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IGCSE · Cambridge (CIE) · 0973

Explain the ribosome assembling amino acids into protein

Ribosomes assemble amino-acid material using mRNA information. A model pool of twelve appropriate units for four-unit chains supports at most three chains if the required types and conditions are met.

Section B16.1 · Chromosomes and genes

Chromosomes and genes · Cambridge IGCSE 0973 · B16.1
Exam scope and assessment notes

Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.

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 material does the ribosome assemble into protein?

What you will learn

  • Trace the material used to build the product
  • Distinguish assembly from information copying

Original teaching model. Counts and records are stipulated; drawings are schematic.

Explain the ribosome assembling amino acids into proteinRibosomes assemble amino-acid material using mRNA information. A model pool of twelve appropriate units for four-unit chains supports at most three chains if the required types and conditions are met.NucleusDNA geneRemains heremRNA copyMade heremRNA moves to cytoplasmCytoplasmmRNABase orderRibosomeAmino acidsOrdered amino-acid chainmRNA bases determine product orderDNA and RNA are not the product material
Ribosomes assemble amino-acid material using mRNA information. A model pool of twelve appropriate units for four-unit chains supports at most three chains if the required types and conditions are met.
Information, material and count key
FeatureMeaning
MaterialAmino acids
InformationmRNA base sequence
AssemblyRibosome joins the product chain
Model count12 appropriate units / 4 per chain = at most 3

Trace the material used to build the product

The ribosome assembles amino acids into protein molecules using the information supplied by mRNA. Amino acids are the building blocks of the product. The RNA bases supply order information, but they are not the amino-acid material itself. Assembly links the material pathway with the information pathway rather than changing DNA or mRNA into protein.

The original model shows separate incoming amino-acid symbols and a message passing through the ribosome. The growing product contains the amino acids joined in the specified order. A classroom line drawing makes the relationship visible without requiring the detailed chemical bonds, carrier molecules or other translation steps beyond the stated syllabus scope.

Distinguish assembly from information copying

If a supplied model requires four amino acids for one complete chain, a pool of twelve appropriate amino acids is enough material for at most three such chains, provided all other stated conditions are met. This is a stipulated material-count exercise, not a cellular production-rate prediction. A shortage of one required type can limit assembly even when the total number of amino acids looks sufficient.

Keep an information interruption distinct from a material shortage. A message can be present but the required amino acids unavailable, or amino acids can be present without the relevant message reaching a functioning ribosome. Neither presence alone guarantees completed protein. The practice asks which supplied part is missing before claiming an outcome.

Sources for this lesson

Pause and explain

Under a four-amino-acids-per-chain model, twelve appropriate amino acids support at most how many chains?

Put the idea to work

Worked example

Does a present message guarantee protein if the required amino acids are absent?

Show the worked solution
  1. Identify the product’s building material.
  2. Retain the missing-material condition.

Answer No. mRNA supplies information, but the required amino acids are the product material; the stated shortage prevents the specified assembly.

Try a topic test

Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.

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From guided practice to a new situation

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.

1 · Guided

Explain the material and information used in ribosome assembly.

Give me a hint

Name the two pathways separately.

Compare my reasoning
  1. Name amino acids as material.
  2. Name mRNA as information determining order.

The ribosome joins amino acids into protein using the order information carried by mRNA; RNA is not converted into amino-acid material.

Look for these in your work

  • Name material
  • Name information
2 · Independent

Calculate the maximum complete chains in a model needing four appropriate amino acids per chain with twelve available.

Give me a hint

Use complete groups of four and retain other conditions.

Compare my reasoning
  1. Divide twelve by four.
  2. Limit the answer to the stipulated adequate-type model.

At most three complete chains, provided the required amino-acid types and other assembly conditions are met.

Look for these in your work

  • Calculate three
  • Retain conditions
3 · Transfer

A pool has twelve amino acids but none of one type required by the stipulated chain. Does total count prove three chains can be made?

Give me a hint

The required types matter as well as the total.

Compare my reasoning
  1. Identify the missing required type.
  2. Reject using total count as sufficient proof.

No. A required amino-acid type is missing, so the total of twelve alone does not establish three complete chains.

Look for these in your work

  • Identify type shortage
  • Reject total-count sufficiency

Common mistakes

  • RNA bases do not turn into amino acids.
  • Total material is not enough if a required amino-acid type is missing.
Recall without your notes

What can you explain now?

Under a four-amino-acids-per-chain model, twelve appropriate amino acids support at most how many chains?

Compare with the explanation

Three with other conditions met

12 divided by 4 is 3.

After trying it yourself, choose your next review. This is your self-assessment.

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Make it stick

Explain trace the material used to build the product and distinguish assembly from information copying. 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.

Keep learning Sciences — Co-ordinated (9-1)

Course scope and assessment

This 9–1 pathway maps all 152 detailed subject-content sections in the published 0973 syllabus for exams in 2028 and 2029. The course map follows the same 2028–2029 section codes as Cambridge's A*–G 0654 syllabus, while keeping 0973's grading and entry rules separate. It adapts lessons from the related single-science courses and excludes clear single-science-only topics. A 0973-specific objective-by-objective review, Core/Supplement audit, human subject-teacher review, supervised laboratory experience and cumulative assessment remain in progress. Written practice is self-checked and does not predict an official grade. The separate 2025–2027 syllabus has not been reconciled here. Cambridge lists 0973 only in a limited number of administrative zones: June in zone 3 and centres in Oman and the UAE; November in zone 3 only. Confirm entry with your centre.

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