Syllabus Edition

First teaching 2023

First exams 2025

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Protein Synthesis (CIE AS Biology)

Exam Questions

2 hours40 questions
1a
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3 marks

The process of transcription is illustrated in Fig. 1.

6-2-fig-2-1Fig. 1

Identify molecule X in Fig. 1 and describe its role during transcription.

1b
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2 marks

From the image in Fig. 1

(i)
Identify strand Y.

[1]

(ii)
State the significance of strand Y in the process of transcription.
[1]
1c
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2 marks

After the process of transcription is completed, molecule Z in Fig. 1 must undergo a few changes before it can move to the cytoplasm.

Describe these changes that are made to molecule Z before it leaves the nucleus.

1d
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2 marks

The genetic code is universal across most forms of life.

Explain the importance of this statement.

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2a
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1 mark

Identify the mRNA sequence that is coded for by the following strand of DNA.

Non-template strand: A T G G G T T C A
Template strand: T A C C C A A G T

2b
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4 marks

Replication and transcription both involve DNA.

Complete Table 1 by using a tick (✓) to indicate which features apply to each of the processes. Use a cross (X) for features that do not apply.

The first row has been completed for you.

Table 1

Feature Replication Transcription
A double-stranded molecule is produced ✓ X
Hydrogen bonds are broken    
Only one strand of DNA acts as a template    
Phosphodiester bonds are formed    
RNA polymerase is used    

2c
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2 marks

Fig. 1 shows the exposed bases (anticodons) of two tRNA molecules involved in the synthesis of a protein.

U G C   A A C
     

Fig. 1

Identify the codon sequence of bases found along the corresponding section of the mRNA strand by completing the boxes.

2d
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2 marks

The structure of an mRNA molecule differs from the structure of a tRNA molecule.

Give two differences between these molecules.

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3a
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1 mark

Gene mutations occur continuously and may affect the polypeptide that the gene codes for.

Define the term gene mutation.

3b
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3 marks

Fig. 1 shows the DNA base sequence of part of a gene, as well as the same part of the gene after a mutation occurred.

Original gene: T A T A G T C T T
Mutated gene: T A T A G T C C T T

Fig. 1

(i)

Identify the type of mutation that occurred in Fig. 1.

[1]

(ii)

Describe the possible effect this mutation may have on the polypeptide.

[2]

3c
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2 marks

Other than the mutation identified at (b)(i), state two types of mutations.

3d
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2 marks

In some cases a mutation may have no effect on the polypeptide at all.

Describe a characteristic of the genetic code that makes this possible.

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4a
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3 marks

Complete the table to state the correct order of events during protein synthesis. 

Stage of protein synthesis Order
Removal of introns  
Synthesis of pre-mRNA  
Movement of mRNA to the ribosome  
Synthesis of peptide bonds  
Formation of hydrogen bonds between the codons and anticodons  
4b
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3 marks

A strand of pre-mRNA has 3000 nucleotides.

1770 of these are introns.

Calculate the number of length of amino acids in the resulting polypeptide. 

4c
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3 marks

Post-transcriptional modification converts pre-mRNA to mRNA in preparation for translation. 

Sometimes errors can occur during this process that leads to some bases not being removed from the mRNA. 

Describe how this would affect the protein created from this mRNA. 

4d
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3 marks

Splicing defects can be caused by gene mutations. 

State three types of gene mutations. 

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5a
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3 marks

Describe the structure of a tRNA molecule.

5b
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2 marks

Explain how tRNA is able to bind to an mRNA molecule during translation. 

5c
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2 marks

During translation, four mRNA codons play important roles in the creation of the polypeptide. 

These are:

  • AUG, which codes for the amino acid methionine
  • UAA, UAG, and UGA, which do not code for any amino acids

Explain the roles of each of these codons in the creation of the polypeptide. 

5d
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2 marks

A polypeptide is 52 amino acids in length. 

Calculate the minimum length of mRNA that would be required to code for this polypeptide. 

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1a4 marks

Fig.1 is a diagram showing a stage in protein synthesis.

6-2-fig-3-1
Fig. 1

(i)
Identify the stage of protein synthesis that is shown in Fig. 1.
[1]
(ii)
Identify A, B and C in Fig. 1.
[3]
1b3 marks

Outline the importance of B in the stage of protein synthesis illustrated in Fig.1.

1c
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2 marks

If molecule C consisted of 380 amino acids, calculate the number of bases in the sequence on the DNA molecule that would code for this molecule.  Show your working.

