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Gene expression and mutation
8 MDCAT Biology questions with answers and explanations.
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Transcription is the process by which:
- 1 mRNA is made from a DNA template
- 2 Protein is made from mRNA
- 3 DNA is copied
- 4 tRNA is destroyed
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Correct answer: mRNA is made from a DNA template
During transcription, RNA polymerase builds an mRNA copy of a gene.
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A codon is a sequence of how many nucleotides on mRNA?
- 1 Two
- 2 Three
- 3 Four
- 4 Six
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Correct answer: Three
Each codon has three nucleotides and codes for one amino acid or a stop signal.
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Which codon is the usual start codon, and which amino acid does it code for?
- 1 UAA, stop
- 2 AUG, methionine
- 3 UGA, tryptophan
- 4 GGG, glycine
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Correct answer: AUG, methionine
Translation normally begins at AUG, which codes for methionine.
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How many different codons are possible?
- 1 20
- 2 61
- 3 64
- 4 4
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Correct answer: 64
Four bases in groups of three give 4 x 4 x 4 = 64 codons.
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Translation takes place at the:
- 1 Nucleolus
- 2 Ribosome
- 3 Lysosome
- 4 Golgi apparatus
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Correct answer: Ribosome
Ribosomes read the mRNA and join amino acids in the order it specifies.
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A point mutation that changes a codon but not the amino acid it codes for is called:
- 1 Missense
- 2 Nonsense
- 3 Silent
- 4 Frameshift
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Correct answer: Silent
The genetic code is redundant, so some changes do not alter the protein. These are silent mutations.
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Sickle cell anaemia is caused by a change in beta globin in which glutamic acid is replaced by:
- 1 Valine
- 2 Glycine
- 3 Alanine
- 4 Lysine
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Correct answer: Valine
A single base change causes glutamic acid to be replaced by valine in haemoglobin, which makes the red cells sickle-shaped.
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Transfer RNA (tRNA) carries:
- 1 DNA to the ribosome
- 2 An amino acid and has an anticodon
- 3 Ribosomes to the nucleus
- 4 A start codon only
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Correct answer: An amino acid and has an anticodon
Each tRNA carries one amino acid and has an anticodon that pairs with a codon on mRNA.