DNA and protein synthesis

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DNA and protein synthesis

Question 1

State the two types of macromolecule from which a ribosome is constructed.

[1]

Describe the role of transfer RNA (tRNA) in the translation step of protein synthesis. Do not include transcription in your answer.

[3]

Table 1 shows the base sequence of part of a template DNA strand from a eukaryotic gene.

Complete Table 1 with the complementary base sequence of the pre-mRNA strand that would be transcribed from this DNA sequence.

Table 1

DNA	T	A	C	G	G	C	T	T	A
pre-mRNA

[1]

In eukaryotic cells, the mature mRNA is typically much shorter than the pre-mRNA from which it was transcribed. Explain why.

[2]

Question 2

Identify the two distinct types of biological macromolecule that associate to form the functional subunits of a eukaryotic ribosome.

[1]

Describe how transfer RNA (tRNA) molecules interact with both mRNA and amino acids during the translation phase of protein synthesis to construct a polypeptide chain.

[3]

Table 1 shows a short segment of the DNA template strand sequence of a specific eukaryotic gene.

Complete Table 1 by writing the complementary nucleotide base sequence of the pre-mRNA transcript produced from this segment.

Table 1

DNA	A	G	T	C	C	A	T	G	C
pre-mRNA

[1]

In eukaryotic cells, the mature mRNA molecule that binds to a ribosome is significantly shorter than the initial pre-mRNA molecule transcribed in the nucleus. Explain the process that causes this difference in length.

[2]

Question 3

Table 1 shows mRNA codons and the amino acids they code for:

1st base	2nd base: U	2nd base: C	2nd base: A	2nd base: G	3rd base
U	Phe	Ser	Tyr	Cys	U
U	Phe	Ser	Tyr	Cys	C
U	Leu	Ser	Stop	Stop	A
U	Leu	Ser	Stop	Trp	G
C	Leu	Pro	His	Arg	U
C	Leu	Pro	His	Arg	C
C	Leu	Pro	Gln	Arg	A
C	Leu	Pro	Gln	Arg	G
A	Ile	Thr	Asn	Ser	U
A	Ile	Thr	Asn	Ser	C
A	Ile	Thr	Lys	Arg	A
A	Met (Start)	Thr	Lys	Arg	G
G	Val	Ala	Asp	Gly	U
G	Val	Ala	Asp	Gly	C
G	Val	Ala	Glu	Gly	A
G	Val	Ala	Glu	Gly	G

A molecular biologist investigated mutations affecting a specific beta-tubulin protein in yeast cells. This polypeptide is normally 445 amino acids long.

The genetic code is described as degenerate. Explain what is meant by this term and use a specific example from Table 1 to support your explanation.

[2]

Calculate the minimum number of bases in the coding region of the mRNA (excluding start and stop codons) required to synthesize this polypeptide.

[1]

Using Table 1, identify which of the following options represents a single-base substitution mutation in the DNA template strand that would cause a change from cysteine (Cys) to tryptophan (Trp):

A: $ACA→ACC\text{ACA} \rightarrow \text{ACC}$
B: $UGU→UGG\text{UGU} \rightarrow \text{UGG}$
C: $ACA→ACG\text{ACA} \rightarrow \text{ACG}$
D: $ACT→ACC\text{ACT} \rightarrow \text{ACC}$

[1]

Question 4

Ribosomes are non-membrane-bound organelles essential for polypeptide synthesis. State the two classes of biological macromolecule that associate to form a ribosome.

[1]

Describe the role of transfer RNA (tRNA) in the translation step of protein synthesis. Do not include transcription in your answer.

[3]

Table 1 shows the base sequence of a section of a template DNA strand from a eukaryotic gene.

Complete Table 1 with the complementary base sequence of the pre-mRNA strand that would be transcribed from this DNA sequence.

Table 1

DNA template strand	A	G	T	C	C	G	T	A	C
pre-mRNA strand

[1]

In eukaryotic cells, the mature mRNA found in the cytoplasm is typically much shorter than the pre-mRNA from which it was transcribed in the nucleus. Explain why.

