Molecular Genetics

Question 1

Define DNA

Answer 1

The genetic material that organisms inherit from their parents. DNA is used to carry the genetic code which is used to synthesise specific polypeptides

Question 2

How is DNA, gene and chromosome related

Answer 2

Genes are units of inheritance that occupy specific locus on DNA molecule, short sequence of nucleotides that codes for particular polypeptide
A molecule of DNA condenses during cell division to form a compact structure called a chromosome. Each chromosome contains one long DNA molecule, usually carrying several hundred or more genes

Question 3

What do nucleotides consist of

Answer 3

Phosphate group
Deoxyribose sugar
Nitrogenous base
(Deoxyribose sugar connected to nitrogenous base, phosphate group attached to deoxyribose sugar)

Question 4

State the structure of DNA

Answer 4

Phosphate group of one nucleotide joins deoxyribose sugar of next nucleotide to form sugar phosphate backbone of the DNA molecule. Nitrogenous bases pair with each other using complementary base-pairing to form double stranded structure, comprising two polynucleotide strands joined in anti-parallel manner

Question 5

State rules of complementary base pairing

Answer 5

Adenine forms double hydrogen bonds with thymine
Guanine forms triple hydrogen bonds with cytosine

Question 6

Describe DNA replication

Answer 6

DNA replicates, following process of semi-conservative replication. Each polynucleotide strand of original DNA acts as template for synthesis of new complementary polynucleotide strand. Two strands of parent, original double helix are separated by enzymes. With assistance of other enzymes, nucleotides are bound to separated polynucleotide strands following rules of complementary base pairing. Results in formation of 2 double-stranded DNA molecules. Each molecule consisting of half of parent strand and newly synthesised daughter strand.

Question 7

Define gene

Answer 7

A unit of inheritance with specific sequence of nucleotides as part of DNA molecule that contains the information to make a polypeptide. Polypeptide folds into protein in rough endoplasmic reticulum or cytoplasm

Question 8

Use of DNA

Answer 8

DNA is used to carry genetic code, which is used to synthesise specific polypeptides. DNA directs RNA synthesis, and through RNA, DNA controls protein synthesis. RNA is intermediate in protein synthesis. Cells can control gene expression. Genes can be expressed or not expressed. Different cells express different genes

Question 9

Define gene expression

Answer 9

The process in which the gene is accessed by enzyme, first to synthesise RNA then proteins and eventually to affect the phenotype of organism

Question 10

Describe how information on DNA is used to synthesise polypeptides
(translation and transcription)

Answer 10

In nucleus, message in gene is copied into an mRNA, process known as transcription. mRNA travels to cytoplasm and attaches to ribosome. As ribosome moves along mRNA, it synthesises a polypeptide. Synthesis of polypeptide chain from mRNA is translation. When ribosome leaves mRNA, polypeptide is released

Question 11

What base replaces adenine in mRNA

Answer 11

Uracil

Question 12

What are codons

Answer 12

Triplets of nucleotide bases, smallest units of uniform length that can code for all the amino acids

Question 13

What are similarities between DNA and RNA

Answer 13

Both have sugar-phosphate backbone
Both contain three common nitrogenous bases: adenine guanine and cytosine

Question 14

What are differences between mRNA and DNA

Answer 14

no. of strands, structure, monomers, pentose sugar, nitrogenous base, ratio of bases, bonds between bases

Question 15

Define mutation

Answer 15

A spontaneous or induced change in DNA sequence of genes, or change in number or structure of chromosomes.

Question 16

Describe mutagens

Answer 16

Mutagens are physical or chemical agents that can cause alterations to DNA, resulting in changes in the sequence of DNA. Rate of spontaneous mutation is greatly increased with presence of mutagens. Mutagens include high energy radiation (gamma rays) or chemical mutagens (tar)

Question 17

Describe genetic engineering

Answer 17

A technique used to transfer genes from one organism to another. Individual genes may be taken from cells of one organism and inserted into cells of another organism of same or different species using a vector. Vectors carry the genes to intended cells.

Question 18

Why is bacteria used to produce insulin

Answer 18

It is relatively easy to transfer genes into bacterium. Bacteria contains plasmids, circular strands of DNA that replicate separately from bacterial DNA. A plasmid only has small number of genes, which may be useful to bacteria under certain conditions is not necessary for its survival. Insulin gene can be inserted easily into plasmid. Bacteria takes short time to replicate. When bacterium replicates, plasmid also replicated, single cell reproduces through repeated cell divisions to form clones of itself, bacteria transcribe and translate insulin gene in plasmid to produce large quantities of insulin

Question 19

Describe obtaining of DNA segment for insertion

Answer 19

Obtain DNA segment in human chromosome containing insulin gene. Cut out gene using restriction enzyme. Enzyme cuts two ends of gene to produce “sticky ends”. Each “sticky end” is single strand sequence of DNA bases. Bases pair with complementary bases to form a double strand

Question 20

Describe replication of obtained insulin gene in bacterium

Answer 20

Obtain plasmid from bacterium. Cut open plasmid with same restriction enzyme, produces “sticky ends” complementary to ends of insulin gene. Mix the plasmid with DNA fragment containing insulin gene. DNA fragment containing human insulin gene will bind to plasmid by complementary base pairing between “sticky ends”, add DNA ligase to seal DNA fragment to plasmid, plasmid is recombinant plasmid. Mix plasmid with E. coli bacterium, apply temporary heat or electric shock, opens cell membrane for plasmid to enter. Transgenic bacterium with insulin gene will be isolated and grown on large scale under optimum conditions. Transgenic bacterium synthesises insulin together with other proteins from plasmid. Insulin must be extracted and purified before use.

Question 21

Describe some benefits of genetic engineering

Answer 21

Low-cost production of medicines
Production of crops that grow in extreme conditions
Development of pesticide and pest resistant crops
Development of food designed to meet specific nutritional goals

Question 22

What are some social issues behind genetic engineering

Answer 22

Some biotechnology companies engineered crops such that plants produce seeds that cannot germinate. Technology such as gene therapy may lead to class distinctions. People with sufficient financial means can benefit from technology. Some people feels it is morally wrong to exploit animals for research.