Scheme biochem 2021
BENGALURU NORTH UNIVERSITY
VI SEMESTER B.Sc EXAMINATION, OCTOBER-2021
(CBCS Scheme)(F&R) 2016-17 Onwards
Subject: Chemistry paper- VIII(Biochemistry)
Chairman:
Chief Examiner:
Prof. Shivappa Siddappa Jugale
Prof: M. Sujatha
Associate Professor & HOD of Chemistry
Associate Professor
G.F.G.C. K.R.Pura . Bangalore.
GCW.KOLAR
9482383116
9164395714
Scheme of valuation
Instructions : 1.Question paper has two parts. Value both the parts.
2. Weightage should be given to the alternate correct answer.
PART-A
Answer any EIGHT of the following questions
1
2
Mention the contribution of following scientists to the development of Biochemistry a).H.G .Khorana
b)Hans Kreb
a) H.G. Khorana showed the interpretation of Genetic code
b) Hans Kreb elucidated Tri carboxyllic acid cycle
Write the Haworth structure of Isomaltose
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Define Isoelectric pH of an amino acid.
It is defined as the pH at which an amino acid exists as a Zwitter ion carrying both positive and negative
charge. Since the net charge is zero, it does not migrate towards any electrode in the electric field.
State Chargaff’s rule of base equivalence.
It states that the no. of purine bases in DNA are same as that of No. of pyrimidine bases .
A+T=G+G(OR)A+T/G+C=1
What is the role of c-AMP in hormone action?
c- AMP acts as a second messenger to peptide hormones such as epinephrine, vasopressin and glucagon.
These hormones bind to the receptor on the membrane and initiate c- AMP synthesis .In turn, c-AMP initiates
chain of reactions. Ex-Activation of protein kinase that phosphorylates several proteins.
Mention any two energy rich compounds other than ATP.
PEP,1,3-DPG,Phosphocreatinine,acetyl-Co-A(any other but only any two)
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Explain Absolute specificity with an example.
It is the type of specificity exhibited by those enzymes that catalyse the reaction of only one substrate.
Ex- .Urease identifies and binds only to Urea during the hydrolysis of urea. Similarly, SDH converts only
succinate to fumerate .(any other example)
Mention any two applications of electrophoresis.
1.used in the separation and identification of proteins ,nucleic acids, amino acids.
2.used in the determination of molecular weight of proteins.
3.Determination of isoelectric pH
4.used in the qualitative and quantitative analysis of complex mixture of proteins.(any two)
How are fatty acids activated during β-oxidation cycle?
Fatty acids are activated outside the mitochondrial membrane. They are converted to fatty acyl-S Co-A in
presence of enzyme Acetyl Co-A synthetase. This reaction requires a molecule of ATP. The energy released
during the cleavage of ATP to AMP and PPi is used to drive the activation reaction.
Write the reaction of urea cycle catalyzed by arginase
.
Define Iodine number and write its significance.
It is defined as” the no. of grams of Iodine required to react with 1.Kg of an oil or fat”. It signifies the “degree
of unsaturation”. Higher the Iodine no. for an oil or fat, higher will be the degree of unsaturation.
Write a note on Genetic code.
1. Genetic code is Triplet because it constitutes three nucleotides.
2.It is specific.(one code –one amino acid)
2. It is universal because a particular code or codon for specific amino acid is same in all organisms.
3.It is degenerate(one amino acid can have more than one code)
4.AUG is initiator codon and there are three terminator codons(UAG ,UGA& UAA)
5.It is unambiguous
(any two)
PART-B
Answer any NINE of the following questions
13a
13b
Discuss the properties of water that makes it ”the solvent of life”.
1. Water is a polar molecule with high dipole moment , high melting and boiling point. So it acts
as universal solvent.
2. Due to Hydrogen bonding , water is capable of dissolving biomolecules like sugars, aldehydes,
ketones and compound containing N-H groups.
