Translation: read a codon table to build a protein

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   mRNA (model, not to scale), 5′ to 3′, not yet cut: AUGGCUUUCUAA. Ari cuts this mRNA into codons, starting at the left end. What is the second codon?

   • GCU, the second group of three bases
   • CUU, the second group after skipping one base
   • GG, the second group of two bases
   • AUG, the first group of three bases
2. 2.

   mRNA (model, not to scale), 5′ to 3′, 18 bases, not yet cut: AUGUUCGGACAUGAAUGA. Bo cuts this mRNA into codons. How many codons does it hold, counting the stop codon?

   • 9 codons, of two bases each
   • 18 codons, of one base each
   • 6 codons, of three bases each
   • 5 codons, because a stop is not a codon
3. 3.

   mRNA (model, not to scale), 5′ to 3′, cut into 5 codons: AUG GUU CAC UCU UGA. Esme counts the bases in this cut mRNA. How many bases does it have?

   • 15 bases, three in each of 5 codons
   • 10 bases, two in each of 5 codons
   • 12 bases, leaving out the stop codon
   • 5 bases, one for each codon

4. Read this first

   Use this

   mRNA codon (model), 5′-GAU-3′, read against a table excerpt of the standard genetic code. Table excerpt: UAG, stop; GAU, aspartic acid; GAC, aspartic acid; GAA, glutamic acid.

5. 4.

   Jun reads the codon GAU in a table excerpt. Which amino acid does GAU code for?

   • stop, the entry listed beside UAG
   • no amino acid, since GAC already codes for aspartic acid
   • glutamic acid, the amino acid listed beside GAA
   • aspartic acid, the amino acid listed beside GAU
6. 5.

   GCU GCC GCA GCG. Table excerpt of the standard genetic code: GCU, alanine; GCC, alanine; GCA, alanine; GCG, alanine. Luz's table excerpt lists four codons beside alanine. What does this show about the genetic code?

   • Several codons can code for one amino acid
   • A codon can code for several amino acids at once
   • The four codons code for four different amino acids
   • The first codon counts, and the other three are copies
7. 6.

   mRNA (model, not to scale), 5′ to 3′, 14 bases, not cut: GCAUGGUUCAUUAA. The ribosome begins at the first AUG. Milo marks where the ribosome begins on this mRNA. Which group of three bases is the start codon?

   • CAU, bases 9 to 11 from the left
   • AUG, bases 3 to 5 from the left
   • UAA, bases 12 to 14 from the left
   • GCA, bases 1 to 3 from the left
8. 7.

   mRNA (model, not to scale), 5′ to 3′, cut into codons: AUG CCU GAA UAG GGU. Noah reads a cut mRNA. What does the ribosome do when it reaches the codon UAG?

   • It stops, and UAG adds no amino acid
   • It goes back to AUG and reads it again
   • It skips UAG and goes on to read GGU
   • It adds one more amino acid, then stops
9. 8.

   mRNA (model, not to scale), 5′ to 3′, 16 bases, not cut: CCAUGUCUGGAUAAGC. The ribosome begins at AUG and ends at a stop codon. How many amino acids does Pia's mRNA add to the chain?

   • 2 amino acids, leaving out the start codon
   • 5 amino acids, cutting groups from the first base
   • 4 amino acids, counting UAA as well
   • 3 amino acids, from AUG up to UAA

10. Use this

    mRNA codon (model, not to scale), 5′-AUG-3′. The tRNA anticodon is written 3′ to 5′ under it, one base under each base: ? ? ?.

11. 9.

    Tala pairs a tRNA with the start codon AUG. Which anticodon does that tRNA carry?

    • AUG, the same letters as the codon
    • UAC, each base paired with its partner
    • UAG, just the last base copied
    • TAC, DNA letters used for the pairing

12. Use this

    tRNA anticodon (model, not to scale), 3′-CAU-5′. The mRNA codon is written 5′ to 3′ above it, one base over each base: ? ? ?.

13. 10.

    Zee sees a tRNA with the anticodon 3′-CAU-5′. Which mRNA codon does it pair with?

    • GUU, just the first two bases paired
    • GUA, each base paired with its partner
    • CAU, the same letters as the anticodon
    • GTA, DNA letters used for the pairing