Dna replication - class-XII
Description: dna replication | |
Number of Questions: 51 | |
Created by: Girish Goud | |
Tags: biology nucleic acids and protein synthesis heredity |
The enzyme DNA polymerase was discovered by
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Kornberg
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Okazaki
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Watson and Crick
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Stahl and Meselson
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Jacob and Monod
Arthur Kornberg purified and characterized DNA polymerase from E. coli cells which is encoded by the polA gene. It catalyzes phosphoryl group transfer. The 3-hydroxyl group of the nucleotide at the 3' end of the growing strand serve as nucleophile for nucleophilic attack at the $\alpha$ phosphorus of the incoming deoxynucleoside triphosphate. Inorganic pyrophosphate is released in the reaction.
Which of the following enzyme is used to join DNA fragments?
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Terminase
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Endonuclease
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Ligase
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DNA polymerase
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. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms may specifically repair double-strand breaks, i.e., a break in both complementary strands of DNA. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA. DNA ligase has applications in both DNA repair and DNA replication.
Deoxyribonucleoside triphosphates serve dual purposes in DNA replication. In addition to acting as substrate, the other function is similar to?
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DNA polymerase
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rRNA
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Topoisomerase
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ATP
DNA replication includes which of the following enzymes?
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DNA ligase
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DNA polymerase and ligase
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RNA polymerase and ligase
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All of the above
DNA polymerase and ligase as well as RNA polymerase and ligase have an important role in DNA replication. DNA replication, like all biological polymerization processes, proceeds in three enzymatically catalyzed and coordinated steps : initiation, elongation and termination. All enzymes mentioned play important roles in these steps of replication.
Which of the following is true about DNA polymerase?
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It can synthesize DNA in the 5' to 3' direction
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It can synthesize DNA in the 3' to 5' direction
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It can synthesize DNA in both directions
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Depend upon the condition
Select the correct statement:
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DNA polymerase has high degree of accuracy
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During DNA replication, only one strand of DNA act as template for synthesis of new strand.
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Taylor has proved by his experiment that DNA is the genetic material
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E. coli has $4.6 \times 10^9$ bp in its genetic material
Which of the following enzyme is used in DNA multiplication?
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RNA polymerase
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DNA endonuclease
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Exonuclease
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DNA polymerase
The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule. During this process, DNA polymerase reads the existing DNA strands to create two new strands that match the existing ones. Every time a cell divides, DNA polymerase is required to help duplicate the cells DNA, so that a copy of the original DNA molecule can be passed to each of the daughter cells. In this way, genetic information is transmitted from generation to generation.
DNA polymerase is needed for
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Replication of DNA
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Synthesis of DNA
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Elongation of DNA
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All of the above
Enzyme responsible for DNA chain elongation is
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DNA polymerase II
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DNA ligase
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RNA poymerase III
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DNA polymerase III
DNA helicase helps in
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Opening supercoils of DNA
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Making DNA helix
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Opening two chains of DNA helix
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Making hydrogen bonds of nitrogenous bases
Helicases move along the double-stranded DNA and separate the strands by breaking hydrogen bonds at the expense of energy from ATP. DNA unwinding by helicases creates topological stress/supercoils in the helical DNA structure which is relieved by the action of topoisomerases. These enzymes transiently break both DNA strands of one chromosome thereby making the other chromosome to pass through the break and relieve the stress. DNA polymerase enzyme synthesizes DNA strands by adding deoxyribonucleotides to 3' end of the primer via phosphodiester bonds; it uses parental DNA as template. Hydrogen bonding between base pairs is facilitated by the presence of hydrogen bond donor (primary and secondary amine groups or hydroxyl groups) and complementary hydrogen bond acceptor (carbonyls and tertiary amines) in bases; it is not enzymatic process. The correct option is C.
Which of the following help in repairing of DNA?
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Ligase
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DNA polymerase I
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RNA primer
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DNA polymerase III
DNA polymerase I serve clean-up functions during replication, recombination, and repair. It has 3' --> 5' proofreading exonuclease activity and 5' --> 3' exonuclease activity. The 5' --> 3' exonuclease activity of DNA polymerase I can replace an error containing the segment of DNA/RNA, paired to the template strand which is then simultaneously replaced by polymerase activity of the same enzyme. The process is called as nick translation. DNA polymerase III with its ten types of subunits has 5' --> 3' polymerization and 3' --> 5' proofreading activities in its $\alpha$ and $\epsilon$ subunits, respectively.
During splicing, the exons are joined and the enzyme which catalyzes this reaction is
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RNA ligase
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RNA catalase
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RNA polymerase
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RNA primase
Exon segments are reunited after splicing by
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RNA primase
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DNA polymerase
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RNA polymerase
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RNA ligase
Which is true for DNA helicases?
