Chapter 14 Molecular Genetics

Question 1

Define the term gene [2] (2012/A1a)

Answer 1

A gene is a unit of inheritance which is part of the DNA and is made up of a sequence of nucleotides [1] that code for the production of a specific polypeptide [1]

Question 2

Describe what is meant by a transgenic organism [3] (2013/B9a)

Answer 2

A transgenic organism is an organism with genetic characteristics that have been altered/modified [1] by the artificial insertion [1] of a modified gene or a gene from another organism [1] using techniques of genetic engineering.

Question 3

Suggest three reasons for the development of transgenic organisms. [3] (2013/B9b)

Answer 3

• To allow for large-scale/reduced cost of production of useful products such as insulin using genetic engineering.
• To enhance agricultural efficiency, e.g. to produce pesticide-resistant crop plants.
• To develop food to meet specific nutritional goals. Thus, improving the nutritional value of food
• To study gene function through mutation of the gene in organisms such as mice.

Question 4

Describe the structure of DNA. [6] (2017/B10 E)

Answer 4

Describe structure of DNA
- Double helix structure comprising 2 antiparallel polynucleotide 1strands.
- Basic building block is DNA nucleotide made of a deoxyribose molecule, phosphate group and a nitrogenous base
- deoxyribose and phosphate of the nucleotides join together to form the backbone of the strands of DNA.
- The four bases found in DNA are adenine, guanine, cytosine and thymine.
- Adenine is complementary to thymine while guanine is complementary to cytosine.
- Hydrogen bonds are present between the complementary base pairs hold the 2 strands together.
- Phosphodiester bonds hold nucleotides on the same strand together

Question 5

Explain how a transgenic organism can be produced. [4] (2017/B10 E)

Answer 5

1. Plasmid is obtained from a bacterium. Isolate a foreign gene from another organism and cut it with a restriction enzyme, which produces 2 sticky ends, [1]
2. and cut the plasmid of the bacterium with the same restriction enzyme to produce complementary sticky ends. [1]
3. Mix the plasmid with the foreign gene and seal using DNA ligase. [1]
4. Mix the recombinant plasmid with bacterium and apply temporary heat or electric shock which opens up the pores in the cell membrane of the bacterium for plasmid to enter, forming a transgenic bacterium.[1]