Syllabus Edition

First teaching 2023

First exams 2025

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Protein Synthesis (SL IB Biology)

Exam Questions

3 hours37 questions
1a3 marks

When a polypeptide is synthesised it is important that the amino acids are combined in the correct order to produce a functional protein.

Outline the process that allows the amino acids to be added to the polypeptide in the correct order. 

1b3 marks

After a polypeptide has been synthesised it must undergo a series of changes before it can become a functional protein.

Describe the changes that occur between polypeptide synthesis and the formation of the functional protein. 

1c2 marks

How might a change in the DNA affect the way that the process of protein folding occurs? 

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2a
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2 marks

The following diagram shows the process of protein synthesis.

Av~i7Cjw_e-1a

(i)

Identify stage X.

[1]

(ii)

State where in the cell stage X occurs.

[1]

2b
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2 marks

Label molecule A and B in the diagram.

2c
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1 mark

State one difference in structure between DNA and molecule A identified at part b).

2d
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1 mark

Molecule B is synthesised from monomers.

Identify the monomers of molecule B.

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3a
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2 marks

The diagram below shows one of the stages in protein synthesis.

e-2a

(i)

Identify the stage of protein synthesis represented by the diagram.

[1]

(ii)

State one reason for your answer in part i).

[1]

3b
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2 marks

Enzyme Y plays an important role during the stage of protein synthesis identified at part a) i).

(i)

Identify enzyme Y.

[1]

(ii)

State the role of this enzyme during protein synthesis.

[1]

3c
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2 marks

Label strands S and T of the DNA molecule.

3d
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2 marks

Explain the purpose of creating an mRNA copy of the genetic code on the DNA molecule.

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4a
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2 marks

The following DNA base triplets form part of a gene coding for a polypeptide.

         CCC  ATA  CTT  GGA

State the mRNA codons that would be transcribed from this section of the gene.

4b
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2 marks

The gene mentioned in part a) formed an mRNA molecule that consisted of 180 nucleotides.

Calculate the number of amino acids that will be coded for by this gene. Show your working.

4c
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2 marks

The table below shows mRNA codons and their corresponding amino acids.

mrna-codons-and-amino-acids-table

Use this table to state the amino acid sequence of the section of the gene given in part a).

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5a
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2 marks

Describe the role of a ribosome in the process of protein synthesis.

5b
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1 mark

The mRNA molecule that is shown in the diagram at part a) carries the genetic code in the form of codons.

Define the term 'codon'.

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6a
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1 mark

The diagram below shows the structure of a tRNA molecule.

structure-of-trna-sq

Identify the type of molecule that would bind to site A.

6b
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2 marks
(i)

Identify the type of bond present at B.

[1]

(ii)

State the purpose of these bonds in a tRNA molecule.

[1]

6c
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2 marks

Describe the role of C in the process of translation.

6d
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1 mark

Before tRNA molecules can partake in translation, they bind to tRNA-activating enzymes.

State the purpose of tRNA-activating enzymes.

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1a3 marks

The following base sequences represent sections of two different alleles of the gene which determines an individual's ability to roll their tongue. 

Allele A (tongue roller): GCCGTAAC
Allele B (non-tongue roller): GCGCTTAC

Outline why two different alleles result in different expressions of a gene.

1b3 marks

Sickle cell anemia is a genetic disorder with symptoms such as dizziness, a rapid heart rate and fatigue. It is caused by an allele that leads to altered haemoglobin proteins. These altered proteins undergo aggregation (sticking together), an event which changes the shape of red blood cells.  This can be seen in the image below.

biology-q2b-3-1-sq-ib-hl

Suggest how sickled red blood cells may result in the symptoms noted above.

1c1 mark

Suggest why the shape of white blood cells is not affected by sickle cell anaemia.        

1d1 mark

Mutations such as the one seen in sickle cell patients are usually caused by an error during DNA replication. 

