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DNA Transcription and Translation

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Lecture B6: DNA Replication, Transcription and Translation

Transcription and Translation and the Genetic Code

DNA Replication, RNA Structure & Function, and Compare DNA & RNA

Transcriptional regualtion. Repression: Hypoxic Genes in Yeast

DNA RNA Protein

Initiation of translation in prokaryotes: initiation factors, initiator codons, 3'end of RNA small ribosomal subunit

A promoter, an operator and regulatory proteins

MCQ MOLECULAR BASIS

1.

According to the Double-Helix model of DNA proposed by James Watson
and Francis Crick (1953), what is the pitch of the right-handed DNA helix
and the approximate distance between two consecutive base pairs?
(A) Pitch = 0.34 nm; Distance per bp = 3.4 nm
(B) Pitch = 3.4 nm; Distance per bp = 0.34 nm
(C) Pitch = 20 nm; Distance per bp = 2.0 nm
(D) Pitch = 34 nm; Distance per bp = 3.4 nm

2.

3.

In eukaryotic chromatin packaging, histones are positively charged basic
proteins that organize into a histone octamer because they are rich in which
pair of basic amino acid residues carrying positive charges in their side
chains?
(A) Valine and Glutamic acid
(B) Lysine and Arginine
(C) Methionine and Tryptophan
(D) Serine and Tyrosine

4.

5.

How many base pairs (bp) of negatively charged DNA helix are wrapped
around a single positively charged histone octamer to form a typical
eukaryotic nucleosome?
(A) 100 bp
(B) 146 bp
(C) 200 bp
(D) 400 bp

6.

7.

In a typical eukaryotic interphase nucleus, the region of chromatin that is
loosely packed, stains light, and is transcriptionally active is termed:
(A) Heterochromatin
(B) Nucleoid
(C) Euchromatin
(D) Satellite DNA

8.

9.

Which of the following statements regarding the Meselson and Stahl (1958)
experiment on Escherichia coli is INCORRECT?
(A) 15N is a radioactive isotope of nitrogen that emits beta particles during
decay.
(B) 15N-DNA can be separated from 14N-DNA only based on densities in a CsCl
gradient.
(C) DNA extracted 20 minutes after transfer from 15N to 14N medium had an
intermediate/hybrid density.
(D) DNA extracted after 40 minutes (II generation) was composed of equal
amounts of hybrid and light DNA.

10.

11.

The haploid content of human DNA is
approximately
(A) 4.6 × 106 bp
(B) 6.6 × 109 bp
(C) 3.3 × 109 bp
(D) 5386 bp

12.

The haploid content of human DNA is
approximately
(A) 4.6 × 106 bp
(B) 6.6 × 109 bp
(C) 3.3 × 109 bp
(D) 5386 bp

13.

A nitrogenous base is linked to the pentose sugar to form a
nucleoside through
(A) a 3′-5′ phosphodiester linkage
(B) a peptide linkage at 2′ carbon
(C) a phosphoester linkage at 5′ carbon
(D) an N-glycosidic linkage at 1′ carbon

14.

15.

A nucleotide is formed when a phosphate group is linked to the OH
of the ______ carbon of a nucleoside through a ______ linkage.
(A) 5′ ; phosphoester
(B) 3′ ; phosphodiester
(C) 1′ ; N-glycosidic
(D) 2′ ; phosphoester

16.

17.

The chemical name of thymine , found in DNA in place of the
base uracil of RNA, is
(A) 5-methyl uracil
(B) 2-amino adenine
(C) 5-methyl cytosine
(D) 6-amino purine

18.

The chemical name of thymine , found in DNA in place of the
base uracil of RNA, is
(A) 5-methyl uracil
(B) 2-amino adenine
(C) 5-methyl cytosine
(D) 6-amino purine

19.

According to the observation of Erwin Chargaff , in a double stranded
DNA the ratios between
(A) A and G, and between T and C, are equal to one
(B) A and C, and between T and G, are equal to one
(C) A and T, and between G and C, are equal to one
(D) purines and phosphates are equal to one

20.

21.

