Protein Synthesis — Practice · Grade 10 Science

Chapter: DNA, Inheritance & Gene Expression

What this practice covers

By the end of Protein Synthesis you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: transcription, mRNA (messenger RNA), codon, translation, ribosome, amino acid, stop codon.

Problem 1

During transcription, a gene's DNA is copied into
  1. a lipid
  2. messenger RNA (mRNA)
  3. a finished protein
  4. a new chromosome
Answer and explanation

messenger RNA (mRNA)

Transcription produces an mRNA copy of the gene; the protein is built later, during translation.

Problem 2

Translation — assembling a protein from mRNA — takes place at the
  1. cell membrane
  2. vacuole
  3. ribosome
  4. nucleus
Answer and explanation

ribosome

Ribosomes read the mRNA codons and link amino acids together into a protein.

Problem 3

Each amino acid is coded by a codon of 3 mRNA bases. How many mRNA bases are needed to code for a protein that is 15 amino acids long?
Answer and explanation

45 bases

3 bases per codon x 15 amino acids = 45 bases.

Problem 4

Explain the difference between transcription and translation.
Answer and explanation

Transcription is copying a gene's DNA into mRNA inside the nucleus; translation is reading that mRNA's codons at a ribosome to build a protein from amino acids. Transcription makes the message, and translation reads it.

Problem 5

A single-base mutation changes a codon, but because the genetic code is redundant, the new codon still specifies the same amino acid. This kind of mutation is described as
  1. nonsense — it creates an early stop signal
  2. a frameshift that shifts every later codon
  3. always fatal to the cell
  4. silent — the protein is unchanged
Answer and explanation

silent — the protein is unchanged

When a changed codon still codes for the same amino acid, the protein is unchanged, so the mutation is 'silent' — possible because several codons can specify the same amino acid.

Problem 6

An mRNA contains AUG followed by GCU. Using a supplied table showing AUG=Met and GCU=Ala, identify the first two amino acids. Explain the reasoning in your own words.
Answer and explanation

Methionine followed by alanine in this simplified translation example.

Read the mRNA codons as supplied, not their complements.

Match AUG to methionine and GCU to alanine.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

An RNA codon changes but still specifies the same amino acid. What kind of protein-sequence effect is possible? Show the reasoning, not just the conclusion.
Hints

Specify template versus coding strand before converting a sequence.

Answer and explanation

It can be synonymous, leaving that amino acid unchanged; other regulatory effects are still possible.

Problem 8

Why must a codon table be read using RNA rather than a DNA template triplet directly?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Translation reads mRNA; the template must first be converted to complementary RNA with correct orientation.

Problem 9

Different sequence changes can have different downstream consequencesDifferent sequence changes can have different downstream consequencesOriginal: AUG GCA UAA → Met–Ala–stopSubstitution: AUG GCU UAA → Met–Ala–stopAnother change: AUG GUA UAA → Met–Val–stopAn insertion can shift downstream reading-frame groups.A sequence change and a functional effect are different claims.
Original supplied-code sequence comparisons, not pathogenic-variant identification or the full range of molecular effects.
Interpret the supplied visual. Why does GCA→GCU not change this amino acid, while GCA→GUA does?
Answer and explanation

The supplied code maps GCA/GCU to alanine and GUA to valine; different codons can share or differ in meaning.

A substitution changes a base; an insertion or deletion changes sequence length. A reading frame groups consecutive bases into codons, so a non-three-base insertion within a translated region can alter downstream grouping. Code redundancy allows a substitution to retain the same amino acid, as GCA and GCU both specify alanine in the supplied entries. Other changes alter an amino acid or termination. Effects depend on location, regulation and protein context; not every mutation is visible or every substitution harmless.

The supplied code maps GCA/GCU to alanine and GUA to valine; different codons can share or differ in meaning.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

Using GCA=Ala, GCU=Ala and GUA=Val, compare a coding-region change that gives GCU versus one giving GUA in mRNA. Explain why neither sequence result alone determines a whole-organism trait.
Answer and explanation

GCU retains alanine; GUA specifies valine. Regulatory context, protein folding/activity and other biological conditions determine downstream effects, so a measured trait needs additional evidence.

GCU retains alanine; GUA specifies valine. Regulatory context, protein folding/activity and other biological conditions determine downstream effects, so a measured trait needs additional evidence.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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