AP Biology flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Hydrogen bond
- A weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom; responsible for water's cohesion and high specific heat.
- Dehydration synthesis
- A reaction that joins two monomers by removing a water molecule, forming a covalent bond; the reverse reaction, hydrolysis, adds water to break the bond.
- Denaturation
- Loss of a protein's three-dimensional shape caused by heat or pH extremes, disrupting hydrogen and ionic bonds but not peptide bonds, which eliminates function.
- Enzyme
- A protein that catalyzes a reaction by lowering activation energy; it is not consumed and does not change the equilibrium of the reaction.
- Phospholipid bilayer
- Two layers of amphipathic phospholipids with hydrophobic tails facing inward and hydrophilic heads outward, forming the structural basis of cell membranes.
- Water potential
- The potential of water to move across a membrane, calculated as psi = psi_s + psi_p; water moves toward lower (more negative) water potential.
- Facilitated diffusion
- Passive movement of solutes across a membrane through channel or carrier proteins down a concentration gradient, requiring no ATP.
- Endosymbiotic theory
- The hypothesis that mitochondria and chloroplasts arose from engulfed prokaryotes, supported by their double membranes, circular DNA, and ribosomes.
- Glycolysis
- The cytosolic pathway that splits glucose into two pyruvate molecules, netting two ATP and two NADH without requiring oxygen.
- Chemiosmosis
- ATP production driven by a proton gradient across a membrane; protons flow through ATP synthase, which phosphorylates ADP to make ATP.
- Fermentation
- An anaerobic pathway that regenerates NAD+ from NADH so glycolysis can continue, producing no additional ATP beyond glycolysis.
- Calvin cycle
- The stroma reactions of photosynthesis in which rubisco fixes CO2 into three-carbon sugars using ATP and NADPH from the light reactions.
- Signal transduction
- The process by which a cell converts an extracellular signal into a response through reception, transduction, and response stages.
- Second messenger
- A small intracellular molecule such as cAMP or Ca2+ that relays and amplifies a signal from a receptor to downstream effectors.
- Cyclin-dependent kinase
- An enzyme that phosphorylates target proteins to drive cell cycle progression; it is active only when bound to a specific cyclin.
- Apoptosis
- Programmed cell death involving controlled dismantling of the cell; important in development and in preventing uncontrolled proliferation.
- Crossing over
- Exchange of DNA segments between homologous chromosomes during prophase I of meiosis, producing recombinant chromatids and increasing genetic variation.
- Law of segregation
- Mendel's principle that two alleles for a gene separate during gamete formation, so each gamete receives only one allele.
- Independent assortment
- Mendel's principle that alleles of genes on different chromosomes segregate independently during meiosis, generating varied gamete combinations.
- Incomplete dominance
- A pattern in which the heterozygote shows a phenotype intermediate between the two homozygotes, as when red and white flowers produce pink offspring.
- Transcription
- Synthesis of an RNA molecule from a DNA template by RNA polymerase; occurs in the nucleus in eukaryotes and the cytoplasm in prokaryotes.
- Translation
- Ribosome-mediated synthesis of a polypeptide, in which mRNA codons are matched with tRNA anticodons to specify amino acids.
- Lac operon
- An inducible prokaryotic operon that is expressed when lactose is present and glucose is scarce, allowing the cell to metabolize lactose.
- Frameshift mutation
- An insertion or deletion of nucleotides not in multiples of three, shifting the reading frame and usually altering all downstream amino acids.
- Hardy-Weinberg equilibrium
- A model predicting constant allele frequencies across generations when no mutation, migration, selection, or drift occurs and mating is random.
- Genetic drift
- Random change in allele frequencies due to chance, most pronounced in small populations, as in bottleneck and founder effects.
- Directional selection
- A mode of natural selection in which one extreme phenotype is favored, shifting the population mean for the trait over generations.
- Reproductive isolation
- A condition in which populations cannot interbreed to produce fertile offspring, often leading to speciation through accumulated genetic differences.
- Trophic efficiency
- The percentage of energy transferred from one trophic level to the next, typically about ten percent; the remainder is lost mainly as heat.
- Carrying capacity
- The maximum population size an environment can sustain indefinitely given available resources; logistic growth levels off at this value.
- Keystone species
- A species whose influence on community structure is disproportionately large relative to its abundance; its removal causes major ecosystem change.
- Primary succession
- Ecological succession beginning on bare substrate without soil, such as new volcanic rock, where pioneer species establish and build soil.