Category: Life Sciences Objective Questions

Life Sciences Multiple Choice Questions on “Nucleic Acids”.

1. The monomeric unit of nucleic acid are called ___________
A. Nucleotides
B. Nucleosides
C. Pyrimidines
D. Purines
Answer: A
Clarification: Nucleotides are the monomeric unit of nucleic acid; therefore, these are considered as polynucleotides. It is made up of three components i.e. nitrogenous base, sugar, and an ion of phosphoric acid. Nucleotides are phosphate easters of the nucleoside.

2. Who discovered nucleic acid?
A. Watson and Crick
B. Griffith
C. Friedrich Miescher
D. Walter Gilbert
Answer: C
Clarification: Friedrich Miescher first discovered nucleic acid from nuclei of pus cells from discarded bandages and called it nuclein. It was later revealed as a mixture of basic protein and phosphorus-containing acid, now called nucleic acid.

3. Name the pyrimidine base which is found in RNA but not in DNA?
A. Thymine
B. Uracil
C. Adenine
D. Guanine
Answer: B
Clarification: Uracil is considered like thymine, but it lacks methyl group at the C5 position. Uracil is a component of RNA whereas it is not found in DNA.

4. Name those purine bases which are commonly found in DNA and RNA?
A. Adenine and guanine
B. Cytosine and thymine
C. Adenine and thymine
D. Cytosine and guanine
Answer: A
Clarification: There are two types of nitrogenous bases in both RNA and DNA, purines and pyrimidines. Adenine and guanine are purines while cytosine and thymine come under pyrimidines.

5. Deoxyribose sugar is found in DNA.
A. True
B. False
Answer: A
Clarification: Ribose sugar is found in RNA, if the hydroxyl group(OH) at the 2^nd position of ribose sugar is replaced by hydrogen (H) it will convert to deoxyribose which is DNA’s sugar.

6. Which of these statements are TRUE for a glycosidic bond?
A. The bond between sugar and the nitrogenous base
B. The bond between the two sugar residues
C. The bond between sugar and phosphate
D. The bond between base and phosphate
Answer: A
Clarification: The glycosidic bond formed between sugar and nitrogenous base during the formation of a nucleoside. This bond is held to be in β-configuration with respect to the ribose sugar leaving it’s base free to rotate around the bond.

7. What is the energy currency of the living cell?
A. GTP
B. NADH
C. FADH
D. ATP
Answer: D
Clarification: ATP is the energy currency of the cell as it acts as a donor of high energy phosphate. It also acts as a chemical link between catabolism and anabolism. In its active form ATP is complexed with Mg²⁺ or Mn²⁺.

8. The primary structure of DNA and RNA proceeds in which direction?
A. 3’ —–> 5҆’
B. 5’ —–> 3’
C. 4’ —–> 6’
D. 3’ —–> 6’
Answer: B
Clarification: The primary structure is described by the order in which bases occur in a polypeptide. The convention is to arrange them from left to right from 5’ end to 3’ end. 5’ end of the polypeptide is attached to phosphate while 3’ end is usually a free hydroxyl group.

9. Which bond is used to stabilize the double helix of DNA?
A. Hydrophobic bond
B. Hydrogen bond
C. Covalent bond
D. Ionic bond
Answer: B
Clarification: Polynucleotide runs on the backbone of the phosphate-sugar chain. The base pairing of these nucleotide gives secondary structure. The secondary structure of DNA is its double helix which held together by hydrogen bonding between the bases.

10. Which of these statements are INCORRECT according to chargaff’s rules?
A. The molar ratio of A to T or C to G = 1
B. The sum of purine = sum of pyrimidine
C. The % C+G ≠ % A+T
D. The composition of DNA remains the same in all the species
Answer: D
Clarification: Erwin Chargaff proposed two rules which played a significant role in the discovery of the double helix structure of DNA. According to its second rule, the composition of DNA varies from one species to other. Statement composition of DNA remains the same in all the species is incorrect.

