Tpic 8D: Genomes and Gene Technologies

Question 1

What is the name of the short lengths of single-stranded DNA used in PCR? [1]

Answer 1

1. Primers

Question 2

During PCR, the mixture is cooled from 95°C to 55°C.

Explain why. [1]

Answer 2

1. To allow joining of primers

Question 3

Explain the function of primers in PCR. [2]

Answer 3

1. To show enzyme where to start;
2. (Enzyme) needs starting strand to attach nucleotides to

Question 4

How many copies of each original DNA molecule would be present after 5 cycles of PCR? [1]

Answer 4

1. 32

Question 5

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment. [4]

Answer 5

1. (Requires DNA fragment,) DNA polymerase, (DNA) nucleotides and primers;
2. Heat to 95°C to break hydrogen bonds (and separate strands);
3. Reduce temperature so primers bind to DNA/strands;
4. Increase temperature, DNA polymerase joins nucleotides (and repeat method)

Question 6

Describe how restriction endonuclease and DNA lipase are used to insert a gene into a plasmid. [2]

Answer 6

1. Restriction endonuclease cuts plasmid
   OR
   Restriction endonuclease produce ‘sticky ends’;
2. Lipase joins gene/DNA and plasmid
   OR
   Ligase joins ‘sticky ends’
   OR
   Ligase forms phosphodiester bonds

Question 7

Recombinant DNA technology can involve the transfer of fragments of human DNA into bacteria. The bacteria are then used to produce human protein.

Give two reasons why bacteria are able to use human DNA to produce human proteins. [2]

Answer 7

1. The genetic code is universal;
2. (The mechanism of) transcription is universal;
3. (The mechanism of) translation is universal

Question 8

Recombinant DNA technology can involve the transfer of fragments of human DNA into bacteria. The bacteria are then used to produce human protein.

Suggest and explain one reason why bacteria might not be able to produce every human protein. [1]

Answer 8

1. Bacteria cannot splice (pre-)mRNA, so cannot remove introns
   OR
   Bacteria do not have Golgi (apparatus), so cannot modify (proteins)

Question 9

Explain the purpose of marker genes. [1]

Answer 9

1. Allows detection of genetically modified cells/organisms

Question 10

A geneticist decided that it would be faster to create a gene using a gene machine than by using reverse transcriptase to convert mRNA into cDNA.

Suggest why the geneticist reached this conclusion. [1]

Answer 10

1. Faster to use gene machine than all the enzyme-catalysed reactions

Question 11

Suggest one advantage of using a plasmid with a gene the codes for a green fluorescent protein, that glows green under UV light. [1]

Answer 11

1. Can quickly identify transformed bacteria using UV light

Question 12

Suggest one reason why DNA replication stops in the polymerase chain reaction. [1]

Answer 12

1. Limited number of primers/nucleotides