DNA Replication

Question 1

When is DNA replicated?

Answer 1

Before every cell division

Question 2

What are the identical cells produced called

Answer 2

Daughter cells

Question 3

What is the first step in DNA replication?

Answer 3

DNA helicase moves up the double helix and breaks the hydrogen bonds between bases, unzipping the DNA

Question 4

what is DNA helicase?

Answer 4

An enzyme

Question 5

What is floating in the nucleoplasm?

Answer 5

Free nucleotides

Question 6

What is on the outside of each original strand of DNA?

Answer 6

Exposed bases which act as templates to form a new chain

Question 7

Which order is the strand on the right in?

Answer 7

3’ to 5’ polarity

Question 8

What order is the strand on the left in?

Answer 8

5’ to 3’ polarity

Question 9

What order is the new chain made in?

Answer 9

5’ to 3’ polarity

Question 10

What is the second stage in DNA replication?

Answer 10

DNA polymerase joins free nucleotides in the nucleoplasm together with covalent phosphodiester bonds, creating a two new chains and forming the sugar phosphate backbone.

Question 11

What is DNA polymerase?

Answer 11

An enzyme

Question 12

How many nucleotides are in each strand of DNA

Answer 12

3.2 billion

Question 13

How many meters of DNA in one chromosome

Answer 13

2.4m

Question 14

How is the strand on the left formed and why?

Answer 14

It is formed in one joined line because it is going from 5’ to 3’, which is the order the new strand is made in.

Question 15

How is the strand on the right formed and why?

Answer 15

In fragments of DNA going from 5’ to 3’. Because the original strand is going from 3’ to 5’, whereas the new stand is made in 5’ to 3’.

Question 16

What joins the fragments of DNA?

Answer 16

An enzyme

Question 17

What is the third stage in DNA replication?

Answer 17

The two strands wind into a double helix and two copies of the original DNA are formed.

Question 18

How are hydrogen bonds formed?

Answer 18

The appear through attraction, don’t need an enzyme.

Question 19

How long does DNA replication take on average?

Answer 19

A few hours

Question 20

How is DNA replication sped up in eukaryotes?

Answer 20

The replication takes place on thousands of sites (replication forks) along the DNA simultaneously

Question 21

Why do bacteria reproduce so quickly?

Answer 21

They have very little DNA

Question 22

What is the generally accepted theory for DNA replication called?

Answer 22

Semi-conservative replication

Question 23

What is another (incorrect) theory for DNA replication called?

Answer 23

Conservative replication

Question 24

Who discovered evidence for semi-conservative replication?

Answer 24

Meselon and Stahl

Question 25

What is the difference between 14N and 15N

Answer 25

They are isotopes of nitrogen - 15N has one extra neutron

Question 26

In their experiment, why ere the bacteria grown in ammonia?

Answer 26

Because nitrogen is very unreactive, but ammonia contains lots of nitrogen is more reactive

Question 27

What was the first step in the Meselon-Stahl experiment?

Answer 27

Grow bacteria on a medium with light nitrogen (14N) for many generations. Purify the DNA and centrifuge to make one band of DNA in the CsCl solution.

Question 28

Where was the band of DNA in the first step?

Answer 28

Near the surface

Question 29

What was the second step in the Meselon-Stahl experiment?

Answer 29

Grow bacteria on a medium with heavy nitrogen (15N) for many generations. Purify the DNA and centrifuge to make one band of DNA in the CsCl solution.

Question 30

Where was the band of DNA in the second step?

Answer 30

Near the bottom

Question 31

What was the third step in the Meselon-Stahl experiment?

Answer 31

Return the bacteria grown with the heavy nitrogen to a medium with light nitrogen, and grow for one generation. Purify DNA and centrifuge.

Question 32

Where was the band of DNA in the third step?

Answer 32

In the middle

Question 33

What was the fourth step in the Meselon-Stahl experiment?

Answer 33

Grow the bacteria with both 14 and 15N on a medium with light nitrogen for two generations. purify DNA and centrifuge.

Question 34

Where was the band of DNA in the fourth step?

Answer 34

On near the surface, one in the middle

Question 35

Why was the band in the middle of the test tube?

Answer 35

When the bacteria grown in just heavy nitrogen reproduce with the light nitrogen present, one strand of each heavy and light bases form, meaning that it is in the middle.