Chapter 5.2: Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy

Flashcards from Chapter 5.2 of Principles of Life, 3rd Edition.

Cellular respiration

The set of metabolic reactions used to harvest energy from molecules like carbohydrates, fueling endergonic reactions through the oxidation of molecules

Kilocalorie

A measure of energy often used for cellular reactions; measured as heat in a laboratory

Aerobic respiration

The type of cellular respiration that occurs with oxygen, comprising glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation to release high levels of energy through the oxidation of glucose

• This process is relatively very efficient, with 34% of the released energy converted to ATP through a series of smaller reactions and 30 ATP molecules produced

Glycolysis

The first stages of both cellular respiration and fermentation, utilizing the 6-carbon glucose in a series of reactions to form two 3-carbon pyruvate, ATP, and NADH molecules

Glycolysis stage 1

The part of glycolysis where glucose is hydrolyzed and phosphorylated by 2 ATP molecules to form fructose, which then forms 2 molecules of glyceraldehyde 3-phosphate

Fructose

The intermediate product of the first stage of glycolysis formed out of a glucose molecule, hydrolyzed and phosphorylated by 2 ATP molecules, before cleaved to form two molecules of glyceraldehyde 3-phosphate (G3P)

Glyceraldehyde 3-phosphate (G3P)

The final product of the first stage of glycolysis as two molecules, formed by cleaving a phosphorylated and hydrolyzed fructose molecule into two phosphate-containing sugars

Glycolysis stage 2

The part of glycolysis where two molecules of G3P are phosphorylated and used to reduce NAD⁺ to NADH, then using the two phosphate groups available on both molecules to phosphorylate two ADP molecules into ATP (making four ATP cumulatively) and leave two pyruvate molecules

Substrate-level phosphorylation

The addition of a phosphate group from G3P molecules to form ATP from ADP twice, being left with two pyruvate molecules at the end of glycolysis

Pyruvate

The 3-carbon molecule formed as the end-product of glycolysis, used for aerobic respiration or fermentation depending on the presence of O₂

Pyruvate oxidation

The second stage of cellular respiration where two 3-carbon pyruvates reduce one molecule of NAD⁺ and oxidize into two 2-carbon acetyl CoA molecules and two CO₂ molecules

• Help produce 3 net ATP molecules

Mitochondrial matrix

The inside of the mitochondria organelle found in eukaryotes, serving as the site of pyruvate oxidation

Acetate

The intermediate product of pyruvate oxidation as a 2-carbon molecule formed after the reduction of NAD⁺ into NADH by pyruvate, later being bound to coenzyme A to form acetyl CoA

Acetyl CoA

The end product of pyruvate oxidation formed out of coenzyme A and one molecule of acetate, catalyzed by the pyruvate dehydrogenase complex, before being used in the citric acid cycle

Citric acid cycle

The third stage of cellular respiration where the two 2-carbon acetyl CoA molecules are completely oxidized to form CO₂ and products for oxidative phosphorylation, using the released energy to reduce three molecules of NAD⁺ and one molecule of FAD, as well as synthesize one molecule of GTP

• These help make 9 molecules of ATP, for 18 total per molecule of glucose

Guanine triphosphate (GTP)

A high-energy compound produced via phosphorylation of GDP in the citric acid cycle, used to drive endergonic reactions or phosphorylate ADP into ATP

Oxaloacetate

A molecule formed out of the acetyl group of acetyl CoA, forming the starting material of the citric acid cycle and reforming for two cycles total

NADH and FADH₂

The two coenzymes that are reduced during the citric acid cycle, forming three and one molecule respectively for use with oxygen in oxidative phosphorylation

Oxidative phosphorylation

The fourth and final stage of aerobic respiration, utilizing H⁺ ions from oxidated NADH and FADH₂ molecules to form a proton gradient in electron transport and using the resulting diffusion for ATP synthesis in chemiosmosis

• Forms 9 ATP molecules in total per molecule of glucose

Electron transport

The first stage of oxidative phosphorylation, where NADH and FADH₂ molecules are oxidized and the resulting electrons are passed through mitochondrial membrane proteins for energized active H⁺ transport

• Utilizes oxygen as an electron acceptor to become reduced and form water for motion

ATP synthase

A protein in the inner mitochondrial membrane that uses the H⁺ gradient to drive ATP synthesis via chemiosmosis at up to 100 molecules per second; this is present in much of life and relies on gradients

• Presence of an alternate channel allows for energy to be used for heat instead of ATP generation

Chemiosmosis

The movement of ions across a membrane from higher to lower concentration; H⁺ performs this through the mitochondrial membrane protein ATP synthase

Proton-motive force

The potential energy of the proton gradient present during oxidative phosphorylation, driving chemiosmosis for ATP synthase

Feedback inhibition

Type of regulation where the product of a pathway binds to and inhibits an enzyme at the early step of the pathway, reducing production to an equilibrium

• Seen in aerobic respiration to control total ATP and glucose levels, regulating processes quickly

Gene transcription

A potential method of regulation where the cell can modify levels of enzymes produced through expression

Fermentation (anaerobic respiration)

The breakdown of glucose without oxygen in the cytoplasm, only partially oxidizing glucose without chemiosmosis and repeatedly re-oxidizing NAD during the formation of pyruvate to allow glycolysis to continue

• Has substantially smaller energy outputs, with only 2% efficiency

CO₂ and ethanol or lactate

The products of fermentation in plants or animals, respectively, formed out of pyruvate from glycolysis

Lactic acid fermentation

Type of fermentation with pyruvate serving as the electron acceptor for NADH after forming 2 ATP, producing lactate; this is found in vertebrate muscle tissue as O₂ is depleted and glycogen is used

• The resulting lactate can be reconverted to pyruvate once oxygen returns

Alcoholic fermentation

Type of fermentation with pyruvate being converted to ethanol and acetaldehyde (intermediately formed out of pyruvate) serving as the electron acceptor for NADH

• The resulting ethanol can be reconverted to pyruvate once oxygen returns