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MOLECULAR BIOLOGY
PART-2
„
„
„
„
GENE
GENE CONCEPT
PROTEIN SYNTHESIS
LAC OPERON CONCEPT
GENE AND GENE CONCEPT
To know about the scientists who
coined various terminologies and
proposed gene hypothesis
Gene was coined by
W Johansen in 1909
„ Gene theory was proposed by
T H Morgan in 1911
„ L Pauling
P li and
d Ingram(1949)
I
(1949)
established the role of genes in
protein synthesis
„
„ The
fine structure of gene
was proposed by Seymour
Benzere(1962)
„ GENE Æ
CISTRON Æ
RECON Æ MUTON
E R Garrod (1908) proposed
‰ One g
gene – one p
product
hypothesis
„ G W Beadle and E L Tatum
(1948) proposed
‰ One gene – one enzyme
hypothesis
„ Yanofsky (1965) proposed
‰ One gene ( cistron) – one
polypeptide hypothesis
„
EUKARYOTIC GENE
PROKARYOTIC GENE
(Unspilt gene)
Has only coding exons
C1 E C2
E
C3
E
(spilt gene)
Has only coding exons
g introns
and non coding
Transcription
E
E
E
(Polycistronic mRNA)
Translation
E
I
E
I
E
Transcription
I
E
E
( Hn – RNA)
RNA S
Splicing
li i
I
I
I
E
E
E
E
(Monocistronic mRNA)
Translation
Many polypeptides or
proteins
t i
One protein
(spilt gene – Philip A Sharp and Richards Roberts- 1979, Noble prize 1993)
CENTRAL DOGMA OF MOLECULAR
BIOLOGY PROPOSED BY CRICK (1958)
DNA
REPLICATION
DNA
TRANSCRIPTION
REVERSE
TRANSCRIPTION
mRNA
TRANSLATION
Polypeptide
yp p
PROTEIN SYNTHESIS
Sensestrand
5’.. ATGGCGCACTAA..
5
ATGGCGCACTAA 3
3’
DNA
Antisensestrand
3’..TACCGCGTGATT..
3
TACCGCGTGATT 5
5’
TRANSCRIPTION
mRNA
5’..AUGGCGCAC
5
AUGGCGCAC UAA..3
UAA 3’
TRANSLATION
tRNA
POLYPEPTIDE
3’..UACCGCGUG……..
3
UACCGCGUG
5’
5
aa1- aa2 - aa3
PROTEIN SYNTHESIS IN PROKARYOTE
TRANSCRIPTION
DNA
RNA polymerase
Mg++
g
mRNA
STEPS OF TRANSLATION
a)) Activation of amino acid
Amino acid
t-RNA amino acyl synthetase
Mg++, ATP
transformylase
amino acyl t-RNA
(aa tRNA)
(aa-tRNA)
b) Chain initiation:
mRNA
IF2
IF3
aa-tRNA
aa
tRNA
GTP
Smaller sub-unit of ribosome (30S)
IF1
Larger sub
sub-unit
unit of ribosome (50S)
c) Chain elongation:
mRNA + ribosome ( 70S)
EF – TU
EF – TS , GTP
peptidyl transferase
EF – G ( translocase )
elongating polypeptide chain
d) Chain
Ch i termination:
t
i ti
Elongating
g
g polypeptide
p yp p
chain
RF1- recognizes UAA & UAG
RF2 recognizes
RF2i
UAA & UGA
RF3- function unknown
Peptidyl synthetase
Rib
Ribosome
dissociation
di
i ti factor
f t
Nascent p
polypeptide
yp p
chain
e) Chain modification:
Nascent polypeptide chain
Deformylase
Exopeptidase
Molecular choperones
Functional / Structural protein
( having one or more polypeptides)
LAC OPERON
LAC OPERON - SWITCHED ON
LAC OPERON – SWITCHED OFF
Q - Which of the following is
wrongly matched?
1) cistron – functional unit of gene
2) recon – unit
it off recombination
bi ti off a
gene
3) muton – unit of mutation of a gene
4)) exon – unit of split
p gene
g
which
does not carry information
Q - The splicing of Hn RNA
helps in
1) removal of exons
2) removal of coding segments
3) removal of introns
4) removal of coding exons
Q -The hypothesis proposed by
G W Beadle and E.L.
G.W.Beadle
E L Tatum based
on their experiment in
Neurospora crassa is
1) one gene- one enzyme
2) one gene- one polypeptide
3) one genegene one product
4) one gene- one function
E R Garrod(1908) proposed
‰ One g
gene – one p
product
hypothesis
„ G W Beadle
ead e a
and
d E L Tatum(1948)
atu ( 9 8)
proposed
‰ One gene – one enzyme
hypothesis
„ Yanofsky(1965) proposed
‰ One gene ( cistron) – one
polypeptide hypothesis
„
Q -The hypothesis proposed by
G.W.Beadle and E.L. Tatum based
on their experiment in
p
crassa is
Neurospora
1) one gene- one enzyme
2) one gene
gene- one polypeptide
3) one gene- one product
4) one gene- one function
Q - In Eukaryotes,
y
, the mRNA is
transcribed from DNA with the
help of the enzyme
1) RNA primase
2) RNA poly I
3) RNA poly II
4) RNA poly III
Q - During transcription mRNA is
synthesized in ---- direction
and
d the
th template
t
l t strand
t
d off
DNA is read in ---- direction
and during translation mRNA
is read in ---- direction.
