chapter-01 - molecular biology

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B.I Molecular Biology

Multiple choice questions

1. The nucleic acids are acidic in nature due to the presence of

a) Nitrogenous bases

b) Pentose sugarsc) Phosphate groups

d) Hydrogen bonds

Obj/

Act. Verb!Ditr. Level

U

Establishes

relationship

Average

2. A monocyclic nitrogenous base present in DNA is

a) Adenine

b) Guaninec) Cytosine

d) Uracil

U

Correlates

Average

3 . The chemical bond formed between pentose sugar and phosphate U

group in DNA molecule is Establishes

a) Glycosidic bond relationship

b) Hydrogen bond

c) Phosphodiester bond

d) Ester bond

4. The components ofUridylic acid are

a) uracil + riboseb) uracil + ribose + phosphatec) uracil + phosphated) uracil+ any acid

U

Batablishes

relationship

Difficult

5. DNA is not present in

a) Episome

b) Chondriosome

c) Nucleoid .

d) Dictyosome

K .Recognises

Difficult

6. The short lived highly unstable RNA is

a) m-RNA

b) t-RNAc) r-RNA

d) mitochondrial RNA

K

Recalls

Easy

7 . A bacterium having radioactive DNA strands is allowed to A

replicate in non-radioactive culture medium for two generations. Analyses. Difficult

The percentage of ra~ioactive bacteria in second generation is

1 3 1



The percentage of radioactive bacteria in second generation is

a) 25%

b) 50%c) 75%

d) 100%

8. The codon recognition ann oft-RNA is

a) amino acid a r mb) DHUarm

c) T'PCarm

d) Anticodon arm

U

Establishes

relationship

Average

9. "The enzyme required for the synthesis ofr-RNA in Eukaryotes is

a) RNA primase

b) RNApolyIc) RNA poly II

d) RNA poly III

u .Establishes

relationship

Average

10. The most acceptable gene hypothesis is

a) one gene-one character

b) one gene-one enzyme

c) one gene-one protein

d) one cistron - one polypeptide

K

Recalls

Difficult

"II. The ds DNA having 21% Thymine will have

a) 21% Cytosine

b) 29% Guanine

c) 79% Adenined) 29% Adenine

A

Analyses

Difficult

12. The enzyme involved in the formation of Okazaki fragments inprokaryotes is

a) DNA poly I

b) DNA poly II

c) DNA poly III

d) RNA poly II

KRecalls

Difficult

13. Which of the following is the correct representation of U

semiconservative replication of DNA ? ~, Discriminatesa) . "Difficult

5'

3'

b) 3'

, 5' \

5 ':: ,;r"

, : _ . . . . ; f

3 '

138

.I'

5 '"



c)

U

Establishes

relationship

Difficult

d)

14. DNA (I») mRNA (/I») protein.

In the above flow chart, (i) and (ii) denote

a) translation and transcription

b) transcription and translation

c) replication and transcription

d) transcription and replication

15. An amino acid which can be coded by three codons exhibits

a) 3-fold degeneracy

b) codon degeneracy

c) commaless codon

d) 2-fold degeneracy

K

Recalls

Difficult

~

16. The enzyme coded by Lac - tgene in E. coli isa)

rl-galactosidase

b) rl - galactoside permease

c) rl- galactoside transacetylase

d) Thiogalactoside transacetylase

U

Correlates

Easy

17. Which of the following shows similar nucleotide sequence on m- U

RNA with the exception of Uridylic acid ? AnalysesDifficult

a) Antisense strand of DNA

b) Sense strand of DNA

c) Anticodons oft-RNA

d) Template of DNA

18. What is the number of amino acids present in a nascent Upolypeptide translated from the m-RNA having 1011 nucleotides Establishes

in the open reading frame? relationshipDifficult

a) 1010

b) 1009

c) 337

d) 336

139



19. Wobble hypothesis supports

a) universality of genetic code

b) degeneracy of genetic code •c) unambiguity of genetic code

d) colinearity of codon

Very short answer questions . .

