DNA Structure and Replication

Question 1

What are the parts of a nucleotide?

Answer 1

A sugar (either ribose or deoxyribose), a phosphate, and a nitrogenous base.

Question 2

What are the pyrimidine bases?

Answer 2

Thymine and Cytosine

Question 3

What are the purine bases?

Answer 3

Adenine and Guanine

Question 4

What kind of base is represented by a pentagon?

Answer 4

A purine

Question 5

What kind of base is represented by a hexagon?

Answer 5

A pyrimidine

Question 6

In the arrangement of nucleotides, what does the sugar bond to?

Answer 6

The last phosphate at carbon 3.

Question 7

In the arrangement of nucleotides, what does the phosphate bond to?

Answer 7

The next sugar at carbon 5.

Question 8

What is the sugar end of the strand called?

Answer 8

3’ end

Question 9

What is the phosphate end of the strand called?

Answer 9

5’ end

Question 10

How many bonds does adenine form with thymine?

Answer 10

2

Question 11

How many bonds does cytosine form with guanine?

Answer 11

3

Question 12

Which kind of bonds would a more stable section of DNA have more of?

Answer 12

More stable sections would have more CG bonds.

Question 13

What happens if the amount of adenine does not equal the amount of thymine?

Answer 13

DNA is not double stranded

Question 14

What happens if the amount of cytosine does not equal the amount of guanine?

Answer 14

DNA is not double-stranded.

Question 15

How are the strands in DNA arranged?

Answer 15

In a double helix.

Question 16

How many base pairs are in a human cell

Answer 16

3 billion

Question 17

How many genes are the 3 billion base pairs in a human cell arranged into?

Answer 17

25 000 genes

Question 18

What percentage of genes do not code for any protein?

Answer 18

Up to 50 % of genes do not code for ANY PROTEIN!

Question 19

How long is the DNA from one cell?

Answer 19

2 m in length.

Question 20

What is a disadvantage [ssDNA] has?

Answer 20

It is easily broken.

Question 21

What is an advantage [dsDNA] has?

Answer 21

It is very stable.

Question 22

Name five differences between RNA and DNA.

Answer 22

1. The sugar used is ribose (has one more oxygen than deoxyribose).
2. Adenine bonds to uracil instead of thymine.
3. Single-stranded molecule.
4. Much shorter than DNA.
5. Unlike DNA, RNA can survive in the cytoplasm if properly prepared. (student losing notes vs losing textbook)

Question 23

What is the order of steps in DNA replication?

Answer 23

1. Starting
2. Building
3. Other Strand
4. Finishing

Question 24

What does DNA helicase do?

Answer 24

Breaks H bonds between strands at an “origin of replication”

Question 25

What does DNA gyrase do?

Answer 25

Releases tension that comes from unwinding.

Question 26

What is the replication fork?

Answer 26

The area where the two strands are separated.

Question 27

What are single stranded binding proteins for?

Answer 27

To keep strands from reannealing.

Question 28

What does Primase do?

Answer 28

It creates a 10-60 base pair strand of RNA (RNA primer) et the exposed end of 3’ of replication fork.

Question 29

What does DNA polymerase III do?

Answer 29

It moves along the old DNA in the 3’ to 5’ direction and adds complementary bases that are phoshorylated (removing 2 Pi)

Question 30

What is the leading strand?

Answer 30

The strand continiously copied from the 3’ to 5’ end.

Question 31

What is the lagging strand?

Answer 31

The strand made from attaching Okazaki fragments together.

Question 32

Why is the lagging strand built in fragments?

Answer 32

Because DNA polymerase III casn only move in the 3’ to 5’ direction.

Question 33

What does DNA polymerase 1 do?

Answer 33

It removes RNA primers and replaces them with the appropriate DNA bases.

Question 34

What does DNA ligase do?

Answer 34

It attaches Okazaki fragments by bonding sugar and phosphates.