Ch 07 Microbial Metabolism
SLOs Differentiate between metabolism, catabolism, and anabolism. Fully describe the structure and function of enzymes. Differentiate between constitutive and regulated enzymes. Describe how enzymes are controlled. Name the chemical in which energy is stored in cells. Create a general diagram of a redox reaction. Identify electron carriers used by cells. List three basic catabolic pathways and the estimated ATP yield for each. Construct a paragraph summarizing glycolysis. Describe the Krebs cycle, and compare the process between bacteria and eukaryotes. Discuss the location and the significance of the ETC. Compare and contrast aerobic and anaerobic respiration. Summarize the steps of microbial fermentation, and list three useful products it can create. Describe how other COHs and how proteins are catabolized.
Metabolism and the Role of Enzymes Metabolism: Def? Catabolism: Provides and for anabolism. Anabolism: Uses and to build large molecules Compare to Fig 7.1 Big Picture
Enzymes: Biological Increase reaction rate by Do not become part of the products Are unchanged in the process Simple enzymes consist of protein alone Conjugated enzymes = Holoenzymes contain protein and nonprotein molecules Fig 7.2
Enzyme Substrate Interaction Active site highly specific Model: Common cofactors: Fe, Mg, Mn Zn Many coenzymes are Vitamin derivatives Oxidoreductases and dehydrogenases, transferases, Hydrolases, Ligases Fig 7.3
Regulation of Enzyme Action Constitutive enzymes, e.g.:? Regulated enzymes Induction and repression Enzyme function is dependent on temperature, ph, osmotic pressure?
Fig 7.4
Metabolic Pathways Fig 7.5 Terminology: Intermediate products, common intermediates, branching points
Metabolic Pathways of Energy Production: COH Catabolism Cellular respiration Aerobic respiration Anaerobic respiration Fermentation The three steps of aerobic respiration 1. Glycolysis (oxidation of to ) 2. Krebs cycle (oxidation of acetyl CoA to ) 3. Oxidative phosphorylation (e - transport chain)
Control of Enzyme Action: Inhibitors Competitive inhibitors vs. Noncompetitive allosteric inhibitors Compare to Fig 7.6
Example: Sulfa drugs
Feedback Inhibition Also known as endproduct inhibition Controls amount of substance produced by a cell Mechanism is allosteric inhibition
Control of Enzyme Synthesis Enzyme repression Protein expression Response time longer than for feedback inhibition Enzyme induction Protein expression when suitable substrates present E.g.: lactase induction in E. coli Fig 7.7
Utilization of Energy Energy is needed to do work. Energy comes directly from the sun, or is contained in chemical bonds. Exergonic vs. Endergonic reactions Exergonic and endergonic rxs. often coupled released energy immediately put to work.
Energy Production: Oxidation-Reduction Reactions Oxidation = loss of e - Reduction = gain of e - Redox reaction: Oxidation reaction paired with reduction reaction.
When a compound loses electrons, it is oxidized. When a compound gains electrons, it is reduced. Rredox reactions are common in cell and indispensable to the required energy transformations. Fig. 7.8
Oxidation-Reduction cont. In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations.
Electron Carriers NAD and FAD are molecular shuttles for e -. They are coenzymes for Oxidoreductases (= enzymes that remove electrons from one substrate and add them to another) Fig. 7.9
ATP ATP hydrolysis powers biosynthesis. Input of energy is required to replenish ATP. In heterotrophs, catabolic pathways provide the energy that generates ATP from ADP. Fig. 7.10
Catabolism Enzymes catabolize organic molecules to precursor molecules and/or energy that cells then use for anabolism. Energy is stored in electrons available in NADH and FADH 2 bonds of ATP Both are are produced during and needed in large quantities for metabolism.
3 Catabolic Pathways
Glycolysis Multi step breakdown of glucose into pyruvate Part of which catabolic pathways (s)? Generates small amount of ATP (how many?) small amount of reducing power (?)
