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CBSE Questions for Class 12 Medical Biology Molecular Basis Of Inheritance Quiz 15 - MCQExams.com
CBSE
Class 12 Medical Biology
Molecular Basis Of Inheritance
Quiz 15
A section of DNA appears as shown above.
When replication occurs, if this molecule is being unzipped in from left to right, which strand will be the leading strand, and why?
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The top strand, because DNA polymerase reads the template strand in a $$5\rightarrow 3$$ direction forming the new strand in a $$3\rightarrow 5$$ direction.
0%
The bottom strand, because DNA polymerase reads the template strand in a $$3\rightarrow 5$$ direction making the new strand in segments running $$3\rightarrow 5$$.
0%
The top strand, because DNA polymerase replicates the template strand in a continuous $$5\rightarrow 3$$ direction.
0%
The bottom strand, because the leading strand is always replicated in a $$5\rightarrow 3$$ direction and the lagging strand is always replicated $$3\rightarrow 5$$.
Explanation
The enzyme for the DNA replication is the DNA polymerase that works in the direction 5'-3'. So, the strand that has the opposite poarity will form the leading starnd and will form contiiuous DNA and the other will be known as the lagging strand and DNA frangments will be formed on that.
So, the correct otpyion is 'The top strand, because DNA polymerase reads the template strand in a 5→3 direction forming the new strand in a 3→5 direction.'
In nucleoside, the nitrogen base is attached to the first carbon of sugar by ............ bond.
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Glycosidic
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Hydrogen
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Phosphodiester
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Phosphate
Explanation
The nitrogen base is attached to the sugar molecule to form the nucleoside. The phosphate groups are attached to the structure to form the nucleotide. There is N- glycosidic bond in the nucleoside which connects the carbon number 1 of sugar with purine or pyrimidine base. The chemical bonding is known as N-glycosidic type of bond.
Thus, the correct answer is option A.
Which of the following loop in the given diagram has ribosome recognition site?
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D-loop
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T loop
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Anticodon Loop
0%
None of the above
Explanation
The
T$$_Ψ$$C
pseudouridine arm (T loop) consists of a stem of 5 base pairs and a loop of 7 unpaired bases. The
T$$_Ψ$$C
loop consists of a
T$$_Ψ$$C
sequence at 5′ - 3′ direction. The
T$$_Ψ$$C
arm has a ribosome recognition site and binds the tRNA molecules to the ribosome.
The okazaki fragments are linked by the enzyme
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Helicase
0%
Topoisomerase
0%
Ligase
0%
DNA polymerase
Explanation
DNA ligase is a specific type of enzyme, a ligase, that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.
Okazaki fragments are short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication.
Enzyme ligase connects (ligates) the two Okazaki fragments into one continuous newly synthesized complementary strand.
Thus, option C is correct.
Wobble hypothesis deals with
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Phenomena of multiple codons coding for the code for a single amino acid
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Phenomena of multiple codons coding for the code for a different amino acid
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Phenomena of anticodon coding for the code for a different amino acid
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Phenomena of anticodon coding for the code for more than one amino acid
Explanation
The wobble hypothesis deals with the phenomenon of degeneracy that is seen in the genetic code through tRNA recognition of more than one codon.
Each tRNA contains a triplet anti-codon that is complementary to a codon in mRNA. The first two pairs should be complementary for binding to occur, but the third pair need not always be complementary. This is the wobble in the genetic code.
Each mRNA is made up of four different nucleotide bases (A, G, U, and C) and codons are made up of three of these bases,
Thus, 64 possible codon configurations exist. So it would be expected that there would be 64 tRNA and 64 associated amino acids.
However, only 21 amino acids exist. This means that some tRNA must bind multiple codons and provide the same amino acid for different codon configurations.
Thus, the correct answer is option A.
In Wobble hypothesis, the pairing of the tRNA anticodon with the mRNA codon proceeds from
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5'-3' end
0%
3'-5 end
0%
Bidirectional
0%
None of the above
Explanation
Wobble hypothesis states the degeneracy of the genetic code. The pairing of the third base varies according to the base at the third position, for example, G may pair with U. The conventional pairing (A = U, G = C) is called Watson-Crick pairing and the second abnormal pairing is called wobble pairing.
tRNA was discovered by ____ and _____.