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Separate DNA strands and establish replication forks
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ATP requiring unwinding enzymes
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Hydrolyse ATP
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All of the above
During DNA replication, two hexamers of helicases are loaded onto each DNA strand. Helicases move along the double stranded DNA and separate the strands by breaking hydrogen bonds between base pairs. ATP hydrolysis provides the required energy for breaking of hydrogen bonds; options B and C are correct. Thereby, DNA is unwound bidirectionally and two potential replication forks are created. The point at which two DNA strands are separated to facilitate the replication is called replication fork; option A is correct. Correct answer is D.
How many types of RNA polymerases are operative in eukaryotes?
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Four
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Three
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Two
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One
Eukaryotes have three RNA polymerases which are structurally distinct complexes, though share certain subunits in common, and have a specific function and specific promoter sequence. RNA polymerase I synthesize preribosomal RNA (pre-rRNA), which contains the precursor for the 18S, 5.8S, and 28S rRNAs. RNA polymerase II is synthesized mRNAs and some specialized RNAs. RNA polymerase III makes tRNAs, the 5S rRNA, and some other small specialized RNAs. Option B is correct.
Which of the enzyme joins the broken strands of DNA?
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Nuclease
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Kinase
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Ligase
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Endonuclease
Two classes of enzymes are most important in generating recombinant DNA molecule. First, restriction endonucleases (also called restriction enzymes) recognize and cleave DNA at specific DNA sequences (recognition sequences or restriction sites) to generate a set of smaller fragments. Second, the DNA fragment to be cloned can be joined to a suitable cloning vector by using DNA ligases to link the DNA molecules together. DNA ligase catalyzes the formation of new phosphodiester bonds in a reaction that uses ATP or a similar cofactor.
Which of the following does not describe a correct function of DNA polymerase?
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It helps to replace RNA primers with DNA nucleotides.
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It adds complementary DNA base pairs in a 5 to 3 direction along the DNA leading and lagging strands.
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It proofreads the replicated DNA and replaces mismatched DNA nucleotides.
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It adds RNA nucleotides along the DNA template in transcription.
DNA polymerase is an enzyme used in the replication of DNA. It ads the DNA primers to the parent chain. This enzyme acts in the 5'-3 direction and thus forms lading stand on the chain that has 3'5' direction.
DNA replication requires
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DNA polymerase
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DNA ligase
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RNA polymerase
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All of the above
RNA polymerase serves as primase during DNA replication and synthesizes RNA/DNA primer which is a stranded segment (complementary to the template) and has a free 3’ hydroxyl group to facilitate the addition of deoxyribonucleotides by DNA polymerase enzyme. DNA polymerase is polymerizing enzyme that has 5’ to 3’ polymerization and 3’ to 5’ exonuclease proofreading activities; it adds deoxyribonucleotides to free 3’ hydroxyl group of primer to synthesize new DNA strands. DNA ligase enzyme joins two Okazaki fragments together via phosphodiester bond between 3' hydroxyl at the end of one fragment and a 5' phosphate at the end of another fragment. Thus, option D is the correct answer.
The helicase enzyme breaks
I. Covalent bonds
II. Hydrogen bonds
III. Ionic bonds
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II only
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I and II
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I and III
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II and III
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I, II and III
DNA ligase helps in
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Joining bits of DNA
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Splitting or separation of two strands of DNA
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Renaturation
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Denaturation
In molecular biology, 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.
DNA polymerase enzyme is required for the synthesis of
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RNA from DNA
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DNA from DNA
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RNA from RNA
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DNA from RNA
DNA polymerase is an enzyme that synthesizes DNA molecules from deoxynucleotides, the building blocks of DNA. It helps in DNA replication (DNA dependent DNA synthesis). This enzyme works in pairs to create two complementary DNA strands from a single original DNA molecule.
The area of unwinding and separation of DNA strands during replication is called
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Origin
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Initiation point
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Primer
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Replication fork
The enzyme which can cut molecules of DNA into segments is known as
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DNA polymerase
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DNA ligase
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Restriction enzyme
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DNA gyrase
Usual method of DNA replication is
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Semiconservative
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Conservative
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Dispersive
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Nonconservative
DNA replication occurs in 5' 3' direction because
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DNA polymerase III can polymerise nucleotides in 5 3 direction
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DNA polymerase I carries out editing
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DNA polymerase I carries out polymerisation
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DNA polymerase II can link up only in 5 3 direction
Experimental material in the study of DNA replication has been
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Escherichia coli
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Neurospora crassa
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Pneumococcus
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Drosophila melanogaster
Enzyme required for removing RNA primer during DNA replication is ______________.
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Primase
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DNA polymerase I
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DNA polymerase III
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Ligase
Which one is involved in DNA repair ?