1d1 mark

If the base sequence on molecule B in Fig.1 was CAU, state the corresponding base sequence to which it would attach on molecule A.

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2a4 marks

Describe the role of the ribosome in translation.

2b3 marks

Fig. 1 shows the base sequence of a gene that codes for a short polypeptide, the RNA codons and the primary structure of this polypeptide.

6-2-fig-4-1Fig.1

(i)
Complete Fig.1 to show the missing DNA triplet and the RNA codons.
[2]
(ii)
State the full name of the type of RNA shown in Fig.1.
[1]
2c2 marks

Describe the role of DNA as indicated in Fig.1.

2d2 marks

Fig. 2 illustrates some changes that are made to the RNA that is produced during transcription.

6-2-fig-4-2
Fig. 2

Contrast the main differences between R and S in Fig.2.

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3a1 mark

Fig.1 is a diagram of a section of mRNA showing the sequence of five of the codons.

The triplets of bases in a DNA molecule that codes for some of the amino acids are listed in Table 1.

6-2-fig-5-1
Fig.1

Table 1

Amino acid Abbreviation DNA triplets on the coding polynucleotide
Aspartic acid Asp CTA, CTG
Glycine Gly CCA, CCG, CCT, CCC
Leucine Leu AAC, AAT, GAA, GAC, GAG, GAT
Proline Pro GGA, GGC, GGG, GGT
Threonine Thr TGA, TGC, TGG, TGT
STOP STOP ATT, ATC, ACT

Identify the amino acid sequence on this section of the mRNA molecule, using the information in Fig.1 and Table 1.

3b3 marks

The five codons in Fig.1 are near the start of the sequence coding for a polypeptide.

Explain the consequence of a mutation which deletes one of the bases from codon 3.

3c2 marks

If the guanine (G) in codon 4 changed to adenine (A), describe and explain the effect this would have on the amino acid sequence of this section of mRNA shown in Fig.1.

3d2 marks

Explain why substitution mutations are less likely to have a dramatic effect on polypeptides than frameshift mutations.

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4a
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3 marks

The DNA in the nucleus is known as nuclear DNA.

In the cells of the grasshopper, Chorthippus brunneus, 20% of the nucleotides in nuclear DNA contain thymine.

Calculate the percentage of nucleotides in the nuclear DNA of C. brunneus that contain guanine and explain your answer in terms of the structure of DNA.

4b
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1 mark

State another location, other than the nucleus, where DNA occurs in cells of C. brunneus.

4c
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5 marks

Fig. 1 is a diagram of a molecule of tRNA.

The region labelled R shows detail of part of the tRNA molecule.

fig6-1-qp-mayjune-2019-9700-21

Fig. 1

(i)

Complete Fig.1 by writing the sequence of bases in the region labelled R.

[1]

(ii)

State the name of region Q and explain the role of region Q in translation.

[3]

(iii)

State the function of region P.

[1]

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5a
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1 mark

State the number of types of amino acid carrying tRNA molecules.  

5b
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1 mark

Fig. 1 shows a section of a polypeptide synthesised during translation. cie-ial-6-2-m-5b

Fig. 1

Complete the diagram to show the missing section in the area shaded grey. 

5c
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6 marks

Fig.1 shows the amino acids alanine and serine. 

Describe the sequence of events that lead to the correct amino acids being joined to the polypeptide strand. 

5d
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2 marks

When the mRNA is read by the ribosome, it is read in a 5' to 3' direction. 

Explain what is meant by mRNA having a 5' and 3' end. 

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1a
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1 mark

Proteins are only synthesised when the genes that code for them are switched on.

Fig. 1 shows two processes, R and S, that occur when a gene is switched on.

6-2-fig-1-1
Fig. 1

Identify processes R and S.

1b
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2 marks

DNA nucleotides form a triplet code, with some of the triplets of bases coding for start and stop signals.

Explain the importance of these signals.

1c
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3 marks

Most mRNA molecules are broken down in the cytoplasm within a few hours after leaving the nucleus.

Suggest the significance of mRNA being easily broken down.

1d
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6 marks

Contrast the differences between DNA replication and DNA transcription.

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2a
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1 mark

The sequence below shows the DNA bases coding for seven amino acids in the enzyme papain. Note that the sequence shown is from the non-template strand.

C  A  A  T  T  T  C  A  A  A  G  T  T  G  C  T  T  T  T  T  G

Fig. 1 shows the genetic code and the amino acids coded for.

mrna-codons-and-amino-acids-table

Fig. 1

Use the information in Fig. 1 to identify the sequence of amino acids in this part of the enzyme.

