Transcription + Translation Exam Questions

Question 1

Describe two differences between the structure of a tRNA molecule and
the structure of an mRNA molecule.

Answer 1

tRNA is a clover leaf shape, mRNA is linear
tRNA has an amino acid binding site, mRNA does not

Question 2

In a eukaryotic cell, the structure of the mRNA used in translation is
different from the structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA
molecules.

Answer 2

mRNA has fewer nucleotides
pre-mRNA has introns and exons
because of splicing

Question 3

Describe how one amino acid is added to a polypeptide that is being
formed at a ribosome during translation.

Answer 3

tRNA brings specific amino acid to ribosome
anticodon on tRNA binds/complementary to codon on mRNA
amino acids join together via condensation reaction forming peptide bonds which form a polypeptide by ATP

Question 4

Describe how mRNA is produced from an exposed template strand of DNA
Do not include DNA helicase or splicing in your answer.

Answer 4

free RNA nucleotides form complementary base pairs
phosphodiester bonds formed
action / catalysed by RNA polymerase

Question 5

describe how mRNA is formed by transcription in eukaryotes.

Answer 5

hydrogen bonds break between DNA bases
only one DNA strand acts as a template
free RNA nucleotides align by complementary base pairing
In RNA, Uracil base pairs with adenine on DNA
RNA polymerase joins adjacent RNA nucleotides together via condensation reaction by phosphodiester bonds
pre-mRNA is then spliced to form mRNA

Question 6

Describe how a polypeptide is formed by translation of mRNA.

Answer 6

(mRNA attaches) to ribosomes
(tRNA) anticodons (bind to) complementary (mRNA) codons;
tRNA brings a specific amino acid;
Amino acids join by peptide bonds;
(Amino acids join together) with the use of ATP;
tRNA released (after amino acid joined to polypeptide);
The ribosome moves along the mRNA to form the polypeptide;

Question 7

What is the proteome of a cell?

Answer 7

The proteome is the full) range of / number of different proteins that a cell
is able to produce (at a given time);

Question 8

Starting with mRNA in the cytoplasm, describe how translation leads to the
production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer.

Answer 8

mRNA associates with a ribosome / ribosome attaches to mRNA;
Idea of association is required
Ribosome moves to / finds the start codon / AUG;
tRNA brings / carries (appropriate / specific) amino acid;
Must be explicitly stated and not inferred.
Anticodon (on tRNA complementary) to codon (on mRNA);
Ribosome moves along to next codon;
Process repeated and) amino acids join by peptide bonds /
condensation reaction (to form polypeptide);

Question 9

The genetic code is described as degenerate.
Negatively charged
What is meant by this? Use an example from Table 1 to illustrate your
answer.

Answer 9

More than one codon codes for a single amino acid;

Question 10

A scientist investigated changes in the amino acid sequence of a human enzyme
resulting from mutations. All these amino acid changes result from single base
substitution mutations.
This enzyme is a polypeptide 465 amino acids long.
Table 2 shows the result of three of the base substitutions.

What is the minimum number of bases in the gene coding for this
polypeptide?

Answer 10

1395

Question 11

describe how mRNA is produced in a plant cell.
TRANSCRIPTION
TRANSCRIPTIONNNNNNNNNNNNNNNNNN

Answer 11

H bonds broken between (complementary) (DNA) bases;
(Only) one of the strands/template strand is used (to make
mRNA/is transcribed);
(Complementary) base pairing so A ⟶ U, T ⟶ A, C ⟶ G, G
⟶ C;
RNA polymerase joins free adjacent nucleotides together via condensation reaction by phosphodiester bonds
pre-mRNA is spliced to form mRNA
Splicing / introns removed to form mRNA

Question 12

Describe the role of a ribosome in the production of a polypeptide. Do not
include transcription in your answer.

Answer 12

mRNA binds to ribosome;
RIBOSOME moves along to start codon
anticodon on tRNA complementary to codon on mRNA
amino acids join together via condensation reaction by ATP to form peptide bonds which form a polypeptide
ribosome then moves to the next codon
and the processs is repeated

Question 13

In a eukaryotic cell, the base sequence of the mRNA might be different
from the sequence of the pre-mRNA.
Explain why.

Answer 13

introns (in pre-mRNA);
Removal of sections of (pre-mRNA) / splicing;