microbial metabolism - rancho santiago community...
TRANSCRIPT
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint® Lecture Slides for
ROBERT W. BAUMAN
MICROBIOLOGY
Chapter 5
Microbial Metabolism
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• The sum total of chemical reactions that take place within cells (of an organism)
Microbial Metabolism
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Catabolism and Anabolism
• Oxidation and ___________ Reactions
• ATP Production and Energy Storage
• The Roles of Enzymes in Metabolism
Basic Chemical Reactions Underlying Metabolism
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2004 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:
• C6H12O6 + 6O2 -> 6CO2 + 6H2O
• 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
Copyright © 2004 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.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.6b
Copyright © 2004 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
Copyright © 2004 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.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.7a
Copyright © 2004 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 ___________________.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.7b
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 6.7c
What is a term for a
huge amount of
energy released all
at once?
• 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.
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Three important electron carriers
• Nicotinamide adenine dinucleotide (NAD+) → NADH
• Nicotinamide adenine dinucleotide phosphate
• (NADP+) → NADPH
• Flavine adenine dinucleotide (FAD) → FADH2
Oxidation and Reduction Reactions
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Energy released from nutrients can be stored in high-energy 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
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
ATP Production and Energy Storage
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
enzyme
• Substrate Products
The Roles of Enzymes in Metabolism
Substrate-level phosphorylation
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
The Roles of Enzymes in Metabolism
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• The turnover number is generally 1-________ molecules per second.
Enzymes
Figure 5.4
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
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)
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.7
Enzyme Activity
Sucrose ------->
fructose + glucose
sucrase
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Many factors influence the rate of enzymatic reactions
• Temperature
• __________
• Enzyme and substrate concentrations
• Presence of ___________
Enzyme Activity
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.8a
Temperature
What happens to a
protein when the
temperature is to high?
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Enzymes can be denatured by temperature and pH
Factors Influencing Enzyme Activity
Figure 5.6
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.8c
Substrate Concentration
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Substances that block an enzyme’s active site
• Do not denature enzymes
• Types of Inhibitors
• Competitive inhibitors
• Noncompetitive inhibitors
Inhibitors
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.10
Competitive Inhibitors
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.11a
Noncompetitive Inhibitors
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.12
Feedback Inhibition
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.12
Feedback Inhibition
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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)
Carbohydrate Catabolism
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• The oxidation of glucose to pyruvic acid, produces ATP and NADH.
Glycolysis
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Occurs in cytoplasm of most cells
• Divided into three stages involving 10 total steps
• Energy-Investment Stage
• Lysis Stage
• Energy-Conserving Stage
Glycolysis
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Glycolysis
• Glucose + 2 ATP + 2 ADP + 2 PO4
– + 2 NAD+ 2 pyruvic acid + 4 ATP + 2 NADH + 2H+
• Net Products = 2 pyruvic acid + 2ATP + 2NADH +2H +
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Alternatives to Glycolysis
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.16
Pentose Phosphate Pathway
•Pentose phosphate pathway –net gain = 2 NADPH, 1 ATP, and five-carbon precursor metabolites
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.16
Pentose Phosphate Pathway
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.17
Entner-Doudoroff Pathway
•Entner-Doudoroff pathway – net gain = 1 ATP, 2 NADPH, and precursor metabolites
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Alternatives to Glycolysis
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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)
Cellular Respiration
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.18
Synthesis of Acetyl-CoA