IB DP Biology- D1.2 Protein synthesis- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
✅ Answer: (B)
Question
Which diagram represents the modified mRNA after transcription?
▶️Answer/Explanation
Answer: A.
Explanation:
What does a mature/modified mRNA look like?
After transcription and RNA processing, a mature eukaryotic mRNA has:
- 5′ cap (G cap)
- Exons only (all introns are removed via splicing)
- 3′ Poly-A tail (AAAAA)
- And the strand is made of RNA → so U (Uracil) is present instead of T (Thymine)
Let’s look at the options:
Option A:
- 5′ cap present
- Only exons are there
- Has poly-A tail
- No introns
- Correct RNA direction 5′ → 3′
- This looks like a perfect mature mRNA!
Option B:
- 5′ cap
- Introns still present
- Poly-U tail (that’s not a thing should be Poly-A!)
- Not fully processed mRNA
Option C:
- Only introns are there, exons are missing.
- Poly-A tail
- Missing exons = NOT functional
Option D:
- 5′ cap
- Has both exons and introns = not yet fully spliced
- Poly-U tail again — No
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
Answer: A. 1
Explanation:
What’s in the image?
The diagram shows one single mRNA strand with multiple ribosomes attached, each one busy making a polypeptide chain that’s a classic example of a polysome or polyribosome
What does that mean?
In prokaryotes (like bacteria), translation can begin even before transcription finishes and multiple ribosomes can hop onto one mRNA strand to translate it simultaneously.
But the key thing is: All those ribosomes are translating the same mRNA, meaning it was transcribed from just one gene.
Only one gene has been transcribed. The multiple polypeptides being made are just copies of the same protein from that one gene’s mRNA.