The number of hydrogen bonds between A and T and between G
and C in a DNA double helix respectively
are
(A) 3 and 2
(B) 2 and 2
(C) 3 and 3
(D) 2 and 3

22.

The number of hydrogen bonds between A and T and between G
and C in a DNA double helix respectively
are
(A) 3 and 2
(B) 2 and 2
(C) 3 and 3
(D) 2 and 3

23.

Histones are rich in the basic amino acid residues
(A) aspartic acid and glutamic acid
(B) glycine and alanine
(C) cysteine and methionine
(D) lysine and arginine

24.

Histones are rich in the basic amino acid residues
(A) aspartic acid and glutamic acid
(B) glycine and alanine
(C) cysteine and methionine
(D) lysine and arginine

25.

The region of chromatin that is loosely packed, stains light and is
said to be transcriptionally active is called
(A) heterochromatin
(B) nucleoid
(C) euchromatin
(D) centromere

26.

The region of chromatin that is loosely packed, stains light and is
said to be transcriptionally active is called
(A) heterochromatin
(B) nucleoid
(C) euchromatin
(D) centromere

27.

In 1928, Frederick Griffith injected a mixture of heat-killed S strain
and live R strain Streptococcus pneumoniae into mice. The result
was that the mice
(A) lived and no bacteria were recovered
(B) lived and only R bacteria were recovered
(C) died and living S bacteria were recovered
(D) died and only R bacteria were recovered

28.

29.

In the experiments of Avery, MacLeod and McCarty, transformation
of R cells into S cells was inhibited by
digestion with
(A) protease
(B) RNase
(C) DNAs
(D) DNase

30.

In the experiments of Avery, MacLeod and McCarty, transformation
of R cells into S cells was inhibited by
digestion with
(A) protease
(B) RNase
(C) DNAs
(D) DNase

31.

Hershey and Chase (1952) labelled the DNA of bacteriophages
with radioactive ______ and the protein coat with radioactive
______.
(A) sulfur; phosphorus
(B) phosphorus; sulfur
(C) nitrogen; carbon
(D) phosphorus; nitrogen

32.

33.

RNA is labile and easily degradable , whereas DNA is chemically
more stable, mainly because every
nucleotide in RNA has a reactive
(A) 3′-phosphate group
(B) 2′-OH group
(C) 5-methyl group
(D) N-glycosidic bond

34.

35.

The scheme in which the two strands separate and each acts as a
template so that every daughter DNA has
one parental and one newly synthesised strand is called ______
replication.
(A) conservative
(B) dispersive
(C) semiconservative
(D) continuous

36.

37.

E. coli grown for many generations in 15NH4Cl medium was
transferred to 14NH4Cl medium. The DNA extracted after one
generation (20 minutes) , when centrifuged in a CsCl
density gradient, showed
(A) only heavy DNA
(B) only light DNA
(C) equal amounts of heavy and light DNA
(D) only hybrid (intermediate density) DNA

38.

39.

DNA-dependent DNA polymerases catalyse polymerisation of
deoxynucleotides only in the direction
(A) 3′ → 5′
(B) 5′ → 3′
(C) both 5′ → 3′ and 3′ → 5′
(D) 5′ → 5′

40.

DNA-dependent DNA polymerases catalyse polymerisation of
deoxynucleotides only in the direction
(A) 3′ → 5′
(B) 5′ → 3′
(C) both 5′ → 3′ and 3′ → 5′
(D) 5′ → 5′

41.

In eukaryotes, DNA replication takes place in the ______ of
the cell cycle, and a failure of cell division after DNA
replication results in
(A) G1-phase; aneuploidy
(B) M-phase; polyploidy
(C) S-phase; polyploidy
(D) G2-phase; monosomy

42.

43.

The figure shows a short polynucleotide chain with four structural features
pointed by the letters P, Q, R and S.
Identify the correct match.
(A) P: free 5′ phosphate; Q: free 3′ OH; R: nitrogenous base; S: pentose sugar
(B) P: free 3′ OH; Q: free 5′ phosphate; R: pentose sugar; S: nitrogenous base
(C) P: nitrogenous base; Q: pentose sugar; R: free 5′ phosphate; S: free 3′ OH
(D) P: pentose sugar; Q: free 5′ phosphate; R: free 3′ OH; S: nitrogenous base

44.

