Topic 2.7: DNA Replication, Transcription & Translation

Question 1

DNA is semiconservative

Answer 1

1) One strand is from an original template molecule and one strand is newly synthesised
2) Each base only pairs with its complementary partner and ensures the sequence is conserved

Question 2

Meselson-Stahl thesis

Answer 2

Supported the theory that DNA replication occurred via a semi-conservative process

Question 3

Models for DNA Replication (3)

Answer 3

1) Conservative Model
2) Semi-Conservative Model
3) Dispersive Model

Question 4

Dispersive Model

Answer 4

New molecules are made of segments of new and old DNA

Question 5

Conservative Model

Answer 5

An entirely new molecule is synthesised from a DNA template (which remains unaltered)

Question 6

Semi-Conservative Model

Answer 6

Each new molecule consists of one newly synthesised strand and one template strand

Question 7

Meselson-Stahl experiment (2)

Answer 7

They incorporated radioactive nitrogen isotopes into
DNA
• Templates were prepared with heavier 15N
• New sequences were replicated with lighter 14N

Question 8

Meselson-Stahl results (2)

Answer 8

The DNA was then separated via centrifugation to determine its composition of radioisotopes
• 1st division: DNA had 15N and 14N (i.e. mixed)
• 2nd division: DNA is mixed or has 14N only

Question 9

DNA Replication Enzymes (2)

Answer 9

1) Helicase

2) DNA Polymerase III

Question 10

Helicase (2)

Answer 10

1) Unwinds and separates the double stranded DNA

2) Breaks the hydrogen bonds between the base pairs

Question 11

DNA Polymerase III

Answer 11

1) Free nucleotides line up opposite complementary partners

2) DNA Pol III covalently joins the free nucleotides together

Question 12

DNA replication

Answer 12

Semi-conservative process whereby pre-existing strands act as templates for newly synthesised str

Question 13

Polymerase Chain Reaction (PCR)

Answer 13

Artificial method of DNA replication that is used to rapidly copy a specific sequence.

Question 14

PCR Steps in a Thermal Cycler

Answer 14

Denaturation (90°)
Annealing (55°)
Elongation (75°)

Question 15

Denaturation

Answer 15

DNA is heated to separate the two strands

Question 16

Annealing

Answer 16

Primers attach to ends of a target sequence

Question 17

Elongation

Answer 17

A heat-tolerant polymerase copies strands (Taq polymerase)

Question 18

30 Cycles in PCR = ? copies

Answer 18

2^30 copies of the target DNA sequence

Question 19

Transcription

Answer 19

Synthesis of an RNA sequence from a DNA template

Question 20

RNA Polymerase

Answer 20

1) Separates the DNA strands (breaks H bonds between base pairs)
2) Covalently joins free complementary RNA nucleotides together

Question 21

Types of RNA

Answer 21

1) mRNA – Transcript used to make protein
2) tRNA – Transfers amino acid to ribosome
3) rRNA – Catalytic component of ribosome

Question 22

Genetic code

Answer 22

Set of rules by which information encoded in mRNA sequences is converted into a polypeptide sequence

Question 23

Codons

Answer 23

Triplets of bases which correspond to a particular amino acid

Question 24

Order of codons

Answer 24

Codons determines the amino acid sequence for a protein

Question 25

Start codon

Answer 25

AUG

Question 26

STOP codons (3)

Answer 26

UAA
UAG
UGA

Question 27

Features of the Genetic Code (2)

Answer 27

1) Universality – All organisms use the same genetic code

2) Degeneracy – Multiple codons may code for the same amino acid

Question 28

Translation

Answer 28

Process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids on a polypeptide chain

Question 29

Steps of translation (Mr Cat App)

Answer 29

1) Messenger RNA (goes to…)
2) Ribosome (reads sequence in …)
3) Codons (recognised by …)
4) Anticodons (found on …)
5) Transfer RNA (which carries …)
6) Amino acids (which join via …)
7) Peptide bonds (to form …)
8) Polypeptides

Question 30

Gene

Answer 30

Sequence of DNA that is transcribed into RNA

Question 31

Human insulin in bacteria (4)

Answer 31

1) The gene responsible for insulin production is extracted from a human cell
2) It is spliced into a plasmid vector (for autonomous replication and expression) before being inserted into a bacterial cell
3) The transgenic bacteria (typically E. coli) are then selected and cultured in a fermentation tank (to increase bacterial numbers)
4) The bacteria now produce human insulin, which is harvested, purified and packaged for human use