How Cells Harvest Energy Chapter 9 Outline Cellular Energy Harvest Cellular Respiration Glycolysis Oxidation of Pyruvate Krebs Cycle Electron Transport Chain Catabolism of Protein and Fat Fermentation

Cellular Respiration Cells harvest energy by breaking bonds and shifting electrons from one molecule to another. aerobic respiration - final electron acceptor is oxygen anaerobic respiration - final electron acceptor is inorganic molecule other than oxygen fermentation - final electron acceptor is an organic molecule

ATP Adenosine Triphosphate (ATP) is the energy currency of the cell. used to drive movement used to drive endergonic reactions

ATP Most of the ATP produced in cells is made by the enzyme ATP synthase. Enzyme is embedded in the membrane and provides a channel through which protons can cross the membrane down their concentration gradient. ATP synthesis is achieved by a rotary motor driven by a gradient of protons.

NAD+ & NADH Nicotinamide adenine dinucleotide, NAD+, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups: with one nucleotide containing an adenosine ring, and the other containing nicotinamide. In metabolism, NAD+ is involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is therefore found in two forms in cells: NAD+ is an oxidizing agent – it accepts electrons from other molecules and becomes reduced, this reaction forms NADH, which can then be used as a reducing agent to donate electrons. These electron transfer reactions are the main function of NAD+.

NAD+ & NADH

The Cellular isms Metabolism: is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Usually divided into two categories. Catabolism and Anabolism Catabolism – breaking down Anabolism – building up

The Cellular isms Catabolism: the set of metabolic pathways which break down molecules into smaller units and release energy. Large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides and amino acids, respectively. These processes produce energy

The Cellular isms Anabolism: the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. Anabolism is powered by catabolism. Many anabolic processes are powered by adenosine triphosphate (ATP). Anabolic processes tend toward "building up" organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules.

Glucose Catabolism Cells catabolize organic molecules and produce ATP in two ways: substrate-level phosphorylation aerobic respiration in most organisms, both are combined glycolysis pyruvate oxidation Krebs cycle electron transport chain

Aerobic Respiration

Stage One - Glycolysis For each molecule of glucose that passes through glycolysis, the cell nets two ATP molecules. Priming glucose priming cleavage and rearrangement Substrate-level phosphorylation oxidation ATP generation

Priming Reactions

Cleavage Reactions

Energy-Harvesting Reactions

Recycling NADH As long as food molecules are available to be converted into glucose, a cell can produce ATP. Continual production creates NADH accumulation and NAD+ depletion. NADH must be recycled into NAD+. aerobic respiration fermentation

Recycling NADH

Stage Two - Oxidation of Pyruvate Within mitochondria, pyruvate is decarboxylated, yielding acetyl-CoA, NADH, and CO2.

Stage Three - Krebs Cycle Acetyl-CoA is oxidized in a series of nine reactions. two steps: priming energy extraction

Overview of Krebs Cycle 1: Condensation 2-3: Isomerization 4: First oxidation 5: Second oxidation 6: Substrate-level phosphorylation 7: Third oxidation 8-9: Regeneration and oxaloacetate

Krebs Cycle

Krebs Cycle

Harvesting Energy by Extracting Electrons Glucose catabolism involves a series of oxidation-reduction reactions that release energy by repositioning electrons closer to oxygen atoms. Energy is harvested from glucose molecules in gradual steps, using NAD+ as an electron carrier.

Electron Transport

Stage Four: The Electron Transport Chain NADH molecules carry electrons to the inner mitochondrial membrane, where they transfer electrons to a series of membrane-associated proteins.

Electron Transport Chain

Chemiosmosis

ATP Generation This process begins with pyruvate, the product of glycolysis, and ends with the synthesis of ATP

Theoretical ATP Yield of Aerobic Respiration

Regulating Aerobic Respiration Control of glucose catabolism occurs at two key points in the catabolic pathway. glycolysis - phosphofructokinase Krebs cycle - citrate synthetase

Control of Glucose Catabolism

Catabolism of Proteins and Fats Proteins are utilized by deaminating their amino acids, and then metabolizing the product. Fats are utilized by beta-oxidation.

Cellular Extraction of Chemical Energy

Fermentation Electrons that result from the glycolytic breakdown of glucose are donated to an organic molecule. regenerates NAD+ from NADH ethanol fermentation lactic acid fermentation