LECTURE 18

Question 1

Double stranded (dsDNA) is the genetic material in

Answer 1

All organisms on earth

Question 2

Single stranded (ssDNA) is the genetic material in some

Answer 2

viruses.

RNA is the genetic material for these viruses

Question 3

RNA has the same structure as DNA except :

Answer 3

1) its single, not doubles stranded
2) sugars is ribose, not deoxyribose
2) urical instead of thymine

Question 4

General requirements for DNA replication

Answer 4

1) enzyme that can catalyze DNA synthesis form deoxyribose
2) Mg++ ions (required for enzyme function)
3) deoxyribose (dNTPs)

Question 5

enzyme that can catalyze DNA synthesis form deoxyribose

Answer 5

• called DNA polymerase

- all organisms contain many different DNA pools (with different roles in replication or repair of DNA)

Question 6

In dsDNA, the two strands are

Answer 6

Antiparallel and complementary

Question 7

The enzyme that replicates DNA is

Answer 7

DNA polymerase

Question 8

DNA polymerase will only attach nucleotides to an

Answer 8

Existing nucleotides free 3’-OH

This means that DNA polymerase cannot initiate synthesis of polynucleotide

Question 9

A new DNA polymer is formed by adding monomer nucleotides to the end, via a _________

Answer 9

3’-OH. Dehydration reaction

Question 10

DNA polymerase lll catalyzes formation of

Answer 10

Phosphodiester bond

Question 11

What determines which bases are chosen and how?

Answer 11

The templates determines it

Question 12

loss of phosphates is an __________ reaction that powers __________

Answer 12

Exergonic reaction

Polymerization

Question 13

Coupling of the exergonic reactions to synthesis is necessary because

Answer 13

Order is being created (individual nucleotides put into an ordered structure)

Question 14

A new DNA polymer is formed by adding

Answer 14

Monomer to the 3’-OH end, via dehydration reactions

Question 15

Replication proceeds in

Answer 15

Both directions from each origin, until the entire molecule is copied

Question 16

Parental dsDNA molecule is

Answer 16

2 complementary, antiparallel strands

Question 17

The DNA helix is unwound by a _____ that acts at the origins as of replication

Answer 17

Helicase

Question 18

Topiosomerase

Answer 18

Moves in front of the fork, to help relive strain due to twisting caused by helicase

Question 19

How does topiosomerase work?

Answer 19

(it cuts one strand, lets the DNA unwind by one turn, and then it “mends” the cut)

Question 20

Single strand biding proteins

Answer 20

• prevents singles strand from coming back together

- easily displaced by DNA pol

Question 21

How many replication forks are there in a bubble?

Answer 21

2, one at each end

Question 22

Primate

Answer 22

Synthesizes a 5-10 net RNA primer, complementary to DNA

Question 23

Does primate needs 3’-OH

Answer 23

NO

Question 24

Sliding clamp

Answer 24

Keeps DNA pol on the template

Question 25

Where does the new DNA strand start from

Answer 25

3’OH of the RNA

Question 26

Synthesis off the leading strand is

Answer 26

Continuous (stops at the end, or when it reaches another fork form a different origin (in eukaryotes) )

Question 27

Lagging strand is synthesized

Answer 27

Discontinuously

Question 28

As more ssDNA is made available at the fork,

Answer 28

Primase makes a primer

Question 29

Okazaki fragments

Answer 29

The lagging stand contains many short segments of the newly synthesized DNA

Question 30

Okazaki fragments must be converted into a

Answer 30

Single continuous strand

Question 31

DNA pol l

Answer 31

Removed one RNA, one nucleotide at a time, from the 5’ end, and replace it with DNA (adding to the 3’ end of the adjacent DNA)

Question 32

Is there a DNA pol that can join an existing 3’ end to an existing 5’ end ?

Answer 32

NO

Question 33

DNA ligand

Answer 33

Seals the gaps between the sugar-phosphates of the adjoining pieces of DNA

Question 34

At each replication bubble, there will be

Answer 34

Two leading strands and two lagging strands