DNA structure and replication

Question 1

what is a nucleotide composed of

Answer 1

a sugar (e.g deoxyribose), a base and a phosphate

Question 2

what are the four types of bases in DNA

Answer 2

• Thymine
• Adenine
• Guanine
• Cytosine

Question 3

which bases pair up with each other

Answer 3

• A and T
• G and C

Question 4

what type of bond forms between complementary bases

Answer 4

Hydrogen bond

Question 5

which two components of a nucleotide for the backbone of DNA

Answer 5

the sugar and phosphate form the sugar phosphate backbone

Question 6

why is DNA said to have an antiparallel structure

Answer 6

• one strand starts at the 3 end’ and ends at the 5’ end (starts with a deoxyribose sugar and ends with a phosphate)
• the other strand starts at the 5’ end and ends at the 3’ end (starts with a phosphate and ends with a deoxyribose sugar)

Question 7

what final shape does DNA form

Answer 7

Double helix

Question 8

how many bases code for an amino acid

Answer 8

3 bases code for an amino acid

Question 9

what is the purpose of DNA replication

Answer 9

to allow a cell to make an identical copy of its DNA

Question 10

what must occur prior to mitosis to ensure the daughter cells have an identical copy of DNA

Answer 10

DNA replication

Question 11

what are the requirements for DNA replication

Answer 11

• DNA
• primers
• Enzymes (DNA polymerase and ligase)
• free nucleotides
• ATP

Question 12

what is a primer

Answer 12

A short strand of nucleotides that will bind to the 3’ end of the template DNA strand allowing DNA polymerase to add free nucleotides

Question 13

what must occur to allow DNA replication to begin

Answer 13

DNA double helix must be unwound and unzipped

Question 14

what enzyme adds free DNA nucleotides to the 3’ end of the primer during DNA replication

Answer 14

DNA polymerase

Question 15

what are the two strands formed during DNA replication

Answer 15

• leading strand
• lagging strand

Question 16

in what direction does DNA polymerase add nucleotides

Answer 16

5’-3’ direction

Question 17

what is the difference between the leading and lagging strand

Answer 17

• the leading strand is synthesised continuously
• the lagging strand is synthesized in fragments

Question 18

why is the lagging strand synthesized in fragments

Answer 18

nucleotides can only be added in a 5’-3’ direction

Question 19

which enzymes joins together the fragments of the lagging strand

Answer 19

ligase

Question 20

what is PCR

Answer 20

a technique used to amplify specific target DNA sequences

Question 21

what are the practical applications of PCR

Answer 21

• provide DNA samples for criminal investigations
• diagnosis of genetic conditions
• proving the identity of a child’s father

Question 22

what is needed to perform PCR

Answer 22

• DNA
• complementary primers
• a thermal cycler
• HEAT TOLERANT DNA POLYMERASE
• a supply of nucleotides

Question 23

what Is the first stage of PCR

Answer 23

DNA is heated between 92 and 98 degrees to denature DNA and separate the two strands

Question 24

what is stage two of PCR

Answer 24

DNA is cooled between 50 and 65 degrees to allow primers to bind to the target DNA sequences

Question 25

what is stage three of PCR

Answer 25

Temperature is raised to between 70 and 80 degrees to allow heat tolerant DNA polymerase to add free nucleotides to the primers at the 3’ end of the DNA strands