Identify the enzyme that is responsible for catalysing the process of DNA replication.

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2a1 mark

Myoglobin is a eukaryotic protein consisting of a single polypeptide chain of 153 amino acids. 

Calculate the minimum number of DNA bases needed to code for Myoglobin.

2b3 marks

Haemoglobin is another eukaryotic protein; it contains both α and ꞵ polypeptide chains.
Some of the first seven amino acids of an α chain of haemoglobin, along with the corresponding bases in the sequence are shown below.  An mRNA codon and amino acid table is also provided.

Amino acid sequence Met (i) Leu (ii) (iii) Ala Asp
Base sequence in DNA antisense strand (3’➞5’) TAC CAC GAC AGA GGA CGG CTG

bilogy-2-6-q1b-ib-hl

Use the information provided to identify the missing amino acids from the sequence of seven shown above.

2c1 mark

A third eukaryotic protein, cytochrome c, is involved in the process of aerobic respiration. The diagram below shows part of the mRNA sequence and its corresponding amino acid sequence for cytochrome c in Mus musculus (house mouse) and Loxodonta africana (African elephant).

biology-2-6-q1c-ib-hl-sq

Identify the tRNA anticodon that corresponds to the amino acid serine (Ser).

2d2 marks

The triplet codes for the amino acid Ile in part (c) demonstrate a property of the genetic code known as degeneracy, or redundancy. 

Use the information in part (c) to:

(i)
Suggest what is meant when we say that the genetic code is degenerate/redundant.

(ii)

Identify one other amino acid that demonstrates this property.

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3a1 mark

Disease X is a genetic condition. It is caused by various mutations, one of which is shown in the diagram below.

biology-2-6-2a-sq-ib-hl

Identify the process marked Y in the diagram.

3b3 marks

The table below shows mRNA codons and their corresponding amino acids.

biology-2-6-2b-sq-ib-hl

Use the table above and your knowledge of protein synthesis to identify the contents of boxes (i)-(iii) in the diagram in part (a).

3c2 marks

Outline the role of transfer RNA in the process of protein synthesis.

3d2 marks

Explain why the protein produced as a result of the disease X mutation shown in part (a) does not function as it should.

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4a2 marks

The table below shows the exposed bases of two tRNA molecules involved in the synthesis of a protein.

Bases of tRNA anticodon UAU GAC
Bases of corresponding DNA antisense strand (i) (ii)


Identify the base sequences found on the corresponding sections of the DNA antisense strands.

4b3 marks

Outline how a gene codes for a polypeptide.

4c2 marks

A polypeptide is formed when a series of amino acids join to form a chain. 

Identify the following:

(i)

The chemical reaction that joins two amino acids together in a polypeptide. 

(ii)
The type of bond that joins two amino acids together in a polypeptide.

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55 marks

Draw an annotated diagram to illustrate the structure of a DNA double helix. You do not have to show the helical shape in your diagram. 

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6a2 marks

The human genome is approximately 3 billion, or 3 000 000 000, base pairs long. A DNA sequencing machine allows for 5.5 x 108 base pairs to be sequenced per hour. 

Using this information calculate the number of days it would take to sequence 1500 genomes of hospital patients using this machine. Give your answer to the nearest day.

6b3 marks

The table below shows part of the DNA base sequence coding for β-haemoglobin and two mutations of this sequence detected in a sickle cell sufferer.

DNA base sequence coding for β-haemoglobin                        
mRNA sequence for β-haemoglobin A C U C C U G A G G A G
DNA base sequence with mutation 1                        
mRNA base sequence with mutation 1 A C U C C U G U G G A G
DNA base sequence with mutation 2                        
mRNA base sequence with mutation 2 A C U C C U G A A G A G

Complete the table with the DNA sequences that will undergo transcription to produce β-haemoglobin, mutated protein 1, and mutated protein 2.