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Brenner and Jacob
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Jacob and Monod
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Hoagland and Zamecnik
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Payen and Persoz
Which option is correct for the amino acid and the total number of their genetic codons?
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Val = 6, Pro = 6
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Arg = 6, His = 6
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Pro = 4, Thr = 4
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Thr = 4, Arg= 4
Explanation
Pro (Proline) has 4 codons CCA, CCG,CCC and CCU
Thr (Threonine) also has 4 codons ACA, ACU, ACG, ACC.
Best method to determine paternity is
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Protein analysis
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Chromosome counting
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Gene counting
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DNA fingerprinting
Explanation
The
dispute regarding paternity
for a
child can
be
resolved
by
using DNA
fingerprinting
.
This
involves identifying differences
in
some specific regions
of
DNA between the child and the parent.
The
sequence
in
such regions
is
called repetitive DNA
. that helps in the identification of similarities between the parent and progeny.
Thus the correct answer is option D.
Dermatoglyphics is connected with
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Skin diseases
0%
Care of skin
0%
Cosmetics
0%
Finger printing
Explanation
The study of ridge patterns of the skin especially of fingertips is Dermatoglyphics.
The ridge patterns of the fingerprints are unique and help in personal identification.
So, the correct answer is option D.
Which of the following amino acids is specified by 4 codons?
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Tyrosine (Tyr)
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Proline (Pro)
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Lysine (Lys)
0%
Methionine (Met)
Explanation
Proline (Pro) amino acid is the amino acid which is specified by 4 mRNA codons; CCU, CCC, CCA, CCG. While methionine is specified by just one codon, the amino acids Lysine and Tyrosine are specified by two codons each. So, the correct answer is option B.
First triplet pair deciphered by Khorana was _________________.
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Serine and Leucine
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Threonine and Histidine
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Cysteine and Valine
0%
Phenylalanine and Isoleucine
Explanation
Khorana generated a poly-UC mRNA and it was translated into polypeptides with an alternating pattern of serine and leucine amino acids.
So, the correct answer is option B.
Polymerisation of DNA nucleotides during the synthesis of lagging strand occurs in
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3' $$\rightarrow$$ 5' direction
0%
5' $$\rightarrow$$ 3' direction
0%
Any direction
0%
Promotor to terminator direction
Explanation
DNA replication is the process which the DNA is replicated and two copies are synthesized.
The two strands of the DNA helix separate and the new strands are formed on the original strands, known as the template strands. The strand which is synthesized in 3'-5' direction is the leading strand and the strand which is synthesized in the opposite 5'-3' direction is the lagging strand which contains the Okazaki fragments.
Thus, the correct answer is option B.
What is $$'A'$$ and $$'B'$$is given diagram?
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Lagging - Movement of helicase
0%
RNA primer - DNA helicase
0%
Single strand binding protein - DNA helicase
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RNA primer - RNA helicase
Explanation
The figure depicts the process of DNA replication. $$A$$ is RNA primer. It is the starting point of DNA synthesis in the lagging strand. $$B$$ is DNA helicase that unwinds the two strands during replication process.
Father of DNA fingerprinting is
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Sunder Lai Bahugana
0%
Wishwanath
0%
Jeffrey
0%
Rockfeller
Explanation
DNA fingerprinting is the process of determining an individual's DNA characteristics, which are as unique as fingerprints. The first patent covering the modern process of DNA fingerprinting was filed by Dr. Alec Jeffrey Glassberg in 1983. DNA fingerprinting is a forensic technique in criminal investigations, comparing criminal suspect's profiles to DNA evidence so as to assess the likelihood of their involvement in the crime.
So, the correct answer is 'Alec Jeffrey'.
What is the relationship between the nucleotide triplets and the amino acids called?
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Genetic code
0%
Transcription
0%
Translation
0%
Replication
Explanation
A.Correct option -A
B.Explanation for correct option -A
The relationship between the nucleotide triplets and the amino acids is called a genetic code.
This determines the sequence of amino acids in the proteins that are to be synthesized.
Which one of the following is major requirement for DNA fingerprinting?
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Electron microscopy
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Electrophoresis
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ELISA
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HPLC
Which one is correctly matched?
