PROGRAM
BSc in Applied Biotechnology
SEMESTER
2
SUBJECT
BO0041 - BIOCHEMISTRY-II
BOOK ID
B1100
SESSION
Winter 2015
No
Q 1
Question/Answer key
Marks Total Marks
10
Define fermentation. List and Explain the types of fermentation add a note on
the significance of fermentation.
( Unit 3 ; Section 3.3.1 )
A 1
Definition of Fermentation:
Fermentation is a process wherein, conversion of a carbohydrate such as simple
sugar into an acid or an alcohol takes place.
1
Listing the types of fermentation:
1) Alcoholic fermentation
2) Lactic acid fermentation
3) Formic acid fermentation
1
Explaining the types of fermentation:
1) Alcoholic fermentation: Fermentation in which sugars are converted into
ethanol and CO2 is called as alcoholic fermentation. Pyruvate is decarboxylated
to acetaldehyde, which is then reduced to ethanol by alcohol dehydrogenase with
NADH as the electron donor.
Eg.: many fungi and some bacteria, algae, and protozoa.
• 2) Lactic acid fermentation: In this process, the reduction of pyruvate to lactate
takes place. It is present in bacteria (lactic acid bacteria, Bacillus), algae
(Chlorella), some water molds, protozoa, and even in animal skeletal muscle.
Lactic acid fermenters can be separated into two groups.
a) Homolactic fermenters:
b) Heterolactic fermenters:
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• 3. Formic acid fermentation: Many bacteria, especially members of the family
Enterobacteriaceae, can metabolize pyruvate to formic acid and other products in
a process sometimes called the formic acid fermentation. Formic acid may be
converted to H2 and CO2 by formic hydrogenlyase.
There are two types of formic acid fermentation.
a) Mixed acid fermentation b) Butanediol fermentation
Significance of fermentation
Significance of fermentation:
• 1) In the absence of aerobic respiration, NADH is not oxidized by the electron
transport chain because no external electron acceptor is available.
2
• 2) In fermentation, the substrate is partially oxidized, ATP is formed by
substrate-level phosphorylation only, and oxygen is not needed.
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Q 2
Explain the various steps involved in glycolytic pathway and add a note on the
regulation of glycolytic pathway.
A 2
( Unit 3 ; Section 3.2 )
Steps involved in glycolytic pathway are:
Glucose 6- phosphate undergoes isomerization to give fructose
• 6 –phosphate in the presence of phosphohexose isomerase and Mg2+.
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8
• Fructose 6 – phosphate is phosphorylated to fructose 1,
• 6– disphosphate by phosphofructokinase. One more molecule of ATP is
broken down to ADP and Mg2+ is required as activator.
• The 6 carbon fructose 1, 6 –diphosphate (fructose – 1, 6 –diP) is split into
glyceraldehyde 3 – phosphate and dihydroxyacetone phosphate by the enzyme
aldolase.
• The enzyme phosphotriose isomerase catalyses the inter conversion of
glyceraldehyde 3 – phosphate and dihydroxyacetone phosphate. Thus, 2
molecules of glyceraldehydes 3 – phosphate are obtained from 1 molecule of
glucose.
• Glyceraldhyde 3 – phosphodehydrogenase converts Glyceraldhyde
• 3 – phosphate to 1, 3- diphosphoglycerate. This step is involved in the
formation of NADH + H + and a high energy compound 1, 3 - diphosphoglycerate.
• The enzyme phosphoglycerate kinase in the presence of Mg2+ , transfers the
energy – rich phosphate from the C-1 of 1-3- diphosphoglycerate to ADP from
ATP leaving the formation of 3 – phosphoglycerate.
• The 3- phosphoglycerate is converted to 2- phosphoglycerate by
phosphoglyceromutase.
• The high energy compound phosphoenol pyruvate is generated from 2 –
phosphoglycerate .The enzyme enolase does this job by the removal of a
molecule of water from 2 – phosphoglycerate .This enzyme requires Mg2+
• The enzyme pyruvate kinase catalyses the transfer of high energy phosphate
from phosphoenol pyruvate to ADP, leading to the formation of ATP. The product
formed is enol pyruvate. Mg2+ is required as activators. Enol pyruvate being
unstable is spontaneously converted to pyruvate (keto form).
