DNA Technology

Question 1

Describe how reverse transcriptase is used to isolate a gene?

Answer 1

Produce MRNA from DNA.
CDNA is produced complementary to that of mRNA, it is shorter as it does not contain introns.
DNA polymerase adds free nucleotides

Question 2

How do restriction endonucleases isolate a gene?

Answer 2

The enzymes cut a double stranded segment of a DNA at a recognition sequence
The cut is in a staggered fashion forming ‘sticky ends’

Question 3

What is the benefit of sticky ends?

Answer 3

If the same restriction enzyme is used DNA from one organism can be combined with that of another

Question 4

Name the type of enzyme used to cut open the plasmid

Answer 4

Restriction endonuclease

Question 5

Name the type of enzyme used to insert the gene into the plasmid

Answer 5

DNA Ligase

Question 6

Explain why some of the plants in stage 5 contained the desired gene in all of their cells
and others did not

Answer 6

1. (DNA of desired gene) copied/replicated
   with host DNA/inside nucleus;
2. Passed on by mitosis/plant grows by
   mitosis;
3. Produces genetically identical cells/clones

Question 7

Why can plants synthesis insect protein?

Answer 7

Genetic code is universal

Can be transcribed and then translated

Question 8

How can a mutation not lead to a change in the amino acid sequence?

Answer 8

Genetic code is degenerate

Mutation in introns

Question 9

A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how.

Answer 9

Tumour suppressor gene inactivated

Leading to uncontrolled cell division

Question 10

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.

Answer 10

Antibody has specific tertiary structure
Complementary to receptor protein
Prevents GF binding to receptor

Question 11

Explain why the pieces of human DNA would be able to join to the cut DNA of the plasmids.

Answer 11

They have sticky ends

Question 12

What is a vector ?

Answer 12

A carrier of DNA into another organism

Question 13

Molecular biologists often use plasmids which contain antibiotic resistance genes. Explain the reason for this

Answer 13

It acts as a marker gene

It allows detection of cells containing plasmid

Question 14

What is recombinant DNA technology?

Answer 14

Involves the transfer of fragments of DNA from one organism to another

Question 15

Describe 3 methods in which fragments of DNA can be produced

Answer 15

conversion of mRNA to complementary DNA (cDNA), using reverse transcriptase

using restriction enzymes to cut a fragment containing the desired gene from DNA

creating the gene in a ‘gene machine’.

Question 16

How can a gene be isolated by reverse transcriptase?

Answer 16

Produces mRNA from DNA resulting in cDNA

DNA polymerase adds nucleotides

Question 17

Why is CDNA shorter than original gene?

Answer 17

It does not contain introns

Question 18

Why is it easier to obtain the gene from mRNA rather than directly from DNA removed from human cells

Answer 18

MRNA is present in large amounts in cell making protein

Question 19

What does ligase do?

Answer 19

Joins two pieces of DNA

Question 20

Molecular biologists often use plasmids which contain antibiotic resistance genes, why?

Answer 20

They act as a maker gene which allows detection of cells containing the plasmid

Question 21

Why would you insert plasmids into the eggs of silkworms rather than into the silkworms?

Answer 21

So that the gene gets into all of the cells

Particularly those that produce the silk

Question 22

suggest how the binding of interferon gamma to its

receptor protein leads to the production of phosphorylated STAT1

Answer 22

Changes shape of the tertiary structure
This activates an enzyme
requires use of ATP

Question 23

What is the first step of the polymerase chain reaction?

Answer 23

High temperature breaks H bonds separating double helix

Question 24

What happens in the annealing stage of the polymerase chain reaction?

Answer 24

Primers bind to strand of DNA. Happens at a lower temperature
Primers are designed to recognise foreign DNA

Question 25

Why is TAQ polymerase used in the polymerase chain reaction and what does it do?

Answer 25

It can work at high temperatures and does not denature

It forms phosphodiester bonds forming back bone of new DNA strand

Question 26

What is the polymerase chain reaction used for?

Answer 26

To amplify fragments of DNA