IBBiologySLTopic QuestionsContinuity & ChangeProtein Synthesis

Syllabus Edition

First teaching 2023

First exams 2025

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Protein Synthesis (SL IB Biology)

Topic Questions

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1
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Which of the following steps is not involved in the process of transcription?

  • The DNA double helix separates into single strands

  • DNA polymerase binds to one of the single strands and moves along the gene

  • Free RNA nucleotides are joined together by covalent bonds

  • The RNA molecule detaches from the DNA template strand at the end of the gene

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2
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In a genetic engineering experiment, a piece of double-stranded DNA containing 18 000 nucleotides coding for a specific polypeptide is transcribed and translated.

What is the total number of amino acids in this polypeptide?

  • 3 000

  • 6 000

  • 9 000

  • 18 000

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3
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A section of a DNA molecule contains the following base sequences:

ATA  CCT  GCA

Which of the following would represent the base sequences of the codons on the mRNA molecule after transcription?

  • ATA  CCT  GCA

  • AUA  CCU  GCA

  • TAT  GGA CGT

  • UAU  GGA  CGU

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4
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Which of the following will lead to the termination of translation?

  • Once the ribosome disassembles into the large and small subunit

  • When the ribosome encounters a stop codon

  • Releasing the free polypeptide from the last tRNA molecule

  • When the ribosome detaches from the mRNA molecule

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5
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The diagram below shows the structure of a tRNA molecule.7-3_q2

Which of the following correctly identifies the different parts of the tRNA molecule?

  1 2 3 4
A. Amino acid binding site Hydrogen bonds Anticodon Sugar-phosphate backbone
B. Amino acids Hydrogen bonds Anticodon Covalent bonds
C. Amino acid binding site Covalent bonds Anticodon Sugar-phosphate backbone
D. Amino acids Hydrogen bonds Codon Covalent bonds

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6
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Which of the following would apply to the polysomes of prokaryotes?

  • Polysomes, containing 80S ribosomes, will appear on the growing mRNA strand along the DNA molecule

  • Polysomes, containing 70S ribosomes, will appear on the growing mRNA strand in the absence of DNA

  • Polysomes, containing 80S ribosomes, will appear on the growing mRNA strand in the absence of DNA

  • Polysomes, containing 70S ribosomes, will appear on the growing mRNA strand along the DNA molecule

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1
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A polypeptide has the following amino acid sequence:

alanine - alanine - valine - lysine - valine - serine

The table below gives the base sequences for the DNA triplets of each amino acid.

Amino acid DNA triplet
serine TCG
valine GTA
lysine AAA
alanine GCT
stop TAA

A mutation in the DNA coding for this polypeptide chain caused the tenth nucleotide to change from an A to a T.

Which of the following would represent the amino acid sequence in the polypeptide after the mutation occurred?

  • alanine - alanine - valine - lysine - valine - serine

  • alanine - alanine - valine - stop - valine - serine

  • alanine - alanine - valine

  • alanine - alanine - valine - serine - valine - serine

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2
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Which of the following processes involve both DNA and RNA?

I. Replication

II. Transcription

III. Translation

IV. Protein synthesis

  • I and II

  • I, II and IV

  • III only

  • II and IV

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3
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A short section of mRNA that was produced after transcription occurred has the following base sequence:

AAACUUCUCAUAGAACGG

The following table shows the base sequence for codons and the corresponding amino acids that they code for.

mrna-codons-and-amino-acids-table

Which of the following would represent the correct amino acid sequence coded for by this section of mRNA?

  • Lys - Leu - Pro - Asp - Gly - Ala

  • Lys - Phe - Pro - Lys - Gly - Ala

  • Lys - Leu - Leu - Asp - Glu - Arg

  • Lys - Leu - Leu - Ile - Glu - Arg

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4
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Which of the following applies to both free and bound ribosomes?

  1. They produce polypeptides that are destined to be used for processes occurring in the cytosol
  2. Translation is interrupted and then re-initiated once movement of the ribosome is complete
  3. They are found in all eukaryotic cells and may be either 70S or 80S
  4. They facilitate the binding of mRNA and tRNA and catalyse the formation of peptide bonds
  5. They have four binding sites to allow the molecules involved with translation to attach to its subunits

  • III. and IV. only

  • IV. and V. only

  • I., III. and IV.

  • II., IV. and V.

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5
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The following steps describes the events taking place during the elongation of a polypeptide in no particular order.

  1. Free tRNA molecules bind to their corresponding amino acids due to their specific anticodon and transport it to the ribosome 
  2. A tRNA with a complementary anticodon binds to the "A" site bringing its specific amino acid along
  3. The initiator tRNA moves from the "P" to the "E" site on the ribosome where it initiates translation
  4. The amino acid carried by the tRNA at the "P" site is linked to the polypeptide chain by a peptide bond
  5. tRNA carrying the peptide chain moves from the "A" site to the "P" site as the ribosome moves in the 5' → 3' direction along the mRNA molecule

Which of these steps contain incorrect information?

  • I., III. and V.

  • II., III. and V.

  • I., III. and IV.

  • I., III., IV. and V.

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11 mark

Which row of the table best describes the events of polypeptide synthesis?

  Type of reaction ATP requirement Location in cell
A anabolic condensation ATP not required mitochondria
B anabolic hydrolysis ATP not required cytoplasm
C anabolic condensation ATP required cytoplasm
D catabolic condensation ATP required mitochondria

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21 mark

A piece of DNA was analysed to find the number of nucleotide bases in each of the polynucleotide strands.  Some of the results are shown below.

  Number of nucleotide bases
  A T G C
Strand 1   30 22  
Strand 2   30 38  

What is the maximum number of amino acids that could be coded for by this DNA?

  • 30

  • 35

  • 40

  • 50

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31 mark

What terminates the formation of a polypeptide chain during protein synthesis in cells?

  • When the ribosome reaches the end of the mRNA molecule.

  • When there are no more tRNA molecules. 

  • When the ribosome reaches a stop codon on the mRNA. 

  • RNA polymerase detaches the polypeptide chain from the ribosome.  

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41 mark

The diagram below represents an electron micrograph of eukaryotic polysomes.

q10_7-3_translation_ib_biology_hl_mcq                      

What is the main advantage that polysomes give to a eukaryotic cell?

  • Translation can be initiated before transcription is complete

  • Allows very long mRNA molecules to be translated

  • They increase the overall rate of translation

  • Allows structurally different polypeptides to be produced from the same mRNA

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