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AUG, ACG - Start or methionine
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UUA, UCA - Leucine
0%
GUU - Alanine
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UAG, UGA - Stop
Explanation
AUG is the start codon that codes for methionine.
UUA codes for leucine but UCA codes for serine.
GUU codes for valine.
UAG, UAA and UGA are stop codons.
Hence, The correct option is D.
Which one represents serine?
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CUU, CUC, CUA and CUG
0%
UAU, UAC, UGU and UGC
0%
UCU, UCC, UCA and UCG
0%
UGU, UGC, UGA and UAG
0%
GUU, GUC, GCU and GCC
Explanation
Serine amino acid is coded by UCU, UCC, UCA, UCG, AGU, AGC codons in the DNA. This represents that genetic code is redundant, i.e., one amino acid is coded from more than one codon.
So the correct answer is "UCU, UCC, UCA and UCG".
Which of the following takes place in DNA fingerprinting?
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Multiple restriction enzymes generate unique fragments
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Polymerase chain reaction amplifies fewer DNA
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Variability of repeated sequences between two restriction sites is evaluated
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A positive identification can be made
Sequence of three bases of DNA constitutes ________.
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Genome
0%
Gene pool
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Genetic code
0%
Genetic drift
Which of the following is useful in solving parental disputes?
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Hybridoma technology
0%
DNA fingerprinting
0%
Western blotting
0%
ELISA
VNTR is employed for _________.
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Protoplasmic culture
0%
DNA finger printing
0%
Regulation of plant growth hormones
0%
Enhancing photosynthesis in desert plant
Explanation
A variable number tandem repeat (VNTR) forms bands that are unique in every individual. It is used in the DNA fingerprint process that is useful in identifying criminals and even used to identify genetic relation between two individuals.
Hence, the correct option is B.
DNA fingerprinting in forensic science was pioneered in India by _____.
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Lalji
0%
Khorana
0%
Bose
0%
Swaminathan
Explanation
DNA fingerprinting in forensic science was pioneered in India by Lalji Singh at CCMB (Centre for Cell and Molecular Biology). He is widely regarded as the father of Indian DNA fingerprinting.
Hence, the correct option is A.
DNA fingerprinting technique was developed by _______.
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Jeffrey
0%
Schleiden and Schwann
0%
Boysen and Jensen
0%
Edwards and Steptoe
Explanation
British geneticist, Sir Alec Jeffrey is widely considered the father of DNA fingerprinting. It is a technique that has revolutionized forensic science.
Schleiden and Schwann proposed cell theory.
Boysen and Jensen expressed the chemical passing down from the tip of the coleoptile with the help of the experiment.
Edwards and Steptoe established the
world's first centre for IVF therapy.
Therefore, the correct answer is option A.
Some steps of DNA fingerprinting are given below. Identify the correct sequence from the options given.
1) Electrophoresis of DNA fragments
2) Hybridisation with DNA probe
3) Digestion of DNA by RENs
4) Autoradiography
5) Blotting of DNA fragments to nitrocellulose membrane
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3 $$\rightarrow$$ 1 $$\rightarrow$$ 5 $$\rightarrow$$ 2 $$\rightarrow$$ 4
0%
1 $$\rightarrow$$ 3 $$\rightarrow$$ 5 $$\rightarrow$$ 4 $$\rightarrow$$ 2
0%
3 $$\rightarrow$$ 1 $$\rightarrow$$ 2 $$\rightarrow$$ 5 $$\rightarrow$$ 4
0%
1 $$\rightarrow$$ 5 $$\rightarrow$$ 3 $$\rightarrow$$ 2 $$\rightarrow$$ 4
Explanation
DNA fingerprinting is also known as DNA profiling. This is the method that is used to identify the criminals and suspects. There are many steps involved in DNA fingerprinting.
The first step is isolating the desired DNA which can be performed chemically, mechanically, or enzymatically.
The second step is cutting the DNA into several pieces by restriction enzymes.
The third step is sorting the DNA pieces by gel electrophoresis. The DNA will be separated by size.
The next step is denaturing the DNA fragments. The next step is blotting the DNA The gel with the size-fractionated DNA is applied to a sheet of nitrocellulose paper or nylon membrane.