[2]

DNA and protein synthesis Questions

Practise AQA A Level Biology DNA and protein synthesis with exam-style questions for A Level Biology. 4 questions, matched to the AQA A Level Biology (7402) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.

DNA and protein synthesis

List view

DNA and protein synthesis

Question 1

State the two types of macromolecule from which a ribosome is constructed.

[1]

Describe the role of transfer RNA (tRNA) in the translation step of protein synthesis. Do not include transcription in your answer.

[3]

Table 1 shows the base sequence of part of a template DNA strand from a eukaryotic gene.

Complete Table 1 with the complementary base sequence of the pre-mRNA strand that would be transcribed from this DNA sequence.

Table 1

DNA	T	A	C	G	G	C	T	T	A
pre-mRNA

[1]

In eukaryotic cells, the mature mRNA is typically much shorter than the pre-mRNA from which it was transcribed. Explain why.

[2]

Question 2

Identify the two distinct types of biological macromolecule that associate to form the functional subunits of a eukaryotic ribosome.

[1]

Describe how transfer RNA (tRNA) molecules interact with both mRNA and amino acids during the translation phase of protein synthesis to construct a polypeptide chain.

[3]

Table 1 shows a short segment of the DNA template strand sequence of a specific eukaryotic gene.

Complete Table 1 by writing the complementary nucleotide base sequence of the pre-mRNA transcript produced from this segment.

Table 1

DNA	A	G	T	C	C	A	T	G	C
pre-mRNA

[1]

[2]

Question 3

Table 1 shows mRNA codons and the amino acids they code for:

1st base	2nd base: U	2nd base: C	2nd base: A	2nd base: G	3rd base
U	Phe	Ser	Tyr	Cys	U
U	Phe	Ser	Tyr	Cys	C
U	Leu	Ser	Stop	Stop	A
U	Leu	Ser	Stop	Trp	G
C	Leu	Pro	His	Arg	U
C	Leu	Pro	His	Arg	C
C	Leu	Pro	Gln	Arg	A
C	Leu	Pro	Gln	Arg	G
A	Ile	Thr	Asn	Ser	U
A	Ile	Thr	Asn	Ser	C
A	Ile	Thr	Lys	Arg	A
A	Met (Start)	Thr	Lys	Arg	G
G	Val	Ala	Asp	Gly	U
G	Val	Ala	Asp	Gly	C
G	Val	Ala	Glu	Gly	A
G	Val	Ala	Glu	Gly	G

A molecular biologist investigated mutations affecting a specific beta-tubulin protein in yeast cells. This polypeptide is normally 445 amino acids long.

The genetic code is described as degenerate. Explain what is meant by this term and use a specific example from Table 1 to support your explanation.

[2]

Calculate the minimum number of bases in the coding region of the mRNA (excluding start and stop codons) required to synthesize this polypeptide.

[1]

Using Table 1, identify which of the following options represents a single-base substitution mutation in the DNA template strand that would cause a change from cysteine (Cys) to tryptophan (Trp):

A: $ACA→ACC\text{ACA} \rightarrow \text{ACC}$
B: $UGU→UGG\text{UGU} \rightarrow \text{UGG}$
C: $ACA→ACG\text{ACA} \rightarrow \text{ACG}$
D: $ACT→ACC\text{ACT} \rightarrow \text{ACC}$

[1]

Question 4

Ribosomes are non-membrane-bound organelles essential for polypeptide synthesis. State the two classes of biological macromolecule that associate to form a ribosome.

[1]

Describe the role of transfer RNA (tRNA) in the translation step of protein synthesis. Do not include transcription in your answer.

[3]

Table 1 shows the base sequence of a section of a template DNA strand from a eukaryotic gene.

Complete Table 1 with the complementary base sequence of the pre-mRNA strand that would be transcribed from this DNA sequence.

Table 1

DNA template strand	A	G	T	C	C	G	T	A	C
pre-mRNA strand

[1]

In eukaryotic cells, the mature mRNA found in the cytoplasm is typically much shorter than the pre-mRNA from which it was transcribed in the nucleus. Explain why.

[2]

DNA and protein synthesis Questions