Biology 1010 Exam 3 Study Outline

Comprehensive vocabulary flashcards covering enzymes, energy, cellular respiration, photosynthesis, and cell signaling pathways based on the Biology 1010 Exam 3 outline.

Enzyme

A biological catalyst, usually a protein, that speeds up reactions by lowering activation energy.

Substrate

The reactant an enzyme acts on.

Product

The substance formed by a chemical reaction.

Activation energy

The minimum energy needed to start a chemical reaction.

Active site

The region of an enzyme where the substrate binds and the reaction occurs.

Allosteric site

A regulatory binding site separate from the active site.

Allosteric activation

Binding at an allosteric site increases enzyme activity.

Allosteric inhibition

Binding at an allosteric site decreases enzyme activity.

Cofactor

A nonprotein helper required for an enzyme to function; often a metal ion.

Coenzyme

An organic helper molecule that assists an enzyme, often carrying electrons or chemical groups.

Ribozyme

An RNA molecule that catalyzes a chemical reaction.

Endergonic reaction

A reaction that requires free-energy input; $\Delta G$ is positive.

Exergonic reaction

A reaction that releases free energy; $\Delta G$ is negative.

Gibbs free energy ($G$)

Energy available to do useful work under the conditions considered.

Delta ($\Delta$)

Symbol meaning change in a quantity.

Enthalpy ($H$)

A heat-related energy measure; at constant pressure, $\Delta H$ reflects heat absorbed or released.

Exothermic reaction

A reaction that releases heat; $\Delta H$ is negative.

Endothermic reaction

A reaction that absorbs heat; $\Delta H$ is positive.

Entropy ($S$)

A measure related to energy dispersal and the number of possible microscopic arrangements.

Free-energy equation

$$\Delta G = \Delta H - T\Delta S$$

Optimum performance

Conditions under which an enzyme works at its highest rate.

Denaturation

Loss of a protein's normal shape, often reducing or eliminating its function.

Competitive inhibition

An inhibitor competes with substrate for the active site; more substrate can often reduce its effect.

Noncompetitive inhibition

An inhibitor binds at another site and reduces enzyme activity; more substrate does not fully overcome it.

Biochemical pathway

A sequence of reactions in which one reaction's product becomes the next reaction's substrate.

Enzyme cascade

A sequence of activations that can amplify a cellular response.

Feedback inhibition

A pathway's final product inhibits an earlier enzyme in that pathway.

Cellular respiration

The process of transferring energy from organic molecules into ATP.

Aerobic respiration equation

Glucose + oxygen $\rightarrow$ carbon dioxide + water + energy (ATP and heat).

Mitochondrion

Organelle where most aerobic respiration stages occur in eukaryotic cells.

Cristae

Folds of the inner mitochondrial membrane that increase surface area.

Mitochondrial matrix

Inner mitochondrial compartment where pyruvate oxidation and the Krebs cycle occur.

Intermembrane space

Space between mitochondrial membranes where protons accumulate during electron transport.

Glycolysis

Cytoplasmic pathway that splits one glucose into two pyruvate; net 2 ATP and 2 NADH.

Pyruvate oxidation

Conversion of pyruvate to acetyl-CoA, releasing CO■ and producing NADH.

Krebs cycle

Matrix pathway that oxidizes acetyl groups, releases CO■, and produces NADH, FADH■, and ATP.

Electron transport system (ETS)

Inner-membrane protein chain that transfers electrons and helps establish a proton gradient.

Oxidative phosphorylation

ATP production driven by the proton gradient generated by electron transport.

ATP synthase

Enzyme that uses proton flow to produce ATP.

Oxygen in respiration

Final electron acceptor in the ETS; combines with electrons and protons to form water.

ATP

Adenosine triphosphate; a main immediate energy-transfer molecule in cells.

NAD■

Oxidized electron carrier that accepts electrons and becomes NADH.

NADH

Reduced form of NAD■ that carries high-energy electrons.

FAD

Oxidized electron carrier that accepts electrons and becomes FADH■.

FADH■

Reduced form of FAD that carries electrons to the ETS.

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

First law of thermodynamics

Energy cannot be created or destroyed; it is transferred or transformed.

