KA2 - Structure And Replication Of DNA

Question 1

A molecule of DNA consists of two strands each composed of repeating units called what?

Answer 1

Nucleotides

Question 2

Name the three parts of a nucleotide

Answer 2

Deoxyribose sugar

Phosphate group

An organic base

Question 3

Name the four DNA bases

Answer 3

Adenine & Thymine

Cytosine & Guanine

Question 4

What position does the C3 and C5 determine?

Answer 4

The 3’ and 5’ end of the DNA strand

Question 5

What carbon is the phosphate group attached to on the deoxyribose sugar?

Answer 5

Carbon 5

Question 6

What carbon is the organic base attached to on the deoxyribose sugar?

Answer 6

Carbon 1

Question 7

What is formed when nucleotides join together?

Answer 7

Nucleotides join together to form the DNA molecules sugar phosphate backbone

Question 8

Where is a strong chemical bond formed?

Answer 8

A strong chemical bond is forms between the phosphate group of one nucleotide and carbon 3 of the deoxyribose sugar on another nucleotide

Question 9

DNA is a double helix. What is meant by this?

Answer 9

There are two strands of nucleotides joined together

Question 10

What type of bond joins the two strands of nucleotides to their complimentary bases?

Answer 10

Weak hydrogen bonds

Question 11

What is determined by the sequence of bases?

Answer 11

An organism genotype is determined by the sequence of bases

Question 12

What is at the 3’ end of each complimentary stand of DNA?

Answer 12

The deoxyribose sugar

Question 13

What is at the 5’ end of each complimentary strand of DNA?

Answer 13

The phosphate grouo

Question 14

How is the chain able to grow and what does this lead to?

Answer 14

The chain is only able to grow by adding nucleotides to its 3’ end

This leads to the two DNA strands with their sugar phosphate backbones running in opposite directions. This is described as anti parallel

Question 15

What must happen in order for the complimentary base pairs to align?

Answer 15

The two strands in a DNA molecule form a twisted coil called a double helix

Question 16

Describe the structure of the double helix

Answer 16

The sugar phosphate backbones are ok the outside and the complimentary base pairs are on the inside

Question 17

When is DNA replication preformed?

Answer 17

At the beginning of cell division

Question 18

Where does DNA replication take place?

Answer 18

In the nucleus

Question 19

What is DNA replication?

Answer 19

DNA replication is the process by which a cell makes an identically copy of its DNA

Question 20

What does DNA replication ensure?

Answer 20

DNA replication ensures that an exact copy of a cells genetic information is passed on to each new daughter cell making it genetically identically to the original cell

Question 21

What does DNA replication maintain in the new daughter cell?

Answer 21

DNA replication maintains the chromosome compliment in the new daughter cell.

Question 22

For DNA replication to occur, what must the nucleus contain?

Answer 22

DNA to act as a template

Primers

A supple of the four types of nucleotide

Enzymes (DNA polymerase & ligase)

Supply of ATP for energy

Question 23

What 3 steps are preformed at the beginning of DNA replication?

Answer 23

1. The shape of DNA is a double helix
2. Before DNA can be replicated, it must first be unwound
3. The weak hydrogen bonds between the bases are then broken to form two template strands

Question 24

What is DNA replicated by?

Answer 24

DNA polymerase

Question 25

What must be present for DNA polymerase to function?

Answer 25

DNA polymerase can only add nucleotides to a pre existing chain of nucleotides. Therefore for DNA polymerase to function, a primer must be present.

Question 26

What is a primer?

Answer 26

A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add DNA nucleotides

Question 27

How does DNA polymerase add DNA nucleotides?

Answer 27

DNA polymerase adds DNA nucleotides, using complimentary base pairing, to the deoxyribose 3’ end of the template DNA strand.

Question 28

DNA polymerase can only add DNA nucleotides in one direction. What does this result in?

Answer 28

The formation of a leading and lagging strand

Question 29

What happens on the leading strand?

Answer 29

On the leading strand, nucleotides are added from the 3’ end of the parental DNA molecule continuously

The primer is then replaced by DNA

Question 30

How is the lagging strand replicated?

Answer 30

The lagging strand is replicated in fragments

Question 31

How does replication of the lagging strand start?

Answer 31

Replication of the lagging strand starts with primer at the 3’ end and adds nucleotides discontinuously as more primer is added

Question 32

What are the fragments joined together by?

Answer 32

The enzyme ligase

Question 33

What happens after the fragments are joined together?

Answer 33

The primer is then replaced by DNA

Question 34

What is PCR?

Answer 34

PCR amplifies DNA using complimentary primers for specific target sequences

Question 35

In PCR, what are primers?

Answer 35

In PCR, primers are short strands of nucleotides which are complimentary to specific target sequences at the two ends of the region of DNA to be amplified

Question 36

What are the four stages of the polymerase chain reaction (PCR)?

Answer 36

1. DNA is heated to between 92 and 98 degrees to separate the strands
2. DNA is then cooled to between 50 and 65 degrees to allow primers to bind to target sequences
3. DNA is then heated to 70 and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA
4. Reaped cycles of heating and cooling, amplify this region of DNA