11. A purified DNA sample of leaf contains 20.0 mole of guanine. Calculate the approximate percentage of purine residues?
A. 30%
B. 40%
C. 60%
D. 20%
Answer: A
Clarification: According to chargaff’s rules, C=G= 20%; A=T
(A+G) + (T+C. =100%
(A+20) + (T+20) =100%
(A+20) + (A+20) = 100%
2A= 100-40%
A = 30%.

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Life Sciences Multiple Choice Questions on “Amino Acid Metabolism”.

1. Which of the following is non-essential amino acid?
A. Lysine
B. Leucine
C. Serine
D. Methionine
Answer: C
Clarification: Non-essential amino acids are those which are produced by the body and need not be supplied in the diet while essential amino acids are not produced in the body so these must be the part of the diet.

2. Which of these amino acids are essential for infants?
A. Methionine
B. Arginine and Histidine
C. Valine
D. Lysine and Leucine
Answer: B
Clarification: Only arginine and histidine are considered essential for infants as arginine is required for proper growth and development while histidine provides inflammatory response and the production of hydrochloric acid in the stomach. These are not produced in the body and must be supplemented in the diet.

3. In which form the nitrogen is incorporated into an amino acid?
A. Nitrite
B. Glutamate
C. Nitrate
D. Ammonium ion
Answer: D
Clarification: Source of nitrogen in all amino acid is ammonium ion. It is the key component of amino acids. The ammonium ion is first incorporated in amino acids and then in other biomolecules.

4. Transamination reaction in amino acid synthesis is catalyzed by enzyme_________
A. Nitric oxide synthase
B. Decarboxylase
C. Aminotransferase
D. Glutamate decarboxylase
Answer: A
Clarification: Transamination is the reaction of an amino acid biosynthetic pathway in which α-amino group from one amino acid is transferred to an α-keto acid and produce new amino acid. This reaction is catalyzed by aminotransferases also known as transaminases.

5. Intermediates of which of the following metabolic pathway have not been used in the synthesis of amino acids?
A. Glycolysis
B. Fatty acid biosynthesis
C. Citric acid cycle
D. Pentose phosphate pathway
Answer: B
Clarification: All amino acids are derived from the intermediates of metabolic pathways like glycolysis, citric acid cycle, and the pentose phosphate pathway. 20 amino acids have been divided into 6 families on the basis of the primary carbon source of each amino acid.

6. Name the amino acid which does not take part in transamination during amino acid catabolism.
A. Proline
B. Threonine
C. Lysine
D. Serine
Answer: D
Clarification: Except serine rest three amino acids i.e. proline, threonine, and lysine take part in transamination during amino acid catabolism. Amino group donor is specific and called aminotransferase while acceptor is almost always α-ketoglutarate.

7. Name those living organisms which secrete nitrogen in the form of urea?
A. Ureotelic
B. Uricotelic
C. Ammonotelic
D. Nitroso compounds
Answer: A
Clarification: All living organisms excrete nitrogen in three ways i.e. ureotelic which excrete in the form of urea; ammonotelic emit nitrogen in the form of ammonia, and uricotelic excrete uric acid.

8. The urea cycle is also referred to as Krebs-Henseleit cycle.
A. True
B. False
Answer: A
Clarification: Urea cycle was discovered by Krebs and Henseleit, so, it is also known as Krebs-Henseleit cycle. The urea cycle is formed by aspartate, Co₂, and ammonia in the cyclic pathway.

9. Name the type of cell in which synthesis of urea cycle takes place?
A. Pancreatic cell
B. Hepatocyte
C. Bowman’s gland cell
D. Urinary epithelium cell
Answer: B
Clarification: Hepatocytes are liver cells in which urea synthesis take place in five enzymatic reactions, first two reactions occur in mitochondria while the rest three reactions take place in the cytosol.

