Lecture 5: Cellular Respiration - Dr. Marcelo Wood (Bio93)

Vocabulary practice flashcards covering key terms, structures, and processes of cellular respiration from Lecture 5.

Cellular Respiration

A catabolic, exergonic pathway in which organic molecules are broken down through the relocation of electrons to oxygen, releasing free energy to drive the synthesis of $ATP$.

Catabolism

Exergonic, energy-yielding metabolic pathways that break down complex organic molecules into simpler compounds, yielding energy to generate $ATP$.

Redox Reaction

A chemical reaction involving the transfer of one or more electrons between reactants, composed of an oxidation component and a reduction component.

Oxidation

The loss of electrons from a substance during a chemical reaction, which increases its positive charge.

Reduction

The gain of electrons by a substance during a chemical reaction, which reduces its positive charge.

OIL RIG

A mnemonic device summarizing electron movements in redox reactions: Oxidation Is Loss, Reduction Is Gain.

Overall Redox Equation for Cellular Respiration

The chemical reaction $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$ ($ΔG = -686\,\text{kcal}$), wherein glucose is oxidized and oxygen is reduced.

Activation Energy ($E_A$)

The initial energy barrier required to start a chemical reaction; enzymes speed up metabolic reactions by lowering $E_A$ without changing $ΔG$.

Mitochondria

The eukaryotic organelles that serve as the primary site of cellular respiration, hosting pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.

Cristae

The extensive infoldings of the inner mitochondrial membrane that provide a large surface area for electron transport chains and $ATP$ synthase.

Mitochondrial Matrix

The internal compartment enclosed by the inner mitochondrial membrane containing mitochondrial DNA, free ribosomes, and the enzymes for pyruvate oxidation and the citric acid cycle.

Intermembrane Space

The compartment situated between the outer and inner mitochondrial membranes into which protons ($H^+$) are pumped during electron transport to create a high concentration gradient.

$$NAD^+$$

Nicotinamide adenine dinucleotide in its oxidized form, acting as a key electron acceptor and oxidizing agent in cellular catabolism.

NADH

The reduced form of nicotinamide adenine dinucleotide that carries two electrons and one proton ($H^+$) harvested from food to the electron transport chain.

Dehydrogenase

An enzyme that strips two hydrogen atoms ($2H^+$ and $2e^-$) from organic fuel, passing one $H^+$ and two $e^-$ to $NAD^+$ while releasing one free $H^+$ into solution.

Glycolysis

The initial stage of cellular respiration occurring in the cytosol, which splits one molecule of glucose into two molecules of pyruvate while producing $ATP$ and NADH.

Substrate-Level Phosphorylation

The direct synthesis of $ATP$ occurring when an enzyme transfers a phosphate group from an organic substrate molecule to ADP, rather than using inorganic phosphate ($P_i$).

Energy Investment Phase

The initial phase of glycolysis in which the cell consumes $2\,\text{ATP}$ molecules to phosphorylate glucose intermediates.

Energy Payoff Phase

The second phase of glycolysis in which substrate-level phosphorylation yields $4\,\text{ATP}$, $2\,\text{NAD}^+$ are reduced to $2\,\text{NADH} + 2H^+$, and two molecules of pyruvate are formed.

Net Yield of Glycolysis

The net production per glucose molecule consisting of $2\,\text{pyruvate} + 2H_2O$, $2\,\text{ATP}$ ($4\,\text{ATP formed} - 2\,\text{ATP used}$), and $2\,\text{NADH} + 2H^+$.

Pyruvate Oxidation

The intermediate transition stage where pyruvate is actively transported into the mitochondrial matrix and converted into acetyl CoA, yielding $CO_2$ and NADH.

Acetyl CoA

The two-carbon intermediate molecule produced from pyruvate oxidation linked to coenzyme A, which enters and feeds into the citric acid cycle.

Citric Acid Cycle

Also called the Krebs cycle; a cyclic metabolic pathway in the mitochondrial matrix that oxidizes acetyl CoA to produce $2\,CO_2$, $3\,\text{NADH}$, $1\,\text{FADH}_2$, and $1\,\text{ATP}$ (or GTP) per turn.

$$\text{FADH}_2$$

A reduced electron carrier synthesized during the citric acid cycle that transfers electrons to complex II of the electron transport chain.

Oxidative Phosphorylation

The third stage of cellular respiration comprising the electron transport chain and chemiosmosis on the inner mitochondrial membrane, generating about $26$ to $28\,\text{ATP}$ per glucose.

Electron Transport Chain

A collection of multi-protein complexes in the inner mitochondrial membrane that sequentially transfer electrons downhill to oxygen ($O_2$), driving the pumping of protons into the intermembrane space.

Chemiosmosis

An energy-coupling mechanism where the potential energy stored in an electrochemical proton gradient across the inner mitochondrial membrane is used to drive $ATP$ synthesis.

Proton-Motive Force

The electrochemical potential generated by the accumulation of $H^+$ in the intermembrane space relative to the matrix, providing the driving force to do work.

ATP Synthase

The smallest rotary motor known in nature; a membrane protein complex that allows passive transport of $H^+$ back into the matrix to catalyze the phosphorylation of ADP to $ATP$.

Fermentation

An anaerobic catabolic pathway in the cytosol that enables glycolysis to continue producing $ATP$ in the absence of $O_2$ by using organic molecules to regenerate $NAD^+$ from NADH.