Biology flashcards, generated for you.

The maintenance of stable internal conditions (pH, temperature, osmolarity) despite external environmental changes, enabling organisms to function optimally.

Anabolism: biosynthetic pathways that build complex molecules from simpler ones, requiring energy input (e.g., protein synthesis). Catabolism: breakdown of complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

Enzymes lower the activation energy (Ea) of reactions by stabilizing the transition state, allowing substrates to reach it more easily. The enzyme-substrate complex forms, positions reactants optimally, and releases product without being permanently altered.

ATP → ADP + Pi releases ~7.3 kcal/mol under cellular conditions. This energy couples to endergonic reactions (e.g., active transport, muscle contraction) by phosphoryl group transfer, making unfavorable reactions thermodynamically favorable.

The electron transport chain pumps H⁺ ions into the intermembrane space, creating a proton gradient (ΔμH⁺). This electrochemical potential drives ATP synthase, which phosphorylates ADP as H⁺ flows through the F₀ subunit, coupling gradient dissipation to ATP production.

Allosteric regulation: inhibitors/activators bind at sites other than the active site, inducing conformational changes that alter enzyme activity (non-competitive). Competitive inhibition: inhibitors compete directly with substrate for the active site and can be overcome by increasing substrate concentration.

When body temperature rises above 37°C, thermoreceptors signal the hypothalamus to trigger vasodilation, sweating, and reduced metabolic heat production. This decreases temperature back to setpoint, eliminating the stimulus and stopping the response—a corrective mechanism.

Carrier proteins bind specific substrates on one side of the membrane, undergo conformational change, and release the substrate on the opposite side. Movement is down the concentration gradient (no ATP required), driven by diffusion of the solute itself.

Myosin heads (powered by ATP hydrolysis) bind actin thin filaments and pivot, pulling them toward the M-line. Ca²⁺ removes tropomyosin blockade, exposing myosin-binding sites. Coordinated, cyclical attachments of millions of myosin heads shorten sarcomeres without filament length changing.

Competitive inhibitors increase the apparent Km (substrate appears less available) without changing Vmax. Mathematically: Km(app) = Km(1 + [I]/Ki). At sufficiently high substrate concentrations, enzyme kinetics normalize, whereas noncompetitive inhibitors reduce Vmax regardless of [substrate].