20. Name the scientist who discovered nucleic acids.

21. Name the scientist who coined the term nucleic acid.

22. Name the nitrogenous base present in DNA but not in RNA.

23. Name the pentose sugar present in DNA.

24. Name the pentose sugar present in RNA.

25. Name the pyrimidine base present in both the DNA and RNA.

26. What is a Nucleoside?

27. What is a Nucleotide?

28. Name the monomeric unit of a nucleic acid IDNA I RNA ?

(anyone of the three to be mentioned in a question)

29. Name the components of uridylic acid.

30. Name the components of deoxycytidine.

U

Establishes

relationshipAverage

K

Recalls

Easy

K

Recalls

E a s y

K

Recalls

Average

K

Recalls

E a s y

K

Recalls

Easy

KRecalls

Average

K

Defines

E a s y

K

Defines

E a s y

K

Recalls

E a s y

U

Identifies

Average

U

Identifies

E a s y

140



31. Name the chemical bond formed between nitrogenous base and U

Identifies

E a s ypentose sugar in a nucleotide.

32. Name the chemical bond formed. between pentose sugar and U

phosphate group in a nucleotide. IdentifiesAverage

33. Name the chemical bonds formed between the complementary UIdentifies

Averagenitrogenous bases in DNA.

34. How many nuclelotide pairs are present in one complete turn of K

DNA helix? RecallsE a s y

35. What is the percentage of adenine in a ds DNA, having 30% of S

cytosine? SolvesDifficult

36. Mention the functions of Unwindase / Gyrase / RNA primase/ DNA K

polymerase I / DNA Polymerase II / DNA Polymerase III / SSBP / Recalls

Windase / Topoisomerase / DNA ligase. E a s y

(Function of each enzyme is a separate question).

37. What is a lagging strand of DNA ? K

Defines

Difficult

38. What is a leading strand of DNA ? K

DefinesDifficult

39. What is ORI site? K

Defines

Average

40. What are Okazaki fragments? K

Defines

Average

41. What is RNA primer? K

Defines

Average

42. Name the short lived! unstable / least occurring type of RNA.

(Each alternative must be a separate question).

K

Recalls

E a s y

43. Name the soluble RNA / Adapter RNA / smallest RNA / RNA that K

carries amino acids. Recalls

(Each alternative must be a separate question). E a s y

141



44. Name the most abundant RNA I largest RNA.

,(Each alternative must be a separate question).

K

Recalls

E a s y

45. Name the scientist who proposed the clover leaf (trifoliate) model of K

t-RNA. RecallsE a s y

46. Which is the amino acid binding site of t-RNA ? U

Identifies

Average

47. Which is the ribosome recognition site of t - RNA ? U

Identifies

Average

48. Which is the decoding (loop) site oft-RNA? U

Identifies

Average

49. Name the scientist who discovered m-I~NA. K

Recalls

E a s y

50. Mention the function oft-RNA. U

Explains

Average

51. Mention one function of m-RNA. U

Explains

Average

52. Mention one function of r-RNA. U

Explains

Average

53. Which part of the t-RNA is recognized by aa-t-RNA synthetase U

enzyme? ExplainsAverage

54. What is monocistronic m-RNA ? K

Defines

Average

55. What is polycistronic m-RNA ? K

Defines

Average

56. What is Hn-RNA I heterogeneous nuclear RNA ? K

Recalls

Average

57. Name the scientist who proposed the fine structure of gene. K

Recalls

E a s y

142



58. What are split genes? K

Defines

Average

59. What are unsplit genes? K

Defines

Average

60. Define Cistron / Muton / Recon / Replicon / Operon / Lac - Operon! K

Codon / Anticodon. Defines

(Each alternate term must be a separate question).Easy

61. Define initiator codon. K

Defines

Average

62. Name the most common initiator codon. K

RecallsEasy

63. Name the amino acid coded by initiator codon. K

Recalls

Easy

6 4 . Name the enzyme that activates amino acid during protein synthesis. K

Recalls

Average

65. Name the enzyme that helps in the formation of peptide bonds K

between amino acids during protein synthesis. RecallsAverage

66. Define transcription. K

Defines

Easy

67. Define Translation. K

Defines

Easy

68. Name the enzyme coded by Lac z / Lac y / Lac a genes of lac- K

operon. Recalls

(Each alternative must be a separate question).Average

69. Which gene of operon produces the repressor protein? K

Recalls

Easy

70. Name the inducer of Lac-operon in E.coli. K

Recalls

Easy

71. Name the scientists who proposed operon concept. K

Recalls

Easy

143



72. Which enzyme catalyses the synthesis of DNA using a RNA K

template? Recalls

Easy

73. Name the codon with double function. K

Recalls

Average

Give reasons for the following (Questions 74 - 92)

74. DNA is acidic in nature / nucleotides are acidic in nature. U

Establishes

relationship

Average

75. DNA replication is semi conservative I semi discontinuous! bi- U

directional. ExplainsDifficult

(Each alternative must be a separate question.)