2b
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2 marks

Table 1 below shows some mRNA codons and the amino acids for which they code.

Table 1

Codon Amino Acid
ACG Threonine
UUA Leucine
CCA Proline
GUA Valine
GCU Alanine
AAU Asparagine

(i)

Identify the DNA non-template strand sequence for leucine.

[1]

(ii)

Identify the amino acid carried by the tRNA with the anticodon CAU.

[1]

2c
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3 marks

Ricin is a protein produced by castor beans. In animal cells, ricin acts as an enzyme. This enzyme removes the adenine molecule from one of the nucleotides in the RNA that makes up the structure of ribosomes. As a result, the ribosome changes shape. Ricin causes the death of cells and is highly toxic to many animals.

Suggest how the effect of ricin on ribosomes could cause the death of cells.

2d
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2 marks

Cycloheximide is a fungicide produced by the bacterium Streptomyces griseus, which binds to specific sites on the eukaryotic ribosomes. This is shown in Fig. 2 below.

mF4_MkPf_2-2

Fig. 2

Explain how cycloheximide stops protein synthesis.

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3a
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3 marks

Explain the role of hydrogen bonds in the process of transcription.

3b
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2 marks

mRNA is a single-stranded molecule involved with the process of protein synthesis.

Explain the importance of mRNA being a single-stranded molecule.

3c
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2 marks

The genome refers to the complete set of genes in a cell while the proteome is the full range of proteins that a cell can produce.

Suggest why the proteome of different cells in an organism may vary despite having the same genome.

3d
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4 marks

Hereditary transthyretin (hATTR) amyloidosis is an inherited condition that causes a blood protein called transthyretin to form clumps in the cardiovascular system, digestive system and around nerve fibres. Drugs designed to bind to the mRNA molecules are used as a form of treatment for this condition.

Suggest why these drugs could be used as a treatment for hereditary transthyretin (hATTR) amyloidosis.

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4a
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3 marks

One mechanism for regulating gene expression in cells uses an enzyme, called an RNase, to break down mRNA as it travels from the nucleus to the ribosome. 

Explain how this would be an effective way to regulate gene expression. 

4b
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4 marks

The RNase enzymes involved in this process must be able to target specific sequences of mRNA. 

The enzymes can achieve this by binding to single stranded RNA. 

i)
Explain the importance of the RNase enzymes being targeted to specific mRNA. 
[2]
ii)
Explain how binding to single stranded RNA would allow the RNase to target the correct mRNA. 
[2]
4c
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4 marks

mRNA can also be used to produce vaccines against certain diseases, such as for Covid-19. 

mRNA vaccines involve injecting mRNA stands that code for viral proteins into the blood, which are then taken in by human immune cells and expressed. 

Explain what happens in the target cell after it takes in the mRNA. 

4d
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1 mark

mRNA vaccines are a relatively recent scientific discovery and have been praised by the scientific community for many reasons. 

One such reason is that the risk of mutation to human DNA is very low. 

Suggest one reason why mRNA vaccines pose a very low risk to the structure of human DNA. 

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5a
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3 marks

Tay-Sachs disease is caused by a mutation to a gene called HEXA on chromosome 15. The HEXA gene codes for a lysosomal enzyme that breaks down toxins in the brain and spinal cord. The mutation causes this enzyme to be non-functional, resulting in a build of up toxins in the brain and spinal cord, which over time destroys the nerve cells in these areas. This disease is usually fatal in babies and young children. 

There are more than 100 different mutations that can lead to this disease. 

A very common form of this mutation is caused by a DNA change in the 11th exon out of 14 in the HEXA gene. 

The template strand of the mutated DNA is as follows:

Non Tay-Sachs sufferer AGG ATG CCG GGA CTG
Tay-Sachs sufferer AGA TAG GAT GCC GGG ACT

Describe the type of mutation that has occurred. 

5b
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3 marks

Fig. 1 shows which mRNA codons code for each amino acid during translation. 

Codon to amino acid key

Fig. 1

Using the table in part (a) as well as the resource in Fig. 1, explain how the resulting protein would be changed by the mutation in the HEXA gene. 

5c
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2 marks

Tay-Sachs disease can be caused by over 100 types of mutations. 

Suggest how it is possible for over 100 different changes in the DNA to result in the same disease. 

5d
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2 marks

Tay-Sachs is an autosomal recessive disease. 

Explain whether a person with Tay-Sachs disease would need to inherit two of the same type of mutation to develop the condition, or whether it could be two different ones. 

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