Unit 3 Biology: Metabolism, Cellular Respiration, and Photosynthesis

Vocabulary flashcards generated from lecture materials covering Chapters 8, 9, and 10 of Campbell Biology (An Introduction to Metabolism, Cellular Respiration and Fermentation, and Photosynthesis).

Metabolism

The totality of an organism's chemical reactions, arising from orderly molecular interactions within the cell.

Metabolic Pathway

A series of chemical reactions in which a specific starting molecule is altered step-by-step by enzymes to yield a specific final product.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds ('downhill' reactions, such as cellular respiration).

Anabolic Pathways

Metabolic pathways that consume energy to build complex molecules from simpler ones ('uphill' reactions, such as protein synthesis from amino acids).

Kinetic Energy

The form of energy associated with the relative motion of objects.

Thermal Energy

Kinetic energy associated with the random movement of atoms or molecules, which is transferred from one body to another as heat.

Potential Energy

Energy that matter possesses because of its location or spatial structure.

Chemical Energy

Potential energy available for release in a chemical reaction as complex molecules are broken down into simpler products.

First Law of Thermodynamics

The principle of conservation of energy, stating that energy can be transferred and transformed, but it cannot be created or destroyed.

Second Law of Thermodynamics

The principle stating that every energy transfer or transformation increases the entropy of the universe.

Entropy

A thermodynamic measure of molecular disorder, or randomness, within a system.

Gibbs Free Energy ($G$)

The portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system.

Exergonic Reaction

A spontaneous chemical reaction that proceeds with a net release of free energy ($\Delta G < 0$).

Endergonic Reaction

A nonspontaneous chemical reaction that absorbs free energy from its surroundings ($\Delta G > 0$).

Energy Coupling

The cellular strategy of using an exergonic process to drive an endergonic one, usually mediated by ATP.

ATP (Adenosine Triphosphate)

A molecule composed of ribose, adenine, and three phosphate groups that powers cellular work by releasing free energy during hydrolysis.

Phosphorylation

The transfer of a phosphate group from ATP to another molecule, forming a more reactive phosphorylated intermediate.

Catalyst

A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction.

Enzyme

A macromolecule (typically a protein) that acts as a biological catalyst to speed up a specific reaction by lowering activation energy barriers.

Activation Energy ($E_A$)

The initial amount of energy that reactants must absorb to contort their bonds into an unstable transition state before a chemical reaction can proceed.

Substrate

The specific reactant molecule upon which an enzyme acts.

Active Site

The specific catalytic region on an enzyme where a substrate binds.

Induced Fit

The change in shape of an enzyme's active site so that it binds more snugly to the substrate upon entry.

Cofactor

Any nonprotein molecule or ion, such as iron or zinc, that is required for the proper functioning of an enzyme.

Coenzyme

An organic cofactor required for enzyme activity, often derived from vitamins.

Competitive Inhibitor

A substance that reduces enzyme activity by entering the active site in place of the normal substrate, whose structure it mimics.

Noncompetitive Inhibitor

A substance that impedes enzymatic reactions by binding to a site away from the active site, altering the enzyme's shape and rendering the active site less effective.

Allosteric Regulation

The binding of a regulatory molecule to a protein at one site that affects the function and shape of the protein at another site.

Cooperativity

A mechanism of allosteric activation in which substrate binding to one active site on a multisubunit enzyme stabilizes active conformations at all other subunits.

Feedback Inhibition

A metabolic control mechanism in which the end product of a metabolic pathway allosterically inhibits an enzyme catalyzing an earlier step in the pathway.

Aerobic Respiration

A catabolic pathway in which organic molecules and oxygen ($\text{O}_2$) are consumed to yield ATP.

Anaerobic Respiration

A catabolic pathway in which organic molecules are broken down using an electron transport chain with a final electron acceptor other than oxygen (e.g., sulfate ion $\text{SO}_4^{2-}$).

Fermentation

A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain or oxygen.

Redox Reactions

Chemical reactions involving the complete or partial transfer of one or more electrons between reactants (oxidation-reduction).

Oxidation

The complete or partial loss of electrons from a substance in a redox reaction.

Reduction

The complete or partial addition of electrons to a substance in a redox reaction.

Reducing Agent

The electron donor in a redox reaction, which becomes oxidized in the process.

Oxidizing Agent

The electron acceptor in a redox reaction, which becomes reduced in the process.

$$\text{NAD}^+$$

Nicotinamide adenine dinucleotide; a coenzyme that functions as an electron carrier during cellular respiration.

Electron Transport Chain (ETC)

A sequence of membrane-bound electron carrier proteins that shuttle electrons down redox reactions, releasing energy used to generate ATP.

