Molecular Basis of Inheritance

Question 1

Nitrogenous Bases

Answer 1

• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

Question 2

DNA is a polymer of:

Answer 2

nucleotides

nucleotides are the monomer of DNA

each consisting of a:
* Nitrogenous base
* Sugar
* Phosphate group

Question 3

Polynucleotide strand has directionality:

Answer 3

from the 5’ end (with the phosphate group) to the 3’ end (with the —OH group of the sugar

5’ and 3’ refer to the numbers assigned to the carbons in the sugar ring

Question 4

DNA direction:

Answer 4

Antiparallel

parallel, but run in opposite directions

Question 5

Structural Model of DNA

Pairing of model DNA:

Answer 5

pairing a purine (A or G) with a pyrimidine (C or T)

Question 6

DNA Replication

Helicases

Enzyme

Answer 6

Enzymes that untwist double helix at the replication forks

Question 7

DNA Replication

Single-strand binding proteins

Enzyme

Answer 7

Bind to and stabilize single-stranded DNA

Question 8

DNA Replication

Topoisomerase

Enzyme

Answer 8

Relieves strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands

Question 9

Can DNA polymerase initiate synthesis?

Answer 9

no, it requires a primer to which they can add nucleotides

The initial nucleotide chain is a short RNA primer

This is synthesized by enzyme primase

Question 10

DNA Polymerase

Answer 10

enzyme that catalyzes synthesis of new DNA at a replication fork

Most DNA polymerases require a primer and a DNA template strand

Question 11

Which side does DNA polymerase add to?

Answer 11

DNA polymerases add nucleotides only to free 3′ end of a growing strand

Question 12

Leading Strand

Answer 12

strand that runs in the 5’ to 3’ direction in the replication fork

opposite the lagging strand

Question 13

Lagging Strand

(and Okazaki fragments)

Answer 13

strand that runs in the 3’ to 5’ direction away from the replication fork

opposite the leading strand

synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase

Question 14

DNA Replication

Primase

Answer 14

Synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand

Question 15

DNA Replication

DNA Polymerase I

Answer 15

Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to 3’ end of adjacent fragment

Question 16

DNA Replication

DNA Polymerase III

Answer 16

Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand

Question 17

DNA Replication

DNA ligase

Answer 17

Joins Okazaki fragments of lagging strand;
On leading strand, joins 3’ end of DNA that replaces primer to rest of leading strand DNA

Question 18

Proofreading

Answer 18

DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides

Question 19

In mismatch repair of DNA:

Answer 19

Repair enzymes replace incorrectly paired nucleotides that have evaded the proofreading process

Question 20

Nucleotide Excision Repair

Answer 20

nuclease cuts out and replaces damaged stretches of DNA