Chapter 7 Cellular Respiration Notes

Metabolism Crash Course The idea of metabolism is broken down into two parts: Anabolism – using monomers to construct polymers using energy Catabolism – breaking down polymers into monomers and releasing energy

Cells Use Redox Reactions to Extract Energy Redox reactions are catalyzed by enzymes Electrons carry energy from one molecule to another Cofactors serve as electron carriers Example: Nicotinamide adenosine dinucleotide (NAD+) NAD+ accepts 2 electrons and 1 proton to become NADH Reaction is reversible In chemical reactions, there is a transfer of one or more electron. These electrons move from one reactant to another reactant. This transfer of electrons is called an oxidation-reduction reaction. The loss of electrons from one substance is called oxidation The addition of electrons to another substance is known as reduction

NAD+ Accepts Electrons to Form NADH When glucose is being oxidized during cellular respiration, each electron that is being passed down during the oxidation, travels with a proton. These protons do not get directly transferred to the oxygen, as it is the final electron acceptor. Instead, the protons get passed on to an electron carrier, called a coenzyme, called nicotinamide adenine dinucleotide. This coenzyme is utilized as an electron carrier because it can cycle easily between the oxidized form (NAD+) and the reduced form (NADH). Enzymes called dehydrogenases remove a pair of hydrogen atoms (2 electrons and 2 protons) from the glucose molecule, oxidizing it. This enzyme delivers the 2 electrons along with 1 proton to NAD+, creating NADH.

Types of Respiration Aerobic respiration Final electron acceptor is oxygen (O2) Anaerobic respiration Final electron acceptor is an inorganic molecule (not O2) Fermentation Final electron acceptor is an organic molecule All three types of cellular respiration are catabolic pathways, however, aerobic cellular respiration is considered the most efficient catabolic pathway.

The Aerobic Respiration of Glucose C6H12O6 + 6O2  6CO2 + 6H2O + energy Energy must be harvested in small steps These small steps involve electron carriers

Glucose Oxidation Proceeds in Four Stages Glycolysis Pyruvate oxidation Krebs cycle Electron transport chain & chemiosmosis

Glycolysis Converts One Glucose to Two Pyruvates

Glucose is First Converted into Two G3P Molecules

Each G3P Molecule is Converted into Pyruvate

The Fate of Pyruvate and NADH

Pyruvate Oxidation Pyruvate is oxidized in the presence of oxygen Occurs in: mitochondria of eukaryotes plasma membrane of prokaryotes Catalyzed by pyruvate dehydrogenase

Pyruvate Oxidation

The Krebs Cycle

The Electron Transport Chain (ETC)

Chemiosmosis

Calculating the Energy Yield of Respiration

Oxidation without O2: Anaerobic Respiration Inorganic molecules (not O2) used as final electron acceptor

Oxidation without O2: Anaerobic Respiration Example 1: Sulfur bacteria Inorganic sulphate (SO4) is reduced to hydrogen sulfide (H2S) Early sulfate reducers set the stage for evolution of photosynthesis

Oxidation without O2: Fermentation Example 2: Alcohol acid fermentation Occurs in yeast Electrons are transferred from NADH to pyruvate to produce ethanol

Oxidation without O2: Fermentation Example 2: Lactic acid fermentation Occurs in animal cells (especially muscles) Electrons are transferred from NADH to pyruvate to produce lactic acid

Catabolism of Protein

Catabolism of Fats

Extraction of Energy from Macromolecules