Cellular Respiration and Fermentation

Flashcards covering the stages of cellular respiration (glycolysis, Krebs cycle, oxidative phosphorylation) and anaerobic fermentation processes as outlined in the Biology II lecture notes.

Cellular Respiration

A metabolic process in animals and plants in which organic substances are broken down to simpler products with the release of energy, which is trapped in the $ATP$ molecule.

ATP ($\text{Adenosine Triphosphate}$)

A nucleotide consisting of the sugar ribose, the nitrogenous base adenine, and a chain of 3 phosphate groups; it serves as a universal form of energy and high-energy molecule that powers cellular work.

Substrate-level phosphorylation

A process of $ATP$ production where an enzyme transfers a phosphate group from a substrate molecule directly to $ADP$, forming $ATP$.

Oxidative phosphorylation

The process in which $ATP$ is formed as a result of the transfer of electrons from $NADH$ or $FADH_2$ to $O_2$ by a series of electron carriers through redox reactions, taking place in the cristae of mitochondria.

Aerobic Respiration

A type of respiration where organic compounds are completely oxidized into carbon dioxide and water with the release of energy ($ATP$ + heat) in a process requiring oxygen.

Glycolysis

A series of biochemical reactions occurring in the cytosol that oxidizes one glucose ($6C$) into two molecules of pyruvate ($3C$), yielding a net of $2\,ATP$ and $2\,NADH$.

Hexokinase

The enzyme in Step 1 of Glycolysis that catalyzes the phosphorylation of glucose to become glucose-6-phosphate by using one molecule of $ATP$.

Phosphofructokinase

The enzyme in Step 3 of Glycolysis that transfers a phosphate group from $ATP$ to fructose-6-phosphate to produce fructose-1,6-bisphosphate.

Pyruvate Oxidation

The link reaction where pyruvate enters the mitochondrial matrix via active transport and undergoes oxidative decarboxylation to be converted into acetyl coenzyme A ($\text{acetyl CoA}$).

Krebs Cycle ($\text{Citric Acid Cycle}$)

An 8-step cycle in the mitochondrial matrix that oxidizes the acetyl group ($2C$) from acetyl CoA to $CO_2$, producing $1\,ATP$, $3\,NADH$, and $1\,FADH_2$ per turn.

Electron Transport Chain ($\text{ETC}$)

A sequence of membrane proteins (electron carriers) in the inner mitochondrial membrane that shuttle electrons down redox reactions to release energy used for pumping protons into the intermembrane space.

Chemiosmosis

The production of $ATP$ via proton movement through $ATP\text{ synthase}$ across a membrane, driven by the proton-motive force or proton gradient.

ATP Synthase

An enzyme and $H^+$ channel that uses the energy from the proton gradient to catalyze the synthesis of $ATP$ by phosphorylating $ADP$.

Malate Shuttle

A shuttle system for active cells (e.g., liver and heart cells) that allows $2\,NADH$ from glycolysis to pass electrons to $2\,NAD^+$ inside the mitochondrion, resulting in a total yield of $38\,ATP$ per glucose.

Phosphoglycerate Shuttle

A shuttle system for normal cells where $2\,NADH$ from glycolysis pass electrons to $2\,FAD$ to form $2\,FADH_2$, contributing to a total yield of $36\,ATP$ per glucose.

Fermentation

An anaerobic catabolic process that produces a limited amount of $ATP$ ($2\,ATP$) from glucose without an electron transport chain, resulting in end products like ethanol or lactic acid.

Alcohol Fermentation

A process in yeast and bacteria where pyruvate is decarboxylated to acetaldehyde (ethanal) and then reduced by $NADH$ to ethanol, releasing $CO_2$.

Lactate Fermentation

A process in muscle cells, fungi, and certain bacteria where pyruvate is directly reduced by $NADH$ to form lactic acid (lactate) without the release of $CO_2$.

Ubiquinone ($\text{Coenzyme Q}$)

A mobile electron carrier within the Electron Transport Chain that receives electrons from $NADH\text{ dehydrogenase}$ or $succinate\text{ dehydrogenase}$ and passes them to $cytochrome\,c\,reductase$.

Oxaloacetate

The four-carbon ($4C$) molecule that combines with the acetyl group ($2C$) from acetyl CoA in the first step of the Krebs Cycle to form citrate ($6C$).