10. Which of these is a hereditary disease caused due to an error in amino acid metabolism?
A. Homocystinuria
B. Albinism
C. Phenylketonuria
D. Branched-chain ketoaciduria
Answer: C
Clarification: Phenylketonuria is a hereditary disorder caused by defective amino acid metabolism in which phenylalanine is not converted to tyrosine and deposited in the body. It is caused due to deficiency of enzyme phenylalanine hydroxylase.

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Life Sciences Multiple Choice Questions on “Bacterial Genome”.

1. Name the area of a bacterial cell which contains a bacterial chromosome.
A. DNA
B. Nucleus
C. Nucleoid
D. Cell wall
Answer: C
Clarification: Nucleoid is the region of the bacterial cell which lacks a limiting membrane and contains the bacterial chromosome. BacteriaI circular dsDNA molecule is associated with polyamines instead of histone proteins.

2. Which of the following is not the nucleotide associated protein?
A. HSP
B. HU
C. H-NS
D. IHF
Answer: A
Clarification: Nucleoid associated proteins are of four types which facilitates compaction of chromosomal DNA by bending, bridging, and wrapping i.e. HU is heat unstable protein, H-NS is histone-like nucleoid structuring, IHF stands for integration host factor, and SMC is structural maintenance protein.

3. Which nucleoid protein assisted in condensation of DNA?
A. SMC
B. IHF
C. HU
D. H-NS
Answer: D
Clarification: H-NS protein helps in condensation of DNA by first binding with the DNA and then these proteins bind with each other and form an aggregate of four or more H-NS units.

4. All bacteria have single circular DNA molecule.
A. True
B. False
Answer: B
Clarification: Prokaryotes like E.coli has only one single circular DNA molecule composed of entire genome while rest contains multiple linear or circular DNA. Like, vibrio cholerae contains two circular chromosomes.

5. Name the group of bacteria which uses histone to condense DNA molecule?
A. Spirochetes
B. Archaebacteria
C. Mycoplasma
D. Cyanobacteria
Answer: B
Clarification: Archaebacteria is a group of prokaryotes which resembles eukaryotes in some aspect and differs from the bacterial group. Archaeans uses eukaryotes like histones to condense their DNA molecules.

6. Extrachromosomal DNA present in prokaryotes is called_______
A. Cocci group of bacteria
B. Chainlike group of bacteria
C. Plasmid
D. Grapelike cluster of bacteria
Answer: C
Clarification: Plasmids are extrachromosomal, autonomous, and self-replicating DNA molecule that maintains discrete genetic element in bacteria. Most plasmids are negatively supercoiled, circular dsDNA molecules but linear plasmids have also been reported.

7. Name the plasmid which makes host cell resistance to the antibiotic.
A. Hfr
B. F-plasmid
C. Col plasmid
D. R-plasmid
Answer: D
Clarification: R plasmid stands for resistance plasmid which makes cell resistant to antibiotics. They have genes which code for enzymes that are capable of destroying or modifying antibiotics.

8. Which of the following is NOT the property of plasmid?
A. Rolling circle replication
B. Narrow host range
C. Two closely related plasmids cannot coexist in the same cell
D. Encodes gene products that are essential for growth
Answer: B
Clarification: Plasmids can have narrow as well as broad host range as when it exists only in a limited number of closely related bacteria, it shows narrow host range while if it transferred to and maintained in a large number of bacteria, it shows broad host range.

9. Name the type of plasmid which has no identified function or phenotypic properties?
A. Cryptic plasmid
B. R-plasmid
C. High-frequency recombination
D. Col plasmid
Answer: A
Clarification: Cryptic plasmids do not code for genes that contribute any phenotypic properties or identified functions. They have no clear use for organisms in which they were identified.

10. Which of the following plasmid found in eukaryotes?
A. Col plasmid
B. 2μ circle
C. F-plasmid
D. Hfr
Answer: B
Clarification: Plasmids are found not only in prokaryotes but also in eukaryotes. Yeast plasmid is a 2μ circle, which is 6.3kb circular, extrachromosomal in nature and found in the nucleus of the yeast strain.

