UNIT 06 / REVIEW

Gene Expression and Regulation

Your DNA has instructions. Reading them correctly remains your problem.

Active recall activities40 original questions · 6 topics

MAKE THE CONNECTION · SIMPLIFIED MODEL

DNA

Transcription

RNA

Translation

Protein

Use this overview to connect processes. Review the details below for mechanisms and exceptions.

01 / DNA replication

DNA is copied semiconservatively. Polymerases extend new strands 5′→3′ using an existing 3′ end; complementary strands run antiparallel.

Common trap: Do not say the lagging strand is synthesized 3′→5′. Its fragments are made 5′→3′, just like every other new DNA strand.

02 / Transcription and RNA processing

RNA polymerase reads a DNA template 3′→5′ and builds complementary RNA 5′→3′. Eukaryotic pre-mRNA is processed before translation.

Common trap: RNA is not a copy of both strands glued together. Also, splicing changes the RNA product, not the genomic sequence.

03 / Translation

Ribosomes read mRNA codons 5′→3′. tRNAs pair anticodons with codons and deliver amino acids; stop codons recruit release factors.

Common trap: Do not read a DNA template directly from a codon chart. Charts describe mRNA codons, and codons must be read in the established frame.

04 / Gene regulation

Cells regulate which genes are expressed, when, and how much. Shared DNA can support different cell identities through different expression patterns.

Common trap: A liver cell does not become different from a neuron because it throws away the unused genes. Most such cells retain essentially the same genome.

05 / Mutations

Mutations alter genetic material. Their effects depend on location, sequence change, cellular context, and environment.

Common trap: Mutations are not always harmful, and a silent coding substitution is not proof that every possible cellular effect is absent.

06 / Biotechnology

PCR amplifies selected DNA, gels separate DNA fragments mostly by size, and engineered DNA can test how sequences affect function.

Common trap: A bright gel band is not proof that a gene is highly expressed. PCR of genomic DNA and measurement of gene expression answer different questions.

Keep going

Original review notes informed by standard biology principles. Check the official AP Biology framework ↗ and OpenStax Biology 2e ↗ for further reading.