Unit 5
DNA and proteins.
How four letters keep instructions: the double helix, transcription and translation, mutations, and how CRISPR edits a gene.
Before this unit
The unit, lesson by lesson
Lessons
4 lessons · 21 practice questions · about 2 hours
The double helix
How DNA is built: two strands, four bases and one pairing rule, the hydrogen bonds that hold the ladder together, Chargaff's rule, and how one molecule becomes two.
From gene to protein
How a gene becomes a protein: transcription into messenger RNA, translation in triplets of letters, start and stop codons, and why the genetic code uses three letters.
Mutations
What a change of one letter in a gene does: silent, missense and nonsense mutations and frameshifts, and why losing three letters does less harm than losing one.
Editing genes with CRISPR
How Cas9 finds one site in a genome, why a wrong letter near the PAM stops it and one at the far end does not, and how the cell's repair knocks a gene out or writes new letters into it.