76. How is DNA replication initiated? U

Establishes

relationship

Difficult

77. Chargoff's base rule is not applicable for RNA. A

Analyses

Difficult

78. G - C Pairing is stronger than A - T Pairing. U

Establishes

relationshipDifficult

79. The nucleotide ratio in RNA is not usually constant (or) highly APredicts

Difficultvariable.

80. The processed m-RNA in eukaryotes is shorter than its gene or in A

Eukaryotes the length of processed m-RNA does not match the PredictsDifficult

length of its gene.

81. Prokaryotic gene is an unsplit gene. U

Correlates

Difficult

82. Eukaryotic gene is a split gene. U

Correlates

Difficult

83. UAA is a terminator codon (non-sense codon) U

Establishes

relationship

Difficult

144



84. AUG is the initiator codon. U

Gives reasons

Difficult

85. 61 codons code for only 20 amino acids. U

Gives reasons

Difficult

86. Lac-operon switches off in the absence of inducer

E.coli.

(lactose) in UGives reasons

Difficult

87. When the extract of heat killed S-cells of Pneumococcus treated U

with DNA is introduced into the culture of live R-cells, there is no Analyses

transformation.Difficult

88. Codons are universal. A

Gives reasonsDifficult

89. Codons are redundantl sensible. A

Gives reasons

Difficult

90. All polypeptides start with methionine as first amino acid, but all A

proteins do not have methionine. Analyses

Difficult

91. Methionine is always the first amino acid brought to the site of A

protein synthesis. Analyses

Difficult

92. Redundancy concept of genetic code does not apply to all amino A

acids. Analyses

Difficult

Short answer questions

93. Draw a neat and labeled diagram ofm-RNA. S ,

Drawing

Average

94. Mention any four structural differences between DNA and RNA. U

Compares

Average

95. Name the nitrogenous bases ofDNAIRNA.

(Each alternative must be a separate question)

K

Recalls

Average

96. Name the pyrimidines present in DNAIRNA. K

Recalls

Average

145



97. Mention the types of nucleotides in DNA.

98. Mention the types of nucleotides in RNA.

99. List two differences between a nucleoside and nucleotide.

100 Draw a neat and labeled diagram of the DNA molecule.

101. Draw a neat and labeled diagram oft-RNA molecule.

102. Mention two functions each for DNA and RNA.

103. List four functions of DNA.

104. Mention two differences between prokaryotic and eukaryotic genes.

105. List four functions of RNA.

106. Mention 4 characteristic features of genetic code.

107. What are terminator codons? Mention two of them.

108. What are non-sense codons? Name any two.

109. Mention two structural and two control genes of lac operon.

110. Name the three types of RNA in a eukaryotic cell.

K

Recalls

Average

K

Recalls

Average

U

Compares

Average

S

Drawing

Average

S

Drawing

Average

U

Compares

Average

K

Lists

Average

U

Compares

Easy

K

Lists

Average

K

Mentions

Average

K

Recalls

Average

K

RecallsAverage

KRecalls

Average

K

Recalls

Easy

146



Ill. Explain the two steps in the activation of amino acid during protein U

synthesis. ExplainsAverage

112. During translation, if the codon is AUG then

i) what is the anti-codon present on the complementary t-

RNA?

ii) Name the amino acid carried by this t-RNA.

U

Identifies

Average

113. How many amino acids are present in a nascent polypeptide S

decoded from the m-RNA with the reading frame having 1002 Solves

nucleotidesl 334 codons? Average

Long answer questions

114. Describe the double helical model of DNA with a neat labeled

diagram.

