Bagrut Biology 5 Units key terms

A membrane-bound or non-membrane-bound structure inside a eukaryotic cell that performs a specific job, such as energy conversion, protein synthesis, or waste breakdown, separating incompatible reactions into compartments.

The accepted description of the plasma membrane as a fluid phospholipid bilayer in which proteins, cholesterol, and glycolipids drift laterally, giving the membrane selective permeability and dynamic behavior.

Two stacked layers of phospholipids with hydrophobic tails facing inward and hydrophilic heads facing outward, forming the core structure of all biological membranes and blocking most water-soluble molecules.

Double-membraned organelle where pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation occur; the inner membrane folds into cristae bearing the electron transport chain and ATP synthase.

Double-membraned plant organelle containing thylakoid stacks and stroma, where light reactions generate ATP and NADPH and the Calvin cycle fixes carbon dioxide into sugar.

Network of membranes continuous with the nuclear envelope; rough ER studded with ribosomes folds and modifies secreted proteins, while smooth ER synthesizes lipids and detoxifies compounds.

Stack of flattened membranous sacs that receives vesicles from the ER, modifies and sorts proteins and lipids by adding sugar groups, then dispatches them to their final destinations.

Acidic vesicle containing hydrolytic enzymes that digest macromolecules, worn-out organelles, and material taken in by endocytosis; abundant in animal cells and rare in plant cells.

Net diffusion of water across a selectively permeable membrane from a region of higher water potential to lower water potential, driven by solute concentration differences between compartments.

Passive movement of polar or charged solutes across a membrane through channel or carrier proteins, down their concentration gradient and without expenditure of cellular energy.

Movement of solutes against their concentration gradient by membrane pumps that consume energy, typically ATP hydrolysis, allowing cells to maintain gradients such as high internal potassium.

Protein catalyst that lowers activation energy by stabilizing the transition state, binds substrates at a specific active site, and is not consumed by the reaction it accelerates.

The minimum energy input required for reactant molecules to reach the transition state and proceed to product; enzymes reduce this barrier without altering the overall free-energy change.

Reversible inhibition in which a molecule resembling the substrate occupies the active site, raising the substrate concentration needed for a given rate but not changing maximum velocity.

Control of enzyme activity by a molecule binding at a site other than the active site, shifting the enzyme between active and inactive conformations and often producing feedback control of pathways.

Loss of a protein's three-dimensional shape and function caused by heat, extreme pH, or chaotropic agents that disrupt hydrogen bonds and other weak interactions stabilizing the structure.

Ten-step cytosolic pathway that splits one glucose into two pyruvate molecules, yielding a net two ATP and two NADH without requiring oxygen; it is the shared first stage of aerobic and anaerobic respiration.

Mitochondrial matrix cycle in which acetyl-CoA is fully oxidized to carbon dioxide, generating NADH, FADH2, and GTP per turn; also called the citric acid or tricarboxylic acid cycle.

Production of ATP in mitochondria driven by a proton gradient built by the electron transport chain and discharged through ATP synthase, using oxygen as the final electron acceptor.

Rotary membrane enzyme that lets protons flow down their electrochemical gradient and couples that flow to the phosphorylation of ADP, forming most of the cell's ATP.

Use of a transmembrane proton gradient as an energy intermediate: protons pumped across a membrane return through ATP synthase, converting stored electrochemical potential into chemical bond energy in ATP.

Light-independent chloroplast pathway in which Rubisco fixes carbon dioxide onto ribulose bisphosphate, and ATP and NADPH from the light reactions reduce the product to sugar while regenerating the acceptor.

Mode of DNA copying in which each parental strand serves as a template, so every daughter double helix contains one old strand and one newly synthesized strand.

Enzyme that adds deoxynucleotides to a growing DNA strand complementary to the template, working only in the 5' to 3' direction and requiring a primer with a free 3' hydroxyl.

Synthesis of an RNA molecule from a DNA template by RNA polymerase, which binds a promoter, unwinds the duplex, and adds ribonucleotides complementary to the template strand.

Ribosome-driven assembly of a polypeptide in which transfer RNA molecules carrying amino acids pair with mRNA codons, and peptide bonds form between successive amino acids.

A triplet of mRNA bases that specifies one amino acid or a stop signal; the genetic code is degenerate, meaning several codons can encode the same amino acid.

Insertion or deletion of a number of bases not divisible by three, which shifts the reading frame downstream and usually destroys the protein from that point onward.

Principle that the two alleles of a gene separate during meiosis so each gamete receives only one, making offspring genotype ratios predictable from parental genotypes.

Principle that alleles of genes on different chromosome pairs are distributed to gametes independently, producing new combinations; it fails for genes on the same chromosome.

Tendency of genes located close together on the same chromosome to be inherited together; recombination frequency between them reflects their physical distance.

Reciprocal exchange of chromosome segments between homologous chromatids during prophase I of meiosis, breaking linkage and generating new allele combinations in gametes.

Model in which allele and genotype frequencies in a population stay constant across generations when there is no selection, mutation, migration, drift, or non-random mating; departures reveal evolution.

Differential survival and reproduction of individuals whose heritable traits suit their environment better, causing those alleles to increase in frequency over generations.

Random change in allele frequencies from generation to generation due to sampling of gametes, strongest in small populations, where it can fix alleles regardless of their effect.

Control mechanism in which a deviation from a set point triggers a response that reduces the deviation, keeping variables such as body temperature and blood glucose within narrow limits.

Peptide hormone released by pancreatic beta cells when blood glucose rises; it promotes glucose uptake into muscle and fat and glycogen storage in liver, lowering blood glucose.

Defense mediated by lymphocytes that recognize particular antigens, including antibody production by B cells and killing of infected cells by cytotoxic T cells, and that leaves memory cells behind.

Process in which an antigen binds the few lymphocytes whose receptors fit it, stimulating those cells to divide into a clone of effector cells and long-lived memory cells.

Maximum population size that a given environment can sustain indefinitely, set by limiting resources; growth slows as population size approaches it, producing logistic rather than exponential growth.

Colonization and community development on a substrate that never previously supported life, such as bare rock or new volcanic land, beginning with pioneer species that build soil.

Investigation in which all variables except the tested independent variable are held constant, and a control group lacking the treatment allows the effect to be attributed to that variable.