Chapter 2- DNA Replication, Transcription And Translation

Question 1

The base sequence on the template strand determines the base sequence on the new strand, how?

Answer 1

Only a nucleotide carrying a base that is complementary to the next base on the template strand can successfully be added to the new strand

Question 2

Why can’t a nucleotide with the wrong base be inserted into the chain?

Answer 2

Because complementary bases form hydrogen bonds with each other, stabilising the structure

Question 3

What does helicase do?

Answer 3

Unwinds the double helix and separates the two strands by breaking hydrogen bonds

Question 4

How is the separation carried out by helicases?

Answer 4

They are a group of proteins that use energy from ATP, this energy is required for breaking the hydrogen bonds between complementary base pairs

Question 5

Double stranded DNA cannot be split into two strands while it is still helical so what does helicase do?

Answer 5

Causes the unwinding of the helix at the same time as it separates the strands

Question 6

What does DNA polymerase do?

Answer 6

Links nucleotides together to form a new strand, using the pre-existing strand as a template

Question 7

How does DNA polymerase link DNA back together?

Answer 7

By making a covalent bond between the phosphate group of the free nucleotide and the sugar of the nucleotide at the existing end of the new strand
The pentose sugar is the 3’ terminal and the phosphate group is the 5’ terminal do DNA polymerase adds on the 5’ terminal of the free nucleotide to the 3’ terminal of the existing strand

Question 8

What is PCR?

Answer 8

Polymerase chain reaction- is a tenchnique used to make many copies of a selected DNA sequence

Question 9

Why is DNA semi-conservative?

Answer 9

Because it is made of two DNA molecules, both composed of an original strand and a newly synthesised strand

Question 10

What is transcription?

Answer 10

Is the synthesis of RNA, using DNA as a template

Question 11

What is the 5 step process of transcription?

Answer 11

1) the enzyme RNA polymerase bonds to a site on the DNA at the start of a gene
2) RNA polymerase moves along the gene separating DNA into single strands and pairing up RNA nucleotides with complementary bases on one strand of DNA, there is no thymine in RNA so uracil pairs to where thymine would
3) RNA polymerase forms covalent bonds with the RNA nucleotides
4) the RNA separates from the DNA and the double helix reforms
5) transcription stops at the end of the gene and the completed RNA molecule is released

Question 12

What is the product of transcription?

Answer 12

Is a molecule of RNA with a base sequence that is complementary to the template strand of DNA- this RNA sequence is identical to the other strand except for uracil

Question 13

What is the DNA strand with the same base sequence as the RNA stand called?

Answer 13

The sense strand

Question 14

The other strand that acts as the template and has complementary base sequence to both the RNA and the sense strand is called?

Answer 14

The antisense strand

Question 15

What is translation?

Answer 15

Is the synthesis of a polypeptide, with an amino acid sequence determined by the base sequence of a molecule of RNA

Question 16

Where does translation take place?

Answer 16

In the cytoplasm known as ribosomes

Question 17

The amino acid sequence of polypeptides is determined by what?

Answer 17

mRNA according to the genetic code

Question 18

What is mRNA?

Answer 18

RNA that carries the information needed to synthesis a polypeptide

Question 19

What is tRNA?

Answer 19

Involved in the decoding of base sequences of mRNA into an amino acid sequence during translation

Question 20

What is rRNA?

Answer 20

Ribosomal RNA is part of the structure of the ribosome

Question 21

What is the genetic code?

Answer 21

A set or rules by which encoded mRNA sequence is converted into proteins (amino acid sequence) by living cells

Question 22

What are codons?

Answer 22

Are triplet of bases which encoded a particular amino acid

Question 23

The are 4 bases so how many condon combinations?

Answer 23

64

Question 24

What does the order of condones determine?

Answer 24

The amino acid sequence for proteins

Question 25

What does a condon always start with?

Answer 25

AUG

Question 26

What are the 2 features of the genetic code?

Answer 26

Universal- everything uses the same code

Degenerate- only 20 amino acids but 64 codons = more than one condon may code for the same amino acid

Question 27

What are the 3 components that work together to synthesise polypeptides?

Answer 27

1) mRNA has a sequence of condone that specifies the amino amino acid sequence of the polypeptide
2) tRNA molecules have an anticodon of three bases that bind to a complementary codon of mRNA and they carry the amino acid corresponding to that codon
3) ribosomes act as the binding site for mRNA and tRNAs and also catalyse the assembly of the polypeptide

Question 28

7 steps of translation : a

Answer 28

1) mRNA binds to the small subunit of the ribosome
2) a molecule of tRNA with an anticodon complementary of the first codon to be translated on the mRNA binds to the ribosome
3) a second tRNA with an anticodon complementary to the second codon on the mRNA then binds. Maximum of 2 tRNAs can be bound at the same time
4) ribosome transfers the amino acid carried by the first tRNA to the amino acid on the second tRNA making a new peptide bond, the second tRNA is now carrying a chain of two amino acids- a dipeptide
5) the ribosome moves along the mRNA so the first tRNA is released, the second becomes the first
6) another tRNA binds the anticodon complementary to the next codon on the mRNA
7) the ribosome transfers the chain of amino acids carried by the first tRNA to the amino acid on the second tRNA, by making a new peptide bond

Question 29

Translation continues along the mRNA until what

Answer 29

A stop codon is reached

Question 30

Production of human insulin in Bacteria is an example of what?

Answer 30

Of the universality of the genetic code allowing gene transfer between species- as the genetic code is the same in every species to any gene can be decided