Features of The Genetic Code
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of DNA, genes & chromosomes. You can test your knowledge on these below.
What is a gene?
A gene is a sequence of DNA bases that codes for a polypeptide or a functional RNA molecule (e.g., tRNA, rRNA).
How is DNA arranged in a chromosome?
DNA is tightly coiled around histone proteins in eukaryotic cells, forming chromosomes that contain multiple genes.
What is a genome?
Genome: The complete set of DNA (genes) in an organism.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains features of the genetic code or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Genetic Code
What is the Genetic Code?
The genetic code is the set of rules that determines how a sequence of DNA bases is translated into an amino acid sequence in a polypeptide.
Key Features of the Genetic Code
Triplet Code
- Each three bases, a triplet in DNA or a codon in mRNA, codes for one amino acid.
- Example: AUG in mRNA codes for methionine.
- Allows for 20 amino acids to be coded using 64 possible codons.
Universal
- The same codons code for the same amino acids in all known organisms (e.g., AUG codes for methionine in bacteria, plants, and humans).
- This supports the theory of evolution as all life shares a common genetic origin.
Degenerate
- More than one codon can code for the same amino acid (e.g., GGU, GGC, GGA, and GGG all code for glycine).
- This reduces the effect of mutations because a change in one base may still result in the same amino acid.
Non-Overlapping
- Each base is only part of one codon or triplet; they do not share bases.
- Example: In AUGGCU, the codons are AUG, GCU, not AUG, UGG, GGC.
- This ensures that the correct polypeptide sequence is produced.
Key Terms
- Genetic Code: The sequence of DNA bases that codes for amino acids in polypeptides.
- Triplet Code: A three-base sequence (triplet / codon) that codes for a single amino acid.
- Codon: A triplet of bases in mRNA that specifies an amino acid.
- Degenerate Code: More than one codon can code for the same amino acid.
- Non-Overlapping: Each base is only part of one codon / triplet.
- Universal: The same codons code for the same amino acids in all organisms.
No answer provided.
Exam Tip
Be careful when defining non-overlapping and degenerate.
No answer provided.
The genetic code is described as triplet, universal, degenerate, and non-overlapping. Explain what each of these terms means (4 marks)
- The triplet code means that each group of three bases in DNA or mRNA codes for one amino acid. (1)
- The universal nature of the genetic code means that the same codons code for the same amino acids in all organisms. (1)
- The code is degenerate, meaning more than one codon can code for the same amino acid. (1)
- The code is non-overlapping: each base is part of only one triplet. Accept codon instead of triplet (as would be applicable to mRNA code) (1)
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!