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Frequently Asked Questions (FAQ’s)
Q1. What is glycolysis?
Ans: Glycolysis (Gr. glykys=sweet; lysis=breaking) is a stepped
process by which one molecule of glucose (6C) breaks in to two
molecules of pyruvic acid (3C). It occurs in cytoplasm outside
the mitochondria. It is anaerobic phase so is common to both
aerobic and anaerobic respiration.
Q2. What is the difference between oxidative phosphorylation
and substrate level phosphorylation?
Ans: Substrate-level phosphorylation occurs during Glycolysis
and the Kreb’s Cycle and involves the physical addition of a
free phosphate to ADP to form ATP. The formation of ATP in
this manner is referred to as substrate-level phosphorylation
because the phosphate donor, 1,3-biphosphoglycerate is a
substrate with high phosphoryl-transfer potential. Oxidative
phosphorylation, on the other hand, takes place along the
electron transport chain, where ATP is synthesized indirectly
from the creation of a proton gradient and the movement of
these protons back accross the membrane through the protein
channel, ATP synthase. As the protons pass through, ATP is
created.
Q3. How pyruvate is converted to acetyl- CoA which is a
precursor for TCA cycle?
Ans: The pyruvic molecules formed in glycolysis enter the
mitochondria, where they are converted to acetyl-CoA. In this
complex series of reactions, pyruvate undergoes oxidative
decarboxylation. First, a carbonyl group is removed as carbon
dioxide, which diffuses out of the cell. Then the two-carbon
fragment remaining is oxidized, and the hydrogen that were
removed during the oxidation are accepted by NAD+. Finally,
the oxidized two-carbon fragment, an acetyl group, is attached
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to coenzyme A, which is manufactured in the cell from one of
the B vitamins, pantothenic acid.
Q4. In which organelle glycolysis is taking place and which one
is a site for TCA cycle?
Ans: Glycolysis is taking place in the cytoplasm of the cell and
TCA cycle takes place in the matrix of the mitochondrion.
Q5. How is cell respiration different from combustion?
Ans: Cell respiration is a biochemical and stepped process and
takes place inside the cells. It is controlled by enzymes and
the energy is released in steps. A number of intermediates are
produced during cell respiration and no light is produced.
Combustion, on the other hand, is a physic-chemical and
spontaneous process and is non-cellular. It is not controlled by
enzymes. No intermediates are produced during combustion
and light may be produced in combustion.
Q6. What is the difference between aerobic and anaerobic
respiration?
Ans: The aerobic respiration takes place inside the mitochondria
in the presence of oxygen. The end products are always inorganic
and more energy (2880 kj) is produced. Carbon dioxide is always
produced during the process.
The anerobic respiration, on the other hand, takes place
outside the mitochondria in the absence of oxygen. One of
the end products is always organic and low energy (210kj) is
produced. Carbon dioxide may or may not be produced during
the process.
Q7. Glycolysis can be separated in to three phases. What are
the three phases of glycolysis and the energy used or produced
in each phase?
Ans: The three phases of glycolysis are priming phase, cleavage
phase and energy-harvesting phase. Glycolysis begins with
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the addition of energy. Two high-energy phosphates from two
molecules of ATP are added to the six-carbon glucose molecule,
producing a six-carbon molecule with two phosphates. Then
the six-carbon molecule with two phosphates is split in two,
forming two three-carbon sugar phosphates. Finally, in a series
of reactions, each of the two three-carbon sugar phosphates is
converted to pyruvate. In the process, energy rich hydrogen is
harvested as NADH, and two ATP molecules are formed.
Q8. What are the site-specific inhibitors of electron transport
chain?
Ans: The site specific inhibitors of electron transport chain
include rotenone, amytal, piercidin, hydrogen cyanide, hydrogen
sulphide, and carbon monoxide.
Q9. Why does FADH2 produce two ATP molecules while NADH
produces three ATP molecules?
Ans: The electrons pair from FADH2 passes over only a part
of the electron transport chain. Therefore, fewer H+ ions are
added to the gradient. The smaller gradient generates only 2
ATP molecules for each pair of electrons. On the other hand,
the electrochemical gradient created as an electron pair passes
from NADH to oxygen is sufficient to drive the synthesis of three
ATP molecules. In other words, the electron from NADH activate
three pumps and those from NADH2 activate two, so 3 ATP and
2 ATP are produced from NADH and FADH2, respectively.
Q10. What is the difference between oxidative phosphorylation
and photophosphorylation?
Ans: The difference between oxidative phosphorylation and
photophosphorylation is as under:
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Oxidative Phosphorylation
Photophosphorylation
It occurs over inner membrane of It occurs over thyllakoid membrane
mitochondria.
of chloroplasts.
It is formation of ATP during cellular It is formation
respiration.
photosynthesis.
of
ATP
The chemical energy is used during Radiant
energy
is
oxidative phosphorylation.
photophosphorylation.
during
used
in
Here NADH and FADH2 are oxidized It is often connected with the synthesis
to form NAD+ and FAD.
of NADPH from NADP+.
Electrons are extruded when reduced Excited chlorophyll
enzymes are oxidized.
extrude electrons.
a
molecules
Protons required for ATP synthesis Protons required for ATP synthesis
are mostly generated by co-enzymes. are obtained from matrix.
It occurs all the time in all cells which It occurs in only green cells when
respire aerobically.
they receive radiant energy.
Q11. What is electron transport chain?
Ans: The passage of energetic electrons through a series of
membrane-associated electron-carrier molecules to proton pumps
embedded within mitochondrial or chloroplast membranes.
Q12. What are uncouplers of oxidative phosphorylation?
Ans: The compounds that increase the permeability of the inner
mitochondrial membranes to protons. e.g. 2,4-dinitrophenol,
dinitrophenol, Pentachlorophenol, Thyroxine, Calcium.
Q13. What is the terminal electron acceptor in the electron
transport chain?
Ans: The terminal electron acceptor in the electron transport
chain is oxygen.
Q14. What is chemiosmosis?
Ans: The passage of high-energy electrons along the electron
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transport chain, which is coupled to the pumping of protons
across a membrane and the return of protons to the original side
of the membrane through ATP-generating channels.
Q15. What is the difference between glycolysis and Kreb’s cycle?
Ans: The difference between glycolysis and Kreb’s cycle is as
under:
Glycolysis
Kreb’s Cycle
It occurs in the cytoplasm outside the It occurs inside
mitochondria.
mitochondria.
the
matrix
of
It occurs in both aerobic and aerobic It occurs only in aerobic conditions.
conditions.
It is a linear pathway.
It is a cyclic pathway.
It produces 2 ATP molecules.
It produces 2 GTP molecules from 2
molecules of aetyl CoA.
It produces two NADH2 molecules Two molecules of acetyl CoA produce
per glucose molecule.
6 NADH2 and 2 FADH2 molecules.
No CO2 is produced.
CO2 is evolved.