3 .Because of its high specific heat and heat of vapourisation , it regulates body temperature thus
acting as “heat buffer”.
4 .Due to its high surface tension, it enables transport of molecules into and out of cell.
5.Low density of ice than liquid water safe gaurds the aquatic and marine life (any three)
What is the principle of Thin layer chromatography? Mention its applications.
This technique is based on the principle of adsorption, and partition of constituents between
stationary and mobile phases.
It is used in the separation , identification and analysis of amino acids ,drugs, and closely related
molecules.
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Write the partial structure of starch and mention the components present in it.
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Define saponification number .Give its significance.
It is defined as “the number of milligrams of KOH required to completely saponify 1g of an oil or
fat”. It is the index of average molecular size of component fatty acid. ”Higher the Saponification
no., smaller is the size of component fatty acid”.
What are triglycerides? Mention their biological importance.
Triglycerides are the components of oils and fats. They are the esters of glycerol with fatty acids.
Simple and Mixed glycerides are the two types.
1.They are the chief energy sources in humans and other animals including insects(9kcal/g )
2.They are stored beneath adipose tissue.
3.They not only yield more energy upon oxidation but also yield more water , thus enabling
hibernating animals and camels to survive for longer period without drinking water.
4.In the form of stored fat under the skin, they act as insulators protecting warm blooded animals
against low temperature.(any three)
What are amino sugars? Give an example.
These are the sugars in which the hydroxyl (-OH)group on the 2nd carbon is replaced by an amino
group. Ex- D-glucosamine, N-acetyl glucosamine, Galactosamine. (any one)
Explain the forces that stabilize tertiary structure of proteins.
Tertiary structure refers to the specific 3-dimentional structure of proteins. It is stabilized by
various side chain interaction such as 1.hydrophobic interactions 2.disulfide linkages 3.hydrogen
bonds and 4.ionic or electrovalent interactions.
How does an amino acid react with ethyl alcohol?
Carboxyl group of an amino acid is esterified with –OH group of ethanol to give respective ester.
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Along with suitable example, explain the role of proteins as 1)Transport agents 2)Antibodies.
1. Proteins serve as transport agents by binding to specific molecules and carrying them to
the desired tissue or organs .ex- Haemoglobin transports oxygen through blood.
2. Many proteins defend the organisms against disease causing microbes like viruses,
bacteria, fungi and other foreign materials(antigens).Ex- Immuno globulins, WBC
Write the structure of sugar phosphate present in RNA.
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Describe the salient features of Watson & Crick model of DNA
1.DNA is a double helix composed of two polynucleotide strands twisted right handedly around
the same central axis.
2. The two strands are antiparallel.
3.The two strands are held together by hydrogen bonds .Hydrophobic interactions between
stacked bases also stabilize the double helix.
4.There are 10 base pairs per turn. The pitch of the helix is 36 A0 and the distance between the
two strands is 20 A0.
5.Base pairing between two strands is according to Chargaff’s rule. Adenine is always paired with
Thymine and Guanine with Cytosine.
6.Adenine and Thymine are held by two Hydrogen bonds and Guanine and Cytosine are held by
three Hydrogen bonds.
7.Double helix has major and minor grooves in which the proteins interact. (any four)
Write the components of a nucleotide. Name the nucleotide present only in DNA.
Nucleotide is composed of a) Nitrogenous base, b) pentose sugar and c) phosphoric acid.
Thymidylic acid.
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Mention the biological role of i) Insulin ii) Adrenalin iii) Oxytosin iv) Testosterone.
Insulin is a peptide hormone secreted by β- cells of pancreas. It decreases the blood glucose level
(hypoglycemic) by promoting lipid and protein synthesis.
Adrenalin or epinephrine is an amino acid derivative produced by adrenal medulla in response to
emotional stress such as fear, anxiety, anger, cold and low levels of blood glucose. It increases
energy yielding metabolic processes like glycolysis, glycogen breakdown, oxidation of fatty acids
etc to prepare the individual for emergencies. Hence it is called as “flight “ or “fight” hormone.
