Gene Expression and Regulation
What you must understand
The central dogma flows DNA → RNA → protein. Transcription (nucleus in eukaryotes) makes mRNA; translation (ribosome) builds protein from codons. Know that the genetic code is redundant but unambiguous, and that codons pair with anticodons on tRNA.
Gene regulation controls when and how much protein is made. In prokaryotes, the operon model (lac and trp operons) shows inducible and repressible control. In eukaryotes, regulation occurs at transcription (transcription factors, enhancers), RNA processing, and translation. Epigenetics (DNA methylation, histone modification) alters expression without changing the DNA sequence.
Mutations change sequence: substitutions may be silent, missense, or nonsense; insertions/deletions can cause frameshifts. Biotechnology tools include PCR, gel electrophoresis, and CRISPR.
Traps
- Transcription makes RNA, not protein; translation makes protein.
- A silent mutation changes a base but not the amino acid.
- The lac operon is inducible (turned on by lactose); the trp operon is repressible.
- Epigenetic changes do not alter the DNA sequence.
Rule of thumb
For any mutation question, determine whether the reading frame changes; frameshifts are usually more damaging than substitutions.
Worked example
A single base deletion shifts the reading frame, altering every downstream codon-often producing a nonfunctional protein.