Exam 2 huge study

Metabolism

The total of all chemical reactions that occur within a cell or organism.

Metabolic pathway

A series of chemical reactions where the product of one reaction becomes the reactant for the next reaction.

Anabolic pathways

Pathways that build larger molecules from smaller molecules and require energy.

Catabolic pathways

Pathways that break larger molecules into smaller molecules and release energy.

Kinetic energy

Energy of motion. Example: a moving object.

Potential energy

Stored energy. Example: chemical energy stored in ATP or glucose.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transferred or transformed.

Second Law of Thermodynamics

Every energy transfer or transformation increases the entropy (disorder) of the universe.

Positive ΔG

Indicates a reaction that requires an input of energy and is endergonic; not spontaneous.

Negative ΔG

Indicates a reaction that releases free energy and is exergonic; can occur spontaneously.

ΔG = ΔH − TΔS

One of the equations for determining free energy change.

ΔG = G(products) − G(reactants)

Another equation to determine the change in free energy.

ATP

Adenosine triphosphate, the main energy-carrying molecule used by cells.

ADP + Pi + energy → ATP

The process of making ATP by adding a phosphate group to ADP using energy.

ATP hydrolysis

The process that breaks ATP down into ADP and phosphate, releasing free energy.

Activation energy (Ea)

The minimum amount of energy required to start a chemical reaction.

Transition state

The unstable, high-energy state that molecules temporarily reach during a chemical reaction.

Enzymes

Biological catalysts, usually proteins, that speed up chemical reactions by lowering activation energy.

Active site

The location on an enzyme where the substrate binds and the chemical reaction occurs.

Allosteric site

A separate location on an enzyme where molecules can bind and change the enzyme's activity.

Induced fit

When an enzyme changes shape slightly after substrate binding, facilitating a more efficient reaction.

Competitive inhibition

Inhibitor binds to the active site, competing with the substrate.

Noncompetitive (allosteric) inhibition

Inhibitor binds to an allosteric site, changing the enzyme's shape and reducing its functionality.

Feedback inhibition

A method of regulating catabolism where the end products inhibit the enzymes involved.

Glycolysis

The metabolic pathway that breaks glucose into pyruvate.

Citric acid cycle (Krebs cycle)

The cycle that further breaks down products of glucose oxidation and produces electron carriers.

Fermentation

A process that allows glycolysis to continue when oxygen is unavailable by regenerating NAD⁺.

NAD⁺

An electron acceptor that becomes reduced to NADH during cellular respiration.

FAD

Another electron acceptor that becomes reduced to FADH₂ during cellular respiration.

A redox reaction

A reaction that involves the transfer of electrons.

Oxidizing agent

Substance that accepts electrons and gets reduced.

Reducing agent

Substance that donates electrons and becomes oxidized.

Substrate-level phosphorylation

The direct production of ATP by transferring a phosphate group from a substrate to ADP.

G3P

Glyceraldehyde-3-phosphate, a sugar molecule produced in the Calvin cycle.

RuBisCO

The enzyme that catalyzes the reaction of carbon fixation in the Calvin cycle.

Photorespiration

When RuBisCO binds to oxygen instead of carbon dioxide, reducing photosynthetic efficiency.

Oxidative phosphorylation

The production of ATP using energy derived from the redox reactions of an electron transport chain and chemiosmosis.

Electron transport chain

A sequence of electron carrier proteins that shuttle electrons during redox reactions, releasing energy used to pump protons across a membrane.

Chemiosmosis

An energy-coupling mechanism that uses the energy stored in a hydrogen ion gradient across a membrane to drive ATP synthesis.

ATP synthase

A membrane-spanning enzyme complex that utilizes the flow of protons down their electrochemical gradient to synthesize ATP from ADP and inorganic phosphate.

Proton-motive force

The potential energy stored in an electrochemical gradient generated by pumping hydrogen ions across a biological membrane.

Pyruvate oxidation

The multi-step reaction in the presence of oxygen that converts a three-carbon product of glycolysis into acetyl-CoA, producing NADH and releasing $CO_2$.

Acetyl-CoA

The entry molecule for the citric acid cycle, formed by attaching a two-carbon fragment of oxidized pyruvate to coenzyme A.

Lactic acid fermentation

An anaerobic pathway in which pyruvate is reduced directly by NADH to form lactate, regenerating $\text{NAD}^+$ without releasing carbon dioxide.

Alcohol fermentation

An anaerobic pathway in which pyruvate is converted into ethanol and $CO_2$, regenerating $\text{NAD}^+$ to sustain glycolysis.

Light-dependent reactions

The initial phase of photosynthesis that absorbs solar energy to generate NADPH and ATP while splitting water to release $O_2$.

Thylakoid

A flattened, membranous sac inside a chloroplast containing chlorophyll and the protein complexes responsible for the light-capturing steps of photosynthesis.

Stroma

The fluid-filled space within a chloroplast surrounding the thylakoid membranes where the Calvin cycle takes place.

Chlorophyll

The primary light-absorbing pigment in plants and algae that captures blue and red wavelengths while reflecting green light.

Photosystem II

A light-harvesting complex in the thylakoid membrane whose reaction center contains $P_{680}$ chlorophyll and oxidizes water molecules.

Photosystem I

A light-harvesting complex in the thylakoid membrane whose reaction center contains $P_{700}$ chlorophyll and passes electrons onward to reduce $\text{NADP}^+$, forming NADPH.

Linear electron flow

The primary pathway of electron transfer during the light reactions that moves electrons through both photosystems to produce ATP, NADPH, and $O_2$.

Cyclic electron flow

An alternative light-driven electron pathway involving only photosystem I that generates ATP without producing NADPH or oxygen.

Carbon fixation

The process of incorporating inorganic carbon from $CO_2$ into organic molecules.

$C_4$ pathway

A photosynthetic adaptation that minimizes photorespiration by physically separating initial carbon fixation in mesophyll cells from the Calvin cycle in bundle-sheath cells.

Crassulacean acid metabolism (CAM)

A temporal adaptation to arid conditions where stomata open at night to fix carbon into organic acids, which are then broken down during the day to supply $CO_2$ for the Calvin cycle.

Coenzyme

An organic non-protein helper molecule, typically derived from vitamins, required for an enzyme to catalyze its specific reaction.

Cellular location of glycolysis

The cytosol of eukaryotic and prokaryotic cells.

Cellular location of the citric acid cycle

The mitochondrial matrix in eukaryotes, or the cytosol in prokaryotes.

Cellular location of oxidative phosphorylation

The inner mitochondrial membrane in eukaryotes, or the plasma membrane in prokaryotes.