Enzyme: A protein that speeds up a chemical reaction by lowering activation energy Substrate: The molecule an enzyme acts upon Active site: The region of an enzyme where the substrate binds Activation energy: Energy needed to start a reaction Competitive inhibitor: A molecule that blocks the active site Allosteric regulation: Control of an enzyme by binding at a site other than the active site Denaturation: Loss of a protein's shape and function Hydrogen bond: A weak attraction between a partly positive hydrogen and a partly negative atom Cohesion: Attraction between molecules of the same substance Adhesion: Attraction between different substances Polar molecule: A molecule with uneven charge distribution Monomer: A small unit that links with others to make a polymer Dehydration synthesis: Joining monomers by removing water Hydrolysis: Breaking a polymer by adding water Carbohydrate: Sugars and starches; main quick energy source Lipid: Fats, oils and steroids; not water-soluble Phospholipid: A lipid with a hydrophilic head and hydrophobic tails; forms membranes Nucleic acid: DNA or RNA; stores and carries genetic information Peptide bond: The covalent link between amino acids Primary protein structure: The sequence of amino acids Secondary protein structure: Alpha helices and beta sheets formed by hydrogen bonds Tertiary protein structure: The overall 3-D folding of one polypeptide Quaternary protein structure: Several polypeptides joined together Fluid mosaic model: The membrane is a flexible layer of lipids with embedded proteins Diffusion: Movement of molecules from high to low concentration Osmosis: Diffusion of water across a selectively permeable membrane Facilitated diffusion: Passive transport through a channel or carrier protein Active transport: Movement against a gradient using energy Endocytosis: Cell takes in material by folding the membrane around it Exocytosis: Cell releases material by vesicles fusing with the membrane Hypotonic solution: Lower solute concentration than the cell; cell gains water Hypertonic solution: Higher solute concentration than the cell; cell loses water Isotonic solution: Equal solute concentration; no net water movement Water potential: A measure of water's tendency to move; it moves from high to low Nucleus: Organelle holding DNA Rough ER: Studded with ribosomes; makes proteins for export Smooth ER: Makes lipids and detoxifies Golgi apparatus: Modifies, sorts and packages proteins Lysosome: Organelle containing digestive enzymes Endosymbiosis: Theory that mitochondria and chloroplasts came from engulfed prokaryotes ATP: The cell's main energy currency Glycolysis: Splitting glucose into two pyruvate in the cytoplasm Krebs cycle: Reactions in the mitochondrial matrix that release CO2 and carry electrons Oxidative phosphorylation: ATP production using the electron transport chain and chemiosmosis Chemiosmosis: ATP made as protons flow back through ATP synthase Fermentation: Making ATP without oxygen by regenerating NAD+ Light reactions: Photosynthesis stage in thylakoids that makes ATP, NADPH and O2 Calvin cycle: Stage that uses ATP and NADPH to build sugar from CO2 Rubisco: The enzyme that fixes carbon dioxide in the Calvin cycle Chlorophyll: The main pigment that absorbs light for photosynthesis Photosystem: A cluster of pigments and proteins that captures light energy Cell cycle: The ordered life of a cell from one division to the next Interphase: G1, S and G2: growth and DNA copying Mitosis: Nuclear division producing two identical nuclei Cytokinesis: Division of the cytoplasm Checkpoint: A control point that decides whether the cell cycle continues Cyclin: A protein that regulates progress through the cell cycle Meiosis: Two divisions that produce four haploid cells Crossing over: Exchange of DNA between homologous chromosomes in prophase I Independent assortment: Random orientation of chromosome pairs, creating variety Nondisjunction: Failure of chromosomes to separate properly Allele: A version of a gene Genotype: The set of alleles an individual has Phenotype: The observable trait Homozygous: Having two identical alleles for a gene Heterozygous: Having two different alleles for a gene Law of segregation: The two alleles for a gene separate into different gametes Law of independent assortment: Genes for different traits are inherited independently if on separate chromosomes Incomplete dominance: Heterozygote shows a blend of the two phenotypes Codominance: Both alleles are fully expressed Sex-linked trait: A trait whose gene lies on a sex chromosome Linked genes: Genes close together on a chromosome that tend to be inherited together Replication: Copying DNA before cell division Semiconservative: Each new DNA molecule has one old and one new strand DNA polymerase: Enzyme that adds nucleotides during replication Helicase: Enzyme that unwinds the DNA double helix Okazaki fragments: Short DNA pieces made on the lagging strand Transcription: Making RNA from a DNA template Translation: Making a protein from mRNA at a ribosome Codon: Three mRNA bases that code for one amino acid Anticodon: Three tRNA bases that pair with a codon Intron: A noncoding region removed from RNA Exon: A coding region kept in mature RNA Operon: A cluster of bacterial genes controlled together Lac operon: An inducible operon that lets bacteria digest lactose when it is present Transcription factor: A protein that helps turn genes on or off Point mutation: A change in a single DNA nucleotide Frameshift mutation: An insertion or deletion that shifts the reading frame PCR: A technique for copying a specific DNA segment many times Gel electrophoresis: Separating DNA fragments by size using an electric current Restriction enzyme: Enzyme that cuts DNA at a specific sequence CRISPR: A gene-editing tool derived from a bacterial defense system Recombinant DNA: DNA combined from different sources Natural selection: Individuals with helpful heritable traits leave more offspring Fitness: An organism's success at passing on its genes Genetic drift: Random change in allele frequencies, strongest in small populations Gene flow: Movement of alleles between populations Founder effect: Drift caused by a small group starting a new population Bottleneck effect: Drift caused by a sharp drop in population size Hardy-Weinberg equilibrium: A model of a non-evolving population: p + q = 1 Speciation: Formation of new species Allopatric speciation: Species form after geographic separation Homologous structures: Similar structures due to shared ancestry Analogous structures: Similar function from separate evolution Phylogenetic tree: A diagram of evolutionary relationships Cladogram: A branching diagram based on shared derived traits Endothermic: Producing body heat from metabolism Negative feedback: A response that reduces the original change Positive feedback: A response that amplifies the original change Signal transduction: A pathway converting a signal outside the cell into a response inside Ligand: A molecule that binds to a receptor Second messenger: A small molecule that spreads a signal inside the cell, like cAMP Apoptosis: Programmed cell death Carrying capacity: The maximum population an environment can support Logistic growth: S-shaped growth that levels off at carrying capacity Exponential growth: J-shaped growth with unlimited resources Keystone species: A species with a large effect on its community relative to its numbers Trophic level: A feeding level in a food chain Primary productivity: Rate at which producers store energy Biogeochemical cycle: Movement of an element between living things and the environment Niche: The role and conditions an organism needs in its ecosystem Competitive exclusion: Two species needing the same resource cannot coexist indefinitely Succession: Gradual change in a community over time Free flashcards from Peabody at peabody.kids/flashcards/tp-ap-biology