1. Unit 4: Genetic Information, Variation and Relationships between Organisms Lesson 2 The Triplet Code
A sequence of three DNA bases, called a triplet, codes for a specific amino acid.
The genetic code is universal, non-overlapping and degenerate.
In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes.
Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.

2. Central Dogma of Genetics
Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.

3. Starter: What does this code tell you?
Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.
DNA is made up of a polymer of nucleotides with 4 different types of nucleotide bases. These are Adenine, Thymine, Cytosine, Guanine. The order of these bases makes a code, which is read in groups of three.

4. The Triplet code
The sequence of 4 different bases is highly specific and different for each gene.
Every 3 bases is called a codon or a triplet code.
A codon codes for 1 amino acid. (a specific order of codons will code for a polypeptide)
Q: How many types of Amino acid are there?
Explain how can complex proteins occur then?
Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.

5. DNA code is…… 1. Universal
All living things use DNA and triplet code as their genetic code to produce proteins
2. Non-overlapping – each codon is read separately:
TCTGATACTGGAGGT is read as 5 codons.
It is not read as TCT, CTG, TGA, GAT etc.
3. Degenerate
More than one codon can code for the same amino acid.
Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.

6. Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.

7. Non-coding DNA
In the DNA sequence, most of the DNA is non- coding. This is both within genes (Introns and Exons) and between different genes.
It does not code for amino acids, which suggests it has other roles:
- we don’t know
- codes for ribosomal RNA
- codes for transfer RNA
- codes for siRNA
- codes for regRNA
Learning Outcomes:
Describe what is meant by a triplet code for DNA
Explain why the DNA code is universal, non- overlapping and degenerate
Discuss how DNA is also made of non-coding DNA even within genes.