Micro 201 9/14 - 9/23
Micro 201 9/14 - 9/23 MICRB 201
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Popular in Microbiology
This 6 page Class Notes was uploaded by Julianna Sickafus on Sunday September 25, 2016. The Class Notes belongs to MICRB 201 at Pennsylvania State University taught by OLANREWAJU SODEINDE in Fall 2016. Since its upload, it has received 26 views. For similar materials see Introductory Microbiology in Microbiology at Pennsylvania State University.
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Date Created: 09/25/16
Microbiology 201 9/14 – 9/23 Measurement of Microbial Growth 1) Direct Counting -counts cells in a chamber of known volume -ie: Petroff-Hauser Chamber -quick and simple -not a viable cell count unless vital stain is used -unless stain is used, it is hard to tell which cells are alive 2) Electronic Counting -also not viable cell count -unless cells from exponential phase are used -ie: Coulter Counter 3) Viable Counts -only viable cells can form colonies on a plate -gives number of colony forming units (CFU’s) -achieved by performing serial dilutions of a sample and determining the number of cells by: -spread plate -pour plate 4) Spectrophotometry -technique based on fact that microbial cells in solution scatter light -cell concentration measured as optical density -not viable cell count -calibration required to convert optical density to cell number -can be found by finding a viable cell count using a different method -quick and convenient Open/Continuous Culture System -growth in constant environment -steady provision of nutrients and waste removal -growth can be maintained at exponential phase -not necessarily maximum growth Environmental Factors and Growth -microbes survive and grow under a wide range of environmental conditions -extremophile -grow under extreme conditions -pH, temperature, pressure -microbes can be classified according to a preferred growth environment 1) Temperature -influences enzyme activity, membrane fluidity, DNA stability -Cardinal Temperatures: -minimum -lowest temperature -microbes will not grow at any temperature less than -optimum -best temperature for growth -maximum -highest temperature -microbes will not grow at temperatures above -each microbe has its own set of cardinal temperatures Psychophile - about 15C optimal Mesophile -about 20C - 40C optimal Thermophile -55C and higher optimal Extreme Thermophile -100C and higher optimal 2) Osmolality -for most microbes, the higher the osmolality, the more difficult the growth -due to plasmolysis -halophile: prefer growth in high salt environments 3) pH -cytoplasmic pH of most organisms is close to neutral -neutrophile -prefer neutral pH environments -acidophile -prefer low pH environments -alkaphiles -prefer high pH environments 4) Oxygen -final electron acceptor in aerobic respiration -not all organisms require oxygen -oxygen can be highly toxic for some organisms -use anaerobic respiration or fermentation instead -classification based on oxygen requirements -aerobe -oxygen required -anaerobe -oxygen toxic -micro aerophile -low oxygen requirement -facultative -indifferent to oxygen Metabolism -two broad classes of metabolic reactions: -endergonic -energetically unfavorable -exergonic -energetically favorable -ATP -major energy carrier of cells -GTP used in some reactions -some electron carriers can also act as energy carriers -NAD+ -nicotinamide adenine dinucleotide -FAD -flavin adenine dinucleotide -many biosynthetic reactions are endergonic and require energy input -energy derived from coupled exergonic reactions -known as metabolic coupling Redox Reactions -energy transfer -electron donor -reducing agent or reductant -electron acceptor -oxidizing agent or oxidant -some energy lost as heat oxidant + electron reductant -when oxidant accepts electron it becomes reductant -when reductant donates electron it becomes oxidant -equilibrium constant of a redox couple is known as the standard reduction potential- E0 -measures tendency of a reductant to donate its electron -redox coupes with more negative E w0ll donate electrons to those with more positive values Direction of Electron Transfer, E , 0nd Redox Reactions -oxidation of reduced macromolecules such as sugars, lipids, etc. -being oxidized = reductants What happens to H /electrons from removed reductants? -transferred to electron carrier (the oxidant) which is reduced -in this state, it becomes the reductant What happens to newly generated reductants? -becomes oxidized by another redox couple with a more positive E0 + NAD + H NADH (-0.32V) ½ O 2 2H 2 H O (20.8V) -because reaction 1 is more negative than 2, electrons move from NADH to O 2 -in this process, energy is released and captured as ATP -aerobic respiration -reverse of photosynthesis where energy input is required -energy derived from sunlight -photons Electron Carriers -NAD, NADP, FAD -cytochromes -contain heme groups quihones -small, membrane localized Enzymes -biological catalyst -increase rate of reaction -highly substrate specific -many are proteins, some are RNAs, others are a combination -not permanently altered -recycled -when functional enzyme consists of protein and non protein parts: -protein component known as apoenzyme -non protein part known as cofactor, prosthetic group, or coenzyme -combination of both : holoenzyme -lower activation energy -energy required to form the transition state intermediate -substrates interact with enzyme at active site (catalytic site) -substrate specific -environmentally sensitive -temperature, pH -enzymes can be inhibited in 2 ways: -competitive inhibitor -binds at active site -competes with substrate -non competitive inhibitor -binds at another site -alter enzyme’s shape -unable to bind to substrate Catabolism -break down of complex molecules to simpler products -produces energy, reductants, and heat -NADH, FADH, NADPH -energy and its reductants consumed by anabolic reactions -oxidation process -catabolite -substrate for catabolic reaction -two main functions: -oxidized to produce energy -broken down to provide smaller substrates for biosynthesis Anabolism -synthesis of complex macromolecules and cells from simpler precursors -also known as biosynthesis -requires reductants and energy input -there are only a few reversible metabolic pathways -can function catabolically or anabolically -amphibolic pathways -some steps in glycolysis and Krebs cycle Oxidation of Glucose -complete oxidation takes place in 3 steps 1) Conversion of Glucose to Pyruvate -3 main pathways in microbes 1) Glycolysis -main pathway for glucose break down -other sugars fed into this pathway -converted to glucose or one of it derivative -2 stages involved: -6 C stage -2 ATP used -3 C stage -ATP and NADH generated -ATP generated in substrate level phosphorylation glucose + 2ADP + 2 NAD = 2 pyruvate + 2 ATP + 2NADH -some steps are amphibolic 2) Pentose Phosphate Pathway -more important for biosynthesis than energy production -provides main reductant -NADPH -generates 3C-7C sugars -used as substrates for biosynthesis -ie: -4C sugars for aromatic amino acids -5C sugars for DNA/RNA 2) Krebs Cycle, TriCarboxylic Acid Cycle (TCA), or Citric Acid Cycle 3) Oxidative Phoshorylation
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