1.2

Question 1

what are dna strands composed of

Answer 1

repeating units called nucleotides

Question 2

what does a nucleotide consist of

Answer 2

• a deoxyribose sugar
• a phosphate group
• a base

Question 3

why are there 4 types of nucleotides

Answer 3

because there are 4 types of bases

Question 4

how is the deoxyribose right of one nucleotide joined to the phosphate of another nucleotide

Answer 4

by a strong chemical bond

Question 5

what do these repeating nucleotides make up

Answer 5

the sugar-phosphate backbone

Question 6

what is the base pair rule

Answer 6

all bases have a complimentary base pair e.g. a+t, g+c

Question 7

how are the 2 strands of dna held together

Answer 7

by weak hydrogen bonds

Question 8

what is the meaning of anti parallel

Answer 8

the strands run in opposite directions

Question 9

what does dna strands start and end with

Answer 9

each strand starts with a deoxyribose sugar at the 3’ end and ends with a phosphate at the 5’ end

Question 10

what is the shape of dna

Answer 10

a double stranded helix

Question 11

dna is the molecule of _______

Answer 11

inheritance

Question 12

what does the base sequence of dna form

Answer 12

the genetic code

Question 13

what does the base sequence determine

Answer 13

it determines the organisms genotype and phenotype

Question 14

what does dna have to do before cell division

Answer 14

make an exact copy of itself

Question 15

what does dna replication ensure

Answer 15

each of the two daughter cells formed have a full set of genetic info
and the diploid chromosome is maintained

Question 16

stages of dna replication

Answer 16

• dna is unwound and hydrogen bonds between bases break to form two template strands
• dna is replicated by dna polymerase which needs primers to start replication
• a primer is a short strand of nucleotides which binds to the 3’ end of the template dna strand allowing dna polymerase to add nucleotides
• dna polymerase adds dna nucleotides using complementary base pairing, to the deoxyribose(3’) end of the new dna strand which is forming
• dna polymerase can only add nucleotides in one direction resulting in the leading strand being replicated continuously and the lagging strand being replicated in fragments
• fragments of dna are joined by ligand

Question 17

what way is the leading strand replicated

Answer 17

continuously

Question 18

what way is the lagging strand replicated

Answer 18

in fragments / discontinuous

Question 19

how are the fragments on the lagging strand joined together

Answer 19

by ligase

Question 20

what does a primer do

Answer 20

binds to 3’ end of the template dna strand allowing dna polymerase to add dna nucleotides

Question 21

what are the requirements for dna replication

Answer 21

• dna template strands
• primers
• a supply of dna nucleotides
• dna polymerase & ligase enzymes
• atp

Question 22

what is pcr

Answer 22

pcr is a technique used to amplify a region of dna

Question 23

what are the stages of pcr

Answer 23

• dna is heated to between 92°c and 98°c to separate the two strands
  -it’s the cooled to between 50 and 65°c to allow primers to bind to the target sequence
• it’s then reheated to between 70 and 80° for heat tolerant dna polymerase to replicate the region of dna
• repeated cycles of heating and cooling are used to amplify the target region of dna

Question 24

what are the uses of pcr

Answer 24

• help solve crimes
• settle paternity disputes
• diagnose genetic disorders