Before this course: Biology: cells, the human body & genes (course 15.5) and Biology Systems: body systems (course 15.5.2). You should know what DNA, genes, chromosomes and alleles are, the base-pairing rule (A-T, C-G) and how to fill in a simple Punnett square. Now we go deeper: how the code is read, how it changes, and how those changes add up to evolution.
01
From gene to protein: reading the code
In simple words
A gene is like a recipe written in a secret code of three-letter words. First the cell copies the recipe onto a note it can carry out of the kitchen office (that is the mRNA). Then a little machine reads the note three letters at a time and clips together the right building blocks, one by one, until it reaches the word that means "stop".
Key facts
- Genetic code: the instructions in a gene that tell a cell how to make a specific protein. The bases are read in three-letter codons (NHGRI).
- Transcription makes an RNA copy of a gene's DNA. This copy, messenger RNA (mRNA), moves from the nucleus to the cytoplasm (NHGRI).
- Translation happens on ribosomes in the cytoplasm, where the mRNA is read and turned into a chain of amino acids (NHGRI).
- Transfer RNA (tRNA) is the adaptor: a specific tRNA pairs with its matching sequence on the mRNA, so the right amino acid is added (NHGRI).
- Numbers: there are 64 codons; 61 specify amino acids and 3 are stop signals (NHGRI). Proteins are built from 20 different amino acids (NHGRI). Because 61 codons share 20 amino acids, most amino acids have more than one codon.
- In the standard code (NCBI), AUG codes for methionine and is the main start codon; UAA, UAG and UGA are the stop codons.
| Codon (mRNA) | Amino acid | Codon (mRNA) | Amino acid |
|---|---|---|---|
| AUG | Methionine (Met), start | GAA, GAG | Glutamic acid (Glu) |
| GCU | Alanine (Ala) | GUG | Valine (Val) |
| UUU, UUC | Phenylalanine (Phe) | ACU | Threonine (Thr) |
| GGC, GGA | Glycine (Gly) | UGG | Tryptophan (Trp) |
| UAA, UAG, UGA | Stop | AAA | Lysine (Lys) |
- In RNA, the base U (uracil) takes the place of T. The mRNA has the same sequence as the gene's coding DNA strand, with U instead of T.
Example (practice sequence, checked with Python)
Coding DNA: ATG GCT TTT GGC TAA. mRNA: AUG GCU UUU GGC UAA. Protein: Met - Ala - Phe - Gly - stop.
Step by step
- Write the coding DNA strand: ATGGCTTTTGGCTAA.
- Rewrite it as mRNA by changing every T to U: AUGGCUUUUGGCUAA.
- Split the mRNA into codons of three, starting at AUG: AUG GCU UUU GGC UAA.
- Look up each codon in the table above and write the amino acid under it.
- Stop when you reach a stop codon. Do not write an amino acid for it.
- Label which steps are transcription (DNA to mRNA) and translation (mRNA to amino acids), and where each happens.
- Check: your chain reads Met - Ala - Phe - Gly and ends at UAA.
Watch on YouTube
Videos by other creators on YouTube, for reference. They are not made by or affiliated with The Future Market.
LESSON 01From gene to protein: reading the code
Read the video script
[Host holding a recipe card] "A gene is a recipe. But the cell does not cook from the original."
[Screen: DNA in the nucleus, an mRNA copy leaving] "First, transcription makes a copy called messenger RNA, and it travels out to the cytoplasm."
[Screen: ribosome reading codons] "Then a ribosome reads the copy three letters at a time. Each three-letter word is a codon."
[Text on screen: 64 codons, 61 amino acids, 3 stops] "There are 64 codons. Sixty-one call for amino acids and three mean stop."
[Host] "Decode AUG GCU UUU GGC UAA and you have built your first tiny protein."
Try it now
Decode this practice mRNA: AUG AAA GAG UGG GGA UAG. Write the amino acid chain. Then write the coding DNA strand it came from (U back to T). Finally, explain in one sentence why the cell needs a stop codon.
ClaudeStuck? Copy a ready-made prompt for Claude
Copy this, open Claude, paste it, and Claude will walk you through the lesson step by step.
For a grown-up: Claude is for adults (18+). Copy this, paste it into Claude, and use the answer to explain the lesson to your child.