Regulation of glycogen metabolism:
The synthetic and degradative pathways of glycogen are reciprocally regulated.
• Glycogen phosphorylase and glycogen synthase are both regulated by
co-valent modifications
2
• Both liver and muscle phosphorylase are activated by a cyclic AMP mediated
activation cascade trigged by the hormonal signal.
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• The two hormones which control glycogenolysis are glucagon from the
pancreas and epinephrine from the adrenal gland.
Q 3
10
Define pentose phosphate pathway. Explain the 2 phases of pentose phosphate
pathway.
( Unit 4 ; Section 4.2 )
A 3
Defining pentose phosphate pathway:
The pentose phosphate pathway (PPP) is primarily an anabolic pathway that
utilizes the 6 carbons of glucose to generate 5 carbon sugars and reducing
equivalents.
2
Explaining the 2 phases of pentose phosphate pathway.
The pentose phosphate pathway consists of two Phases::
• 1. Oxidative phase and 2. Non –oxidative Phase.
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• 1. The Oxidative Phase
• In this phase, two molecules of NADP+ are reduced to NADPH, utilizing the
energy from the conversion of glucose-6-phosphate into ribulose
5-phosphate.
• The first reaction of this phase is the oxidation of glucose 6-phosphate by
glucose 6-phosphate dehydrogenase (G6PD) to form 6-phosphoglucono-lactone,
an intramolecular ester.
• NADP+ is the electron acceptor, and the overall equilibrium lies far in the
direction of NADPH formation.
• The lactone is hydrolyzed to the free acid
6-phosphogluconate by a specific lactonase, then 6-phosphogluconate
undergoes oxidation and decarboxylation by 6-phosphogluconate dehydrogenase
to form the ketopentose ribulose 5-phosphate. This reaction generates a second
molecule of NADPH.
• Phosphopentose isomerase converts ribulose 5-phosphate to its aldose
isomer, ribose 5-phosphate. In some tissues, the pentose phosphate pathway
ends at this point.
• 2. Non-oxidative phase
• In tissues that require primarily NADPH, the pentose phosphates produced in
the oxidative phase of the pathway are recycled into glucose 6-phosphate.
• In this non-oxidative phase, ribulose 5-phosphate is first epimerized to xylulose
5-phosphate.
• Then, in a series of rearrangements of the carbon skeletons, six five-carbon
sugar phosphates are converted to five six-carbon sugar phosphates, completing
the cycle and allowing continued oxidation of glucose
• 6-phosphate with production of NADPH.
• Continued recycling leads ultimately to the conversion of glucose 6-phosphate
to six CO2.
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• Two enzymes unique to the pentose phosphate pathway act in these
interconversions of sugars: transketolase and transaldolase.
• Transketolase: This enzyme catalyzes the transfer of a two-carbon fragment
from a ketose donor to an aldose acceptor.
• Transaldolase: This enzyme catalyzes a reaction similar to the aldolase
reaction of glycolysis: a three-carbon fragment is removed from sedoheptulose
7-phosphate and condensed with glyceraldehyde 3-phosphate, forming fructose
6-phosphate and the tetrose erythrose
4-phosphate.
Q 4
10
Discuss the steps involved in synthesis of palmitic acid.
( Unit 6 ; Section 6.2 )
A 4
Discussing the steps involved in synthesis of palmitic acid:
1) Formation of acetoacyl-ACP:
• To start with, one molecule of actyl-CoA and one molecule of malonyl-CoA
bind to the multi-enzyme complex.
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• The acetyl-CoA and malonyl-CoA are transferred to the SH group of ACP by
the action of acetyl-CoA transacylase and malonyl-CoA transacylase,
respectively.
• The next step is the condensation between the acetyl and malonyl units to
form a 4-carbon unit, β-keto acyl-ACP or acetoacetyl-ACP.
• During this condensation one molecule of carbon dioxide is lost. The synthesis
of fatty acids from acetyl-CoA and malonyl-CoA is carried out by
β-keto-ACP
synthase (CE).