The Steps of Glycolysis Compare to Fig 7.2
Pyruvate to Acetyl CoA Acetyl group of acetyl-coa enters TCA cycle Transition step Krebs cycle generates ATP and reducing power Precursor metabolites Other names for Krebs cycle? generates Acetyl-CoA from Pyruvate (decarboxylation)
The Krebs Cycle: A Carbon and Energy Wheel Takes place where?
Krebs Cycle Compare to Fig 5.13
Electron Transport Chain Formed by series of electron carriers located in... Oxidation/Reduction reactions. Reduced electron carriers from glycolysis and TCA cycle transfer their electrons to the electron transport chain Allows transport of protons (H + ) outside of the membrane Generates proton gradient or proton motive force (pmf) In final step, O 2 accepts electrons and hydrogen, forming water.
Principal Compounds in the e - Transport Chain NADH dehydrogenase, Flavoproteins, Coenzyme Q, Cytochromes
The Generation of ATP Phosphorylation: Substrate level phosphorylation: ATP synthesis via direct transfer of a high-energy PO 4 to ADP. Oxidative phosphorylation: ATP synthesis coupled to electron transport. NADH entering electron transport chain gives rise to 3 ATP FADH 2 enter electron transport chain at later point less energy released and only 2 ATP produced
The Terminal Step Catalyzed by cytochrome aa 3, also known as cytochrome oxidase. 2H + + 2e - + ½ O 2 H 2 0 Potential side reaction of respiratory chain: Incomplete reduction of O 2 to superoxide ion (O 2- ) and hydrogen peroxide (H 2 O 2 ) Aerobes produce enzymes to deal with these toxic oxygen products: Superoxide dismutase Catalase Streptococcus lacks these enzymes but still grow well in O 2 due to the production of peroxidase.
Inorganic O 2 -containing molecules, other than free oxygen is final e - acceptor, e.g.: NO 3 - Anaerobic Respiration Terminal step utilizes Nitrate reductase NO 3 - + NADH NO 2 - + H 2 O + NAD + Examples for other final e - acceptors: SO 4 2-, CO 3 3- Strict anaerobes and facultative anaerobes Involves glycolysis, Krebs cycle, and ETC ATP yield lower than in aerobic resp. because only part of TCA operates under anaerobic conditions.
Anaerobic Respiration cont.: Denitrification Further reduction of nitrite to nitric oxide (NO), nitrous oxide (N 2 O), or N 2 Some species of Pseudomonas and Bacillus INSERT Denitrifying rx from Nitrogen reduction lab
Fermentation - Incomplete oxidation of glucose. Does not involve Krebs cycle or ETC - Organic molecules are final electron acceptors. - Some organisms can repress production of ETC proteins when no O 2 Energy yield low Great diversity of end products:
Alcohol and Lactic Acid Fermentation
Catabolism of other Compounds Polysaccharides and disaccharides Amylases for digestion of (very common) Cellulase for digestion of (only bacteria and fungi have this enzyme) Disaccharidases: Sucrase, Lactase, etc. Proteins are broken down into amino acids by proteases: - Amino groups are removed through deamination.
In Lab: Biochemical Tests for Bacterial Identification: Fermentation Tests Different bacterial species produce different enzymes Test detects presence of enzyme Example: Lactose Fermentation
Protein Catabolism Protein Extracellular proteases Deamination, decarboxylation, dehydrogenation, desulfurylation Amino acids Organic acid Krebs cycle Decarboxylation
Overview of COH Catabolism
Summary of Aerobic Respiration in Prokaryotes
Location of Carbohydrate Catabolism Pathway Eukaryote Prokaryote Glycolysis Preparatory step Krebs cycle ETC
ATP produced from complete oxidation of one glucose using aerobic respiration Pathway Glycolysis Intermediate step Krebs cycle By Substrate-Level Phosphorylation By Oxidative Phosphorylation From NADH From FADH Total
Anabolic Pathways not covered, except for protein and DNA biosynthesis, which will be covered in Ch 8. Case File: Not so sweet Inside the Clinic: Vitamin D Deficiency