45.

In the diagram of a nucleosome, the parts marked X, Y and Z are respectively
(A) X: DNA; Y: histone octamer; Z: H1 histone
(B) X: histone octamer; Y: DNA; Z: H1 histone
(C) X: H1 histone; Y: DNA; Z: histone octamer
(D) X: DNA; Y: H1 histone; Z: histone octamer

46.

47.

A transcription unit in DNA is defined primarily by three regions,
namely
(A) exon, intron and promoter
(B) operator, promoter and repressor
(C) origin of replication, promoter and terminator
(D) promoter, structural gene and terminator

48.

49.

In the structural gene of a transcription unit, the strand that acts as
the template has the polarity
(A) 5′ → 3′ and the same sequence as RNA
(B) 3′ → 5′, since RNA polymerase catalyses polymerisation only in
the 5′ → 3′ direction
(C) 3′ → 5′ and is displaced during transcription
(D) 5′ → 3′ and carries the promoter

50.

51.

With reference to the coding strand, the promoter is located
towards the
(A) 3′-end of the structural gene, and it provides the binding site
for DNA ligase
(B) 5′-end (upstream) of the structural gene, and it provides the
binding site for RNA polymerase
(C) 3′-end of the structural gene, and it ends transcription
(D) 5′-end of the structural gene, and it binds the release factor

52.

53.

If the sequence of the coding strand in a transcription unit is 5′ATGCATGCATGCATGCATGCATGCATGC-3′, the sequence of the
mRNA transcribed from it is
(A) 5′-AUGCAUGCAUGCAUGCAUGCAUGCAUGC-3′
(B) 5′-UACGUACGUACGUACGUACGUACGUACG-3′
(C) 3′-AUGCAUGCAUGCAUGCAUGCAUGCAUGC-5′
(D) 5′-ATGCATGCATGCATGCATGCATGCATGC-3’

54.

55.

A cistron is a segment of DNA coding for a polypeptide. The
structural gene in a transcription unit is
(A) polycistronic mostly in eukaryotes and monocistronic mostly in
bacteria
(B) monocistronic in both bacteria and eukaryotes
(C) monocistronic mostly in eukaryotes and polycistronic mostly in
bacteria
(D) polycistronic in both bacteria and eukaryotes

56.

57.

Sequences that appear in the mature or processed RNA are called
______, while the intervening sequences
removed from the primary transcript are called ______.
(A) introns; exons
(B) cistrons; operons
(C) exons; introns
(D) promoters; terminators

58.

59.

In bacteria, transcription of mRNA, tRNA and rRNA is catalysed by
(A) a single DNA-dependent RNA polymerase
(B) three different RNA polymerases, one for each RNA
(C) DNA polymerase III
(D) RNA polymerases I, II and III

60.

61.

In bacteria, the RNA polymerase associates transiently with ______
to initiate and with ______ to terminate transcription.
(A) rho factor; sigma factor
(B) DNA ligase; rho factor
(C) release factor; sigma factor
(D) sigma factor; rho factor

62.

63.

In eukaryotic nuclei, RNA polymerase III is responsible for the
transcription of
(A) 28S, 18S and 5.8S rRNAs
(B) tRNA, 5srRNA and snRNAs
(C) hnRNA, the precursor of mRNA
(D) mRNA directly without any processing

64.

65.

The cell-free system for protein synthesis that helped in deciphering
the genetic code was developed by
(A) Har Gobind Khorana
(B) Severo Ochoa
(C) Marshall Nirenberg
(D) George Gamow

66.

The cell-free system for protein synthesis that helped in deciphering
the genetic code was developed by
(A) Har Gobind Khorana
(B) Severo Ochoa
(C) Marshall Nirenberg
(D) George Gamow

67.