• 2)
Formation of palmitic acid from acetoacyl ACP:
• The acetoacetyl-ACP is reduced by NADPH dependent β-keto reductase (KR)
to form β- OH acyl-ACP.
• The β- hydroxy acyl-ACP is then dehydrated by a dehydratase (DH) to form
enoyl-ACP. The enoyl-ACP is again dehydrated by enoyl reductase (ER) to form
butyryl-ACP. Here, a molecule of NADPH is used for the reduction.
• 3) Release of palmitate from the multi-enzyme complex: The palmitic acid
(fatty acid with 16 carbons) formed is released from the multi enzyme complex by
thio-esterase or de-acylase (TE).
Q 5
10
List and explain the different steps involved in β oxidation of fatty acids.
( Unit 7 ; Section 7.3 )
A 5
Listing the steps involved in β oxidation of fatty acids
The β-oxidation of fatty acids in mitochondria occurs via four recurring steps
namely
• a) Oxidation by FAD
2
• b) Hydration,
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• c) Oxidation by NAD+ and
• d) Thiolysis.
Different steps involved in β oxidation of fatty acids.
a)Oxidation by FAD: In β oxidation of fatty acids the first step is the oxidation of
the fatty acid by FAD. This reaction is catalyzed by acyl- CoA dehydrogenase.
The enzyme catalyzes the formation of a double bond between the C-2 and C-3.
The end product is a trans-Δ2-enoyl-CoA (ά-β- unsaturated acyl- CoA).
• b) Hydration: The next step is the hydration of the bond between C-2 and C-3.
This reaction is catalyzed by enoyl-CoA hydratase. The end product is
L-3-hydroxyacyl CoA.
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• c) Oxidation by NAD+: The third step is the oxidation of L-3-hydroxyacyl CoA
by NAD+, catalyzed by L-3-hydroxyacyl CoA dehydrogenase. This converts the
hydroxyl group into a keto group. The end product is 3-keto acyl-CoA.
• d) Thiolysis: The final step is the cleavage of 3-keto-acyl-CoA by the thiol
group of another molecule of CoA. This reaction is catalyzed by β-ketothiolase.
The thiol is inserted between C-2 and C-3, which yields an acetyl-CoA molecule
and an acyl-CoA molecule.
This process of degradation continues until the entire chain is cleaved into
acetyl-CoA units. For every cycle, one molecule of FADH2, NADH and
acetyl-CoA are formed and the acyl-CoA gets shortened by two carbon atoms.
Q 6
10
Explain the Hatch-slack pathway of CO2 fixation in plants.
( Unit 5 ; Section 5.4 )
A 6
Explaining the Hatch-Slack pathway of CO2 fixation in plants.
• Certain plants fix CO2 in a different photosynthetic mechanism called C4
pathway.
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• The C4 plants, which typically grow in high light intensity and temperatures,
contain dimorphic chloroplasts; i.e. chloroplasts in mesophyll cells are granal
(with grana) whereas chloroplasts in bundle sheath are agranal (without grana).
• The leaf is said to exhibit kranz anatomy.
• The presence of two types of cells leads to segregation of photosynthetic work
i.e. light reactions and dark reactions separately.
• C4 plants are photosynthetically more efficient than C3 plants and C4 plants
there is a low rate of photorespiration and water loss with unusual leaf structure.
The steps involved in C4 pathway are as follows:
• 1) In the mesophyll cell, phosphoenolpyruvate (C3) accepts CO2 to form
oxaloacetate (C4); a reaction catalyzed by phosphoenolpyruvate carboxylase.
• 2) Oxaloacetate is converted to malate (C4) by NADP+– linked malate
dehydrogenase.
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• 3) Malate enters the bundle-sheath cell and releases CO2, forming pyruvate
(C3); catalyzed by NADP+ - linked malate enzyme.
• 4) Pyruvate returns to the mesophyll cell and is used to regenerate
phosphoenolpyruvate. This reaction, catalyzed by pyruvate-Pi dikinase, is
unusual in that it requires ATP and Pi and breaks a high-energy bond to generate
AMP and pyrophosphate i.e. the AMP is phosphorylated by ATP in the presence
of pyruvate kinase to form two molecules of ADP.
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