Glycolysis

A series of reactions that splits glucose into two molecules of pyruvate in the cytosol, yielding a net 2 ATP and 2 $\text{NADH}$.

Substrate-Level Phosphorylation

The enzyme-catalyzed formation of ATP occurring when a phosphate group is transferred directly from an intermediate substrate molecule to ADP.

Acetyl CoA

Acetyl coenzyme A; the entry compound for the citric acid cycle, formed from a two-carbon fragment of pyruvate attached to coenzyme A.

Citric Acid Cycle

An eight-step metabolic cycle that completes the breakdown of glucose by oxidizing pyruvate-derived acetyl CoA to $\text{CO}_2$.

Chemiosmosis

An energy-coupling mechanism that uses energy stored in an $\text{H}^+$ gradient across a membrane to drive cellular work, such as ATP synthesis by ATP synthase.

Proton-Motive Force

The potential energy stored in an $\text{H}^+$ electrochemical gradient generated by pumping hydrogen ions across a membrane.

Alcohol Fermentation

Glycolysis followed by the conversion of pyruvate to ethyl alcohol, releasing $\text{CO}_2$ and regenerating $\text{NAD}^+$.

Lactic Acid Fermentation

Glycolysis followed by the reduction of pyruvate directly by $\text{NADH}$ to form lactate without releasing $\text{CO}_2$.

Obligate Anaerobes

Organisms that carry out only fermentation or anaerobic respiration and cannot survive in the presence of oxygen ($\text{O}_2$).

Facultative Anaerobes

Organisms that can survive using either fermentation or aerobic respiration depending on oxygen availability.

Photosynthesis

The process within chloroplasts that converts solar energy into chemical energy stored in sugar molecules.

Autotrophs

Organisms that sustain themselves without eating anything derived from other organisms ('self-feeders').

Photoautotrophs

Organisms that use light energy to synthesize organic molecules from carbon dioxide and water.

Heterotrophs

Organisms that obtain organic material by consuming other organisms or their dead organic matter.

Mesophyll

The interior tissue of a leaf where chloroplasts are mainly located.

Stomata

Microscopic pores in the leaf epidermis through which $\text{CO}_2$ enters and $\text{O}_2$ exits.

Stroma

The dense fluid surrounding thylakoids within a chloroplast where the Calvin cycle takes place.

Thylakoids

Connected membranous sacs inside chloroplasts stacked into columns called grana, containing chlorophyll.

Chlorophyll

A green pigment located in thylakoid membranes that absorbs light energy to drive photosynthesis.

Photon

A discrete particle of electromagnetic light energy containing a fixed quantity inversely related to wavelength.

Absorption Spectrum

A graph plotting a pigment's light absorption versus wavelength.

Action Spectrum

A graph depicting the relative effectiveness of different wavelengths of light in driving photosynthesis.

Chlorophyll a

The primary light-capturing pigment in chloroplasts that directly participates in the light reactions.

Photosystem

A light-capturing unit in thylakoid membranes consisting of a reaction-center complex surrounded by light-harvesting complexes.

Light-Harvesting Complex

Pigment molecules bound to proteins that absorb photons and transfer energy to chlorophyll a in the reaction-center complex.

Reaction-Center Complex

An association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor.

Primary Electron Acceptor

A molecule in the reaction center that accepts excited electrons from chlorophyll a and becomes reduced.

Linear Electron Flow

The primary pathway of light reactions involving PS II and PS I that produces ATP, $\text{NADPH}$, and $\text{O}_2$ using light energy.

Cyclic Electron Flow

A photoexcited electron pathway involving only PS I that generates ATP without producing $\text{NADPH}$ or oxygen.

Calvin Cycle

An anabolic pathway in the stroma that uses ATP and $\text{NADPH}$ to fix $Sockets\text{CO}_2$$ into glyceraldehyde 3-phosphate (G3P).

Rubisco

RuBP carboxylase-oxygenase; the enzyme catalyzing carbon fixation by attaching $\text{CO}_2$ to ribulose bisphosphate (RuBP).

Photorespiration

A costly metabolic pathway consuming $\text{O}_2$ and organic fuel while releasing $\text{CO}_2$ without generating ATP or sugar, occurring when rubisco binds $\text{O}_2$ instead of $\text{CO}_2$.

$\text{C}_4$ Plants

Plants that minimize photorespiration by incorporating $\text{CO}_2$ into four-carbon compounds in mesophyll cells prior to exporting them to bundle-sheath cells.

CAM Plants

Plants that conserve water using crassulacean acid metabolism, opening stomata at night to fix carbon into organic acids and running the Calvin cycle during the day.