Appendix

Question 1

Erwin Chargaff

Answer 1

1949, discovered Chargaff’s Rule. Ratio of bases constant within a species. A always occurs in the same amount as T, and the same applies to G and C. From this evidence, Watson and Crick suggested that each rung of the helix is composed of a base pair.

Question 2

Hershey and Chase

Answer 2

1952, blender experiment, discovered that DNA is the genetic material, not protein. Used a bacteriophage and labelled either protein coat with sulfure or DNA with phosphorus. Viruses and bacteria were agitated to separate them. Found that bacteria were only radioactive when DNA was labelled.

Question 3

Rosalind Franklin

Answer 3

1953. Used X-ray crystallography to show that DNA is a double helix

Question 4

Watson and Crick

Answer 4

1953. Stole Franklin’s picture to deduce structure of DNA

Question 5

Gel electrophoresis procedure

Answer 5

1. PCR used to amplify available amount of DNA
2. Restriction enzymes used to cut DNA into fragments
3. DNA is separated by placing fragments into agarose gel. DNA attracted to positive terminal. Smaller fragments move faster.

Question 6

Regions used for DNA profiling

Answer 6

Coding regions are identical and useless. Variations occur in non-coding regions, called variable length tandem repeats.

Question 7

Name of fragments in DNA profiling

Answer 7

Restriction Fragment Length Polymorphisms

Question 8

Limitations of DNA profiling

Answer 8

Contamination, denatured DNA, not enough DNA

Question 9

Natural examples of clones

Answer 9

Monozygous twins, asexual reproduction

Question 10

Benefit of cloning

Answer 10

Can be difficult to produce genetically modified organisms, easier to make 1 then clone

Question 11

2 methods of cloning

Answer 11

1. Splitting of embryo

2. Somatic cell nuclear transfer

Question 12

Explanation of embryo fragmentation

Answer 12

In the early stage of development, all cells making up an embryo are totipotent, and it is possible to split an 8 cell embryo into 8 cells, which would then be implanted into surrogates to become 8 clones

Question 13

Somatic cell nuclear transfer

Answer 13

1. Donor cells are taken from the organism to be cloned and cultured in a lab
2. Unfertilized egg is taken from another organism
3. Egg is enucleated
4. Enucleated egg is fused with the donor cell
5. Fused cell is cultured until an embryo is formed
6. Embryo is transplanted into a surrogate

Note: not entirely identical because mDNA comes from egg

Question 14

Procedure for gene transfer

Answer 14

1. Desired gene is isolated. mRNA is first isolated, then reverse transcriptase is used to convert it to cDNA
2. Bacterial plasmid is isolated
3. Plasmid is prepared using restriction endonucleases
4. Gene and opened plasmid are merged in a process called ligation, using DNA ligase
5. Plasmid transferred back to bacterium

Question 15

PCR procedure

Answer 15

Polymerase chain reaction.

1. Denaturation. Temperature is increased to separate DNA into single strands
2. Annealing. Temperature is decreased to allow primers to bind to DNA, bracketing the target sequence
3. Extension. Temperature increased slightly and enzyme taq polymerase binds to DNA to add nucleotides

Process is repeated and the amount of DNA increases exponentially

Question 16

Chromatography definition

Answer 16

Technique used to separate mixtures based on the movement of different substances on a piece of paper by capillary action

Question 17

Mobile and stationary phases in paper chromatography

Answer 17

Stationary: paper
Mobile: solvent, usually a mix of propanone and petroleum ether

Question 18

Mobile and stationary phases in thin layer chromatography

Answer 18

Stationary: silica gel, aluminium oxide, or cellulose
Mobile: solvent

Question 19

Retention factor

Answer 19

Ratio of the distance moved by a pigment to the distance moved by the solvent. Constant, value for an unknown substance can be compared to known values for identification