Protein Synthesis — Drills · Grade 10 Science

Chapter: DNA, Inheritance & Gene Expression

What these drills covers

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

6 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

Transcription produces
  1. a protein
  2. a messenger RNA copy of a gene
  3. a new DNA double helix
  4. a ribosome
Answer and explanation

a messenger RNA copy of a gene

Transcription copies a gene's sequence into messenger RNA; translation then uses that RNA to assemble a protein.

Problem 2

A codon is
  1. a single base
  2. a sequence of three bases specifying one amino acid or a stop
  3. a whole gene
  4. a protein subunit
Answer and explanation

a sequence of three bases specifying one amino acid or a stop

Three consecutive mRNA bases form a codon, which specifies one amino acid or signals the end of the coding sequence.

Problem 3

A coding sequence contains 300 mRNA bases, including one stop codon. How many amino acids does the resulting polypeptide contain?
Answer and explanation

99

300 / 3 = 100 codons, one of which is a stop and specifies no amino acid, leaving 99 amino acids.

Problem 4

In RNA, the base that replaces thymine is
  1. adenine
  2. cytosine
  3. uracil
  4. guanine
Answer and explanation

uracil

RNA uses uracil in place of thymine, so a DNA adenine is transcribed as uracil in the messenger RNA.

Problem 5

A single base substitution changes a codon from GGC to GGU. Both specify glycine. Explain why the protein is unaffected and what this reveals about the genetic code.
Answer and explanation

Because both codons specify glycine, the amino acid sequence is unchanged, so the protein folds and functions as before; this is a silent mutation. It reveals that the genetic code is redundant: several codons can specify the same amino acid, usually differing in the third base. That redundancy means some substitutions have no effect on the protein, which is why a change in DNA does not always produce a change in phenotype.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Explain why deleting one base usually damages a protein more than substituting one base.
Answer and explanation

A substitution changes at most one codon, so at most one amino acid differs and the change may even be silent. A deletion shifts the reading frame for everything downstream, so every subsequent codon is read in the wrong grouping and almost all the remaining amino acids are wrong, often with a premature stop codon appearing. The scale of the damage differs: one position against the whole remainder of the sequence.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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