Foundations

Signals from one embryonic region can influence cell fate in another.

In a random-mating diploid model, genotype frequencies are reweighted by relative survival and normalized by mean fitness.

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.

The canonical glycolytic pathway converts one six-carbon glucose into two three-carbon pyruvates.

Pyruvate dehydrogenase converts pyruvate to acetyl-CoA with CO₂ release and NADH formation.

A respiratory electron-transport chain couples favourable electron transfers to an electrochemical proton gradient across a membrane.

Fermentation regenerates oxidized electron carriers by transferring electrons to metabolic organic intermediates, permitting substrate-level ATP production without the aerobic respiratory chain.

In oxygenic photosynthesis, photosystems II and I use absorbed light to drive electron transfer from water toward reduction of NADP⁺.

The Calvin–Benson cycle carboxylates ribulose-1,5-bisphosphate through RuBisCO, reduces the resulting carbon compounds using ATP and NADPH, and regenerates the acceptor.

NAD(H) and NADP(H) commonly carry hydride equivalents, while flavins can participate in one- or two-electron chemistry.

For a typical saturated even-chain fatty acyl-CoA, β-oxidation repeats oxidation, hydration, oxidation and thiolytic cleavage.

In the canonical fatty-acid-synthase pathway, ATP-dependent acetyl-CoA carboxylation supplies malonyl units.

Gluconeogenesis makes glucose from suitable noncarbohydrate precursors.

Glycogen synthase uses activated UDP-glucose to extend glucan chains, while branching creates additional nonreducing ends.

The oxidative pentose-phosphate route converts glucose-6-phosphate toward pentose phosphate with CO₂ release and NADPH formation.

PLP-dependent transamination transfers an amino group between an amino acid and a keto acid without requiring free ammonia as the immediate product.