DNA Replication And Recombination

Question 1

Meselson And Stahl’s Experiment

Answer 1

An experiment that demonstrated that the mode of DNA replication is semi-conservatively. The DNA was first replicated in 14N medium which produced a band of 14N and 15N hybrid DNA.

Question 2

Origin Of Replication

Answer 2

Site where DNA replication is initiated

Question 3

Semiconservative Replication

Answer 3

Replication in which the two nucleotide strands of DNA separate, and each serves as a template for the synthesis of a new strand. All DNA replication is by this method.

Question 4

Replicon

Answer 4

Unit of replication consisting of DNA from the origin of replication to the point at which replication on either side of the origin ends.

Question 5

Replication Fork

Answer 5

Point at which a double-stranded DNA molecule separates into two single strands that serve as templates for replication.

Question 6

Theta Replication

Answer 6

Replication of circular DNA that is initiated by the unwinding of the two nucleotide strands, producing a replication bubble. Unwinding continues at one or both ends of the bubble, making it progressively larger. DNA replication on both of the template strands is simultaneous with unwinding until the two replication forks meet.

Question 7

Bidirectional Replication

Answer 7

Replication at both ends of a replication bubble.

Question 8

Replication Bubble

Answer 8

Segment of a DNA molecule that is unwinding and undergoing replication.

Question 9

Continuous Replication

Answer 9

Replication of the leading strand of DNA in the same direction as that of unwinding, allowing new nucleotides to be added continuously to the 3’ end of the new strand as the template is exposed.

Question 10

Direction Of Replication

Answer 10

DNA is synthesized in the 5’ to 3’ direction.

Question 11

Requirements Of Replication

Answer 11

A single-stranded DNA template, Raw materials (deoxyribonucleoside triphosphates - dNTPs) to be assembled into a new nucleotide strand and enzymes and other proteins that “read’ the template and assemble the dNTPs into a DNA molecule.

Question 12

DNA Polymerase

Answer 12

Enzyme that synthesizes DNA.

Question 13

Leading Strand

Answer 13

DNA strand that is replicated continuously.

Question 14

Lagging Strand

Answer 14

DNA strand that is replicated discontinuously.

Question 15

Okazaki Fragment

Answer 15

Short length of newly synthesized DNA produced by discontinuous replication on the lagging strand; these fragments are eventually joined together.

Question 16

Discontinuous Replication

Answer 16

Replication of the lagging strand of DNA in the direction opposite that of unwinding, which means that DNA must be synthesized in short stretches (Okazaki fragments).

Question 17

Initiator Protein

Answer 17

Protein that binds to an origin of replication and causes a short section of DNA to unwind, allowing helicase and other single-strand-binding proteins to attach to the polynucleotide strand.

Question 18

DNA Helicase

Answer 18

Enzyme that unwinds double-stranded DNA by breaking hydrogen bonds that exist between the bases of the two nucleotide strands of a DNA molecule.

Question 19

Primase

Answer 19

Enzyme that synthesizes a short stretch of RNA on a DNA template; functions in replication to provide a 3’-OH group for the attachment of a DNA nucleotide.

Question 20

DNA gyrase

Answer 20

Topoisomerase enzyme that relieves the torsional strain that builds up ahead of the replication fork.

Question 21

Single-Strand-Binding Protein (SSB)

Answer 21

Protein that attaches tightly to the exposed single-stranded DNA during replication and prevents the formation of secondary structures that would interfere with replication.

Question 22

Primer

Answer 22

Short stretch of RNA on a DNA template; provides a 3’-OH group for the attachment of a DNA nucleotide at the initiation of replication.

Question 23

Replication Licensing Factor

Answer 23

Protein that ensures that replication takes place only once at each origin of replication; required at the origin before replication can be initiated and removed after the DNA has been replicated.

Question 24

DNA Ligase

Answer 24

Enzyme that catalyzes the formation of a phosphodiester bond between adjacent 3’-OH and 5’-phosphate groups in a DNA molecule without adding another nucleotide to the strand.

Question 25

Mismatch Repair

Answer 25

Process that corrects mismatched nucleotides in DNA after replication has been completed. Enzymes excise incorrectly paired nucleotides from the newly synthesized strand and use the original nucleotide strand as a template for replacing them.

Question 26

Proofreading

Answer 26

Process by which DNA polymerases remove and replace incorrectly paired nucleotides in the course of replication.

Question 27

Telomerase

Answer 27

Ribonucleoprotein enzyme that replicates the ends (telomeres) of eukaryotic chromosomes. The RNA part of the enzyme has a template that is complementary to repeated sequences in the telomere and pairs with them, providing a template for the synthesis of additional copies of the repeats.

Question 28

End-Replication Problem

Answer 28

The ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis which leads to a progressive shortening of chromosomes.

Question 29

G Overhang

Answer 29

A guanine-rich sequence of nucleotides that protrudes beyond the complementary C-rich strand at the end of a chromosome.

Question 30

Holliday Junction

Answer 30

Special structure resulting from homologous recombination that is initiated by single-strand breaks in a DNA molecule.

Question 31

Heteroduplex

Answer 31

DNA consisting of two strands, each of which is from a different chromosome.

Question 32

Homologous Recombination

Answer 32

Exchange of genetic information between homologous DNA molecules.