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Life Sciences Multiple Choice Questions & Answers (MCQs) focuses on “Sex Determination”.

1. Genes of sex linked characters are located on the ___________
A. Chromosome 18
B. Chromosome 13
C. Chromosome 14
D. Sex chromosome
Answer: D
Clarification: The characters are said to be sex linked if their genes are located on the sex chromosome. According to modern genetics, the x-chromosome linked character is called sex-linked character while y-linked characters are called male limited characters.

2. In sex linkage, reciprocal cross yield identical results.
A. True
B. False
Answer: B
Clarification: In the case of sex linkage reciprocal cross do not yield identical results, but it shows a criss-cross inheritance pattern, i.e. male transmits its sex linked genes to all daughters who in turn transmit them to half of their male progeny.

3. Which of the following is X-linked recessive disorder?
A. Color blindness
B. Sickle cell anemia
C. PTC tasting
D. Albinism
Answer: A
Clarification: In humans, three proteins in the cons cells act as color sensors, the two color sensors are encoded by X-linked genes while one is encoded by a gene located on the seventh autosome.

4. Which of the following statement is NOT true regarding Partial sex linkage?
A. The X-Y chromosome pair during meiosis
B. Pairing occurs in the terminal region
C. The inheritance pattern in the PAR region show sex-linkage
D. PAR stands for the pseudo autosomal region
Answer: C
Clarification: The inheritance pattern of the genes present in such terminal regions (PAR) of the sex chromosome is not like that of sex-linked genes but it resembles that of autosomal genes.

5. Identify the disease which causes excessive production of uric acid.
A. Duncan muscular dystrophy
B. Lesch-Nyhan syndrome
C. Hunter syndrome
D. Hemophilia
Answer: B
Clarification: Lesch-Nyhan syndrome is an X-linked disorder which is the example of congenital hyperuriemic (excessive production of uric acid). It causes HGPRT (Hypoxanthine Guanine Phosphoribosyl Transferase) gene defective.

6. Which of the following characteristics does not belong to the Hunter syndrome?
A. Muscular deterioration
B. Abnormal hairiness
C. Mental retardation
D. Long protruding tongue
Answer: A
Clarification: Hunter syndrome is an X-linked recessive disorder where the affected person have long protruding tongue and mental retardation while muscular deterioration occurs in another disorder called Duncan muscular dystrophy.

7. Which of the following is NOT a sex-limited role?
A. Pitch of voice
B. Musculature
C. Baldness
D. Milk production
Answer: C
Clarification: Baldness is a sex-influenced character, not a sex-limited character. Sex-limited characters are those whose development is limited to only one of the two sexes.

8. Which of the following disease is characterized by excessive trinucleotide repeats (CAG)?
A. Cystic fibrosis
B. PTC tasting
C. Dwarfism
D. Huntington’s disease
Answer: D
Clarification: Huntington’s disease is an autosomal disorder which is caused by excessive trinucleotide repeats, approx 50 to 100 times more than normal condition.

9. What is pedigree analysis?
A. Record of inheritance pattern
B. Linkage map
C. Quantitative genetic
D. Polygene analysis
Answer: A
Clarification: Pedigree is a record of inheritance of certain genetic traits for two or more than two generations presenting in the form of a diagram.

10. Name the principle on which pedigree analysis work?
A. Regression
B. Probability
C. Random mating
D. ANOVA
Answer: B
Clarification: Pedigree analysis is used to study the transmission genetics where controlled process is not possible and it works on the principle of probability.

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Life Sciences Multiple Choice Questions on “Structure of dsDNA”.

