Study Unit 9: Pathways That Harvest Chemical Energy

Flashcards related to Pathways That Harvest Chemical Energy

Cellular Respiration Purpose

The main purpose of cellular respiration is to couple energy from the oxidation of food (e.g. glucose) to ATP synthesis.

Overall Oxidation of Glucose

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (heat and ATP)

Four Stages of Cellular Respiration

Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, Oxidative Phosphorylation

Five Principles of Metabolic Pathways

A series of separate reactions, each catalyzed by a specific enzyme, often similar in all organisms, compartmentalized in eukaryotes, and regulated by key enzymes.

Three Catabolic Processes

Energy from glucose is harvested through glycolysis, cellular respiration, and fermentation.

Redox Reactions

Transfer of electrons, often associated with transfer of hydrogen ions (dehydrogenation).

Coenzyme NAD+

NAD+ is a key electron carrier in redox reactions.

Glycolysis

Glycolysis is the stepwise degradation of glucose and occurs in nearly all living cells.

Glycolysis Phases

Preparatory, cleavage, and oxidation/payoff phases.

Oxidation-Reduction in Metabolic Pathways

Energy released by glucose oxidation is trapped via the reduction of NAD+ to NADH.

Substrate-Level Phosphorylation

Energy released transfers a phosphate from the substrate to ADP, forming ATP.

Net Products of Glycolytic Pathway

Glucose + 2NAD+ + 2ADP + 2Pi → 2Pyruvate + 2NADH + 2H+ + 2 ATP + 2H2O

Pyruvate Oxidation

Pyruvate is oxidized to produce carbon dioxide (CO2), NADH, and acetyl-CoA in the mitochondrial matrix.

Citric Acid Cycle (CAC)

Completely oxidize the acetyl group to 2 molecules of CO2, capturing energy by GDP, NAD+, and FAD; occurs in the mitochondrial matrix.

Net Products of Citric Acid Cycle

Results in 3 NADH, 1 FADH2, and 1 GTP (ATP).

Oxidative Phosphorylation

High energy electron carriers (NADH and FADH2) produced at any stage in respiration converge at the electron transport chain (ETC).

Oxidative Phosphorylation and ETC

ETC is coupled to oxidative phosphorylation- the redox reactions of the ETC convert the energy in the electrons to potential energy used to synthesize ATP

Oxidative Phosphorylation Process

Electrochemical proton gradient (chemiosmosis) that drives the ATP-synthase motor in the mitochondrion.

Oxidative Phosphorylation

Consists of an electron transport chain and ATP synthase.

ATP Synthase

An enzyme with two parts: F0 unit (transmembrane H+ channel) and F1 unit (projects into the matrix; rotates to expose active sites for ATP synthesis).

Anaerobic cellular respiration

Many bacteria and archaea use alternate electron acceptors such as SO4 -2, NO3 - , Fe3+, and CO2

Fermentation

Pyruvate produced from glycolysis can be reduced to lactic acid or ethanol (alcohol).

Lactic Acid Fermentation

Occurs in animal, human, and some bacteria cells; pyruvate is reduced to lactic acid, regenerating NAD+.

Ethanol Fermentation

Occurs in yeasts (fungi) and some plant cells; pyruvate releases carbon dioxide, and the acetaldehyde produced is reduced to form ethanol, regenerating NAD+.

Allosteric Regulation

Indicators of energy available to the cell are concentrations of ATP, NAD+ , and NADH.