1) 5’ →3’, 3’ → 5’ and 5’ → 3’
2) 5’
5 →3
→3’, 5
5’ → 3
3’ and 5
5’ → 3
3’
3) 3’ →5’, 3’ → 5’ and3’ → 5’
4) 3’ →5’, 5’ → 3’ and 5’ → 3’
Sensestrand
PROTEIN SYNTHESIS
5’.. ATGGCGCACTAA.. 3’
DNA
Antisensestrand
(Template strand)
3’..TACCGCGTGATT.. 5’
mRNA
5’.. AUGGCGCACUAA..
5
AUGGCGCACUAA 3
3’
TRANSCRIPTION
TRANSLATION
tRNA
POLYPEPTIDE
3’.. UACCGCGUG..
3
UACCGCGUG 5
5’
aa1—aa2—aa3
aa1
aa2 aa3
Q - During
D i transcription
t
i ti
mRNA
RNA is
i
synthesized in ---- direction and the
template strand of DNA is read in --- direction and during translation
mRNA is read in ---- direction.
1) 5’
5 →3’,
3,3
3’ → 5
5’ and 5
5’ → 3
3’
2) 5’ →3’, 5’ → 3’ and 5’ → 3’
3) 3’ →5’,
5’ 3’ → 5’ and3’
d3’ → 5’
4)) 3’ →5’,, 5’ → 3’ and 5’ → 3’
Q - What sequence in the template
strand of DNA corresponds
to the first amino acid inserted
i t protein?
into
t i ?
1) TAC
2) AUG
3) UAG
4) AAA
PROTEIN SYNTHESIS
Sensestrand
5’.. ATGGCGCACTAA.. 3’
Antisensestrand
3’..TACCGCGTGATT.. 5’
TRANSCRIPTION
mRNA
5’.. AUGGCGCACUAA..
5
AUGGCGCACUAA 3
3’
TRANSLATION
tRNA
POLYPEPTIDE
3’.. UACCGCGUG..
3
UACCGCGUG 5’
5
aa1—aa2—aa3
aa1
aa2 aa3
Q - What sequence in the template
strand of DNA corresponds to the
first amino acid inserted into
protein?
1) TAC
2) AUG
3)) UAG
4) AAA
Q - In protein synthesis,
synthesis
translation involves
1) decoding of triplet codons of
tRNA by
y anticodons of mRNA
2) decoding of triplet codons of
mRNA by anticodons of tRNA
3) decoding of triplet codons of
rRNA by anticodons of tRNA
4) synthesis of mRNA from DNA
Q - Which of the following statement is
wrong with respect to chain initiation
step of protein synthesis in E.coli?
1)) 5’ end of mRNA attaches to 30S
ribosome with the help of IF3
2)) Formyl
y methionine tRNA decodes
AUG with the help of IF2
3)) 50S ribosome attaches to the initiation
complex with the help of IF1
4)) This p
process derives the energy
gy from
ATP
Chain initiation
mRNA
IF2
IF3
aa-tRNA
aa
tRNA
GTP
Smaller sub-unit of ribosome (30S)
IF1
(INITIATION COMPLEX)
Larger sub-unit of ribosome (50S)
Q - Which of the following statement is
wrong
g with respect
p
to chain initiation
step of protein synthesis in E.coli
1)) 5’ end of mRNA attaches to 30S ribosome
with the help of IF3
2) Formyl methionine tRNA decodes AUG
with the help of IF2
3) 50S ribosome attaches to the initiation
complex
l with
ith the
th h
help
l off IF1
4) This process derives the energy from
ATP
Q - Which of the following factors
are labelled as translocase that
help in the movement of
ribosome on mRNA?
1) EF – TU and EF- TS
2) EF- G and eEF2
3) eEF1 and eEF1B
4) 23S and 28S rRNA
Q - Peptide bond formation occurs
during protein synthesis with the
help of the enzyme
1)Amino acyl tRNA synthetase
2)Peptidyl
) p y transferase
3)Peptidyl synthetase
4)Transformylase
Q - If a segment of an mRNA has a
sequence
q
5’ GUACCGAUC 3’ , which
of the following could have been the
template DNA molecule?
1) 3’CAUGGCUAG 5’
2) 5’CATGGCTAG3’
3) 5
5’CAUGGCUAG3’
C UGGCU G3
4) 5’GATCGGTAC3’
Sensestrand
5’..… GTACCGATC….. 3’
(CODOGEN)
Antisensestrand
(CRYPTOGRAM)
3’..… CATGGCTAG….. 5’
mRNA
5’..… GUACCGAUC…..
