Transcription and translationAQA A-Level Biology: Subtopic test

1. 1
   A human liver cell transcribes the gene for albumin, a protein made in large amounts by the liver. The albumin gene contains several introns.

   (a)

   Which enzyme joins RNA nucleotides together during transcription of the albumin gene?

   [1 mark]

   • ARNA polymerase
   • BDNA polymerase
   • CDNA ligase
   • DATP synthase

   (b)

   What is the direct product of transcription of the albumin gene in the liver cell?

   [1 mark]

   • AMature mRNA with the introns already removed
   • BPre-mRNA containing both exons and introns
   • CA polypeptide
   • DtRNA

   (c)

   Describe what happens to the product of transcription of the albumin gene before it can be translated.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   At a ribosome in the cytoplasm of a cell, a polypeptide is being made by translation of a molecule of mRNA. Transfer RNA molecules are bringing amino acids to the ribosome.

   (a)

   Which statement about the role of ATP in translation is correct?

   [1 mark]

   • AIt joins mRNA nucleotides together
   • BIt forms the hydrogen bonds between codons and anticodons
   • CIt supplies energy to attach amino acids to tRNA and to form peptide bonds
   • DIt is the source of the amino acids

   (b)

   What is the role of the ribosome in translation?

   [1 mark]

   • AIt makes mRNA from the DNA template
   • BIt carries amino acids to the mRNA
   • CIt removes introns from pre-mRNA
   • DIt holds the mRNA and tRNA in position so that a peptide bond forms between amino acids

   (c)

   A tRNA molecule with the anticodon UAC arrives at the ribosome. Explain which mRNA codon it binds to and what happens to the amino acid it carries.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Bacteria and human cells both transcribe their genes to make RNA. In bacteria, ribosomes can begin translating an mRNA molecule while it is still being made. In human cells, translation does not begin until the RNA has left the nucleus.

   (a)

   Explain why a bacterial RNA can be translated while it is still being made, whereas human RNA must first leave the nucleus.

   [3 marks]

   (b)

   Describe the role of RNA polymerase in transcription.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher investigated translation in a cell-free system containing ribosomes, tRNA, amino acids, ATP and the necessary enzymes. Experiment 1: a synthetic mRNA made only of uracil (UUUUUU and so on) was added, and a polypeptide made only of phenylalanine was produced. Experiment 2: as in experiment 1 but with no ATP; no polypeptide was made. Experiment 3: as in experiment 1 but with no ribosomes; no polypeptide was made. Experiment 4: a synthetic mRNA made of repeating AC units (ACACAC and so on) was added, and a polypeptide of alternating threonine and histidine was produced. In a separate investigation she isolated the pre-mRNA of a human gene, which was 2400 bases long, and the mature mRNA from the same gene, which was 900 bases long and included a stop codon.

   (a)

   Explain what the results of the four experiments show about translation.

   [6 marks]

   (b)

   Explain how the 2400-base pre-mRNA was made and how it became the 900-base mRNA, and calculate the number of amino acids in the polypeptide it codes for, assuming that all 900 bases are translated.

   [6 marks]

   Total for question 4: 12 marks

End of questions