Foundations

Cell theory describes the organization and reproduction of cellular life.

DNA's base sequence stores biological information.

Gene expression produces functional RNA or protein from gene information.

Complementary base pairing allows DNA strands to serve as copying templates.

DNA duplication, nuclear division and cytoplasmic division are distinct events in a typical mitotic cycle.

Typical diploid meiosis halves the number of chromosome sets through two divisions after one DNA replication.

A diploid individual's paired alleles can segregate into gametes.

Selective membranes and transport proteins regulate movement between a cell and its surroundings.

Mutation changes DNA sequence and can introduce inherited variation.

Movement contributes to gene flow when genetic material enters a population's reproduction.

Allele segregation and phenotype dominance are different questions.

DNA-binding regulators and cellular signals affect transcription.

DNA-associated marks can affect expression without changing DNA sequence.

Replicative DNA polymerases extend a primer's 3′ end while copying a template, synthesizing DNA 5′→3′.

Eukaryotic nuclear DNA is packaged with histones into nucleosomes and replicated from multiple origins.

Polymerase proofreading can remove a wrongly incorporated nucleotide during synthesis.

In homology-directed double-strand-break repair, end processing can produce single-stranded DNA that searches for and invades a homologous duplex.

Transcription begins through regulated recognition of promoter DNA and recruitment of RNA polymerase.

Many eukaryotic pre-mRNAs acquire a 5′ cap and 3′ poly(A) tail, and introns are removed while exons are joined.

Translation reads mRNA codons 5′→3′ and extends a polypeptide from its amino to its carboxyl end.

Linked loci share a chromosome; meiotic recombination can separate their alleles.

Chromosomal inheritance can change through nondisjunction or rearrangements such as deletion, duplication, inversion and translocation.

Actin filaments, microtubules and intermediate filaments organize different structural and dynamic functions in eukaryotic cells.

In the eukaryotic secretory pathway, many membrane and exported proteins enter the rough endoplasmic reticulum, undergo processing and move in vesicles through the Golgi toward selected destinations.

Animal extracellular matrix provides structural and signalling interactions through secreted proteins and cell-surface receptors.

A receptor can convert ligand binding into an intracellular response through protein conformational changes, phosphorylation cascades or second messengers such as cyclic AMP and calcium.

Cyclin abundance and cyclin-dependent kinase regulation help order cell-cycle transitions.

Apoptosis is a regulated route of cell removal initiated by appropriate internal or external signals.

Aminoacyl-tRNA synthetases couple amino acids to cognate tRNAs using ATP-dependent activation.

Canonical eukaryotic initiation recruits a small ribosomal complex near the capped mRNA end and scans for a start codon in a suitable context.