Explain mRNA base sequence determining amino-acid order
mRNA base order determines amino-acid order. Identical-copy counts and material amounts do not substitute for sequence information or establish an exact decode without the required record.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall the nucleus, DNA base pairing, gametes, fertilisation, enzymes, membrane carriers and chemical synapses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What determines the specific amino-acid order during this assembly?
What you will learn
- Link the message order with the assembled chain
- Separate a general coding relationship from an exact decode
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Nuclear source | Gene coding information |
| Message information | mRNA base order |
| Product information | Specific amino-acid order |
| Distinction | Copy number is not sequence order |
Link the message order with the assembled chain
The specific sequence of amino acids in the protein is determined by the sequence of bases in mRNA. The message carries order information copied from the gene, and the ribosome uses that information during assembly. This connects the earlier gene-base relationship with the required nuclear-message-cytoplasmic-product sequence.
An original record stipulates that message A specifies alanine–lysine–proline and message B specifies alanine–proline–lysine. The products contain the same named amino acids but in different orders. These are supplied short-chain records, not complete natural proteins or an invitation to invent exact mRNA bases without a provided code key.
Separate a general coding relationship from an exact decode
The number of message molecules is a different quantity from the order of bases in a message. Copying the same specified message several times does not itself reorder its information. Conversely, having enough amino-acid material does not establish which order will be assembled unless the relevant message information is supplied.
The original information-order diagram places message sequence before ordered assembly, keeping the physical amino-acid material separate. Detailed transcription and translation chemistry are outside this section’s stated requirement. The learning aim is to explain that the message order determines amino-acid order, without claiming an exact sequence or functional effect that the record does not provide.
Pause and explain
What do identical additional message copies change directly in the stipulated record?
Worked example
Does making more copies of the same message automatically change its specified amino-acid order?
Show the worked solution
- Distinguish copy number from sequence.
- Retain the same information in the stipulated copies.
Answer No. More copies change message number, not the specified sequence order in identical messages.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State how mRNA relates to specific amino-acid order.
Give me a hint
Use sequence on both sides.
Compare my reasoning
- Identify the mRNA base sequence.
- Connect it with the assembled amino-acid sequence.
The sequence of bases in mRNA determines the specific sequence of amino acids assembled into the protein.
Look for these in your work
- Name message sequence
- Name product sequence
A supplied message A specifies alanine–lysine–proline and B specifies alanine–proline–lysine. Compare their product orders.
Give me a hint
Check the second and third positions.
Compare my reasoning
- Retain the common first amino acid.
- Identify the later order difference.
Both start with alanine; A then has lysine and proline, while B has proline and lysine, so the specified orders differ.
Look for these in your work
- Use the supplied records
- Compare order
A record gives five identical message copies but no coding key. Can copy count reconstruct every message base?
Give me a hint
Count and sequence evidence differ.
Compare my reasoning
- Identify five as a molecule count.
- State that exact base-order information is absent.
No. Five copies describe message number, not every base in the message; the exact sequence cannot be reconstructed from the count alone.
Look for these in your work
- Separate count and sequence
- State missing information
Common mistakes
- Copy number is not base order.
- An exact decode requires supplied coding evidence.
What can you explain now?
What do identical additional message copies change directly in the stipulated record?
Compare with the explanation
Message number rather than sequence order
The copies have the same stated information.
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Make it stick
Explain link the message order with the assembled chain and separate a general coding relationship from an exact decode. Use the stated cell, chromosome sets and information pathway before opening the solutions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.