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Week 14 · Assignment: Traditional alternative (no AI)

Week 14 — From Template to Protein: The Gene-Expression Report — Traditional alternative (no AI)

Introduction to Biology Free sample edition
Traditional alternative (no AI), unpublished. In the course this is a separate assignment that ships unpublished beside the adaptive assignment: same objective, no AI. An instructor who prefers it publishes it and unpublishes or deletes the adaptive one, as the note at its top says.

Instructors: publish this instead of the adaptive version if you prefer, and unpublish or delete the adaptive one.

Assignment 13 of the term — carry a gene from template to protein, count what the genetic code gives you, and explain to a friend whether every one-letter change alters a protein.

This week you followed a gene from DNA to protein — transcription writes an mRNA from the template strand in the nucleus, and translation reads that mRNA in codons of three at a ribosome in the cytoplasm — and you met the redundancy of the genetic code. In this assignment you work four short problems, interpret each one, and explain to someone who has never studied biology whether every one-letter change alters a protein. This week's lecture tutorial, quiz, discussion, and Biology Lab & Inquiry practise the same ideas from other angles. It builds on Week 13's base-pairing rule, which is the rule RNA polymerase uses to write each message.

The task

The two decoded genes are model sequences built for this course, with every codon call from the standard genetic code table. Gene 1's template strand is 3′-TAC CGA ATA ACT-5′, and its mRNA is 5′-AUG GCU UAU UGA-3′. Use this codon table: AUG = Met (start); GCU and GCC = Ala; UAU = Tyr; GAG = Glu; GUG = Val; UAA, UAG, UGA = stop.

Work these four problems, showing your arithmetic:

  1. Gene 1's mRNA, 5′-AUG GCU UAU UGA-3′, has 12 bases, and the genetic code is read 3 bases at a time. How many codons does the mRNA contain?
  2. Gene 1's mRNA has 4 codons, and the last codon, UGA, is a stop codon that codes for no amino acid. How many amino acids are in the protein?
  3. The genetic code uses 4 bases, read 3 at a time, and 3 of the resulting codons are stop codons. How many codons code for amino acids?
  4. 61 codons code for amino acids, but there are only 20 common amino acids. How many more codons than common amino acids are there?

Beside each answer, add one brief interpretation:

  • Problem 1: explain where reading starts and why it moves in steps of three (the reading frame), and name where in the cell translation happens.
  • Problem 2: show, triplet by triplet, that Gene 1's template pairs to its mRNA and scan the mRNA for T, name the protein from the codon table, and explain what ends the chain at the stop codon.
  • Problem 3: name the three stop codons, and explain the two jobs the start codon AUG does.
  • Problem 4: explain the redundancy of the genetic code with the GCU and GCC pair, and contrast it with the change from GAG to GUG in sickle cell disease.

Explain it to a non-expert

A friend reads a news story about "typos in DNA" and asks, "Does every one-letter change in a gene change the protein it makes?" Write a 3–5 sentence message that explains, in everyday words, why some one-letter changes leave a protein the same and others change it, connects it to your Problem 4 work, and names one limit, including that Gene 1 is a model sequence built for this course. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a friend asking why bread dough rises. Model answer: "The yeast in the dough breaks down sugar when there is little oxygen, a process called fermentation, and it gives off carbon dioxide gas. The gas gets trapped in the stretchy dough, so the dough puffs up. This explains the rise, but it does not tell you exactly how long your dough needs, which depends on things like how warm your kitchen is."

Use that pattern for your friend's question, with your own wording and evidence.

Show your arithmetic. A reader should be able to reproduce every number you report from the bases, codons, and counts in the problems without guessing which values or steps you used.

Deliverables

Submit a single report containing:

  • the four answers, each with the arithmetic shown and the brief interpretation the task names for that problem;
  • your message to your friend, explaining in everyday words why some one-letter changes leave a protein the same and others change it, with one limit; and
  • a one-line restatement of Gene 1's template and mRNA as you used them, so your results are reproducible.

Keep it to roughly one page. Clear and correct beats long.

Choose how you show it. Present your report as written text, or as a recorded audio or video explanation of about three minutes with a transcript, or as a labelled hand-drawn sketch of the mRNA split into codons with a short note. Every form is graded by the same scoring criteria. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

This version is designed to be completed without AI: do the arithmetic, the interpretations, and the writing yourself, without a chatbot or other AI tool. You may use a calculator, a spreadsheet, or a printed codon table. Submitting AI-generated work as your own, or copying another student's work, is an integrity violation under the course policy.

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