1. Who described the structure of DNA double helix?
A. Peter Mitchell
B. Andre Jagendorf
C. Ernest Uribe
D. Watson and Crick
Answer: D
Clarification: DNA double helix was first described in 1953 by Watson and Crick using X-ray diffraction. DNA fibers were obtained by Franklin and Wilkins. Watson, Crick, and Wilkins were awarded a noble prize in 1962.

2. Which form of DNA is described by Watson-Crick model?
A. B-DNA
B. Z-DNA
C. A-DNA
D. Quadraplex DNA
Answer: A
Clarification: There are many forms of DNA which are biologically important, out of which Watson-Crick double helix model describes the B form of DNA. The confirmation of DNA would depend on the hydration level, base modification etc.

3. How many base pairs are there in every helical turn of Watson-Crick double helix model?
A. 32.3
B. 11.6
C. 20
D. 10.4
Answer: D
Clarification: Watson-Crick double helix model consists of 10.4 base pairs per helical turn. Since one helical turn formed by 360° and there would be 34.3° twist angle per residue among adjacent base pair.

4. Which one of the following statement is INCORRECT for Z-DNA?
A. Left-handed DNA
B. Mostly found in alternating purine-pyrimidine sequences
C. Only one deep, narrow groove
D. Anti glycosidic bond conformation
Answer: D
Clarification: Anti glycosidic bond conformation is incorrect as in Z-DNA the sugar and glycosidic bond conformations alternate, anti for C and syn for G while in B form there is only anti glycosidic bond conformation.

5. The third strand of triple helix is paired in which scheme?
A. Hoogsteen base pair scheme
B. Intermolecular base pair scheme
C. Intramolecular base pair scheme
D. G-quartet scheme
Answer: A
Clarification: Triple helix formed by three strands polypurine, polypyrimidine and the third strand which lay in the major groove of DNA and makes a hydrogen bond to duplex. The third strand is paired in hoogsteen base pairing scheme where the central strand is purine rich.

6. Name the nitrogenous base which is found in abundance in G-quadruplex?
A. Adenine
B. Guanine
C. Cytosine
D. Thymine
Answer: B
Clarification: When nucleic acid sequences are rich in guanine and can form four-stranded structure, it will term as G-quadruplex. It is a square arrangement of guanine, stabilized by hoogsteen hydrogen bonding.

7. The stability and formation of G-quadruplex depends on __________
A. Monovalent cation
B. Divalent cation
C. Bivalent cation
D. Pentavalent ion
Answer: A
Clarification: A monovalent cation is responsible for the stability of G-quadruplex as it is present in the center of the tetrad. It can be formed in either DNA or RNA.

8. Which of this factor is not responsible for thermal denaturation of DNA?
A. PH
B. Temperature
C. Ionic strength
D. Humidity
Answer: D
Clarification: When DNA duplex is laid open to the specific conditions like temperature, pH, or ionic strength it will interrupt the hydrogen bond between strands and they are no longer held together. After denaturation, the strand separates as individual coils and the double helix is denatured.

9. Double-stranded DNA with high GC content has higher thermal stability than that of lower GC content?
A. True
B. False
Answer: A
Clarification: There is three hydrogen bond in G:C while only two between A: T, this shows higher no of hydrogen bonds and interaction in G:C than A:T. Higher G:C content has a higher melting temperature. So, it has more thermal stability as compared to A:T.

10. What is the term given to the supercoiling of circular DNA?
A. Twist number
B. Linking number
C. Writhe number
D. Cross-linking
Answer: B
Clarification: Linking number defines the no. of times one strand crosses other in closed circular DNA. It is the sum of twist number (total number of helical turn) and writhe number (supercoiling in the helix).
Lk = Tw + Wr.

11. Which of them is used to introduce negative supercoiling in DNA?
A. Type 1 topoisomerase
B. Ethidium bromide
C. Gyrase/ type 2 topoisomerase
D. SYBR gold
Answer: C
Clarification: Type 1 topoisomerase break only one strand of DNA while gyrase works on both the strands, it breaks and reseal both DNA strands and introduce negative supercoils. Ethidium bromide and SYBR gold are used to stain DNA molecules.

