Energy, Chemical Reactions, and Cellular Respiration Lecture Flashcards

A set of vocabulary flashcards covering energy forms, thermodynamics, chemical reaction types, enzyme kinetics and regulation, and the stages of cellular respiration.

Potential energy

The energy of position or stored energy, such as the concentration gradient across a plasma membrane.

Kinetic energy

The energy of motion, such as the movement of atoms or the falling of an electron from a higher-energy shell to a lower-energy shell.

Chemical energy

A form of potential energy stored in a molecule’s chemical bonds, which is used for movement, molecule synthesis, and establishing concentration gradients.

Triglycerides, Glucose, and ATP

The primary molecules that function in the storage of chemical energy in the human body.

Electrical energy

Kinetic energy resulting from the movement of charged particles, such as ions moving across the plasma membrane of a neuron.

Mechanical energy

Energy exhibited by objects in motion due to an applied force, such as muscle contraction for walking.

Heat

Kinetic energy produced by the movement of atoms, ions, or molecules that is usually not available to do work and is measured as temperature.

First law of thermodynamics

The principle stating that energy can neither be created nor destroyed, only changed in form.

Second law of thermodynamics

The principle stating that whenever energy is transformed, some energy is lost to heat and the amount of usable energy decreases.

Metabolism

The collective term for all biochemical reactions occurring in living organisms.

Decomposition reaction

A chemical reaction where an initial large molecule is broken down into smaller structures, categorized as catabolism ($AB \rightarrow A + B$).

Synthesis reaction

A chemical reaction where two or more structures combine to form a larger structure, categorized as anabolism ($A + B \rightarrow AB$).

Exchange reaction

The most prevalent type of reaction in the human body, where groups are exchanged between two chemical structures ($AB + C \rightarrow A + BC$).

Oxidation-reduction reaction (redox reaction)

An exchange reaction involving the movement of electrons; the structure losing an electron is oxidized, and the structure gaining an electron is reduced.

Exergonic reactions

Reactions where the reactants have more chemical bond energy than the products, resulting in a net release of energy.

Endergonic reactions

Reactions where the reactants have less chemical bond energy than the products, requiring energy to be supplied for a net increase in potential energy.

ATP cycling

The continuous cycle of forming ATP from ADP and phosphate through exergonic reactions and splitting ATP to provide energy for endergonic reactions.

Activation energy ($E_a$)

The amount of energy required to break existing chemical bonds to initiate a chemical reaction.

Enzymes

Biologically active globular protein catalysts that accelerate chemical reactions by lowering the required activation energy.

Active site

A unique three-dimensional pocket within an enzyme's structure that temporarily forms an enzyme-substrate complex.

Cofactors

Nonprotein substances (organic or inorganic) required to ensure an enzyme-catalyzed reaction occurs; organic cofactors are specifically called coenzymes.

Kinases

A subclass of transferase enzymes that function to transfer phosphate groups between chemical structures.

Saturation

The point where substrate concentration is so high that all available enzyme molecules are engaged in a reaction.

Optimum temperature for human enzymes

The temperature, usually $40^\circ\text{C}$ ($104^\circ\text{F}$), at which human enzyme activity is most efficient.

Competitive inhibitor

A substance that resembles a substrate and competes for occupation of the enzyme’s active site.

Noncompetitive inhibitor (allosteric inhibitor)

A substance that binds to the allosteric site rather than the active site, inducing a conformational change that prevents substrate binding.

Metabolic pathway

A series of enzymes where the product of one enzyme becomes the substrate for the next.

Negative feedback

A regulatory mechanism where the end product of a metabolic pathway acts as an allosteric inhibitor to turn off an enzyme early in the pathway.

Cellular respiration

An exergonic multistep metabolic pathway where organic molecules are oxidized and disassembled to release energy for ATP synthesis.

Glycolysis

The first stage of glucose oxidation, occurring in the cytosol and requiring no oxygen, which yields a net of $2\,ATP$ and $2\,NADH$.

Intermediate stage

The stage where pyruvate is converted to acetyl CoA by pyruvate dehydrogenase within the mitochondrial matrix, producing $NADH$ and releasing $CO_2$.

Citric acid cycle

A cyclic metabolic pathway in the mitochondrial matrix that produces $1\,ATP$, $3\,NADH$, and $1\,FADH_2$ per turn of the cycle.

Electron transport system (ETS)

A series of electron carriers and $H^+$ pumps in the mitochondrial cristae that use energy from $NADH$ and $FADH_2$ to create an $H^+$ gradient for ATP production.

Oxidative phosphorylation

The process of forming ATP from the phosphorylation of ADP using energy from the electron transport system, with oxygen as the final electron acceptor.

Lactate dehydrogenase

The enzyme that converts pyruvate into lactate when oxygen is insufficient, allowing the regeneration of $NAD^+$ to sustain glycolysis.

Beta oxidation

The process by which fatty acids are enzymatically broken down two carbons at a time to form acetyl CoA for entry into the citric acid cycle.