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+.
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
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
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
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
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.
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.
ATP Generation • This process begins with pyruvate, the product of glycolysis, and ends with the synthesis of ATP
Regulating Aerobic Respiration • Control of glucose catabolism occurs at two key points in the catabolic pathway. • glycolysis - phosphofructokinase • Krebs cycle - citrate synthetase
Catabolism of Proteins and Fats • Proteins are utilized by deaminating their amino acids, and then metabolizing the product. • Fats are utilized by beta-oxidation.
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