In order to analyze a Southern Blot, a radioactive genetic probe is used in a hybridization reaction with the DNA. The X-ray film helps to analyze the fragments.
Thus the correct answer is option A.
The sequence of amino acids in a protein is determined by _________.
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Genetic code
0%
mRNA
0%
tRNA
0%
rRNA
Explanation
The genetic code includes the set of rules by which information encoded within genetic material is translated into proteins by living cells. The genetic code defines how sequences of these nucleotide triplets, called codons, specify which amino acid will be added next during protein synthesis.
Thus the correct answer is option A.
In DNA fingerprinting, the process of DNA hybridization with the help of a specific DNA probe is called ________.
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Western blotting
0%
Northern blotting
0%
Southern blotting
0%
All the above
Explanation
Edward Southern in 1975 first developed the technique of southern blotting. It is used in DNA fingerprinting. The probes or markers that are radioactive synthetic DNA segments target a specific nucleotide sequence that is complementary to VNTRs sequences and hybridizes them.
Western blotting is based on immunochromatography where proteins are separated into polyacrylamide gel based on their molecular weight.
Northern blotting is conducted to detect RNA sequences,
Hence, the correct option is C.
Arrange in a sequence the given protocol for DNA fingerprinting:
(a) Denaturating DNA
(b) Blotting
(c) Extraction of DNA
(
d) Fragmenting DNA
(e) Separation of DNA fragments by electrophoresis
(f) Hybridisation with the probe
(g) Exposure on film to make a DNA fingerprint
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c $$\rightarrow$$ d
$$\rightarrow$$
e
$$\rightarrow$$
a
$$\rightarrow$$ b
$$\rightarrow$$
f
$$\rightarrow$$
g
0%
a
$$\rightarrow$$
c
$$\rightarrow$$
d
$$\rightarrow$$
e
$$\rightarrow$$
b
$$\rightarrow$$
f
$$\rightarrow$$
g
0%
a
$$\rightarrow$$
c
$$\rightarrow$$
b
$$\rightarrow$$
d
$$\rightarrow$$
e
$$\rightarrow$$
f
$$\rightarrow$$
g
0%
c
$$\rightarrow$$
e
$$\rightarrow$$
d
$$\rightarrow$$
b
$$\rightarrow$$
a
$$\rightarrow$$
f
$$\rightarrow$$
g
Explanation
DNA fingerprinting involves the following steps:
1. Isolation of DNA from sample cell.
2. If DNA is less in amount, it can be amplified using polymerase chain reaction (PCR).
3. Digestion of this DNA by restriction endonucleases.
4. These DNA fragments are electrophoresed in agarose gel. These fragments can be visualized by the EtBr-UV system.
5. Separated DNA fragments are transferred to nitrocellulose membrane using southern blotting.
6. Probing for VNTRs is done using labeled DNA probes.
7. The hybridized fragments can be detected by autoradiography.
Hence, the correct option is A.
Thermostable enzymes Taq and Pfu isolated from thermophilic bacteria are
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DNA polymerases
0%
DNA ligases
0%
Restriction endonucleases
0%
RNA polymerases
Explanation
Thermophilic bacteria that live in hot springs and hydrothermal vents. Taq polymerase and Pfu polymerase are enzymes isolated from thermophilic bacteria. These enzymes are used in polymerase chain reaction as these enzymes are able to withstand the protein-denaturing conditions (high temperature) required during polymerase chain reaction ( PCR ).
So, the correct option is 'DNA polymerases'.
Select the correct statements for DNA fingerprinting.
(i) It is ELISA based technique.
(ii) It is PCR based technique.
(iii) It is used by forensic scientists.
(iv) It is based on the fingerprints of the individual.
(v) It is a test for paternity.
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0%
i, ii, iii
0%
ii, iii, v
0%
i, iv, v
0%
i, iii, iv
Explanation
If DNA is present in less amount, it can be amplified using polymerase chain reaction (PCR). Thus
, DNA fingerprint is based on a PCR technique.
DNA fingerprinting is used by forensic scientists as well as in paternity tests.
DNA fingerprinting can be done by using samples such as blood, saliva, hair.
Hence, the correct option is B.