Which of the following codons does not code for any amino acid and
has no corresponding tRNA?
(A) UGG
(B) AUG
(C) UGA
(D) UGU

68.

Which of the following codons does not code for any amino acid and
has no corresponding tRNA?
(A) UGG
(B) AUG
(C) UGA
(D) UGU

69.

The nucleotide sequence of an mRNA cannot be predicted exactly
from the amino acid sequence Met-PhePhe-Phe-Phe-Phe-Phe,
because the genetic code is
(A) universal
(B) contiguous
(C) triplet
(D) degenerate

70.

71.

Charging (aminoacylation) of tRNA, the first phase of translation,
requires
(A) ATP and the linking of the amino acid to its cognate tRNA
(B) GTP and the release factor
(C) NADPH and the ribosome
(D) DNA ligase and the small subunit

72.

73.

In bacteria, the enzyme (ribozyme) that catalyses peptide bond
formation during translation is
(A) a protease in the small subunit
(B) DNA polymerase
(C) 23S rRNA of the large subunit
(D) 16S rRNA of the small subunit

74.

75.

Untranslated regions (UTRs) of an mRNA are present
(A) only at the 3′-end, after the stop codon
(B) only at the 5′-end, before the start codon
(C) at both the 5′-end (before the start codon) and the 3′-end (after the
stop codon)
(D) only within the translational unit between AUG and the stop codon

76.

77.

During initiation of translation, the start codon AUG is recognised only
by the ______, and translation is terminated when a ______ binds to
the stop codon.
(A) initiator tRNA; release factor
(B) sigma factor; rho factor
(C) release factor; initiator tRNA
(D) charged tRNA of Phe; ribozyme

78.

79.

The operator region of an operon is generally
(A) adjacent to the terminator and binds the release factor
(B) adjacent to the promoter and binds a repressor protein
(C) within the structural gene and binds the ribosome
(D) an inducer-binding site on the repressor gene

80.

81.

In the lac operon, the genes z, y and a code respectively for
(A) permease, beta-galactosidase and transacetylase
(B) repressor, permease and beta-galactosidase
(C) transacetylase, permease and beta-galactosidase
(D) beta-galactosidase, permease and transacetylase

82.

83.

The term i in the i gene of the lac operon is derived from the word
______ and the gene codes for the ______.
(A) inhibitor; repressor
(B) inducer; permease
(C) initiator; beta-galactosidase
(D) inhibitor; transacetylase

84.

85.

One approach of HGP identified all the genes expressed as RNA,
called ______, while the other sequenced the whole genome and
later assigned functions to regions, called ______.
(A) SNPs; microsatellites
(B) Expressed Sequence Tags; Sequence Annotation
(C) Sequence Annotation; Expressed Sequence Tags
(D) BAC; YAC

86.

87.

For sequencing in HGP, DNA fragments were cloned in
bacteria and yeast using the vectors
(A) pBR322 and plasmids
(B) BAC and YAC
(C) cosmids and phagemids
(D) Ti plasmid and retrovirus

88.

For sequencing in HGP, DNA fragments were cloned in
bacteria and yeast using the vectors
(A) pBR322 and plasmids
(B) BAC and YAC
(C) cosmids and phagemids
(D) Ti plasmid and retrovirus

89.

According to the salient features of the human genome, the largest
known human gene is ______ with 2.4 million bases, and the
chromosome with the fewest genes is
(A) insulin; chromosome 21
(B) dystrophin; chromosome 1
(C) beta globin; chromosome Y
(D) dystrophin; chromosome Y

90.

91.

Single-base DNA differences occurring at about 1.4 million locations in
the human genome are known as
(A) SNPs
(B) VNTRs
(C) ESTs
(D) microsatellites

92.

Single-base DNA differences occurring at about 1.4 million locations in
the human genome are known as
(A) SNPs
(B) VNTRs - VNTRs are minisatellite tandem repeats used as Southern
blot probes
(C) ESTs - ESTs (Expressed Sequence Tags) are genes expressed as
RNA in HGP, not single nucleotide polymorphisms
(D) microsatellites - microsatellites are short repetitive DNA stretches