I'm learning "Genetics & Evolution: evidence" on The Future Market. Lesson 1: "From gene to protein: reading the code". What the lesson teaches: - Genetic code: the instructions in a gene that tell a cell how to make a specific protein. The bases are read in three-letter codons (NHGRI). - Transcription makes an RNA copy of a gene's DNA. This copy, messenger RNA (mRNA), moves from the nucleus to the cytoplasm (NHGRI). - Translation happens on ribosomes in the cytoplasm, where the mRNA is read and turned into a chain of amino acids (NHGRI). - Transfer RNA (tRNA) is the adaptor: a specific tRNA pairs with its matching sequence on the mRNA, so the right amino acid is added (NHGRI). - Numbers: there are 64 codons; 61 specify amino acids and 3 are stop signals (NHGRI). Proteins are built from 20 different amino acids (NHGRI). Because 61 codons share 20 amino acids, most amino acids have more than one codon. - In the standard code (NCBI), AUG codes for methionine and is the main start codon; UAA, UAG and UGA are the stop codons. - Codon (mRNA) - Amino acid - Codon (mRNA) - Amino acid The exercise I'm working on: Decode this practice mRNA: AUG AAA GAG UGG GGA UAG. Write the amino acid chain. Then write the coding DNA strand it came from (U back to T). Finally, explain in one sentence why the cell needs a stop codon. I'm stuck. Please: 1. Explain the main idea in plain, simple words with one everyday example. 2. Walk me through the exercise one small step at a time. Ask me what I've done so far before giving the next step. 3. Don't just give me the final answer. Help me do it myself, and check my work when I share it.
I'm a parent helping my child (about 8 years old) with a lesson called "From gene to protein: reading the code" from the course "Genetics & Evolution: evidence". Here's what the lesson says: A gene is like a recipe written in a secret code of three-letter words. First the cell copies the recipe onto a note it can carry out of the kitchen office (that is the mRNA). Then a little machine reads the note three letters at a time and clips together the right building blocks, one by one, until it reaches the word that means "stop". The activity: Decode this practice mRNA: AUG AAA GAG UGG GGA UAG. Write the amino acid chain. Then write the coding DNA strand it came from (U back to T). Finally, explain in one sentence why the cell needs a stop codon. Please explain this so an 8-year-old understands: short sentences, a fun everyday example, and no hard words. Then give me 3 simple questions I can ask my child to check they understood, and a way to do the activity together, one tiny step at a time.
Sources
- NHGRI Talking Glossary, Genetic Code: www.genome.gov/genetics-glossary/Genetic-Code
- NHGRI Talking Glossary, Codon: www.genome.gov/genetics-glossary/Codon
- NHGRI Talking Glossary, Transcription: www.genome.gov/genetics-glossary/Transcription
- NHGRI Talking Glossary, Translation: www.genome.gov/genetics-glossary/Translation
- NHGRI Talking Glossary, Transfer RNA: www.genome.gov/genetics-glossary/Transfer-RNA
- NHGRI Talking Glossary, Amino Acids: www.genome.gov/genetics-glossary/Amino-Acids
- NCBI (NIH), The Genetic Codes, standard code: www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?chapter=tgencodes#SG1
My notes
Saved on this device
02
Mutations: when the code changes
This lesson is part of full access: every course and every level for one payment.
03
Inheritance patterns and testing your predictions
This lesson is part of full access: every course and every level for one payment.
04
Population genetics: the Hardy-Weinberg check
This lesson is part of full access: every course and every level for one payment.
05
How evolution works: selection, drift and more
This lesson is part of full access: every course and every level for one payment.
06
The evidence: fossils, DNA and evolution we can watch
This lesson is part of full access: every course and every level for one payment.
07
Reading evolutionary trees and judging claims
This lesson is part of full access: every course and every level for one payment.
++
Final project
This lesson is part of full access: every course and every level for one payment.
??
Quiz
What are transcription and translation?
Transcription copies a gene's DNA into mRNA; translation reads the mRNA on ribosomes to build a chain of amino acids.
How many codons are there, and how many are stop signals?
64 codons; 3 are stop signals (61 specify amino acids).
What protein does AUG GCU UUU GGC UAA make?
Met - Ala - Phe - Gly, then stop.
Why is a frameshift usually worse than a single-base missense change?
Every codon after the frameshift is read in the wrong groups, so the rest of the protein changes.
What is the amino acid change in the sickle cell variant of beta-globin?
Glutamic acid is replaced by valine at position 6 (Glu6Val).
What ratio do you expect from a cross of two RrYy parents when the genes are on different chromosomes?
9 : 3 : 3 : 1.
A chi-square result is 0.71 and the critical value is 7.81. What do you conclude?
The results fit the prediction; the differences could easily be chance.
If 1 in 100 people show a recessive trait, about what share are carriers under Hardy-Weinberg?
About 18% (2pq with q = 0.1, p = 0.9).
Name the four forces that change allele frequencies.
Mutation, natural selection, genetic drift and gene flow.
Why has the hemoglobin S allele stayed common where malaria is common?
One copy (sickle cell trait) helps protect against severe malaria, even though two copies cause sickle cell disease.
Name four independent lines of evidence for evolution from the course.
Fossils (Tiktaalik), DNA comparisons (human and chimpanzee genomes), evolution observed in the wild (Darwin's finches) and in the lab (E. coli citrate use).
Did humans evolve from chimpanzees?
No. Humans and chimpanzees share a common ancestor from about 6 million years ago.
EX
Final exam
This lesson is part of full access: every course and every level for one payment.
CE
Certificate
This lesson is part of full access: every course and every level for one payment.