EasyBiologyHigh School (11–12)Heredity and Evolution › Molecular Basis of InheritanceNumericalAPA-LevelIB
A student asks why the genetic code uses three bases for each codon…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student asks why the genetic code uses three bases for each codon. The RNA has four bases.
- How many different codons could a code with 2 bases make?
- How many with 3 bases?
- How many with 4 bases?
- The real code has 61 codons for 20 amino acids. On average, how many codons are there for one amino acid? Give two decimal places.
Need a reminder? The key ideaShow
A codon has three bases. Of the 64 codons, 61 code for amino acids and 3 are stop codons, and AUG is the start codon. A point mutation can be silent, missense or nonsense. An insertion or a deletion of 1 or 2 bases shifts the reading frame, and an insertion or a deletion of 3 bases keeps it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. 4 bases. Codons of 2, 3 and 4 bases. 61 codons and 20 amino acids.
Plan. The number of codons is to the power of the number of places.
Step 1. (a) . This is less than 20, so two bases are not enough.
Step 2. (b) . This is more than enough.
Step 3. (c) .
Step 4. (d) .
Answer: ; ; ; .
Check. The code has a few more codons than amino acids. This is why most amino acids have more than one codon.
Discussion (0)
Log in to join the discussion.
Loading…