1A - DNA replication

Question 1

How do cells store their genetic information?

Answer 1

All cells store their genetic information in the base sequence of DNA.

Question 2

Describe the structure of a nucleotide.

Answer 2

Nucleotide subunits consist of a deoxyribose sugar, phosphate and a base.

They bond to form a strong sugar-phosphate backbone.

Question 3

Describe base pairing

Answer 3

Base pairing is specific, with adenine pairing with thymine and cytosine pairing with guanine.

Question 4

What are Prokaryotes?

Give examples

Answer 4

Prokaryotes are organisms like bacteria which usually no nucleus and have a single circular chromosome and smaller circular plasmids.

Question 5

What are Eukaryotes?

Give examples

Answer 5

· Eukaryotes are organisms like yeast, plants and animals and all have linear chromosomes in the nucleus. Chromosomal DNA of eukaryotic cells is tightly coiled and packaged with associated proteins (called histones).

Eukaryotes contain organelles such as mitochondria and chloroplasts (in green plants) which contain circular chromosomes. Yeast are unusual because they also have plasmids with circular DNA.

Question 6

Describe the first stage of DNA replication

Answer 6

-DNA helix is unwound and the hydrogen bonds are denatured this opens up two template strands to be copied

Question 7

What is the purpose of PCR?

Answer 7

PCR refers to Polymerase Chain Reaction which is a technique used to amplify DNA(make multiple copies) of a specific target sequences.

· It involves repeated cycles of heating and cooling to amplify the target region of DNA.

Question 8

What are primers in PCR?

Answer 8

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

Question 9

Why are two different primers needed in polymerase chain reaction?

Answer 9

· Two different primers are needed to locate the two ends of the region to be amplified.

Question 10

Describe the structure of DNA

Answer 10

DNA is composed of 2 chains of nucleotides (double stranded).

The two nucleotide chains run antiparallel with a deoxyribose sugar at the 3’ end and phosphate group at the 5’ end of each strand respectively.

The nucleic acid bases are paired by hydrogen bondingin the centre to form a double helix

Question 11

When does DNA replication occur?

Answer 11

· Replication occurs prior to cell division.

Question 12

What is the first step in the procedure of PCR?

Answer 12

· DNA is heated to between 92 and 98°Cto separate the strands.

Question 13

What is the base sequence of DNA used for?

Answer 13

• to make proteins

- to control what proteins are made

Question 14

What are bacteria cells useful in

Answer 14

• genetic engineering

- horizontal gene transfer (to another bacteria cell)

Question 15

What is the purpose of the DNA found within organelles in eukaryotic cells?

Answer 15

-the DNA (circular chromosomes) codes for some of the proteins used in the organelles

Question 16

What makes up the strong sugar-phosphate backbone?

Answer 16

• phosphate
• deoxyribose sugar
• covalent bonds

Question 17

Why is DNA replicated before the cell divides?

Answer 17

-so the new cells have full copies of the genetic information

Question 18

Explain why primers are necessary for DNA replication.

Answer 18

So DNA polymerase can add nucleotides to the 3′ end of the new strand

To give DNA polymerase a start point for replication

Question 19

Describe anti parallel structure in DNA

Answer 19

• One strand of nucleotides goes 5’ - 3’

- The other goes the opposite direction, 3’-5’

Question 20

What is a primer in DNA replication?

Answer 20

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

Question 21

Describe the second stage of DNA replication

Answer 21

-DNA polymerase needs a complementary primer to start from, the primer binds to the 3’ end of a DNA strand

Question 22

Describe the third stage of DNA replication

Answer 22

-DNA polymerase adds new nucleotides to the 3’ end of the growing strand (using complementary base pairing so the correct bases match the template)

Question 23

Describe the fourth stage of DNA replication

Answer 23

-DNA polymerase can only add nucleotides in one direction, thus resulting in one strand being replicated continuously (leading stand) and the other strand is replicated in Okazaki fragments and the fragments are joined together by DNA ligase

Question 24

What enzyme is DNA replicated by?

Answer 24

DNA is replicated by the enzyme DNA polymerase.

Question 25

What does DNA replication require to start replication

Answer 25

· DNA polymerase needs primers to start replication.

Question 26

What is the second step in the procedure of PCR?

Answer 26

It is then cooled to between 50 and 65°C to allow primers to bind to target sequences.

Question 27

What is the third step in the procedure of PCR?

Answer 27

It is then heated to between 70 and 80°C for heat-tolerant DNA polymerase to replicate the region of DNA.

Question 28

What are practical applications of PCR?

Answer 28

· Practical applications of PCR. PCR can amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders.