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AQA A-Level Biology (Paper 1) Smart practice A mixed round aimed at your weak spots
Unit 1
Biological molecules
Monomers and polymers; carbohydrates
Monomers, polymers and carbohydrates
0%
Lipids
Lipids
0%
Proteins
General properties of proteins
0%
Many proteins are enzymes
0%
Nucleic acids are important information-carrying molecules
Structure of DNA and RNA
0%
DNA replication
0%
ATP
ATP
0%
Water; inorganic ions
Water and inorganic ions
0%
Unit 2
Cells
Cell structure
Structure of eukaryotic cells
0%
Structure of prokaryotic cells and of viruses
0%
Methods of studying cells
0%
All cells arise from other cells
All cells arise from other cells
0%
Transport across cell membranes
Membrane structure, diffusion and osmosis
0%
Active transport and co-transport
0%
Cell recognition and the immune system
Antigens, phagocytosis and T lymphocytes
0%
B lymphocytes, antibodies and vaccination
0%
HIV, monoclonal antibodies and the ELISA test
0%
Unit 3
Organisms exchange substances with their environment
Surface area to volume ratio
Surface area to volume ratio
0%
Gas exchange
Adaptations of gas exchange surfaces
0%
Human gas exchange, ventilation and lung disease
0%
Digestion and absorption
Digestion and absorption
0%
Mass transport in animals
Haemoglobin and the transport of oxygen
0%
The heart, cardiac cycle and cardiovascular disease
0%
Blood vessels and tissue fluid
0%
Mass transport in plants
Xylem and the cohesion-tension theory
0%
Phloem and translocation by mass flow
0%
Unit 4
Genetic information, variation and relationships between organisms
DNA, genes and chromosomes
DNA, genes and chromosomes
0%
DNA and protein synthesis
Genome, proteome, transcription and splicing
0%
Translation: ribosomes, tRNA and ATP
0%
Genetic diversity can arise as a result of mutation or during meiosis
Gene mutations and chromosome non-disjunction
0%
Meiosis and genetic variation
0%
Genetic diversity and adaptation
Genetic diversity and adaptation
0%
Species and taxonomy
Species and taxonomy
0%
Biodiversity within a community
Biodiversity within a community
0%
Investigating diversity
Investigating diversity
0%
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Translation: ribosomes, tRNA and ATP

Practise 18 exam-style questions on Translation: ribosomes, tRNA and ATP for AQA A-Level Biology (Paper 1). Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with the Study Helper on hand if you get stuck.

  • 18 questions
  • 1–8 marks each
  • Instant marking
  • No sign-up needed
18 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

Cells use only 20 different amino acids to make proteins, but they contain more than 40 different types of tRNA molecule. Each type of tRNA has a different anticodon.

Suggest why cells contain more than 20 types of tRNA.

Model answer

The genetic code is degenerate: most amino acids are coded for by more than one codon. Each type of tRNA has an anticodon complementary to a particular codon, so several different types of tRNA, with different anticodons, carry the same amino acid.

Explanation

There are 61 codons for 20 amino acids, so most amino acids have several codons. A tRNA binds to a codon through its complementary anticodon, so different codons for the same amino acid need tRNAs with different anticodons, all carrying that amino acid. A common error is to write that the code is degenerate because one codon codes for several amino acids, which is the wrong way round.

Mark scheme
  1. 1 mark

    The genetic code is degenerate / (most) amino acids are coded for by more than one codon

    Do not accept 'the amino acids are degenerate' or 'one codon codes for more than one amino acid'.

  2. 1 mark

    Each anticodon is complementary to a different codon, so several types of tRNA carry the same amino acid

    Accept 'different tRNAs with different anticodons are needed for the different codons of the same amino acid'.

Question 2

2 marks

Explain what happens when a ribosome reaches a stop codon on an mRNA molecule.

Model answer

A stop codon does not code for an amino acid, and no tRNA has an anticodon complementary to it, so no further amino acid is added. Translation ends: the completed polypeptide is released and the ribosome detaches from the mRNA.

Explanation

Stop codons mark the end of the coding sequence. Because no tRNA binds to them, the polypeptide cannot be extended and is released. A common error is to say that the stop codon codes for a 'stop amino acid'.