6c2 marks

The table below shows some examples of amino acids, their structures, and the mRNA codons that code for them.

biology-q4c-3-1-sq-ib-hl-png

Suggest why mutation 2 from part (b) is of no concern to the scientists studying this patient's DNA

6d1 mark

A karyogram, such as the one shown in the image below, can be used to detect some Mutations

biology-q4d-sq-ib-hl

State why this karyogram could not be used to detect sickle cell anaemia.

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73 marks

Describe the role of tRNA in the process of translation.

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82 marks

Ribosomes are made of ribosomal RNA (rRNA). Messenger RNA (mRNA), transfer RNA (tRNA) and DNA are all involved in the synthesis of proteins.

Complete the table to show the differences between DNA, mRNA and tRNA.

Type of nucleic acid

Number of polynucleotide strands in the molecule

The nitrogenous base uracil present (✓) or not present (X)

DNA

   

mRNA

   

tRNA

   

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9a4 marks

Enzymes play an important role during transcription and translation.

Discuss the importance of enzyme-substrate specificity in the activation of tRNA molecules.

9b3 marks

The tRNA-activating enzyme relies on phosphorylation.

Outline the role of phosphorylation during translation.

9c2 marks

Enzymes, such as the tRNA-activating enzyme, are proteins.

State, with named examples, two functions of proteins.

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104 marks

Contrast protein synthesis in eukaryotes with protein synthesis in prokaryotes. 

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113 marks

Radiation and mutagenic chemicals can cause mutations in DNA that result in new alleles. 

Explain how mutations in DNA can affect the final protein product.

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1a1 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 sense strand.

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

The image shows the genetic code (mRNA codons).

mrna-codons-and-amino-acids-table

Use the image to identify the sequence of amino acids in this part of the enzyme.

1b2 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 coding strand sequence for leucine.

[1]

(ii)

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

[1]

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2a2 marks

As enzyme Y in part a) moves along the DNA, the base sequence on the template strand is as follows:

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

Identify the tRNA anticodons that would bind with the mRNA produced from this section of DNA.

2b2 marks

The transcription factor shown in part a) is a protein.

Suggest, with a reason, how a mutation in the gene that codes for the transcription factor protein might affect the expression of the gene shown in part a).

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3a8 marks

One mark is available for clarity of communication throughout this question.

Compare and contrast the processes of DNA replication and transcription.

3b6 marks

Explain the relationship between the genetic code and proteins.

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4a
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4 marks

Discuss the importance of hydrogen bonds in the process of translation.

4b
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4 marks

Draw labelled diagrams contrasting the structure of an mRNA and tRNA molecule.

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5a
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3 marks

Part of the gene coding for a specific polypeptide contains the following base sequence:

                     CATAGTTGGCCA

The following table contains some of the codons on messenger RNA and the amino acids that they code for:

Codons Amino acid coded for by codons
AUU / AUC / AUA Isoleucine (Ile)
UUA / UUG / CUU / CUC / CUA / CUG Leucine (Leu)
GGU / GGC / GGA / GGG Glycine (Gly)
ACU / ACC / ACA / ACG Threonine (Thr)
UCU / UCC / UCA / UCG Serine (Ser)
GUU / GUC / GUA / GUG Valine (Val)
UAA / UAG / UGA STOP

Using the information provided, identify the amino acid sequence for this part of the polypeptide.

5b
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3 marks

The cells that synthesise this polypeptide was exposed to a mutagen that caused a substitution mutation that changed the DNA base sequence in the following way:

                  CATACTTGGCCA

Using the table from part a), explain the effect this mutation will have on the polypeptide produced.

5c
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2 marks

This polypeptide forms part of the active site of an enzyme that catalyses a metabolic reaction.

Suggest the effect that the mutation mentioned in part b) would have on the enzyme.

5d
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1 mark

Based on the information provided in part a), explain how it could be possible for a mutation to have no effect on the polypeptide.

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