Session 5

Question 0

Describe the process and role of translation

Answer 0

Making a polypeptide
Genetic code is triplet (degenerate)

Initiation: AUG codon recognition, methionyl tRNA, ribosome
Elongation: N–>C chain growth, aminoacyl tRNA
Termination: STOP codon recognition (releasing factor, H2O)

Peptidyl transferase makes peptide bonds

Question 1

Describe the process and role of transcription

Answer 1

Occurs in nucleus, DNA –> mRNA
Initiation - promoter recognition (TATA/Pribnow box, upstream), transcription initiation factors, RNA polymerase
Elongation - 5’–>3’
Termination - sequence dependent

Pre-mRNA –> mature mRNA involves capping (methionyl cap), tailing (poly-A tail), splicing (removes introns) –> open reading frame

Question 2

Define the term ‘gene’

Answer 2

A unit of hereditary; a transcription unit
A length of DNA on a chromosome that contains the code for a protein as well as sequences necessary for its expression (such as promotor and terminator sequences, introns)

Question 3

List and summarise the major reactions involved in the process of RNA maturation in eukaryotes and explain their importance in gene expression

Answer 3

Pre-mRNA –> mature mRNA
Methionyl cap, splicing introns out, add a polyA tail
Gene expressed in open reading frame (ORF), includes untranslated region (UTR)

Question 4

Explain the nature of the triplet code and be able to apply the genetic code

Answer 4

Triplet code is degenerate - more than one triplet codes for an amino acid

Question 5

Comprehend the implications of the degeneracy of the genetic code

Answer 5

Substitution can change the primary sequence which affects tertiary structure
A mutation affecting the stop codon can cause the protein to be much longer and malfunctional

Question 6

Contrast the different types of RNA molecule i.e. mRNA, rRNA and tRNA

Answer 6

mRNA (messenger RNA) - 2%, 100000s kinds, few copies of each
rRNA (ribosomal RNA) - 80%, few kinds, many copies of each
tRNA (transfer RNA) - 15%, 100 kinds, very many copies of each

Question 7

Compare and contrast gene expression in mammalian and bacterial cells and explain how the differences can be exploited clinically

Answer 7

Bacteria have simple promotors and ribosomes, different transcription and translation factors, short lived mRNA, single RNA polymerase, coupling transcription-translation, no post transcriptional processing
Prokaryote ribosome - 30s + 50s = 70s
Eukaryote ribosome - 40s + 60s = 80s

Question 8

Predict the effect of various mutations in a gene

Answer 8

Depends on the amount of difference in the protein

Premature or delayed stop codons will cause truncated/elongated proteins that may not function correctly or at all

Question 9

Explain how mutations outside the coding region can affect gene expression

Answer 9

Mutations to promotor regions can either constitutively activate or deactivate it