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Science lesson plan · 11th grade (Year 12 in England) · 30 minutes

Bases, codons and amino acids: genetic code calculations

Cells, genetics and evolution

CCSS NGSS.HS-LS1-1CCSS NGSS.HS-LS3-1England: GCSE Biology: Inheritance, variation and evolution (protein synthesis)

Objective and success criteria

Students will: Bases, codons and amino acids: genetic code calculations.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: From gene to protein: transcription and translation

Leads to: the next skill in this area.

Materials: Microscope images or slides, Cell diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (From gene to protein: transcription and translation). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. What does a sequence of three bases (a codon) code for? (one protein / one amino acid / one gene / one chromosome) → one amino acidPrompt: Proteins are chains of these units.
  2. Protein synthesis: which statement is NOT true? (The order of bases decides the order of amino acids. / Transcription happens in the nucleus. / Translation happens at ribosomes. / Each base codes for one amino acid.) → Each base codes for one amino acid.Prompt: Does DNA ever leave the nucleus?
  3. Why is an mRNA copy needed? DNA could be used directly… (mRNA is made of amino acids / DNA is a protein / DNA is too large to leave the nucleus, so a smaller copy carries the code to the ribosome / Ribosomes are inside the nucleus) → DNA is too large to leave the nucleus, so a smaller copy carries the code to the ribosomePrompt: Where are ribosomes found?

Hook · 3 min

  • Show a microscope image of cells and ask what students think they are looking at.
  • Share the objective: Bases, codons and amino acids: genetic code calculations. Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: A protein contains 141 amino acids. What is the minimum number of mRNA bases needed to code for it (ignore the stop codon)?
  • Step 1: 141 × 3 = 423
  • Step 2: So the answer is: 423
  • Answer: 423
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. A protein contains 200 amino acids. What is the minimum number of mRNA bases needed to code for it (ignore the stop codon)? → 600Prompt: Each amino acid is coded by one codon.
  2. The coding part of an mRNA molecule is 453 bases long, including one stop codon at the end. How many amino acids are in the protein? → 150Prompt: Divide by 3 to find the number of codons.

You do: independent practice · 7 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. DNA has 4 different bases. How many different sequences are possible for a group of 1 base? → 4Prompt: There are 4 choices for each position.
  2. A protein contains 50 amino acids. What is the minimum number of mRNA bases needed to code for it (ignore the stop codon)? → 150Prompt: Each amino acid is coded by one codon.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: From gene to protein: transcription and translation.
  • Use concrete materials: microscope images or slides.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.

Free lesson plan from eurekami.com/lesson-plan-builder

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Bases, codons and amino acids: genetic code calculations

Name

Date

Score/ 6

  1. Question 1

    The coding part of an mRNA molecule is 63 bases long, including one stop codon at the end. How many amino acids are in the protein?

    Answer

  2. Question 2

    A protein contains 120 amino acids. What is the minimum number of mRNA bases needed to code for it (ignore the stop codon)?

    Answer

  3. Question 3

    DNA has 4 different bases. How many different sequences are possible for a group of 2 bases?

    Answer

  4. Question 4

    The coding part of an mRNA molecule is 453 bases long, including one stop codon at the end. How many amino acids are in the protein?

    Answer

  5. Question 5

    A protein contains 300 amino acids. What is the minimum number of mRNA bases needed to code for it (ignore the stop codon)?

    Answer

  6. Question 6

    DNA has 4 different bases. How many different sequences are possible for a group of 3 bases?

    Answer

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Answer key: Bases, codons and amino acids: genetic code calculations

  1. 1. 20

  2. 2. 360

  3. 3. 16

  4. 4. 150

  5. 5. 900

  6. 6. 64