Download power pack 5 dna replication

HIGH YIELD
TERMS
For AIIMS, AFMC, AIPMT, JIPMER
1.DNA REPLICATION
1. Heterocyclic function of DNA
When DNA directs the synthesis of molecules other
itself. Egs. Protein synthesis, DNA synthesis.
2. Autocatalytic function
When DNA directs the synthesis of DNA itself.
3. Conservative replication
A new DNA is formed over the template of old
structure.
4. Semi conservative replication
In each replica, one strand is old and the other new.
5. Disruptive replication
Old DNA undergoes fragmentation.
6. Mathew Messelson and
Franklin Stahl – 1958
Conducted experiments In E.coli DNA to study
Semi conservative replication.
7. J. H. Taylor and P. Woods – 1957
Proved that Eukaryotes also shows
semi conservative DNA replication. They conducted
experiments in Vicia faba ( bean ).
8. Kornberg – 1956
Succeeded in demonstrating the synthesis on DNA
in test tube. He extracted an enzyme from bacterium
E.coli that was capable of linking free DNA
molecules. He named the enzyme as DNA polymerase.
9. DNA polymerases
Enzyme for DNA synthesis. Three forms of DNA
polymerases are found in prokaryotes.
DNA polymerase I – DNA repairing enzyme.
DNA polymerase II – DNA repairing enzyme.
DNA polymerse III – DNA replicating enzyme.
10. Kornberg Enzyme
DNA polymerase I is called as Kornberg enzyme.
It is the actual DNA repairing enzyme.
11. Eukaryotic DNA polymerases
5 types are present. DNA polymerase Alpha, Beta
Gamma, Delta, and Epsilon.
12. Zipper duplication
Sequential opening of DNA duplex and its replicati
on to form two DNA strands .
13. Origin of replication – Ori.
Starting point of DNA replication. It usually contai
ns sequences rich in weak A-T base pairs .Only
double bonds are present between A – T.
14. Helicase
Enzyme that unwinds DNA strands.
15. Topoisomerases
Enzyme that reduce the tension during DNA
unwinding.
16. DNA gyrases
In prokaryotes, the DNA polymerases and topoiso
merases are replaced by Gyrases.
17. SSB proteins
Single Stranded Proteins – stabilize the separated
DNA strands.
18. Primase
RNA polymerase is called Primase. It helps DNA
polymerse to start DNA synthesis.
19. RNA primer
Short strand of RNA synthesized to start DNA syn
thesis.
20 DNA polymerase III
establish phospho diester bonds between nucleotides.
21.Leading strand
DNA strand in which continuous synthesis occurs in the
5’ – 3’ direction. Replication is continuous.
22. Lagging strand
the second strand in which DNA synthesis occurs by
producing segments of DNA.
23. Okasaki fragments
named by R.Okasaki. The short DNA fragments synthesi
sed in the lagging strand. Okasaki fragments are formed
because DNA polymerase can act only in the 5’-3’ direction
The replication is thus discontinuous. It contains 1000
1500 nucleotides.
25. DNA ligase
Enzyme that joins DNA segments. Discovered by Khorana.
MCQs based on DNA replication
1. DNA polymerase is required for the synthesis of
a. DNA from DNA
b. RNA from RNA c. RNA from DNA d. DNA from
RNA
2. origin of replication is
a. one in all organisms
b. one in prokaryotes and many in eukaryotes
c. one in eukaryotes and many in prokaryotes d. several in all.
3. Okasaki segments are small pieces of DNA containing 1000 to 1500 nucleotides and
are formed in
a. lagging strand
b. leading strand
c. sense strand
d. non sense strand
4. The area of unwinding and separation of DNA strands during replication is called
a. origin
b. initiation point c. primer
d. replication fork
5. In DNA replication, the primer is
a. small deoxy ribonucleotide polymer b. small ribo nucleotide polymer
c. helix destabilizing protein
d. enzyme taking part in joining nucleotides
to their complementary template bases
6. Topoisomerase is involved in
a. producing RNA primer b. joining DNA segments c. producing nick in DNA
d. separation of DNA strands
7. DNA strand is synthesized in the direction
a. 5’-3’
b. 3’-5’
c. 1’-3’
d. 6’-1’
8. Okasaki fragments are joined by
a. DNA polymerase III
b. DNA ligase
c. DNA polymerse II
d. DNA polymerse I
9. Leading strand during DNA replication is formed
a. continuously
b. in short segments
c. first
d. ahead of replication
10. In proof reading during DNA replication
a. wrong nucleotides are inserted
b. wrong nucleotides are taken out
c. wrong nucleotides are removed and correct ones are inserted
d. mutations are prevented
11. E.coli fully labeled with N15 is allowed to grow in N14 medium. The two strands of
DNA molecule of the first generation bacteria have
a. different density and do not resemble parent DNA
b. different density but resemble parent DNA
c. same density and resemble parent DNA
d. same density but do not resemble parent DNA
CBSE 1992
12. DNA having labeled thymidine is allowed to replicate in medium having nonradioactive thymidine. After three duplication, the DNA molecules having labeled
thymidine shall be
a. one molecule
b. two molecules
c. four molecules
d. eight molecules
AIIMS 1993
13. DNA replication is
a. conservation and discontinuous
b. semi conservative and semi discontinuous
c. semi conservative and discontinuous
d. conservative
AIPMT 1999
14. In vitro synthesis of RNA and DNA was carried out first by
a. Kornberg and Nirenberg
b. Ochoa and Kornberg
c. Ochoa and Nirenberg
d. Nirenberg and Khorana
BHU 1996
15. Semi conservative DNA / chromosome replication using N15 was demonstrated by
a. Messelson
b. Taylor
c. Messelson and Stahl
d. Hershey and Chase
AIIMS 1994
16. DNA replication requires
a. DNA polymerase only
b. RNA polymerase and translocase
c. DNA ligase only
d. DNA polymerse and DNA ligase
CPMT 1994
17. Ligase is an enzyme required for
a. breaking DNA
b. joining DNA bits
c. renaturation of DNA
d. proof reading
AIIMS 1994
18. The one which is capable of self replication is
a. DNA
b. RNA
c. Enzyme
d. Protein
CPMT 1998
19. DNA duplication or multiplication is known as
a. replication
b. transcription
c. transduction
d. translation
20. DNA replication in eukaryotes commences
a. from both ends of chromosomes simultaneously
b. several sites along DNA of a chromosomesimultaneously
c. from centromere to either ends
d. from one end of the chromosome to the other
ANSWER KEY
CPMY 1998
BHU 2001
DNA replication
1. a
2.b
3.a
4.a
5.b
6.c
7.a
8.b
9.a
10.c
11.a
12.b
13.b
14.b
15.c
16.d
17.b
18.a
19.a
20.b