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Ligase
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Primase
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DNA polymerase III
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DNA polymerase I
DNA replication is
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Conservative and discontinuous
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Semiconservative and semidiscontinuous
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Semiconservative and discontinuous
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Conservative
New strand formation on a DNA template can be initiated only by ________________.
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DNA polymerase I
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DNA polymerase III
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RNA primer
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DNA primer
Isotopes used in proving semi-conservative replication of DNA were
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$^{14}N, ^{14}C$
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$^{14}C, ^{31}P$
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$^{14}N, ^{15}N$
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$^{14}N, ^{31}P$
DNA replication requires
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DNA polymerase
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DNA ligase
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RNA polymerase
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All the above
In bacterial DNA replication, synthesis starting from the site of origin of replication
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Involves RNA primers
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Requires telomerase
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Proceeds unidirectionally
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Moves bidirectionally
Consider the following statements and choose the correct option.
(ii) RNA polymerase I transcribes snRNA.
(iii) RNA polymerases II transcribes tRNA.
(iv) RNA polymerase II transcribes hnRNA.
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1 and 2 are correct.
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1 and 3 are correct.
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1, 2 and 4 are correct.
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2 and 3 are correct.
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1 and 4 are correct.
Eukaryotes have three RNA polymerases which are structurally distinct complexes, though share certain subunits in common, and have a specific function and specific promoter sequence. RNA polymerase I synthesize preribosomal RNA (pre-rRNA), which contains the precursor for the 18S, 5.8S, and 28S rRNAs.
Choose the correct answer from the alternatives given.
A restriction enzyme breaks bonds between the
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base pairs of a DNA molecule
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sugar and phosphate components of a nucleic acid molecule
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base pairs of a DNA-RNA hybrid molecule.
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exons and introns of a DNA molecule
Restriction enzymes are the enzymes that have the capability to cleave the phosphodiester bonds between the sugar molecule and the phosphate molecule. It has a property of cleaving DNA molecules at or near a specific sequence of bases. This is produced by certain strains of bacteria. Each restriction enzyme cleaves around a specific DNA sequence. Example: EcoR1 splices around sequence GAATTC, BamH1 cleaves around GGATCC, etc.
Replication of DNA on its lagging strand is initiated by.
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DNA polymerase III
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RNA primer
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DNA polymerase I
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DNA ligase
Choose the correct answers from the alternatives given :
Which enzyme catalyzes the synthesis of a new strand for a DNA molecule by linking nucleotides to the developing strand?
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DNA ligase
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DNA polymerase
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Single-strand binding proteins
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Topoisomerase
DNA polymerase is an enzyme that synthesis DNA molecules from deoxyribonucleotides which are the building blocks of DNA. Each nucleotide contains a sugar molecule (deoxyribose sugar), a phosphate molecule, and any one of the nucleotides (adenine, guanine, cytosine and thymine). They basically help in DNA replication by working in pairs to form a new DNA molecule.
A bacterium with completely non-radioactive DNA was allowed to replicate in radioactive medium for three generation what $ \%$ of the bacteria should contain radioactive DNA:
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$ 25\%$
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$ 75\%$
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$ 0\%$
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$ 100\%$
Choose the correct answers from the alternatives given :
In DNA replication, the Okazaki fragments on the lagging strand are joined together by
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DNA ligase
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DNA polymerase
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Primase
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Helicase
DNA ligase is an enzyme that facilitates the joining of the strands of the DNA by assisting the formation of phosphodiester bonds between two nucleotides.
During replication, DNA gyrases takes part in
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Nicking DNA in eucaryotes
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Nicking DNA in procaryotes
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Synthesis of prier in eucaryotes
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Synthesis of primer in procaryotes
Which enzyme catalyses the synthesis of a new strand for a DNA molecule by linking nucleotides to the developing strand?
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RNA polymerase
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DNA ligase
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DNA polymerase
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Topoisomerase
- RNA polymerase helps in DNA dependent RNA synthesis. This process is known as transcription. DNA strands are used as a template to synthesize RNA molecules.
- DNA ligase is used to join DNA segments during DNA repair or during replication (to join Okazaki fragments of the lagging strands).
- DNA polymerase works in the pair to synthesis new strand for DNA molecule from deoxyribonucleotides. In other words, it helps in DNA dependent DNA synthesis.
- Topoisomerase enzyme participates in overwinding or unwinding of DNA. During DNA replication or transcription, DNA becomes overwound ahead of the replication fork. It binds to DNA and cut the phosphate backbone of either one or both the DNA strands.
Thermostable enzymes Taq and Pfu isolated from thermophilic bacteria are
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DNA polymerases
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DNA ligases
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Restriction endonucleases
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RNA polymerases
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 ).
