Chapter 20 - Molecular Genetics

Question 1

What are nucleotides made up of?(3)

Answer 1

1) deoxyribose (sugar) molecules
2) phosphate group (p)
3) nitrogen-containing base

Question 2

What are the complementary base pairings?

Answer 2

Adenine bonds with thymine and guanine bonds with cytosine.

Question 3

Define gene.

Answer 3

A gene is a unit of inheritance. It is a small segment of DNA that is made of a specific sequence of nucleotides. Each gene codes for a particular polypeptide that determines a particular characteristic in a organism.

Question 4

What determines the polypeptides formed in a DNA?

Answer 4

Nucleotide sequence in the gene

Question 5

What is the formula for the different combinations of nucleotides? (N)

Answer 5

4^n

Question 6

What is a codon?

Answer 6

Three nucleotides forming a triplet code that codes for one amino acid for each codon. E.g. ATC, TAC

Question 7

Define gene mutation.

Answer 7

A change in the nucleotide sequence of a gene, which may or may not lead to a change in the protein product or phenotype.

Question 8

Name 2 examples of gene mutation and briefly describe.

Answer 8

1) albinism - absence or defect in enzyme that produces pigment
2) sickle-cell anaemia - red blood cell sickle-shaped

Question 9

Define DNA.

Answer 9

It is made up of 2 strands of polynucleotides twisted around each other to form a double helix. The two strands are held together by hydrogen bonding. It is made up of deoxyribose sugar, phosphate group and nitrogenous base. DNA carries genetic information that determines the characteristics of an organism.

Question 10

How are proteins made?

Answer 10

1) the DNA unzips and unwinds, then transcribed into a messenger RNA (mRNA) during transcription where Adenine pairs with Uracil in the nucleus.
2) the mRNA attaches itself to a ribosome in the cytoplasm. The transfer RNA (tRNA) translates mRNA into a sequence of amino acids joined together to form a polypeptide while the ribosome moves along the mRNA.
3) amino acids are continually attached until the ribosome reaches the stop codon, and it will leave.

Question 10

What are 5 differences of DNA and RNA?

Answer 10

1) DNA’s sugar unit is deoxyribose while RNA’s is ribose.
2) nitrogen-containing bases are adenine, thymine, guanine and cytosine for DNA - it’s the same for RNA except uracil replaces thymine
3) ratio of A:T and G:C is 1:1 in DNA while there is no fixed ratio in RNA.
4) DNA is a large insoluble molecule while RNA is small and soluble.
5) DNA is a permanent molecule while RNA is temporary and only made when needed.

Question 11

Define genetic engineering.

Answer 11

The manipulation of an organism’s genetic material.

Question 12

Explain the production of human insulin gene using bacteria.

Answer 12

1) isolate insulin gene from Human DNA and cut it with a restriction enzyme, which produces 2 sticky ends.
2) cut the plasmid of the bacteria with the same restriction enzyme.
3) mix the plasmid with the DNA
4) insert the insulin gene into plasmid DNA using DNA ligase.
5) mix plasmid with bacteria and apply temporary heat or electric shock which opens up the pores in the cell membrane for plasmid to enter.
6) the transgenic bacterium will then be isolated and grown in fermenters for mass production.

Question 13

What are other applications of genetic engineering? (3)

Answer 13

1) creation of transgenic plants that are resistant to herbicides.
2) creation of transgenic plants that are pest-resistant.
3) healthy genes can be transferred from one person to the cells of another person with defective genes.

Question 14

What are the 4 advantages of genetic engineering?

Answer 14

1) low cost production of medicine makes drugs like human insulin more affordable.
2) development of pesticides resistant crops reduces the use of costly pesticides that might damage the environment.
3) development of food that meets nutritional goals improves nutritional quality.
4) production of crops that grow in extreme conditions allows farmer to grow crops in conditions that are not favorable to cultivate most crops.

Question 15

Name 4 differences of selective breeding and genetic engineering.

Answer 15

1) organisms involved in selective breeding (SB) must be closely related or of same species, while in genetic engineering (GE), genes from an organism can be inserted into non-related species.
2) during SB, there is a possibility that defective genes will be transmitted to the offspring, but in GE, selection of genes before transfer eliminates the risk of a defective gene.
3) SB is slow and involves several generations, while GE is a process that uses individual cells that reproduces quickly in labs.
4) SB is less efficient as organisms require more food and grow more slowly, while GE is more efficient as transgenic organisms grow faster and require less food.

Question 16

What are the 5 disadvantages of genetic engineering?

Answer 16

1) genetically-modified crops that produce insect toxin may result in death of insects and loss in biodiversity. (Environmental)
2) poorer farmers may not be able to benefit if prices of seeds of modified crops are not regulated. (economic)
3) genes that code for antibiotic resistance may accidental incorporate into bacteria that causes diseases, making antibiotics ineffective in treating diseases (human)
4) genetic engineering may lead to class distinctions and some religions do not approve of it. They may boycott genetically modified products. (Social&ethical)
5) insects that feed on corns may develop resistance to toxin in corns, subsequently developing resistance to pesticides that behave in the same way as corn plant toxin

Question 17

What are transgenic organisms?

Answer 17

They are organisms that have been genetically engineered by insertion of a modified gene or a gene from another organism.

Question 18

State the significant of the order of bases in a DNA molecule.

Answer 18

Different order of bases will result in different genes. Each specific order of bases code for a particular polypeptide which determines a specific characteristic.