Home / IB DP Biology-D1.2 Protein synthesis -FA 2025- IB Style Questions For HL Paper 1

IB DP Biology-D1.2 Protein synthesis -FA 2025- IB Style Questions For HL Paper 1

Question

Which diagram represents the modified mRNA after transcription?

▶️Answer/Explanation

Ans. A

After transcription, messenger RNA (mRNA) can be modified in a number of ways, including:
  • Adding a 5′ cap and 3′ polyadenylated tail

    These modifications help transport the mRNA to ribosomes and protect it from degradation. 

     RNA splicing

    This process removes non-coding introns and links coding exons together. 

     N6-methyladenosine (m6A) methylation

    This is one of the most common modifications to mRNA. It can affect many cellular events, including splicing, translation, and degradation. 

     2′-O-methylation

    This modification can dramatically affect the structure and stability of RNA. 

     Editing of adenosine (A) to inosine (I)

    This modification is also known as deamination and can strongly modulate the expression of target RNAs. 

     Other types of mRNA modifications include N1-methyladenosine (m1A), 5-methylcytosine (m5C), and pseudouridine. 

 These modifications can alter the RNA structure, which can affect how proteins bind to it. This can regulate mRNA stability and translation. 

Question

The diagram shows the structure of a peptide.

How many bases are required in an mRNA molecule to code for this peptide?

A. 18

B. 36

C. 54

D. 72

▶️Answer/Explanation

Ans. C

To count the number of bases required in an mRNA molecule to code for a peptide, you can use the following method:
  1. Identify the number of amino acids
  2. Calculate the number of codons
  3. Calculate the total number of nitrogen bases
    in the above question
  • If a polypeptide chain has 18 amino acids, then the number of codons required is 60.
  • Each codon has 3 nitrogen bases, so the total number of nitrogen bases for the amino acids is 18 x 3 = 54 

Question

This DNA sequence was used to synthesize a polypeptide.

DNA (sense strand): 3′ T A C T G A 5′

DNA (template strand): 5′ A T G A C T 3′

Which are the bases of the tRNA (anticodons)?

A. T A C   T G A

B. U A C   U G A

C. A U G   A C U

D. A T G   A C T

▶️Answer/Explanation

Ans:C

Question

The image shows a polysome in a bacterial cell.

How many genes have been transcribed?

A. 1

B. 2

C. 3

D. 4

▶️Answer/Explanation

Ans:A

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