Oxytosin is a peptide hormone containing 9 amino acids. It causes contraction of smooth muscles
in the uterus during child birth. It also causes contraction of muscles of the mammary glands
promoting release of milk during lactation.
Testosterone is a steroid hormone. It promotes the development of secondary sexual
characteristics in male and regulates sexual behavior.
What are essential fatty acids? Give an example.
These are not synthesized by the animal cells but are essential for the normal growth and
regulation of metabolic activities and hence they are to be supplemented through diet.
Ex: Linoleic acid, Linolenic acid, a Arachidonic acid and so on. (any one)
Explain the following classes of enzymes with suitable example.
i)Oxidoreductases ii)Transferases.
i)Oxidoreductases are the class of enzymes that catalyse oxidation or reduction reactions which
involve hydrogen or electron transfer.
Ex: LDH that catalyses the oxidation of lactate to pyruvate.
ii) Transferases are the enzymes that catalyse group transfer (other than hydrogen or water)
from one substrate to the other.
Ex: Hexokinase that transfers phosphate group from ATP to hexoses like glucose or galactose.
What is Michaelis-Menten constant? Write its significance.
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Michaelis-Menten constant (Km) is characteristic of an enzyme that reflects the affinity of the
enzyme for its substrate. It is” the substrate concentration at half the maximum velocity”.
Smaller the Km value, greater is the affinity of an enzyme for its substrate and vice versa.
Write the structure of ATP and explain the structural features that make it a high energy
molecule.
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Structural features that make it a high energy molecule:
1.Electrostatic force of repulsion between the negative charges on phosphate groups
2.Standard free energy of hydrolysis is -30.5kj/mole
3.Localization of –ve charges cause strain on p-o-p bond due to repulsion
4.Opposing resonance of p-o-p destabilize the bonds (any two)
What are energy coupling reactions? Give an example.
These are a couple of reactions in which “ the energy released by an exergonic reaction is utilized
to drive an endergonic reaction forward.
Ex:
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22a
Write the reactions of glycolysis catalyzed by the following enzymes.
i)Hexokinase ii) Tryose phosphate isomerase
i)Hexokinase catalyses the phosphorylation of glucose to glu-6-PO4.It requires a molecule of ATP
and Mg++ ion (prosthetic group)
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ii)Tryose phosphate isomerase catalyse the isomerization of glyceraldehye-3-PO4 to dihydroxy
acetone phosphate.
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Write the enzymatic reactions for the i) conversion of fumerate to malate .ii)formation of
carbamoyl phosphate.
ii)
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What is Gluconeogenesis?
Gluconeogenesis is a metabolic process that occurs in the liver especially during starvation where
the glucose is synthesized from non-carbohydrate precursors such as pyruvate, lactate,
triglycerides ,and amino acids.
Explain i) Leading and Lagging strands ii) Translation.
i)Leading strand is newly synthesized strand during DNA replication. It is complementary to the
parent strand. It is copied in the direction advancing replication fork in 5’-3’ direction and is
synthesized continuously. Lagging strand is synthesized discontinuously in 3’-5’ direction away
from replication fork. The small fragments of DNA are called okazaki fragments
ii)Translation is a process in which proteins are synthesized in response to the cell’s need. It is
directed by DNA through m-RNA and requires r-RNA and t-RNA along with activated amino acids.
What is Transcription?
It is a process in which the genetic information present in DNA is transcribed on to m-RNA and the
base sequence of m-RNA is complementary to a segment of DNA with specific sequence(DNA
template).
Give any two applications of DNA finger printing.
It is used in the personal identification, as biological evidence to identify criminals for forensic
purposes, to diagnose inherited disorders both in parents and new born babies, in solving
paternity disputes.( any two)
What is Transamination? Give an example.
It refers to the transfer of an amine group from an amino acid to α-keto acid in presence of
enzyme transaminase.
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