Select the correct match of enzyme with its related function
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DNA polymerase - Synthesis of DNA Strands
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Helicase - Unwinding of DNA helix
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Ligase - Joins together short DNA segments
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All of these
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.
Choose the correct answers from the alternatives given :
RNA polymerase
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can produce several polypeptide chains at one time through the creation of polysomes
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starts transcribing at an AUG triplet on one DNA strand
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transcribes both introns and exons
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transcribes both DNA strands, but always in a $5' \, \rightarrow \, 3'$ direction
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.
Which of the following is known as joining enzyme or repair enzyme of DNA?
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Transcriptase
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Endonucleases
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Ligases
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Polymerase
In molecular biology, DNA ligase is a specific type of enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA.
DNA polymerase enzyme is required for the synthesis of
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RNA from DNA
-
DNA from DNA
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RNA from RNA
-
DNA from RNA
DNA polymerase enzyme helps in DNA dependent DNA synthesis by addition of deoxyribonucleotides, building blocks of DNA. This enzyme uses DNA as the template and synthesizes DNA. This process is also known as replication.
Which of the following statements are correct?
(i) RNA polymerase I transcribes rRNAs.
(ii) RNA polymerase II transcibes snRNAs.
(iii) RNA polymerase III transcibes hnRNA,
(iv) RNA polymerase II transcribes hnRNA.
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(i) and (ii)
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(i) and (iii)
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(i), (ii) and (iv)
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(i) and (iv)
RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides). Twelve of its subunits have identical or related counterparts in RNA polymerase II (Pol II) and RNA polymerase III (Pol III). The other two subunits are related to Pol II initiation factors and have structural homologues in Pol III. Ribosomal DNA transcription is confined to the nucleolus, where about 400 copies of the 42.9-kb rDNA gene are present, arranged as tandem repeats in nucleolus organizer regions. Each copy contains a 13.3 kb sequence encoding the 18S, the 5.8S, and the 28S RNA molecules, interlaced with two internal transcribed spacers, ITS1 and ITS2, and flanked upstream by a 5' external transcribed spacer and a downstream 3' external transcribed spacer. Because of the simplicity of Pol I transcription, it is the fastest-acting polymerase and contributes up to 60% of cellular transcription levels in exponentially growing cells.
Select the correct option that correctly fill the blanks i - iv
I. Less than (i) of genome represents structural genes that code for proteins.
II. Chemical substance that binds with repressor and convert it into a non-DNA binding State is (ii).
III. In prokaryotes, during replication RNA primer is removed by (iii) whereas in eukaryotes it is removed by (iv).
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(i) - 5%, (ii) regulator, (iii) - DNA polymerase II, (iv) - DNA polymerase $\beta$
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(i) - 10%, (ii) - regulator, (iii) - DNA polymerase I, (iv) - DNA polymerase $\alpha$
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(i) - 2%, (ii) inducer, (iii) - DNA polymerase I, (iv) - DNA polymerase $\beta$
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(i) - 50%, (ii) inducer, (iii) - DNA polymerase III, (iv) - DNA polymerase $\alpha$
The human genome is made of 3 billion DNA base pairs and out of them 2% only are responsible for coding for proteins and the rest may have regulatory functions. In an inducible operon such as the Lac Operon the inducer binds to the repressor to inactivate it such that the repressor can no longer bind to the operator and the gene expression can take place. DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication. This is responsible for proof reading and excising or removing off the RNA primers required for initiation of replication. DNA polymerase, beta, also known as POLB, is an enzyme present in eukaryotes involved in base excision and repair, also called gap-filling DNA synthesis.
DNA replication takes place at ________ phase of the cell cycle
-
G$ _1$
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S
-
G$ _2$
-
M
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.
Choose the correct answer from the alternatives given :
The enzyme DNA dependent RNA polymerase catalyses the polymerisation reaction in ________ direction.
-
Only 5 $\rightarrow$ 3
-
Only 3 $\rightarrow$ 5
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Both (a) and (b)
-
None of these
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.
Choose the correct answer from the alternatives given :
Other than DNA polymerase, which are the enzymes involved in DNA synthesis?
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Topoisomerase
-
Helicase
-
RNA primase
-
All of these
Process of DNA synthesis whereby a parent DNA molecule is faithfully copied, giving rise to two identical daughter molecules is called DNA replication. In DNA synthesis, DNA polymerase plays an important role having the capability to elongate an existing DNA strand but cannot initiate the synthesis. So, the synthesis is initiated with the help of RNA primer formed by RNA primase RNA primase synthesises the short RNA primer of about 10 nucleotides that is elongated by DNA polymerase to form an Okazaki fragment of DNA during DNA replication. Helicase unzips the two strands of DNA and topoisomerase reduces the coiling tension developed due to the unwinding of the two strands.