Mark scheme
  1. 1 mark

    No tRNA has an anticodon complementary to a stop codon / a stop codon does not code for an amino acid

    Accept 'no amino acid is brought to the stop codon'.

  2. 1 mark

    Translation stops AND the polypeptide is released (from the ribosome) / the ribosome detaches from the mRNA

Question 3

3 marks

Compound E binds to the ribosomes in the cytoplasm of eukaryotic cells and stops them moving along mRNA.

Explain how compound E stops these cells producing polypeptides.

Suggest and explain what happens to the tRNA molecules that are bound to a ribosome when compound E is added.

Model answer

If the ribosome cannot move along the mRNA, the next codon is never brought into position, so no further tRNA can bind with its amino acid and no more peptide bonds form. The polypeptide is never completed. The tRNA molecules already on the ribosome stay bound to their codons and are not released, so they cannot pick up more amino acids and be used again.

Explanation

During translation the ribosome must move along the mRNA one codon at a time so that each new codon can pair with a tRNA anticodon and the next peptide bond can form. Moving on also releases the tRNA that has given up its amino acid, so that it can be reused. If the ribosome stalls, the polypeptide stays unfinished and the tRNAs stay trapped on the ribosome.

Mark scheme
  1. 1 mark

    The next codon is not moved into (position in) the ribosome / exposed, so no further tRNA can bind (with its amino acid)

    Points 1 and 2 are for how polypeptide production stops; point 3 is for the tRNA. Accept 'no more anticodons can bind to codons'.

  2. 1 mark

    No further peptide bonds form / no more amino acids are added, so the polypeptide is not completed (or released)

    Ignore 'translation stops' unqualified.

  3. 1 mark

    The tRNAs stay bound to the codons / are not released, so they cannot collect / carry more amino acids

    Both the idea that they are not released and the consequence are needed. Accept 'they cannot be reused'. Do not accept 'the tRNAs are destroyed / hydrolysed'.

Question 4

5 marks

Describe the structure of a tRNA molecule and explain how its structure allows it to carry out its role in translation.

Model answer

A tRNA molecule is a single strand of RNA nucleotides (containing ribose and the bases A, U, C and G) folded into a clover-leaf shape. The shape is held by hydrogen bonds between complementary bases in some regions. On one loop is the anticodon, a sequence of three bases that is complementary to a particular mRNA codon and binds to it by complementary base pairing. At the other end is the amino acid binding site, where one specific amino acid attaches. Because each tRNA with a particular anticodon always carries the same amino acid, the amino acids are brought to the ribosome in the order set by the codons on the mRNA.

Explanation

Link each structural feature to the role of tRNA: the anticodon makes sure the tRNA binds only to its complementary codon, and the binding site carries the matching specific amino acid, so the codon sequence determines the amino acid sequence. Common errors are to call tRNA double-stranded, to confuse the anticodon with a codon, or to write 'tRNA has an amino acid' instead of describing the binding site.

Mark scheme
  1. 1 mark

    Single (polynucleotide) strand (of RNA nucleotides)

    Max 3 if the answer does not say that the anticodon binds to, or is complementary to, a codon on mRNA. Max 5. Reject 'double-stranded' or 'double helix'.

  2. 1 mark

    Folded into a clover-leaf shape

    Accept a description of a clover leaf (three loops and an arm).

  3. 1 mark

    (Shape) held by hydrogen bonds between (complementary) bases / base pairs

  4. 1 mark

    Anticodon: a sequence of three bases (on one loop / at one end)

  5. 1 mark

    Anticodon binds to a complementary codon on mRNA (by complementary base pairing)

    Accept 'anticodon pairs with the codon by hydrogen bonds'.

  6. 1 mark

    Amino acid binding site (at the other end)

  7. 1 mark

    Each tRNA (with a particular anticodon) carries a specific amino acid, so amino acids are brought in the order of the codons

  8. 1 mark

    Contains ribose / uracil (RNA nucleotides)

    Reject 'deoxyribose' or 'thymine'.

Ready to try the rest? Every answer you write is marked against the mark scheme, so you can see exactly where the marks are.

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