2.7 DNA Replication, Transcription and Translation

Question 1

Fill in the blank. DNA replication is a ____ _____ process.

Answer 1

Semi-conservative.

Question 2

Why is DNA a semi-conservative process?

Answer 2

When a new double stranded DNA molecule is formed:
One strand will be from the original template molecule.
One strand will be newly synthesized.

Question 3

Fill in the blanks. Adenine (A) pairs with _____.

Cytosine (C) pairs with _____.

Answer 3

Thymine

Guanine

Question 4

Name the experiment that proved that DNA replication was semi-conservative.

Answer 4

The Meselson-Stahl experiment in 1958.

Question 5

What were the 3 hypotheses which had been proposed for the method of replication of DNA?

Answer 5

Conservative model
Semi-conservative model
Dispersive model

Question 6

Which is heavier, 15N or 14N?

Answer 6

15N.

Question 7

Outline the results of the first division and second divison.

Answer 7

1st division: DNA had 15N and 14N (mixed).

2nd division: DNA was mixed/had 14N only.

Question 8

What is the polymerase chain reaction?

Answer 8

An artificial method of DNA replication used to rapidly copy sequences.

Question 9

What are the three steps to PCR?

Answer 9

Denaturation, annealing and elongation.

Question 10

Where does PCR occur?

Answer 10

In a thermal cycler.

Question 11

Outline the denaturation step of PCR.

Answer 11

DNA is heated, separating strands.

Question 12

Outline the annealing step of PCR.

Answer 12

Primers attach to the ends of a target sequence.

Question 13

Outline the elongation step of PCR.

Answer 13

A heat-tolerant polymerase copies strands.

Question 14

What would a standard PCR of 30 cycles generate?

Answer 14

Roughly 2^30 copies of the target DNA sequence.

Question 15

What two enzymes are vital for DNA replication?

Answer 15

Helicase and DNA polymerase.

Question 16

What is the role of helicase in DNA replication?

Answer 16

Unwinds double helix and separates polynucleotide strands

Breaks hydrogen bonds which exist between the complementary base pairs

Question 17

What is the role of DNA polymerase in DNA replication?

Answer 17

• Synthesizes new strands from the parental template strands

- Cleaves the two excess phosphates and uses the energy released to link the nucleotide to the new strand

Question 18

Define transcription.

Answer 18

The process by which an RNA sequence is produced from a DNA template.

Question 19

What does RNA polymerase do in transcription?

Answer 19

• Separates the DNA strands and synthesizes a complementary RNA copy
• Removes the additional phosphate groups and uses the energy to join the nucleotide to the growing sequence
• It then detaches from the DNA molecule as the double helix reforms

Question 20

What is a gene in transcription?

Answer 20

The sequence of DNA that is transcribed into RNA.

Question 21

What is the antisense strand?

Answer 21

The strand that is transcribed - it is complementary to the RNA sequence.

Question 22

What is the sense strand?

Answer 22

The strand that is not transcribed - it is identical to the RNA sequence, but with T instead of U)

Question 23

Define the genetic code.

Answer 23

The set of rules by which information encoded within mRNA sequences is converted into amino acid sequences (polypeptides) by living cells.

Question 24

Fill in the blank. The coding region of an mRNA sequence always begins with a ____ ____ (AUG) and terminates with a ____ ___codon

Answer 24

Start codon

Stop codon

Question 25

What are codons?

Answer 25

Triplets of bases.

Question 26

What encodes the production of a polypeptide?

Answer 26

The base sequence of an mRNA molecule.

Question 27

Define translation.

Answer 27

The 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 28

Outline the process of translation (6 steps)

Answer 28

1. Ribosomes bind to mRNA in cytoplasm and move along molecule until it reaches a start codon.
2. Anticodons on tRNA molecules align codons according to complementary base pairing.
3. Each tRNA molecule carries a specific amino acid.
4. The ribosome moves alone the mRNA molecule creating a polypeptide chain until it reaches a stop codon.
5. Translation ceases, and the polypeptide chain is released.

Question 29

Outline the three steps of producing human insulin in bacteria.

Answer 29

1. The gene responsible for insulin production is extracted from a human cell.
2. It is spliced into a plasmid vector before being inserted into the cell.
3. The bacteria are then selected and cultured in a fermentation tank.