Question 1

What is the difference between transcription and translation?

Accepted Answer

Transcription is the process of making an mRNA copy from a DNA template in the nucleus. It involves RNA polymerase binding to a promoter region and synthesising a complementary mRNA strand. Translation is the process of using the mRNA sequence to assemble a polypeptide chain at a ribosome in the cytoplasm. During translation, tRNA molecules bring specific amino acids to the ribosome, and the sequence of codons on mRNA determines the order of amino acids.

Question 2

How does a mutation cause cystic fibrosis?

Accepted Answer

Cystic fibrosis is most commonly caused by a deletion of three nucleotides in the CFTR gene, resulting in the loss of a phenylalanine amino acid at position 508 (ΔF508). This mutation causes the CFTR protein to misfold and be degraded before it reaches the cell membrane. Without functional CFTR chloride channels, chloride ions cannot be transported out of cells, leading to thick, sticky mucus in the lungs, pancreas, and other organs.

Question 3

What is gene therapy and how does it work?

Accepted Answer

Gene therapy involves introducing a functional copy of a gene into a patient's cells to treat a genetic disorder. This is often done using a viral vector, such as a modified adenovirus, which carries the therapeutic gene into target cells. For example, in cystic fibrosis, a functional CFTR gene can be delivered to lung epithelial cells via an aerosol spray. However, gene therapy is still experimental and faces challenges like immune responses and short-term expression.

Question 4

What is the difference between somatic and germline gene therapy?

Accepted Answer

Somatic gene therapy targets non-reproductive cells (e.g., lung, liver cells) and affects only the individual patient. It does not affect future generations. Germline gene therapy targets eggs, sperm, or embryos, and the genetic change is heritable. Germline therapy is currently banned in many countries due to ethical concerns about 'designer babies' and unforeseen long-term consequences.

Question 5

How do mutations affect protein structure?

Accepted Answer

Mutations can change the amino acid sequence of a protein. A substitution mutation may replace one amino acid with another (e.g., in sickle cell anaemia, glutamic acid is replaced by valine), which can alter the protein's shape and function. Insertions or deletions cause frameshift mutations, shifting the reading frame and changing all subsequent amino acids, often leading to a non-functional protein. Silent mutations do not change the amino acid due to the degeneracy of the genetic code.

Question 6

What are the ethical issues surrounding genetic screening?

Accepted Answer

Genetic screening can identify individuals at risk of genetic disorders, but it raises ethical concerns such as privacy of genetic information, potential discrimination by employers or insurers, and psychological impact of knowing one's risk. There is also the risk of eugenics if screening leads to selective abortion or pressure to terminate pregnancies. A balanced approach involves informed consent, counselling, and regulations to prevent misuse.

Topic 2: Genes and Health

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