U,SSkill,

explains

Difficult

115. Explain the semiconservative replication of DNA molecule with the U,S

help of labeled diagram. Skill,explains

Difficult

116. Describe the clover leaf model of t-RNA molecule with a neat U, S

labeled diagram. Draws,explains

Difficult

117. Explain the experiment of O.T. Avery that proved DNA as the U

genetic material. ExplainsDifficult

118. List five differences between DNA and RNA. U

Compares

Average

119 Explain five characteristic features of the genetic code. U

Explains

Average

120 Explain the process of Transcription with the help of labeled

diagram.

U,S

Draws,explains

Average

121. Explain amino acid activation and chain initiation steps of protein U

synthesis. ExplainsDifficult

147



122. Mention the genes of Lac-operon and their functions. U

Explains

Average

123. Explain the structure ofm-RNA with a neat labeled diagram. U,S

Draws,

explains

Difficult

148



ANSWERS

Multiple choice answers (one mark each)

1. c

2. c

3. d

4. b

5. d

6. a

7. b

8. d

9. b

10. d

11. b

12. c

1 3 . c

14. b

15. a

16. a

17. b

18. d

19. b

Very short answers (one.mark each)

20. Friedrich Meischer

21. Altmann

22. Thymine

23. Deoxyribose

24. Ribose

25. Cytosine

26. It is a combination of nitrogenous base and pentose sugar.

27. It is a combination of nitrogenous base, pentose sugar and phosphate.

28. Nucleic acid - Nucleotide

DNA - Deoxyribose nucleotide

RNA - Ribose nucleotide

149



29. Uracil, ribose sugar and phosphate.

30. Cytosine and deoxyribose sugar.

31. N - ~ - Glycosidic bond IN ~ glycosylic bond

32. Ester bond I phospho ester bond.

33. Hydrogen bonds.

34. Ten pairs

35. 20% of adenine

36. Unwindase - unwinding the two strands of DNA molecule during proteinsynthesis.

Gyrase - relieves the tension of supercoiled regions of DNA.

RNA primase - produces RNA primers to initiate (replication)- polynucleotide

formation complementary to the template strands of DNA.

DNA polymerase I - replaces RNA primers by polydeoxy ribonucleotide

fragments.

DNA polymerase II - it helps in proofreading and DNA repairing.

DNA polymerase III - catalyses the polymerization of deoxy ribonucleotides in

5' - 3' direction.

SSBP (Single Strand Binding Protein) - these are helix destabilizing proteins

that keeps two strands of DNA in separated condition during replication.

Windase - it helps in winding of the polynucleotide strands of DNA.

Topoisomerase - breaks and reseal the DNA strands.

DNA ligase - joins the fragments of DNA or Okazaki fragments.

37. It is the strand of DNA formed discontinuously against the sense strand during

replication.

38. It is the daughter strand of DNA formed continuously towards the replication

fork during replication.

39. The point at which the uncoiling of DNA begins during replication is calledOR! site. .

40. Short single stranded discontinuous DNA fragments formed away from the

replication fork during replication.

41. It is a short fragment of RNA formed by RNA primase at the beginning of DNA

replication.

42. m-RNA Imessenger RNA

150



43. t-RNA / Transfer RNA.

44. r-RNA / ribosomal RNA.

45. Robert W. Holley.

46. CCA 3'OH end / 3' OH end oft-RNAICCA end.

47. T \fIC loop / T -loop

48. Anticodon / NODOC loop

49. Volkin

50. It transfers amino acid to the site of protein synthesis! Transfer of aa to the siteof protein synthesis.

51. It carries the genetic message from DNA (genes) in the form of codons for the

synthesis of a polypeptide or protein.

52. It is a structural component of ribosomes that helps in translation process of

protein synthesis.

53. Dihydroxy Uridine Loop / DHU loop

54. The m-RNA transcribed by a single cistron / The m-RNA that carries codes for

a single polypeptide.

55. The m-RNA transcribed from many cistrons / The m-RNA that carries codes

for many polypeptides.

56. The RNA transcribed by eukaryotic gene having coding exons and non-coding

introns.

57. Seymour Benzere

58. The genes having coding exons and non-coding introns.

59. The genes having only coding sequences (exons) are called Unsplit genes.

60. Cistron : It is the functional unit of gene that codes for a single polypeptide.

Muton : It is a unit of cistron that undergoes mutation.

