How many Carbon atoms are present in a Pyruvate molecule ?
- A.2
- B.3
- C.4
- D.5
Correct answer
Explanation
The correct answer is B, 3. Pyruvate, the ion of pyruvic acid (CH3COCOOH), is a three-carbon molecule. It is formed at the end of glycolysis, the first stage of respiration, which takes place in the cytoplasm of every living cell. In glycolysis one molecule of glucose, which has six carbon atoms, is split into two molecules of pyruvate of three carbons each, with a small net gain of two ATP. What happens next depends on oxygen. With oxygen, pyruvate enters the mitochondria, loses one carbon as carbon dioxide and becomes acetyl coenzyme A, which feeds the Krebs cycle. Without oxygen, muscle cells turn it into lactic acid and yeast turns it into ethanol and carbon dioxide. Option A is wrong because two carbons is the acetyl group of acetyl CoA, made after pyruvate loses a carbon. Option C is wrong because four carbons is oxaloacetate, the molecule that starts the Krebs cycle. Option D is wrong because five carbons is alpha-ketoglutarate, an intermediate of the Krebs cycle. Exam tip: glucose 6C gives two pyruvate 3C; acetyl CoA 2C joins oxaloacetate 4C to make citrate 6C.
Practice Questions
View allConsider the following statement : "Atomic number of an element is a more fundamental property than its atomic mass." Who among the following scientists has made the above statement ?
- A.Dmitri Mendeleev
- B.Henry Moseley
- C.J.J. Thomson
- D.Ernest Rutherford
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In 1913 the English physicist Henry Moseley showed that atomic number, not atomic mass, is the fundamental property of an element.
Read the full explanation →The energy of a photon, whose momentum is 10 MeV/c, where c is the speed of light, is given by
- A.10 MeV
- B.100 MeV
- C.1 MeV
- D.0.1 MeV
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For a photon, energy equals momentum multiplied by the speed of light, E = pc, so a momentum of 10 MeV/c gives an energy of exactly 10 MeV.
Read the full explanation →People prefer to wear cotton clothes in summer season. This is due to the fact that cotton clothes are
- A.good absorbers of water
- B.good conveyors of heat
- C.good radiators of heat
- D.good absorbers of heat
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Cotton soaks up sweat well, and as that sweat evaporates from the cloth it takes heat away from the body and keeps us cool.
Read the full explanation →Cell wall is not present in cells of
- A.Bacteria
- B.Plants
- C.Fungi
- D.Humans
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Human cells, like all animal cells, have only a flexible plasma membrane on the outside and no rigid cell wall.
Read the full explanation →The enzymes which catalyze the same reaction but have different amino acid compositions are commonly referred as :
- A.Isoenzymes
- B.Isotopes
- C.Isomers
- D.Coenzymes
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Isoenzymes, also called isozymes, are different molecular forms of an enzyme that speed up the same chemical reaction but differ in their amino acid sequence.
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