Molecular genetics

Question 1

relationship between DNA, genes & chromosomes

Answer 1

• DNA: a molecules that carries genetic info that is important for cellular activities (cell divison & differentiation)
• gene: a unit of inheritance, born on a particular locus of a chromosome, a small segment of DNA that code for the production of polypeptides/protein or controls a particular chracteristic of an organism
• chromosome: rod-like structure visible in nucelus during cell division, made up of the molecule DNA

Question 2

structure of DNA

Answer 2

• 2 polynucleotide strands: twist around each other to form a double helix, anti-parallel and run in opp directions
• Each nucleotide: ✓ a phosphate group, a deoxyribose sugar, and a nitrogenous base
• Sugar-phosphate backbone: ✓ phosphate groups and deoxyribose sugars
• 4 nitrogenous bases: adenine, cytosine, guanine and thymine - adenine is complementary to thymine, cytosine is complementary to guanine
• Complementary bases pair with each other and form hydrogen bonds (hold the two strands of DNA together)

Question 3

rule of complementary base pairing

Answer 3

• adenine always bonds with thymine - adenine is complementary to thymine
• cytosine is complementary to guanine
• complementary bases pair with each other and form hydrogen bonds (hold the two strands of DNA together)

Question 4

define genetic engineering

Answer 4

~ is a technique used to transfer genes from one organism to another. Individual genes may be cut off from the cells of the same or different species. The transferred gene can express itself in the recipient organism

Question 5

explain how a gene that controls the production of human insulin can be inserted into bacterial DNA
to produce human insulin in medical biotechnology

Answer 5

1. Cut the human insulin gene out of the chromosome using a restriction enzyme (cuts the restriction site at the two ends of the gene to produce ‘sticky ends’)
2. Cut the plasmid from bacterium with the same restriction enzyme. This produces “sticky ends’ complementary to the ends of the insulin gene.
3. Mix the plasmid with the DNA fragment containing the human insulin gene. The human insulin gene will bind to the plasmid by complementary base pairing b/w their ‘sticky ends’.
4. Add the enzyme DNA ligase to seal the human insulin gene to the plasmid. This plasmid containing DNA from two different organisms is called recombinant plasmid.
5. Mix the recombinant plasmid with (E. coli) bacterium. Apply temporary heat or electric shock. This opens up pores in the cell surface membrane of the bacterium for the plasmid to enter.
6. This transgenic bacterium will use the new gene to make insulin in ferementers under optimal conditions for growth & development. The insulin protein has to be extracted and purified before it can be used.

Question 6

social and ethical implications of genetic engineering, with reference to a named example

Answer 6

• some feel that it is morally wrong to exploit animal for medical research especially when the animals are designed to suffer eg, the oncomouse (transgenic mouse into which a gene that causes cancer has been introduced) develops cancer for use in testing potential cancer drugs
• Some may deliberately create new combi of genes which they may use in chemical or biological warfare.
• objections to consuming animal genes in plants or vice versa eg, vegetarians will object to use of insulin obtained from animals/vegetarians may object to transfer of animal genes into crop plants
• resulting deaths of useful insects like honey bees & butterflies, that feed on nectar of GM crop plants may result in a loss of biodiversity