Recon: It is a unit of cistron that undergoes recombination.

Replicon : It is a unit of DNA that undergoes replication.

Operon : It is a co-ordinated assembly of regulatory and structural genes meant

to perform a specific metabolic activity.

151



Lac-operon: It is an operon concerned with lactose metabolism found in E.coli

bacterium.

Codon : A unit of three nucleotides on m-RNA that codes for a specific amino

acid during protein synthesis.

Anticodon: A unit of three nucleotides on t-RNA that decodes the codon of m-

RNA.

61. The codon on m-RNA where the formation of polypeptides is initiated.

62. AUG.

63. Methionine! f-methionine

64. Amino acyl t-RNA synthetases.

65. Peptidyl transferase

66. The process of formation of m-RNAlRNAs from the antisense strand of DNA

with the help of RNA polymerase.

67. The process of decoding of codons on m-RNA into a sequence of amino acids

forming a polypeptide chain.

68. a) Lac x - J 3 galactosidaseb) Lac y - J 3 galactoside permease (m - protein)c) Lac a - J 3 galactoside transacetylase (thiogalactoside transacetylase)

69. Regulator gene

70. Lactose

71. Francis Jacob and Jacques Monad.

72. Reverse transcriptase (RNA dependent DNA polymerase)

73. AUG.

74. Due to the presence of phosphate group.

75. Semi conservative: The parental strands are conserved in daughter DNA

molecules OR the daughter DNA molecules have one parental and one new

strand.

Semi discontinuous: Because the leading strand is produced continuously and

lagging strand is produced discontinuously.

Bi-directional: Because the leading strand is produced towards the replication

fork and lagging strand is produced away from the replication fork.

152



The two strands of DNA molecule are antiparallel and the enzymes are direction

specific.

76. RNA primer initiates the formation of polynucleotide in 5' ~ 3' direction by

providing pre-existing 3' - OH end.

77. Because it is single stranded.

78. Because 3H bonds bind G and C but only 2H bonds bind A and T.

79. Due to the absence of complimentary base pairing it is single stranded.

80. Because the eukaryotic gene is a split gene and the transcribed and processed m-

RNA has intron portions.

81. Because it contains continuous coding sequences or exons.

82. Because it contains coding exons and non-coding introns.

83. Because it terminates protein synthesis as it does not code for any amino acid.

84. Because it initiates the process of polypeptide synthesis / protein synthesis.

85. Due to the property of genetic code called degeneracy, most amino acids are

coded for by more than one codon. Hence the number of codons exceed the

number of amino acids.

86. The repressor binds to operator and prevents transcription.

87. Because heat hydrolyses DNA.

88. A codon codes for the same amino acid in all organisms.

89. Redundant - A single amino acid can be coded by 2 or 3 codons.

Sensible - A codon codes for a specific amino acid.

90. Although methionine is the first amino acid translated, it is removed

subsequently during polypeptide maturation in many proteins.

91. The initiator codes - AUG codes for methionine.

92. Some amino acids like tryptophan and methionine have one codon each.

153



Short answers

93. Diagram with any 4 labels.

m-RNA, codon, 3' end, 5' end, nucleotide

( Y 2 X 4 = 2 marks)

94. DNA

• Double stranded molecule.

• It contains adenine guanine

cytosine and thymine.

• Pentose sugar is deoxyribose.

• It contains large number of

nucleotides.

• Chains are antiparallel.( Y 2 x 4 = 2 marks)

RNA• Single stranded molecule.

• It contains adenine, guanine, cytosine

and uracil.

• Pentose sugar is ribose.

• It contains fewer nucleotides.

• Being a single chain does not exhibit

antiparallel nature.

95. DNA - Adenine I Guanine I Cytosine and Thymine

RNA - Adenine IGuanine ICytosine and Uracil

( Y 2 + Y 2 + Y 2 + Y 2 = 2 marks.)

96. DNA - Cytosine (C) and Thymine (T)

RNA - Cytosine (C) and Uracil (U)

Pyrimidines of DNA -1mark, RNA -1mark = 2 marks)97. a) Deoxy adenosine monophosphate I dAMP/ d-Adenylic acid

b) Deoxy Guanosine monophosphatel dGMP I d-Guanylic acidc) Deoxy Cytidine monophosphate/ dCMPI d-Cytidylic acid

d) Deoxy thymidine monophosphate/ dTMP / d-Thymidylic acid.