Which one of the following techniques is used for identifying a DNA sequence that binds to a particular protein and is based on the idea that the phosphodiester bonds in the region covered by the protein are protected from digestion by deoxyribonucleic?
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0%
Finger printing
0%
Foot printing
0%
RAPD
0%
FISH
Production of human protein in bacteria by genetic engineering is possible because
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Human chromosome replicate in bacterial cell
0%
Mechanism of gene regulation is identical in humans and bacteria
0%
Bacterial cell can undertake RNA splicing
0%
Genetic code is universal
Explanation
Order of nucleotides in mRNA determines the amino acid sequence in the polypeptide chain of protein during translation. As genetic code is universal, hence same order of nucleotides will result in the incorporation of same amino acid during translation in various organisms. That is why production of human protein in bacteria by genetic engineering is possible.
So, the correct option is 'Genetic code is universal'.
Which of the following is not required for any of the techniques of DNA finger printing available at present
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0%
DNA-DNA hybridisation
0%
Polymerase chain reaction
0%
Zinc finger analysis
0%
Restriction enzymes
Explanation
A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. This proves that it does not require any DNA fingerprinting techniques.
So the correct option is 'Zinc finger analysis'.
The semi dwarf wheat varities are develop from the introduction of dwarf gene.
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0%
Lerma
0%
$$Norin-10$$
0%
$$Norin-q$$
0%
Both $$(2)$$ and $$(3)$$
Suppose evolution on earth has occurred in such a way that there are 96 amino acids instead of 20 and DNA has 12 different types of nitrogen bases. DNA synthesis however occurs in the same way as today. The minimum number of bases per DNA codon would be
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0%
12
0%
8
0%
2
0%
3
Explanation
Correct Option-C
Explanation-
Evolution has occurred in such a way that there are 96 amino acids instead of 20 and DNA has 12 different types of nitrogen bases.
We can clearly know if only one base form one amino acid, there would be only 12 amino acids.
Suppose, 2 bases make one amino acid, then the total number of amino acids will be = $$(12)^{2}$$= 144
So, 2 bases in a pair are sufficient to make 96 amino acids.
Hence, the correct option is C.
In an
in vitro
translation experiment, poly(UC) RNA template produced poly(Ser-Leu), while poly(AG) RNA template produced poly (Arg-Glu) polypeptide. Which one of the following options represents correct interpretations of the codons assignments for Ser, Leu, Arg, and Glu.
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0%
Ser-UCU, Leu-CUG, Arg-AGA, Glu-GAG
0%
Ser-CUC, Leu-GAG, Arg-UCU, Glu-AGA
0%
Ser-AGA, Leu-UCU, Arg-GAG, Glu-CUC
0%
Ser-GAG, Leu-AGA, Arg-CUC, Glu-UCU
Explanation
A poly(UC) RNA has nucleotide sequence UCUCUCUCUCUC. It codes for amino acid sequence poly(Ser-Leu).
As we know, three codon codes for an amino acid. Hence, in this case, first three codons, that is UCU codes for Ser. The next three codons, that is CUC codes for Leu.
Similarly, a
poly(AG) RNA has nucleotide sequence AGAGAGAGAG. It codes for amino acid sequence poly(Arg-Glu).
As we know, three codon codes for an amino acid. Hence, in this case, first three codons, that is AGA codes for Arg. The next three codons, that is GAG codes for Glu.
Thus, the correct answer is option A.
The human genome contains (a) billion nucleotide bases. The average gene consists of (b) bases. Which option is correct for a & b?
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0%
$$a = 3, b = 3000$$
0%
$$a = 5, b = 3000$$
0%
$$a = 3, b = 2000$$
0%
$$a = 4, b = 3000$$
Explanation
The Human Genome Project revealed that human genome consists of about 3 billion base pairs which reside in 23 pairs of chromosomes. The average gene consists of about 3000 bases.
So, the correct answer is A.
RNA polymerase subunit that recognises and binds to promoter is
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$$\alpha$$-subunit
0%
$$\beta$$-subunit
0%
$$\gamma$$-subunit
0%
$$\sigma$$-subunit
Explanation
DNA-directed RNA polymerases (also known as DNA-dependent RNA polymerases) are responsible for the polymerization of ribonucleotides into a sequence complementary to the template DNA.
