1.2 Structure and replication of DNA

Question 1

Describe the structure of a DNA molecule.

Answer 1

DNA is a large double stranded helix made up of repeated units called nucleotides

Question 2

Name the four nucleotide bases

Answer 2

Adenine
Thymine
Cytosine
Guanine

Question 3

What are nucleotides

Answer 3

Nucleotides in a chain are joined together by sugar phosphate bonds to make long chains of nucleotides called polynucleotides

Question 4

How are sugar phosphate backbones made

Answer 4

A strong chemical bond forms between the phosphate group of one nucleotide and the carbon 3 of the deoxyribose sugar on another one. neighbouring nucleotides become joined together ina long permanent strand in which sugar molecules alternate with phosphate groups forming the DNAs strong sugar phosphate back bone

Question 5

Explain the terms of anti parallel in terms of DNA

Answer 5

The arrangement of the two strands with there sugar phosphate backbones running in opposite directions. The double helix is described as having two anti-parallel chains of nucleotides

Question 6

Identify and describe the 3 prime and 5 prime ends in a DNA double stranded molecule

Answer 6

Primer is added to the 3 end of DNA
Strand A is lagging and B is leading

Question 7

Stage one of DNA replication

Answer 7

Double stranded helix unwinds

Question 8

Stage two of DNA replication

Answer 8

Hydrogen bonds between nucleotide bases break seperating the strands

Question 9

Stage three of DNA replication

Answer 9

A primer attaches to each template strands

Question 10

Stage four of DNA replication

Answer 10

DNA polymerase adds free complementary nucleotides to the 3 end of a growing dna strand

Question 11

Stage five of DNA replication

Answer 11

Hydrogen bonds form between bases

Question 12

Stage six of DNA replication

Answer 12

Strong bonds form between sugars and phosphates creating strong sugar phosphate backbones.

Question 13

When does DNA replication within a cell take place

Answer 13

DNA replicates prior to cell division (mitosis) and identical copies of DNA are passes to daughter cells

Question 14

Identify and explain the roles of the key essential substances required for DNA replication

Answer 14

DNA molecule -
Primers
Nucleotides
Enzymes (ligase, polymerase)
ATP

Question 15

Why is ligase needed in dna replication

Answer 15

In DNA replication, ligase joins together fragments of newly synthesized DNA to form a seamless strand1.

Question 16

Why is a DNA molecule needed in DNA replication

Answer 16

To act as a template for a new DNA molecule to be made

Question 17

Why are primers needed in DNA replication

Answer 17

DNA polymerases can only attach new DNA nucleotides to an existing strand of nucleotides

Question 18

Why is polymerase needed in DNA replication

Answer 18

it creates new DNA strands by adding nucleotides that are complementary to the template strand

Question 19

State the purpose of the polymerase chain reaction

Answer 19

PCR is a labotory technique for the amplification of DNA. This is a technique that can be used to create many copies of a piece of DNA in vitro (outside the body) Scientests use PCR machines to amplify DNA outside an organism

Question 20

State the role of primers in PCR

Answer 20

PCR amplifies DNA using complimentary primers for specific target sequences.

Question 21

What is a primer?

Answer 21

A primer is a single stranded piece of dna complementary to a specific target sequence at the 3 end of the DNA strand to be replicated

Question 22

State the role of enzymes in pcr

Answer 22

The polymerase is called taq polymerase which is heat tolerant and replicates the region of DNA

Question 23

Stage one of PCR

Answer 23

DNA is heated to 90 degrees. This denatures DNA which breaks the hydrogen bonds separating the bases.

Question 24

Stage two of PCR

Answer 24

Cool to 50 degrees. Primers are added which anneals (binds) to specific target sequences of DNA

Question 25

Stage three of PCR

Answer 25

Heat to 70 degrees. Taq polymerase adds free DNA nucleotides to complamentery DNA nucleotides

Question 26

Give examples of the practical applications of PCR

Answer 26

-Forensics in solving crime
- Settle paternity disputes
- Diagnose genetic disorders