Unit 1 KA2 - Structure + replication of DNA

Question 1

what does DNA stand for?

Answer 1

deoxyribonucleic acid.

Question 2

what forms the genetic code?

Answer 2

the base sequence of DNA.

Question 3

what determines the genotype of an organism and the structure of its proteins?

Answer 3

the base sequence of DNA.

Question 4

what is a base made of?

Answer 4

repeating units of nucleotides.

Question 5

what is a protein made of?

Answer 5

amino acids joined by peptide bonds.

Question 6

what is the structure of chromosomes and where are they found?

Answer 6

thread-like structures found in the nucleus of the cell and contain DNA, which is tightly wound around proteins called histones.

Question 7

what are the bases in DNA held together by?

Answer 7

hydrogen bonds.

Question 8

describe the structure of a DNA molecule.

Answer 8

the DNA nucleotides bond to form a sugar-phosphate backbone.
made up of two antiparallel strands (the strands run in opposite directions to each other) joined through weak hydrogen bonds that link complementary pairs of nucleotide bases.
the molecule is wound into a double-stranded helix.

Question 9

what are the needs for DNA replication?

Answer 9

template DNA, ATP, DNA nucleotides, and the enzymes DNA polymerase + DNA ligase.

Question 10

what is a primer?

Answer 10

a short strand of nucleotides that binds to the 3’ end of the template DNA strand, allowing DNA polymerase to add complementary DNA bases to the exposed bases on the template strand.

Question 11

what is DNA polymerase?

Answer 11

an enzyme that adds complementary DNA nucleotides to the 3’ end of the new DNA strand that is forming.

Question 12

what is DNA ligase?

Answer 12

an enzyme that joins the fragments of the lag strand.

Question 13

what are DNA nucleotides?

Answer 13

building blocks of DNA made up of 3 parts; deoxyribose sugar, phosphate and a base.

Question 14

describe the complementary base pairing rule.

Answer 14

the nucleotide containing the base adenine binds with the nucleotide containing the base thymine and the nucleotide containing the base guanine binds with the nucleotide containing the base cytosine.

Question 15

what happens in the first stage of DNA replication?

Answer 15

the template DNA strand unwinds from its double helix and forms 2 parallel strands.
hydrogen bonds break between complementary nucleotides of the template strand.

Question 16

what happens in the second stage of DNA replication?

Answer 16

primers bind to the 3’ end of the template strands.

Question 17

what happens in the third stage of DNA replication?

Answer 17

DNA nucleotides can only add nucleotides to the 3’ end of the new strand forming.
this results in a lead strand which replicates continuously and a lag strand which replicates in fragments.

Question 18

what happens in the fourth stage of DNA replication?

Answer 18

the fragments of the lag strand are joined by the enzyme DNA ligase.

Question 19

what happens in the fifth stage of DNA replication?

Answer 19

each of the daughter strands contains 1 copy of the template strand hence DNA replication is said to be semi-conservative.
each daughter strand then reforms a double helix.

Question 20

at the end of the 3’ strand is phosphate/deoxyribose and at the end of the 5’ strand is phosphate/deoxyribose.

Answer 20

deoxyribose, phosphate.

Question 21

what does PCR stand for?

Answer 21

polymerase chain reaction.

Question 22

what is PCR?

Answer 22

amplification of DNA in vitro to solve crimes, settle paternity suits and diagnose genetic disorders.

Question 23

what happens in the first stage of PCR?

Answer 23

DNA is heated to between 92C and 98C to separate strands.

Question 24

what happens in the second stage of PCR?

Answer 24

cooling to between 50C and 65Callows primers to bind to target sequences.

Question 25

what happens in the third stage of PCR?

Answer 25

it is then heated to between 70C and 80C.

heat tolerant DNA polymerase (taq polymerase) then replicates the region of DNA.

Question 26

what happens in the fourth stage of PCR?

Answer 26

repeated cycles of heating and cooling amplify this target region of DNA.