RNA polymerases are enzymes and are composed of a variable number of subunits.
(1) α subunit initiates and activates the core assembly to form a platform on which the beta subunits can interact.
(2) β subunit is involved in chain initiation and catalysis of polynucleotide formation in the template-dependent manner.
(3) γ subunit facilitates assembly of RNA polymerase (RNAP) and stabilizes assembled RNAP.
(4) σ subunit/ factor is a protein needed only for initiation of RNA synthesis. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters.
So, the answer is D.
During protein synthesis in an organism at one point the process comes to a halt. Select the group of the three codons from the following, from which any one of the three could bring about this halt.
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0%
$$UUU,UCC,UAC$$
0%
$$UUC,UUA,UAC$$
0%
$$UAG,UGA,UAA$$
0%
$$UUG,UCA,UCG$$
Explanation
Stop codon are sequences of DNA transcribed as RNA that stop
translation or halt protein synthesis, this typically occurs when protein synthesis is completed. There are three RNA stop :
UAG, UAA, and UGA
So,
the correct answer is '
U
A
G
,
U
G
A
,
U
A
A'
Choose the correct answers from the alternatives given :
RNA polymerase
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0%
can produce several polypeptide chains at one time through the creation of polysomes
0%
starts transcribing at an AUG triplet on one DNA strand
0%
transcribes both introns and exons
0%
transcribes both DNA strands, but always in a $$5' \, \rightarrow \, 3'$$ direction
Explanation
RNA polymerase transcribes both exons and introns present in DNA which are consecutively present in the RNA too, although, introns are removed by splicing in a mature mRNA. Exons are the segment of the genetic material or DNA/RNA that code for an amino acid but introns do not code for any amino acid sequence or protein. Introns have a regulatory function in both replication and transcription processes.
So, the correct option is 'transcribes both introns and exons'.
The DNA model proposed by Watson and Crick
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combined many of the findings of other researches also studying DNA such as Rosalind Franklin and Chargaff.
0%
showed the double helix nature of the molecule
0%
presented a molecule with sugar-phosphate backbones on the outside and paired bases on the inside
0%
all of the above
Explanation
Watson and Crick proposed a famous model of DNA double helix. Most of their clues regarding DNA structure came from Rosalind Franklin. Franklin was an expert in powerful technique for determining the structure of molecules, known as X-ray crystallography. When the crystallized form of a molecule such as DNA is exposed to X-rays some of the rays are deflected by the atoms in the crystal, forming a diffraction pattern that gives clues about the molecule structure. Watson and Crick proposed their model and said that the DNA molecule consists of two helically twisted strands connected together by base pairs, which align themselves in such a manner just like the steps of the ladder. Each strand consists of alternating molecules of the deoxyribose sugar and phosphate groups. The linkage between sugar and phosphate molecule is called a phosphodiester bond.
So, the correct option is 'all of the above'.
If the length of E. coli DNA is 1.36 mm, then how many base pairs are present in E. coli?
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0%
$$3.6 \times 10^4$$
0%
$$3.6 \times 10^6$$
0%
$$4.0 \times 10^6$$
0%
$$4.6 \times 10^6$$
Explanation
The distance between two consecutive base pairs is 0.34x109m, the total length of double helix DNA in an organism can be calculated by multiplying the total number of base pairs with the distance between two consecutive base pairs.
the total length of double helix DNA= total number of base pairs x distance between consecutive base pairs.
1.36 = X x 0.34 x 109
X= 1.36/ 0.34x109
So, the correct option is '
4.0x
10
6
'.
Choose the correct answers from the alternatives given :
Which of the following regarding DNA is not true?
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0%
Complementary base pairs consist of one purine and one pyrimidine
0%
Side rails of the DNA double helix are made of alternating molecules of phosphate and ribose
0%
Complementary base pairs are joined by hydrogen bonds
0%
Amount of thymine equals the amount of adenine
Explanation
According to the chargaff's rule the amount of purine is equal to the amount of pyrimidine in a DNA. The base pairing that occurs in DNA is complementary such that A bonds with T and G bonds with C, vice verse is also true. The complementary base pairs like A and T are joined with each other by double hydrogen bonds while G and C are bonded to each other with triple hydrogen bonds. The DNA double helix side rails are made of alternating phosphate and deoxyribose sugar molecules
So, the correct option is 'Side rails of the DNA double helix are made of alternating molecules of phosphate and ribose'.
