PowerPoint Lecture Slides for MICROBIOLOGY ROBERT W. BAUMAN Chapter 5 Microbial Metabolism
Microbial Metabolism The sum total of chemical reactions that take place within cells (of an organism)
Metabolic processes guided by 8 elementary statements Every cell acquires Metabolism requires energy from light or from catabolism of nutrients Energy is stored in Cells catabolize nutrients to form precursor metabolites Precursor metabolites, energy from ATP, and enzymes used in anabolic reactions Enzymes plus ATP form Cells grow by assembling macromolecules Cells reproduce once they have doubled in size
Basic Chemical Reactions Underlying Metabolism Catabolism and Anabolism Oxidation and Reactions ATP Production and Energy Storage The Roles of Enzymes in Metabolism
Catabolism and Anabolism pathways release energy by breaking down complex molecules to simpler compounds. This energy is stored in organic molecules until it needs to do work in the cell. pathways consume energy to build complicated molecules from simpler compounds. The energy released by catabolic pathways is used to drive anabolic pathways.
Chemical reactions can be classified as either exergonic or endergonic based on free energy. An exergonic reaction proceeds with a net release of free energy and delta G is negative. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Free energy released by a reaction is then available to perform. For the overall reaction of cellular respiration: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O delta G = -686 kcal/mol Through this reaction 686 kcal have been made available to do work in the cell. The products have 686 kcal less energy than the reactants. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
An endergonic reaction is one that absorbs free energy from its surroundings. Endergonic reactions store energy, delta G is positive, & reactions are nonspontaneous. Fig. 6.6b Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
If cellular respiration releases 686 kcal, then photosynthesis, the reverse reaction, must require an equivalent investment of energy. Delta G = + 686 kcal / mol. Photosynthesis is steeply endergonic, powered by the absorption of light energy. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Reactions in closed systems eventually reach equilibrium and can do no work. A cell that has reached metabolic equilibrium is dead! is one of the defining features of life. Fig. 6.7a Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Cells maintain disequilibrium because they are open with a constant flow of material in and out of the cell. A cell continues to do work. Fig. 6.7b Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
A catabolic process in a cell releases free energy in a series of reactions, not in a single step. Some reactions of respiration are constantly pulled in one direction. Therefore the product of one reaction does not accumulate, but becomes the reactant in the next step. What is a term for a huge amount of energy released all at once? Copyright 2004 Pearson 2002 Pearson Education, Education, Inc. publishing Inc., as publishing Benjamin Cummings as Benjamin Cummings Fig. 6.7c
Sunlight provides a daily source of free energy for the photosynthetic organisms in the environment. Nonphotosynthetic organisms depend on a transfer of free energy from photosynthetic organisms in the form of. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Oxidation and Reduction Reactions Transfer of electrons from molecule that donates electron to molecule that accepts electrons These reactions are always coupled Cells use electron carrier molecules to carry electrons (often in H atoms)
Oxidation and Reduction Reactions Three important electron carriers Nicotinamide adenine dinucleotide (NAD + ) NADH Nicotinamide adenine dinucleotide phosphate (NADP + ) NADPH Flavine adenine dinucleotide (FAD) FADH 2
ATP Production and Energy Storage Energy released from nutrients can be stored in highenergy phosphate bonds of ATP Phosphorylation organic phosphate is added to substrate Anabolic pathways use some energy of ATP by breaking a
ATP Production and Energy Storage Cells phosphorylate ADP to ATP in three ways Substrate-level phosphorylation phosphorylation Photophosphorylation Anabolic pathways use some energy of ATP by breaking a phosphate bond
The Roles of Enzymes in Metabolism Enzymes are organic catalysts increase the likelihood of a reaction They are not permanently changed in the reaction activation energies Speed up reactions for a substrate Substrate enzyme Products Substrate-level phosphorylation
The Roles of Enzymes in Metabolism Six categories of enzymes based on mode of action Often named after substrate or action Hydrolases remove hydrogens Isomerases rearrange atoms Ligases or polymerases join molecules (add monomers) Lyases - breaking of chemical bonds Oxidoreductases Transferases transfer functional groups
Enzymes The turnover number is generally 1- molecules per second. Figure 5.4
The Makeup of Enzymes Most enzymes are proteins Some are RNA molecules called ribozymes Holoenzymes are composed of Apoenzymes - protein portions that are inactive if not bound to co-factors Cofactors nonprotein (inorganic ions or coenzymes)
Enzyme Activity Figure 5.5
Enzyme Activity sucrase Sucrose -------> fructose + glucose Figure 5.7
Enzyme Activity Many factors influence the rate of enzymatic reactions Temperature Enzyme and substrate concentrations Presence of
Temperature What happens to a protein when the temperature is to high? Figure 5.8a
Factors Influencing Enzyme Activity Enzymes can be denatured by temperature and ph Figure 5.6
ph Figure 5.8b
Substrate Concentration Figure 5.8c
Inhibitors Substances that block an enzyme s active site Do not denature enzymes Types of Inhibitors Competitive inhibitors Noncompetitive inhibitors
Competitive Inhibitors Figure 5.10
Noncompetitive Inhibitors Figure 5.11a
Feedback Inhibition Figure 5.12
Feedback Inhibition Figure 5.12
Carbohydrate Catabolism Organisms oxidize carbohydrates as the primary energy source for anabolic reactions Glucose used most commonly Glucose catabolized by Glycolysis Cellular respiration Utilizes (glycolysis), Krebs cycle, and electron transport chain; results in complete breakdown of glucose to carbon dioxide and water Fermentation Utilizes glycolysis then converts pyruvic acid into another compound (organic waste products)
Figure 5.14
Glycolysis The oxidation of glucose to pyruvic acid, produces ATP and NADH.
Glycolysis Occurs in cytoplasm of most cells Divided into three stages involving 10 total steps Energy-Investment Stage Lysis Stage Energy-Conserving Stage
Glycolysis Glucose + 2 ATP + 2 ADP + 2 PO 4 + 2 NAD + 2 pyruvic acid + 4 ATP + 2 NADH + 2H + Net Products = 2 pyruvic acid + 2ATP + 2NADH +2H +
Glycolysis Figure 5.14
Glycolysis Figure 5.14
Alternatives to Glycolysis Yield fewer molecules of ATP than glycolysis Reduce coenzymes and yield different metabolites needed in anabolic pathways Two pathways Pentose phosphate pathway Entner-Doudoroff pathway
Pentose Phosphate Pathway Pentose phosphate pathway net gain = 2 NADPH, 1 ATP, and five-carbon precursor metabolites Figure 5.16
Pentose Phosphate Pathway Figure 5.16
Entner-Doudoroff Pathway Entner-Doudoroff pathway net gain = 1 ATP, 2 NADPH, and precursor metabolites Figure 5.17
Alternatives to Glycolysis Pentose phosphate pathway: Uses pentoses and NADPH Produces 1ATP + 2 NADPH Operates with glycolysis Entner-Doudoroff pathway: Produces 2 NADPH + 1ATP Does not involve glycolysis Pseudomonas, Rhizobium, Agrobacterium
Figure 5.14
Cellular Respiration Pyruvic acid completely oxidized to produce ATP by a series of redox reactions Three stages of cellular respiration Synthesis of acetyl-coa (Intermediate step) Krebs cycle Electron Transport Chain (ETC)
Synthesis of Acetyl-CoA Figure 5.18
Synthesis of Acetyl-CoA Results in: Two molecules of acetyl-coa Two molecules of Two molecules of