From Gene to Protein · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How a gene builds its protein

Science · Genetics & Evolution · ages 15-16
Name ______________________   Date ____________

  1. Where is mRNA made, and where is it read?

    • Made in the nucleus, read at the ribosome
    • Made at the ribosome, read in the nucleus
    • Made and read inside the gene

  2. How many bases make one codon?

    • One
    • Two
    • Three

  3. Why must the mRNA message leave the nucleus?

    • Ribosomes that build the chain sit outside it
    • DNA would dissolve in the cytoplasm
    • Codons only exist outside the nucleus

  4. Using the mini table, what ends the chain in AUG GGG UAA?

    • GGG, which codes glycine
    • UAA, which is a stop triplet
    • AUG, which restarts it

  5. Using the mini table, what does AUG UUU code for?

    • Stop, then glycine
    • Start, then phenylalanine
    • Phenylalanine, then start

  6. Why is the genetic code read in threes rather than pairs?

    • Triplets copy faster than pairs
    • Pairs give 16 words, too few for 20 amino acids
    • The nucleus only admits triplets

  7. A cell needs lots of one protein fast. Which plan fits how genes work?

    • Print many mRNA copies of the gene at once
    • Move ribosomes into the nucleus
    • Read the DNA in pairs for speed

  8. A student decodes AUGUUUGGG as AUG UUU GGG but starts from the second letter instead. What goes wrong?

    • Nothing, any start point gives the same chain
    • Every triplet shifts, so the acids come out wrong
    • The chain only gets longer
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How a gene builds its protein W1-mt_PdNyzTl8Ye-s1

  1. Made in the nucleus, read at the ribosome · Transcription copies in the nucleus, then translation reads outside it.
  2. Three · Every codon is a three base word naming one amino acid.
  3. Ribosomes that build the chain sit outside it · The builders live outside, so the instructions must travel to them.
  4. UAA, which is a stop triplet · UAA is a stop triplet, so the ribosome releases the chain there.
  5. Start, then phenylalanine · AUG means start and UUU means phenylalanine.
  6. Pairs give 16 words, too few for 20 amino acids · Sixty four triplet words cover all 20 acids plus stops.
  7. Print many mRNA copies of the gene at once · One gene can birth many messages, and ribosomes build from each.
  8. Every triplet shifts, so the acids come out wrong · The frame is set by the start codon, and shifted frames spell gibberish.
Worksheet · LightMySky