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Life Sciences Multiple Choice Questions on “Nucleotide Metabolism”.

1. Salvage pathway is used in the synthesis of ___________
A. Amino acid
B. Carbohydrate
C. Nucleotide
D. Fatty acid
Answer: C
Clarification: Nucleotide synthesis takes place by two pathways: salvage pathways and de novo pathways. In de novo pathway pyrimidine base is assembled first and then attached to ribose while in the salvage pathway preformed base is recovered and reconnected to a ribose sugar.

2. All deoxyribonucleotide is synthesized by the ribonucleotides.
A. True
B. False
Answer: A
Clarification: Deoxyribonucleotide cannot be synthesized directly from de novo and salvage pathway but it is generated by the reduction of ribose from the corresponding ribonucleotide.

3. Name the precursor of RNA?
A. Glutamine
B. Cytidine
C. Orotidylate
D. Uridylate
Answer: D
Clarification: Uridylate or UMP is a major pyrimidine nucleotide formed by the decarboxylation of orotidylate (OMP) during pyrimidine synthesis. UMP further gets converted to a ribonucleotide, and act as a precursor of RNA.

4. The activity of which of the following enzyme is inhibited by the chemotherapeutic agent during deoxyribonucleotide synthesis?
A. Dihydrofolate reductase
B. Ribonucleotide reductase
C. Thymidylate synthase
D. CTP synthetase
Answer: A
Clarification: Methotrexate and aminopterin are two anticancer drugs which inhibits the activity of dihydrofolate reductase. This will stop the formation of deoxyribonucleotide or DNA and the growth of the cell stops.

5. Which of the following is not the precursor of a purine ring?
A. Glutamine
B. Lysine
C. Glycine
D. Aspartate
Answer: B
Clarification: Purine ring is derived from various precursors like glutamine (N2 and N9), glycine (C4, C5, and N7), aspartate (N1), Co₂ (C6), folate (C2 and C8). Except for lysine, all are the precursor of purine ring.

6. During purine synthesis the activity of amidotransferase enzyme is inhibited by the antitumor agent, mark the correct one.
A. Aminopterin
B. Methotrexate
C. Texol
D. Azaserine
Answer: D
Clarification: Azaserine is the structural analog of glutamine and works as an antitumor agent by preventing the activity of enzyme amidotransferase which in turn block purine synthesis.

7. What is the final product of purine degradation in mammals?
A. Guanine
B. Inosine
C. Uric acid
D. Hypoxanthine
Answer: C
Clarification: Punine nucleotides are sequentially degraded from inosine to hypoxanthine and guanine and finally to the uric acid which is excreted with the urine in the human being while in some other animals it is further degraded to urea and ammonia.

8. Name the deficiency in which T and B lymphocyte do not develop properly?
A. XLA
B. CVID
C. SCID
D. Multiple myeloma
Answer: C
Clarification: Severe combined immunodeficiency syndrome (SCID. is caused by the deficiency of adenosine deaminase which leads to increase in the cellular concentration of dATP. High level of dATP reduces dNTPs in T-lymphocytes.

9. Which of the following disorder is caused due to the high serum level of urate?
A. Gout
B. Galectosemia
C. Cystic fibrosis
D. Maple syrup urine disease
Answer: A
Clarification: Gout is caused due to the high amount of uric acid, which is the product of purine degradation. It involves precipitation of sodium urate crystals in the joints and causes inflammation.

10. Name the genetic disorder which is caused by the deficiency of enzyme HGPRT?
A. SCID
B. Lesch-Nyhan syndrome
C. Cystic fibrosis
D. Down syndrome
Answer: B
Clarification: This genetic disorder is caused by the deficiency of enzyme hypoxanthine-guanine phosphoribosyl-transferase (HGPRT). This results in increase rate of purine biosynthesis by de novo pathway and overproduction of urate.

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