( Y 2 + Y 2 + Y 2 + Y 2 = 2 marks.)

98. RNA nucleotides are

i) Adenosine monophosphate IAMP IAdenylic acid

ii) Guanosine monophosphate / GMP / Guanylic acid

iii) Cytidine monophosphate I CMP I Cytidylic acid

iv) Uridine monophosphate / UMP / Uridylic acid

(~+ Y 2 + ~+ ~=2marks.)

99. Nucleoside• It is made up of

nitrogenous base and

pentose sugar.

• It is slightly alkaline.

(1 + 1 = 2 marks.)

Nucleotide• It is made up of nitrogenous base,

pentose sugar and phosphate.

• It is acidic in nature.

154




Helix 1, helix 2, nitrogenous base, deoxyribose sugar, phosphate, phospho-di-

ester bond, 3' end, 5' end.

(Diagram - 1mark, labels (any four) - 1= 2 marks)


CCA, 3' end, 5'end, DHU arm, 1'PC arm, anticodon arm, anticodon, central

petal, lateral petals (arms), small arm, amino acid arm.

(diagram - 1, labels (any four - I =2 marks)

102. DNA

• It is a hereditary material.

• It is self replicating.

• Itdirects protein synthesis.

• Itcan produce RNA.

( Y l x 2 x 2 =4 marks)

RNA

• It is hereditary material in a few viruses.

• It is synthesized against a DNA

template.

• It assists in protein synthesis.• RNA usually does not produce DNA.

103. • It is the genetic material.

• It is the master molecule of metabolic activities as it contains codes for

all the proteins.

• It shows autocatalytic function.

• It can undergo mutations.

• It synthesizes different types of RNA by transcription.

( Y l x 4 =2 marks)

104. Prokaryotic gene

• Transcribes polycistronic

m-RNA.

• Unsplit gene.

• Onlyexons

( Y l x 2 x 2 =2 marks)

Eukaryotic gene

~ Transcribes monocistronic m-RNA.

• Split gene.

• Introns and exons

105. • Genetic RNA carries hereditary characters.

• m-RNA carries the message from DNA (gene) in the form of tripletcodons.

• t-RNA carries specific amino acids to the site of ribosome.

• r-RNA helps in binding of m-RNA and t-RNA to the ribosomal surface.

(Y l x 4 = 2 marks)

106. Any four of the following:

• Genetic code consists of triplet codons.

• Genetic code is unambiguous.

155



• Genetic code is universal.

• Genetic code is degenerate.

• AUG is the initiating codon.

• It is commaless.

• 61 out of 64 codons code for amino acids.

• 3 codons are terminator codons - UAA, UAG and UGA.

( ~ x 4= 2 marks)

107. The codons that terminate the polypeptide chain synthesis (translation) arecalled terminator codons.

UAA, UAG and UGA (Ochre, Amber, Opal)

(Definition - 1, two examples = Y2+ Y2= 2 marks)

108. The codons that do not code for any amino acids are called non-sense codons.Also called chain terminator codons.

Ochre IAmber I opal or UAA' I UAGI UGA.

(Definition -1mark, examples - ~ + ~ - 1 = 2 marks)

109. • Structural genes - Lac - Z, Lac - Y, Lac - A (any 2)

• Control genes - Regulator (R), Promoter (P) and Operator (0) (any two)

(structural genes - Y 2 + Y2;control genes Y2+ Y 2 =2 marks)

110. • Genetic RNA

• m-RNA

• t-RNA

• r-RNA(All 3 =2 marks; Y2mark less for each type that is not mentioned.

111. Amino acid +ATPA min oacy/

synthetase ) aminoacyl adenylate + PP

The amino acyladenylate combines with specific t-RNA molecule to form

aminoacyl t-RNA.

Aminoacyl adenylate + t-RNA ---» aminoacyl t-RNA + AMP

(each step 1mark x 2 =2 marks)

112. i) UAC

ii) Methionine(1 + 1=2 marks)

113. 333 amino acids.

156



Long answers

114. Diagram and any 4 correct labels• Antiparallel

• complementary

• helically coiled

• 2 polydeoxyribonucleotide strands.

