Microbial Metabolism
The Metabolism of Microbes
Two Types of Metabolism
Reference: https://sites.google.com/site/rccmicrobiology/chapter-8-microbial-metabolism
- Metabolism: general term for all chemical reactions and physical workings of the cell.
- Anabolism (or biosynthesis): process that results in synthesis of cell molecules and structures.
- Catabolism: opposite or compliment of anabolism, they break bonds and often produce energy.
- Metabolites: compounds given off by the complex networks of metabolism.
- Enzymes: Catalyzing the Chemical Reactions of Life
- Enzymes are catalysts, increase the rate of chemical reaction with being part of the reaction.
- Energy of activation: amount of energy required to initiate bonds to bond or break.
- Substrate: reactant molecules.
- Enzyme is larger than the substrate.
- Enzyme structure
- Simple enzymes: consist of just protein.
- Conjugate enzymes: consist of protein and non-protein.
- Also referred to as haloenzyme.
- The protein is called the apoenzyme and non-protein molecules are called cofactors.
- Cofactors: organic molecules, also known as coenzymes.
- Help perform alterations to active site.
- Apoenzymes: Specificity and the Active Site
- Active site (or catalytic site): location the substrate binds.
- Induced fit: enzyme slightly adjusting shape to better fit the substrate.
- Cofactors: Supporting the Work of Enzymes
- Metallic cofactors: metals that participate in precise functions between the enzyme and its substrate.
- Metals help bring the substrate and the active site closer together.
- Participate directly in chemical reactions with enzyme-substrate complex.
- General function of coenzyme is to remove functional group from one substrate and add it to another.
- One of the the most important components of coenzymes are vitamins.
- Location and Regularity of Enzyme Action
- Exoenzymes: enzymes that are transported extracellularly.
- Endoenzymes: enzymes that are retained intracellularly and function there.
- Constitutive enzymes: enzymes always present and in relatively constant amounts regardless of the amount of substrate.
- Ex: proteins involved in utilizing glucose.
- Induced enzyme: enzyme not constantly present and is produced only when its substrate is present.
- Synthesis and Hydrolysis Reactions
- Condensation reactions: anabolic reactions that require enzymes to form covalent bonds between smaller substrate molecules.
- Usually require ATP and release one water molecule.
- Hydrolysis reaction: breaking of bonds that requires water to be an input.
- Transfer Reactions by Enzymes
- Oxidation and Reduction
- Oxidation: loss of electrons.
- Reduction: gain of electrons.
- Some enzymes add or remove functional groups from substrates to substrates.
- The Role of Microbial Enzymes in Disease
- Some microbes use enzymes to avoid host defenses or promote their multiplication in tissues.
- Some use enzymes to cause tissue damage.
- Sensitivity of Enzymes to Their Environment
- In general enzymes operate in natural temperature, pH, and osmotic pressure of an organisms habitat.
- Labile: chemically unstable.
- Low temperature: catalysis.
- High temp: denaturation.
- Pathways are often a linear path where one product is a reactant (substrate) for another.
- Direct Controls on the Actions of Enzymes
- Competitive Inhibition
- Molecules with similar structures as normal substrates can occupy the active site.
- Molecular blocks further activity of the enzyme.
- Feedback Control
- Negative feedback: product fed back to system and cancels an enzyme's activity.
- Allosteric enyzmes have an additional regulatory site for other molecules besides the substrate which causes a shift of the active site to be distorted and no longer bind to its substrate.
- Feedback inhibition: allosteric inhibitors that can temporarily stop the action of the enzyme.
- When at some point the end product is used up and more of it is needed, the enzyme will be released from inhibition and resume catalysis.
- Controls of Enzyme Synthesis
- Enzyme repression: means to to stop further synthesis of an enzyme somewhere along its pathway.
- Excess products can cause the genetic apparatus responsible for the enzyme to automatically be suppressed.
- Enzyme induction: enzymes appear only when suitable substrates are present; synthesis of enzyme is enzyme is induced by its substrate.
- Energy: capacity to do work or cause change.
- Exergonic: release of energy as it goes forward.
- Endogonic: addition of energy drives a reaction forward.
- Redox reactions: reaction of electron donors and receptors.
- Phosphorylate: add an inorganic phosphate to ADP or other compound.
- Dehydrogenation: removal of hydrogens.
- Nitrate test can find what type of cellular respiration the cell undergoes.