Second law of thermodynamics

Energy transfers increase total entropy; some energy becomes dispersed and less available for work.

Photosynthesis

Process that uses light energy to make energy-rich organic molecules from CO■ and water.

Chloroplast

Organelle where photosynthesis occurs in plants and algae.

Thylakoid

Flattened chloroplast membrane sac containing light-reaction machinery.

Granum / grana

A stack / stacks of thylakoids.

Stroma

Chloroplast fluid where the Calvin cycle occurs.

Chlorophyll

Pigment that absorbs light energy for photosynthesis.

Light reactions

Thylakoid-membrane reactions that use light to produce ATP and NADPH and release O■.

Photosystem II (PSII)

Photosystem that replaces electrons by splitting water and initiates linear electron flow.

Photosystem I (PSI)

Photosystem that re-energizes electrons used to produce NADPH.

Photolysis

Light-driven splitting of water during photosynthesis.

Photophosphorylation

Production of ATP using light energy.

NADP■

Oxidized electron carrier that accepts electrons and becomes NADPH.

NADPH

Reduced electron carrier that supplies reducing power to the Calvin cycle.

Calvin cycle

Stromal reactions that use CO■, ATP, and NADPH to produce carbohydrate precursors.

Carbon fixation

Incorporation of inorganic CO■ into an organic molecule.

Rubisco

Enzyme that catalyzes CO■ fixation in the Calvin cycle.

G3P

Three-carbon sugar used to build carbohydrates and other organic molecules.

RuBP

Five-carbon molecule that accepts CO■ at the start of the Calvin cycle.

C3 plant

Plant whose first stable product of CO■ fixation is a three-carbon compound.

C4 plant

Plant that initially fixes CO■ into a four-carbon compound and concentrates CO■ around rubisco.

Photorespiration

Process in which rubisco reacts with oxygen, reducing photosynthetic efficiency.

Desmosome

Anchoring junction that helps hold neighboring cells together.

Tight junction

Cell junction that seals spaces between neighboring cells and restricts leakage.

Plasmodesmata

Channels through plant cell walls that connect neighboring cell cytoplasms.

Gap junction

Channel connecting animal cells for exchange of ions and small molecules.

Autocrine signaling

A cell releases a signal that acts on the same cell.

Synaptic signaling

A neuron releases neurotransmitter across a synapse to a target cell.

Neurotransmitter

Chemical released by a neuron that carries a signal across a synapse.

Paracrine signaling

A signal acts locally on nearby cells.

Endocrine signaling

Hormones travel through the bloodstream to distant target cells.

Direct-contact signaling

Cells communicate through physical contact or membrane-bound signals.

Ligand

A signaling molecule that binds to a receptor.

Target cell

A cell with the receptor needed to respond to a particular signal.

Hydrophilic signal

Water-soluble signal that generally binds to a cell-surface receptor.

Hydrophobic signal

Lipid-soluble signal that can often cross the membrane and bind an intracellular receptor.

Cell-surface receptor

Membrane protein that binds an external signal and triggers an intracellular response.

Intracellular receptor

Receptor inside the cell that binds a signal, often a hydrophobic hormone.

G protein

Membrane-associated signaling protein that acts as a GTP/GDP-regulated switch.

GTP

Guanosine triphosphate; binding commonly activates a G protein.

GDP

Guanosine diphosphate; G-protein-bound GDP is associated with the inactive state.

Kinase

Enzyme that adds a phosphate group to another molecule, often a protein.

Phosphatase

Enzyme that removes a phosphate group from a molecule.

Phosphorylation

Addition of a phosphate group to a molecule.

Dephosphorylation

Removal of a phosphate group from a molecule.

Kinase cascade

A series of kinase activations that relays and can amplify a signal.

Steroid hormone receptor

Intracellular receptor that binds a steroid hormone and can regulate gene expression.

DNA-binding domain

Part of a protein that binds specific DNA sequences.

Cofactor in gene regulation

A helper molecule or protein that interacts with a regulator to affect gene expression.

Different responses to the same signal

Cells respond differently because they may have different receptors and intracellular pathways.

Cell signaling environment

Signals usually travel through extracellular space unless cells communicate through direct junctions.