AP Biology cheat sheet

Water is polar; hydrogen bonding between molecules gives it high cohesion, adhesion, specific heat, heat of vaporization, and surface tension.

pH = -log[H+]; each unit change is a tenfold change in hydrogen ion concentration.

Carbon forms four covalent bonds, enabling diverse skeletons: straight chains, branches, and rings.

Dehydration synthesis joins monomers by removing water; hydrolysis breaks polymers by adding water.

Proteins have four structural levels; shape determines function, and denaturation destroys function without breaking peptide bonds.

Nucleic acids are polymers of nucleotides joined by phosphodiester bonds between the 3' hydroxyl and 5' phosphate.

Lipids are hydrophobic and include fats (glycerol + fatty acids), phospholipids (amphipathic), and steroids (four fused rings).

Enzymes lower activation energy; they are not consumed and do not alter the equilibrium position of a reaction.

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells compartmentalize reactions in organelles.

Surface area to volume ratio decreases as cell size increases, limiting the efficiency of diffusion for large cells.

Ribosomes synthesize proteins; free ribosomes make cytosolic proteins, bound ribosomes make proteins for secretion or membranes.

Mitochondria and chloroplasts are double-membrane organelles containing their own DNA and ribosomes, consistent with endosymbiosis.

The fluid mosaic model describes membranes as a phospholipid bilayer with embedded proteins, cholesterol, and glycolipids.

Simple diffusion moves small nonpolar molecules down their gradient; facilitated diffusion uses channels or carriers and needs no ATP.

Active transport moves solutes against a gradient using ATP, directly or via a coupled gradient such as the Na+/K+ pump.

Water potential psi = psi_s + psi_p; water moves from higher (less negative) to lower water potential.

Glycolysis occurs in the cytosol, uses 2 ATP, produces 4 ATP and 2 NADH, and nets 2 ATP and 2 pyruvate per glucose.

Pyruvate oxidation and the citric acid cycle occur in the mitochondrial matrix and yield NADH, FADH2, ATP, and CO2.

Oxidative phosphorylation couples electron transport to chemiosmosis; ATP synthase uses the proton gradient to make ATP.

Fermentation regenerates NAD+ so glycolysis can continue when oxygen is absent; it yields no additional ATP.

Photosynthesis light reactions split water, release O2, and produce ATP and NADPH in the thylakoid membranes.

The Calvin cycle uses ATP and NADPH to fix CO2 via rubisco into three-carbon sugars; it occurs in the stroma.

Photosystems are arranged as antenna complexes feeding a reaction center; electrons flow through an electron transport chain.

Cellular respiration and photosynthesis are redox processes; electron carriers (NAD+/NADH, NADP+/NADPH) shuttle reducing power.

Signal transduction has three stages: reception, transduction, and response.

G protein-coupled receptors activate G proteins that exchange GDP for GTP and then activate an effector enzyme.

Receptor tyrosine kinases dimerize and autophosphorylate upon ligand binding, then activate downstream pathways.

Second messengers such as cAMP and Ca2+ amplify signals; a small number of ligand molecules can produce a large response.

The cell cycle has interphase (G1, S, G2) and mitotic phase; DNA replicates during S phase.

Checkpoints at G1, G2, and the spindle checkpoint verify conditions before the cell proceeds.

Cyclins and cyclin-dependent kinases (Cdks) regulate progression; cyclin degradation inactivates Cdks.

Apoptosis is programmed cell death; loss of apoptotic control and checkpoint failure contribute to cancer.

Meiosis produces four haploid cells; homologous chromosomes separate in meiosis I and sister chromatids separate in meiosis II.

Crossing over in prophase I and independent assortment in metaphase I generate genetic variation.

Mendel's law of segregation: two alleles separate during gamete formation, so each gamete carries one allele.

Law of independent assortment applies to genes on different chromosomes or far apart on the same chromosome.

Punnett squares predict genotype and phenotype ratios for single-gene crosses.

Linked genes do not assort independently; recombination frequency between them reflects distance.

Incomplete dominance produces an intermediate phenotype; codominance expresses both alleles simultaneously.

Non-Mendelian patterns include multiple alleles, polygenic traits, and sex-linked traits on the X chromosome.

Transcription copies DNA into mRNA using RNA polymerase; in eukaryotes it occurs in the nucleus.

Translation at the ribosome reads mRNA codons 5' to 3' and pairs them with tRNA anticodons to add amino acids.

The genetic code is redundant but not ambiguous; a codon specifies one amino acid, though several codons may specify the same amino acid.

Eukaryotic mRNA undergoes processing: 5' cap, poly-A tail, and splicing to remove introns.

Operons in prokaryotes coordinate gene expression; the lac operon is inducible and the trp operon is repressible.

Regulation occurs at transcription, RNA processing, translation, and post-translational levels.

Mutations include substitutions (silent, missense, nonsense) and insertions/deletions that can cause frameshifts.

Epigenetic regulation such as DNA methylation and histone modification alters gene expression without changing DNA sequence.

Natural selection acts on phenotypic variation within a population; individuals with higher fitness leave more offspring.

Evolution is a change in allele frequencies in a population over generations.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, no selection, and a large population.

Hardy-Weinberg equations: p + q = 1 and p^2 + 2pq + q^2 = 1, where p and q are allele frequencies.

Directional, stabilizing, and disruptive selection describe how selection shifts or narrows a trait distribution.

Genetic drift (bottleneck and founder effects) changes allele frequencies by chance, especially in small populations.

Gene flow reduces differences between populations; mutation is the ultimate source of new alleles.

Reproductive isolation (prezygotic or postzygotic) can lead to speciation; allopatric and sympatric modes differ by geography.

Energy flows through ecosystems in one direction; nutrients cycle through biotic and abiotic reservoirs.

Trophic levels transfer roughly 10% of energy; the rest is lost as heat, so food chains are short.

Photosynthesis and cellular respiration are the main pathways moving carbon between atmosphere and organisms.

The nitrogen cycle relies on fixation, nitrification, assimilation, ammonification, and denitrification by microbes.

Population growth is exponential when resources are unlimited and logistic when limited by carrying capacity.

Species interactions include competition, predation, herbivory, mutualism, commensalism, and parasitism.

Primary succession begins on bare substrate; secondary succession follows disturbance where soil remains.

Biodiversity increases ecosystem resilience; keystone species have disproportionate effects on community structure.