• Double stranded

• Left handed helix

• Backbone formed by deoxyribose sugar and phosphate

groups held together by phosphodiester bond.

• The complementary base pairing (A =T, C = = G) between the

helices is by hydrogen bonds.

• One complete turn measuring 34Aohaving a major groove

and a minor groove.(Diagram - 2, labels (at least 4) - I, explanation (6 points) = _ 2 = 5

marks)

115. Diagrams and any six points.

• ORI site• Unwinding by the enzyme unwindase I helicase• SSBP destabilizes the strands and stress is relieved in

supercoiled regions by gyrase.

• RNA primase - RNA primer.

• Leading strand formation towards replication fork - DNA

poly Ill.

• Formation of Okazaki fragments - away from replication

fork.

• Replacement of RNA primers - DNA poly I

• DNA fragments are joined by DNA ligase.

• Proofing of strands (DNA poly II and Topoisomerase)

• Winding of parental strands with lagging and leading strands

to produce 2 similar daughter molecules by the enzyme

windase.

(Diagrams - 2, labels (any four) - I, explanation (6 points) - 2 = 5

marks)

116. • Single stranded I discovery I trifoliate• 3'OH end having terminal nucleotides - CCA

• 5' end ends in G

• T loop (T",C loop)

• DHU loop

• Anticodon loop

• Variable short arm

(Diagram - 2, labels (any 4) - 1, 4 points x ~ _2 =5 marks)

157



117. • Based on the Griffith's experiment OT Avery, Mccleond,

Mccarty, carried out experiments which proved that the

transforming principle is DNA.

Separate the Organic molecules from the extract of S-strain.

(1mark for each step x 5 = 5 marks)

118. DNA

• Mostly double stranded

• Nucleotides are AGCT

• Deoxyribose sugar

• It acts as the templatetranscription.

• B-DNA, A-DNA and Z-DNA types - coexist in a

DNA molecule.

RNA

• Single stranded except insome viruses.

• Nucleotides are AGCU.

for·. Ribose Sugar

• It is involved in the process

of protein synthesis.• Many types like m-RNA, r-RNA, t-RNA.

(DNA points ~ x 5 = 2 ~; RNA points ~ x 5 = 2 ~ = 5 marks)

119 Any five of the following:

• Genetic code consists of triplet codon.

• Genetic code is unambiguous.

• Genetic code is universal.

• Genetic code is degenerate.

• AUG is the initiating codon.

• It is commaless.

• 61 out of 64 codons code for amino acids.

• 3 codons are terminator codons - UAA, UAG and UGA.

(Each feature + explanation ( ~ + ~ = 1markx 5 =5 marks)

120 • Unwinding by unwindaselhelicase

• Sense strand

• Antisense strand

• Roles of RNA polymerases m-RNA

• Rewinding of separated strands.(Diagrams - 2, labels (any 4) - I, explanation - 2 =5 marks)

121. Amino acid activation: 2 steps - 1 mark each.amin o a c y l

Amino acid +ATP s y n t h e t a s e ) amino acyladenylate + pp

Aminoacyl adenylate + t-RNA s y : ; : ~ t . ! aminoacyl t-RNA + AMP

158



Chain Initiation:

• Binding of smaller sub-unit of ribosome to 5' end of m-RNA.

• Binding of methionine - tRNA to the initiating codon of m-RNA with the help oflF, IF2, IF3and ATP.

• Attachment of larger sub-unit of ribosome.

Diagram must show smaller unit and larger units of ribosome, m-

RNA, aa, t-RNA with UAC anticodon binding to AUG codon on m-

RNA.

(Amino acid activation - 1 mark, diagram of initiation steps - 2,

explanation - 2 =5 marks)

122. • Mentioning of 5 genes (~ mark each.)

• Mentioning of5 functions (~mark each.) =2 Y 2 marksTotal =5 marks

123. Structure of m-RNA:

• 5'P leader and with cap.

• 3' OH end with poly A tail

• Leader sequence

• Initiator codon region - reading frame

• Variable coding region - reading frame

• Terminator codon region - reading frame

(Diagram - 2 marks, explanation (6 points x ~ - 3)=5 marks)

159

chapter-01 - molecular biology

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