- Aerobic respiration (oxygen in reactants): oxidative processing of an organic molecule yielding ATP, CO2, and water (requires O2 as a final electron acceptor).
- C6H12O6 + 6O2 + 38ADP + 38P(inorganic) --> 38ATP + 6CO2 + 6H2O
- PROKARYOTES: RELEASES 38 ATP! (averaged)
- EUKARYOTES: RELEASES 36 ATP.
- Process:
- Glucose-->[glycolysis]-->2 pyruvate & 2 ATP & 2 NADH-->[Pre-Kreb's]-->2 Acetyle 6As & 2 CO2+2 NADH -->[Krebb's Cycle or TCA]-->4CO2 & 2ATP & 6NADH & 2 FADH2 --> [ETC + chemiosmosis]-->34 ATP + 6 H2O
- [Glycolysis]: Direct phosphorylation.
- Eukaryotes & Procaryotes: occurs in cytoplasm.
- [Pre-Kreb's]
- Eukaryotes: Mitochondrial membranes.
- Procaryotes: occurs on the cytoplasm side of membrane.
- [Kreb's Cycle] - Two cycles
- Prokaryotes: occurs in the cytoplasm.
- Eukaryotes: mitochondial matrix
- [ETC-Chemiosmosis] = [Oxidative Phosphorylation]
- 10(NADH)x3---->30 ATP
- 2(FADH2)x2---->4 ATP
- cricae
- Fermentation: oxidative processing of an organic molecule yielding ATP, organic acid, plus/minx CO2 and does not require oxygen, uses an organic final electron acceptor.
- C6H12O6 + 2ADP + 2P(i) --> 2ATP + Organic Acid +/- CO2
- RELEASE 2 ATP
- Process:
- Glucose --> [glycolysis] --> 2 ATP & 2 NADH & 2 pyruvate --> [recycle NAD+ and excrete acid] --> Acid
- Lactic Acid Fermenter: Releases Lactic Acid by combining H + pyruvate.
- Alcohol Fermenter: Release Alcohol
- Anaerobic Respiration: oxidative processing of an organic molecule yielding a range of ATP and various end products.
- Does not require O2, but uses inorganic electron acceptor.
- C6H12O6 + 3-37ADP + 3-37P(i) + SNC --> 3-37ATP + H2S NO2(-) CH4 + Organic Molecules
- 3-37 ATP commonly written "2<ATP<37"
- (S)
- SO4 - Sulfate
- (N)
- NO3
- NO2
- (C)
- CO2
- CO3(-) - Carbonate
- Releases 2<ATP<38.
- Process:
- Glucose --> [glycolysis] -->2,2,2-->[Pre-kreb's/Kreb's]
- Glycolysis
- Energy In: 2 ATP
- Energy Out: 4 ATP
- Net ATP: 2
- Chemicals in between are intermediates.
- Pre-Krebs: Transition Reaction(mitochondrial matrix/bacterial cytoplasm)
- Pyruvic acid molecule broken to form CO2 and a two carbon acid groups, which enters Kreb's cycle as Acetyle CoA. NADH is produced.
- Oxidative Phosphorylation
- Uses integral proteins e.g. cytochromes
- Series of redox reactions.
- Protons pumped from matrix into intermembrane space.
- Hydrogen gradient drives chemiosmosis.
- Final Electron Acceptor is O2 (Aerobic) or other inorganic acceptors (Anaerobic).
- Water is final product (Aerobic)
Two Types of Metabolism
- Metabolism: sum total of all chemical reactions & physical working occurring in a cell.
- Catabolism of Other Substances
- Polysaccharides (CHO) --> [hydrolysis] --> Monosaccharides --> [glycolysis]
- Lipids --> [hydrolysis] --> Glycerol + Fatty Acids (hydrocarbons; lots of energy)
- Glycerol --> [glycolysis]
- Fatty Acids --> [Boxidation] -->Two Carbon Fragments (Acetyle CoA) --> [Kreb's Cycle]
- Protein --> [hydrolysis] --> Amino Acids (contain amino group, NH3) --> [Deanimation] --> Carboxylic Acid --> [Kreb's Cycle]
- Anabolism
- Photosynthesis
- 6CO2 + 6H2O + Energy --> C6H12O6 + 6O2
Reference: https://sites.google.com/site/rccmicrobiology/chapter-8-microbial-metabolism