AP Biology Unit 3: Cellular Energetics and Enzyme Mechanics Review

Vocabulary flashcards covering enzyme kinetics, controls, cellular respiration, photosynthesis, and bioenergetics based on AP Biology exam review items.

Transition state stabilization

The mechanism by which an enzyme speeds up a reaction by binding to and stabilizing the transition state within the enzyme-substrate complex, thereby decreasing the activation energy of the reaction.

Alcohol dehydrogenase (ADH)

An enzyme that facilitates the breakdown of ethyl alcohol ($C_2H_5OH$) into nontoxic substances; it also binds methyl alcohol, converting it into toxic formaldehyde.

Competitive inhibition

A form of enzyme inhibition where an inhibitor competes directly with the substrate for the active site; increasing substrate concentration overcomes this inhibition by increasing the proportion of active sites bound to substrate.

Amylase

A protein enzyme that catalyzes the breakdown of starch into simple sugars.

Iodine starch indicator

A chemical solution that turns dark-blue in the presence of starch and light-brown when starch is absent, used to determine the rate of amylase-catalyzed starch breakdown.

Atmospheric carbon dioxide ($CO_2$)

The raw material entering plant leaves through stomata that is used during photosynthesis to synthesize sugars and other organic compounds.

ATP hydrolysis coupling

An exergonic, energy-releasing reaction that cells link to energy-requiring reactions to drive essential cellular functions.

Chloroplast proton gradient

A difference in hydrogen ion concentration across the thylakoid membrane (e.g., $\text{pH } 4$ in the thylakoid space versus $\text{pH } 8$ in the stroma) that powers ATP synthase to generate ATP even in the absence of light.

Enzymatic cellular contents control (Test tubes 3 and 7)

Experimental control tubes containing bacterial cellular extracts and substrate without the target enzyme, designed to test whether the isolated bacterial factors possess endogenous enzymatic activity.

Thermodynamic heat loss in photosynthesis

The dissipation of captured light energy as heat during metabolic conversions, resulting in only a portion of captured energy being stored in chemical bonds for growth and repair.

Rate of an enzyme-catalyzed reaction

A quantitative measure of reaction speed, experimentally determined by measuring either the rate of disappearance of substrate or the rate of appearance of product.

Gelatin digestion assay control

A negative control setup in which exposed black camera film containing gelatin is submerged in pure water without digestive enzymes (such as trypsin, lipase, or amylase) to observe non-enzymatic clearing.

Light-dependent reactions

Photosynthetic reactions that depend on photosystems I and II to convert solar energy into chemical energy stored in ATP and NADPH.

Light-independent reactions

Photosynthetic metabolic reactions occurring in the chloroplast stroma that consume the ATP and NADPH generated by light-dependent reactions to reduce carbon dioxide into sugars.

Mitochondrial proton gradient

A hydrogen ion concentration gradient across the inner mitochondrial membrane that favors the downhill movement of protons into the mitochondrial matrix to synthesize ATP.

Lactic acid fermentation

An anaerobic metabolic pathway triggered by oxygen shortage in muscle tissue that produces a buildup of lactic acid.

Phosphagen system

An immediate, short-term ATP-generating system in muscle cells whose rate of ATP production increases and decreases rapidly within the first 10 to 20 seconds of intense exercise.

Direct ammonia excretion

The elimination of nitrogenous waste directly as toxic, highly soluble ammonia into freshwater environments, which conserves metabolic energy compared to converting it to urea.

Denatured enzyme control

An experimental negative control consisting of an enzyme solution pretreated by boiling to verify whether product formation occurs in the absence of functional catalytic activity.

Peroxidase

An enzyme found in many organisms that catalyzes the breakdown of hydrogen peroxide into water and oxygen gas ($O_2$), showing a pH-dependent activity curve that declines significantly above its optimum.

Elysia chlorotica

A species of sea slug capable of photosynthesis, demonstrated experimentally by its ability to grow when exposed to light in the absence of external food sources.

Cytosol

The liquid cellular compartment outside organelles where the enzymatic reactions of glycolysis take place.

Respirometer $CO_2$ absorbent

A chemical substance included inside a respirometer to remove carbon dioxide gas produced during aerobic respiration, allowing volumetric gas changes to accurately reflect oxygen consumption.

Glycolysis

The initial metabolic pathway in carbohydrate catabolism that is shared by both aerobic cellular respiration and alcoholic fermentation.