Biology: Cells to AP Biology · Module 6 of 15
Gene Expression & Biotechnology
How genes become proteins, what happens when that process changes, and how scientists manipulate it directly.
Transcription & Translation
- Transcription copies a gene's DNA sequence into messenger RNA (mRNA) in the nucleus.
- Translation reads the mRNA in three-base codons at a ribosome, building a protein one amino acid at a time.
- The flow of information is often summarized as DNA → RNA → protein — the "central dogma."
If a DNA template strand reads T-A-C, what mRNA codon is transcribed?
Solution. A-U-G — RNA uses uracil instead of thymine, and pairs complementary to the template (T pairs with A, A pairs with U, C pairs with G).
Mutations
- A mutation is a change in the DNA sequence; it can occur spontaneously or be caused by mutagens (e.g. UV light, chemicals).
- Point mutations change a single base; insertions and deletions can cause a "frameshift," shifting every codon after that point.
- Some mutations are harmful, some are neutral, and a few are beneficial, providing raw material for evolution.
Why do insertion or deletion mutations often have a more drastic effect on a protein than a substitution?
Solution. Inserting or deleting a base shifts the reading frame for every codon that follows (a frameshift), likely changing the entire amino acid sequence downstream, whereas a substitution usually only changes one codon.
Gene Regulation
- Not all genes in a cell are "turned on" at once; gene regulation controls which genes are expressed, when, and how much.
- This is why cells with identical DNA (e.g. a skin cell and a nerve cell) can look and function completely differently — they express different sets of genes.
A liver cell and a muscle cell in the same person have identical DNA. Why do they look and behave so differently?
Solution. Gene regulation causes each cell type to express a different subset of genes, even though they share the same complete genome.
Biotechnology
- Genetic engineering directly manipulates an organism's DNA, such as inserting a gene from one species into another (recombinant DNA).
- CRISPR-Cas9 is a modern gene-editing tool that can precisely cut DNA at a targeted sequence, allowing genes to be removed, added, or edited.
- Applications include GMO crops, gene therapy for genetic diseases, and producing medicines like insulin in bacteria.
How is human insulin commercially produced for diabetics today?
Solution. The human insulin gene is inserted into bacteria through genetic engineering, which then produce insulin in large quantities as they grow and reproduce.
Check yourself
2 of this module's 5 quiz questions. Pick your answers, then check them in the app, with an explanation for every question.
1. What molecule is produced during transcription?
2. What is the correct order of the "central dogma" of molecular biology?