

Actually, pyruvate does not enter the citric acid cycle but undergoes some chemical grooming in which a carboxyl group is removed and given off as co2. The 2 carbon compound remaining is oxidised while a molecule of NADH+ is reduced to NA,DH.

Coenzyme adjoins with 2 carbon groups to form acetyl coenzyme An abbreviated as acetyl-CoA so I can say acetyl coA is the best.

Q18: Energy that is released from glucose during respiration but not transferred to ATP bonds can be detected as




D heat

ANS:D - heat

No answer description is available.

Q19: During cellular respiration, most of the ATP made, is generated by

A oxidative phosphorylation

B photophosphorylation

C glycolysis

D substrate-level phosphorylation

ANS:A - oxidative phosphorylation

90percnt of ATP is produced in oxidative phosphorylation.

Q20: Oxidation of a molecule involves

A gain of electron

B loss of electron

C gain of proton

D loss of proton

ANS:B - loss of electron

An easy pneumonia to remember this rule by is:


Oxidation Is Loss and Reduction Is Gain.

Q21: Most of the enzymes of the citric acid cycle in a eukaryotic cell are located in the

A inner mitochondrial membrane

B cytosol

C mitochondrial matrix

D intermembrane space

ANS:C - mitochondrial matrix

TCA enzymes are located in the mitochondrial matrix, except Succinate dehydrogenase which is anchored onto the inner mitochondrial membrane, where it acts as complex II in ETC.

Q22: Cholesterol can be synthesized de novo in

A pancreas

B intestine

C liver

D cell membrane

ANS:C - liver

Why is in the liver?

I think that is in the cell membrane!

Q23: In eukaryotes, electron transport occurs in

A membranes and mitochondria

B endoplasmic reticulum

C cytoplasm

D all of the above

ANS:A - membranes and mitochondria

No answer description is available.

Q24: Important function of cholesterol is to

A modulate fluidity

B enhance blood circulation

C prevent bile salts formation

D None of these

ANS:A - modulate fluidity

The best answer choice here is that the Cholesterol Modulates Fluidity. Which is what it is known for.

High levels of cholesterol impedes blood circulation. Which is why patients have hypertension, and need to be put on statins amongst other drugs when dietary modifications fail.

In my opinion, Option A is the best answer choice.

Q25: Which of the following enzyme does not take part in the TCA cycle?

A Citrate synthase

B Iso-citrate dehydrogenase

C Pyruvate dehydrogenase

D Malate dehydrogenase

ANS:C - Pyruvate dehydrogenase

Pyruvate Dehydrogenase doesn't take part in TCA cycle activity, what it does is that it produce the acetyl coA to be used to produce Citrate when the Acetyl coA condenses with Oxaloacetate.

Q26: Standard redox potential for a substance is measured under standard condition and is expressed as

A mili-Ampere

B Volt

C without unit

D Ohm

ANS:B - Volt

No answer description is available.

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