In the Watson and Crick model of DNA, the steps of the ladder are composed of
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0%
sugars
0%
a purine and a pyrimidine
0%
two purines
0%
a sugar and a phosphate molecule
Explanation
In the Watson and Crick model of DNA, the "steps" of the ladder are composed of a purine and pyrimidine and the “backbone” is made up of a sugar and a phosphate molecule. The model is called a double helix because of two long strands of DNA twist around each other like a twisted ladder.
So, the correct option is 'a purine and a pyrimidine'.
Select the correct match of enzyme with its related function
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0%
DNA polymerase - Synthesis of DNA Strands
0%
Helicase - Unwinding of DNA helix
0%
Ligase - Joins together short DNA segments
0%
All of these
Explanation
DNA polymerase is the enzyme required for the addition of nucleotides into a DNA strand being synthesized from an existing strand of DNA. Helicase refers to another enzyme that functions in unwinding of the double helix structure of DNA wound around one another to result in a melted region of DNA strand to begin the replication of DNA. The joining of the short segments of DNA created during replication of the lagging strand (3' to 5') happens due to the enzyme ligase that acts as a molecular glue.
So, the correct option is 'All of these'.
Choose the correct answer from the alternatives given :
The enzyme DNA dependent RNA polymerase catalyses the polymerisation reaction in ________ direction.
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0%
Only 5 $$\rightarrow$$ 3
0%
Only 3 $$\rightarrow$$ 5
0%
Both (a) and (b)
0%
None of these
Explanation
The two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyze the polymerization in only one direction, that is, 5
→
→
3, the strand that has the polarity 3
→
→
5 acts as a template, and is also referred to as template strand. The other strand which has the polarity 5
→
→
3 and the sequence same as RNA (except thymine at the place of uracil) is displaced during transcription. This strand (which does not code for anything) is referred to as coding strand.
So, the correct answer is 'O
nly 5 → 3'.
DNA replication takes place at ________ phase of the cell cycle
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0%
G$$_1$$
0%
S
0%
G$$_2$$
0%
M
Explanation
In eukaryotes, the replication of DNA takes place at S-phase of the cell cycle. The replication of DNA and cell division cycle should be coordinated. A failure in cell division after DNA replication results into chromosomal anomaly.
In a DNA molecule, the phosphate group is attached to carbon ______of the sugar residue of its own nucleotide and carbon ______ of the sugar residue of the next nucleotide by ______ bonds.
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5', 3', phosphodiester
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3', 5', phosphodiester
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5', 3', glycosidic
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3', 5', glycosidic
Explanation
A phosphodiester bond is a covalent bond in which a phosphate group joins adjacent carbons through ester linkages. The bond is the result of a condensation reaction between a hydroxyl group of two sugar groups and a phosphate group. The diester bond between phosphoric acid and two sugar molecules in the DNA and RNA backbone links two nucleotides together to form oligonucleotide polymers. The phosphodiester bond links a 3' carbon to a 5' carbon in DNA and RNA. During the reaction of two of the hydroxyl groups in phosphoric acid with a hydroxyl group in two other molecules, two ester bonds in a phosphodiester group are formed. the 3’ end has a free hydroxyl group at the 3’ carbon of a sugar, and the 5' end has a free hydroxyl group or phosphate group at the 5’-carbon of a sugar. The synthesis proceeds from the 5’ to the 3’ end.
So the correct option is "5', 3', phosphodiester".
If the sequence of bases in DNA is GCTTAGGCAA then the sequence of bases in its transcript will be
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GCTTAGGCM
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CGAATCCGTT
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CGAAUCCGUU
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AACGGAUUCG
Explanation
mRNA strand is complementary to one of the DNA strands i.e., template strand. In RNA, uracil is present instead of thymine which is complementary to adenine. Cytosine and guanine are also complementary to each other. Hence, the sequence of bases in transcript would be CGAAUCCGUIJ.
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Practice Class 12 Medical Biology Quiz Questions and Answers
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