5
GUACCGAUC
3’
3
(CODON)
tRNA
(ANTICODON)
3’..… CAUGGCUAG….. 5’
Q - If a segment of an mRNA has a
sequence 5’ GUACCGAUC 3’ , which
of the following could have been the
template DNA molecule?
1) 3’CAUGGCUAG 5’
2) 5’CATGGCTAG3’
3)) 5’CAUGGCUAG3’
4) 5’GATCGGTAC3’
Q - A fragment of DNA nucleotide
arrangement is
5’ ….ATGGCAGCTTAT….3
5
ATGGCAGCTTAT 3’
What will be the anticodons in
tRNAs which will translate the
codons p
produced by
y this part
p
of
DNA?
1) 5’UAC3’
2) 3’UAC5’
3 UAC5
3) 5’AUG3’
4) 3’AUG5’
5’CGU3’
3’CGU5’
3
CGU5
5’GCA3’
3’GCA5’
5’CGA3’
3’CGA5’
3
CGA5
5’GCU3’
3’GCU5’
5’AUA3’
3’AUA5’
3
AUA5
5’UAU3’
3’UAU5’
5’ ATGGCAGCTTAT 3’
( Sensestrand )
noncoding
Anticodons of tRNA are
complementary to
sense strand
t
d (noncoding)
(
di )
3’ UACCGUCGAAUA 5’(tRNA)
1) 5’UAC3’
2) 3’UAC5’
3)) 5’AUG3’
4) 3’AUG5’
5’CGU3’
3’CGU5’
5’GCA3’
3’GCA5’
5’CGA3’
3’CGA5’
5’GCU3’
3’GCU5’
5’AUA3’
3’AUA5’
5’UAU3’
3’UAU5’
Q - The reading frame of mRNA
having 1002 nucleotides
translated into a nascent
polypeptide having amino
acids numbering
1) 333
2) 666
3) 999
4) 1001
Q- Consider the statements given
below and find the answer among
the options given below.
Statement A: UAA, UAG and UGA
codons
d
i mRNA
in
RNA tterminate
i t th
the
synthesis of poylpeptide chain
Statement B: UAA, UAG and UGA
codons
codo
sa
are
e not
ot recognized
ecog ed by ttRNA
1) Both statements A and B are correct
and B is not the reason for A
2) Both statements A and B are correct
and B is the reason for A
3) Statement A is correct and B is wrong
4) Statement A wrong and B is correct
Q-The replacement of any onenucleotide base in a codon
changing the specificity for
amino acid is
1)Mis sense mutation
1)Mis-sense
2) non-sense mutation
3) silent mutation
4) frame shift/gibberish mutation
Q- Which among the following is
wrongly
l matched?
t h d?
1) Lac Z gene – β galactosidase
2) Lac y gene – β galactoside permease
3) Lac A gene – Transacetylase
4)) Operator
p
gene
g
– Repressor
p
protein
p
Q- Operator gene of Lac operon
i turned
is
t
d on when
h lactose
l t
molecules bind to
1) promoter site
2) operator site
3) regulator gene
4) repressor protein
LAC OPERON - SWITCHED ON
Q- Operator gene of Lac operon
is turned on when lactose
molecules bind to
1) promoter
t site
it
2)) operator site
3) regulator gene
4) repressor protein
Q- A synthetic mRNA of
repeating sequence
5 CA CA CA CA CA CA CA C…3
5’
C 3’
is used for a cell-free protein
synthesizing system like the one
used by Nirenberg. If we assume
that protein synthesis can begin
without the need for an initiator
codon what product or products
codon,
would you expect to occur after
protein synthesis?
1) one protein,
protein with an alternating
sequence of two different types
of amino acids
2) one protein, consisting of a single
type of amino acid
3) two proteins with an alternating
sequence of two different types of
amino acids
4) one protein
t i with
ith an alternating
lt
ti
sequence of three different types of
amino acids
mRNA
5’ CACACACACACA 3’
(codon)
tRNA
3’ GUGUGUGUGUGU 5’
(
(anticodon)
)
POLYPEPTIDE
Val – Cys – Val – Cys
( i
(aminoacids)
id )
1) one protein,
protein with an alternating
sequence of two different types
of amino acids
2) one protein, consisting of a single
type of amino acid
3) two proteins with an alternating
sequence of two different types of
amino acids
4) one protein
t i with
ith an alternating
lt
ti
sequence of three different types of
amino acids
Q- Match the following operon genes
Column I
A)) Structural gene
g
B) Operator gene
C) Promoter gene
D) Regulator gene
Column II
i)) Binding
g site for
repressor gene
ii) Codes for repressor
protein
iii) Codes for enzyme
proteins
t i
iv) Binding site for RNA
polymerase
1)
2)
3)
4)
A
i
ii
iv
iii
B
iii
i
i
i
C
ii
iii
ii
iv
D
iv
iv
iii
ii
Q-The Pribnow box is represented by
1)
2)
3)
4)
5` ATATTA 3`
5`
5 AATAAT 3
3`
5` TATAAT 3`
5` TATAA 3`