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UIUC MCB 100 - Exam 2 Study Guide

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MCB 100 1st EditionExam # 2 Study Guide Lectures: 14 -25 Lecture 14 (February 23)What is the difference between total count and viable count in terms of bacterial growth? How do you calculate the concentration of bacteria? Define generation time and growth rate. What is direct microscopic count? Describe MPN, the most probable number. What is the dry-weight method? What is turbidity? What are the 4 phases of the bacterial growth curve? I. Mathematical considerations of bacterial growthA. Total bacteria cell count vs. viable cell count B. The total count includes dead bacteriaC. The viable count enumerates only those that can grow and reproduce i. A known volume of a liquid sample, usually 0.10 mL, is spread on the surface ofan agar plate that will allow bacteria to growii. After an appropriate incubation period, visible colonies of bacteria form iii. One can estimate the number of bacteria that were in the sample by counting the number of colonies that appear on the plate 1. Concentration of bacteria = (number of colonies)/(amount plated x dilution) D. Bacterial growth is not so much about the growth of an individual, but the growth of the bacterial populationE. Bacteria reproduce by binary fission F. When the conditions are good for growth the bacterial population increases at an exponential rate G. Generation time: time it takes for a microbial population to doublei. Ex. 30 minutes per generation B. Growth rate: generations per unit of time [1/(generation time)] i. Ex. 2 generations per hour B. Formula to determine the number of bacteria in a growing population: i. Total number of bacteria = (initial number of bacteria) x (2^the number of generations) II. Methods of enumerating microorganisms i. Direct microscopic count: relatively fast but labor intensive. Microscopy works best for things that are larger than bacteria, like blood cells. Works best for samples with a concentration of b/w 10-200 mil cells per mL. A dead cell may look the same as a living cell, especially for bacteria 1. Ex. Breed smear = direct count technique used in dairy industry in the past. A sample is smeared on a slide and examined. A count is made of the bacteria concentration and particulate matter such as dirt and straw(used to see if a sample of milk from a farm is clean enough to accept at the dairy) ii. Membrane Filter method: similar to viable count except it is used for samples with a low concentration of bacteria. A known volume of water is run through asterile filter. Microbes are trapped on the filter. The filter is placed on the medium and allowed to incubate. 1. Concentration of bacteria = (number of colonies)/(amount filtered) ii. Most Probable Number (MPN): a statistical way of estimating the viable number of bacteria in a liquid sample by inoculating tubes of broth and counting the number of tubes that show growth. 1. Results: 1. One coliform is enough to produce a positive result after incubation2. A bubble in the Durham tube indicates the presence of coliform bacteria3. The bubble is carbon dioxide produced by the fermentation of lactose4. A higher concentration of coliforms in the sample gives more positive tubes ii. Dry-weight method: a liquid sample is run through a filter that has been previously weighed; microorganisms are trapped on the filter. Filter is baked dry to remove the water and reweighed. The increase in weight is proportional to the number of microorganisms that are trapped in the filter. 1. Advantage: some microorganisms are difficult to count by other methods because they form clumps of cells that are hard to separate 2. Disadvantage: dirt and other particulate contaminants will also be trapped by the filter . Turbidityi. Turbid means "cloudy"ii. Liquid broth culture that contains a lot of bacteria looks cloudy whereas a sample of sterile broth medium looks cleariii. There's a direct relationship between the concentration of bacteria in a liquid cultureand the absorbance or scattering of light as it passes through the sample, one can use a spectrophotometer to measure the number of bacteria in a liquid sample III. The 4 phases of a bacterial growth curve A. Phase 1: Lag phase: No detectable growth of the population of bacteriaB. Phase 2: Log phase/exponential phase: population of bacteria is growing at a steady,fast, exponential rateC. Phase 3: Stationary phase: population stops growing b/c the medium has run out of some essential nutrient or is just too crowded. New cells are still forming, but the number of cells that form is equaled by the number of cells that dieD. Phase 4: Decline/death phase: population of cells declines because toxic waste products have accumulated or essential nutrients are used up. Phase 4 may be difficult to detect by turbidity readings.Lecture 15 (February 25) Define metabolism. What is the difference and functions of of anabolic reactions and catabolic reactions? What are the functions of enzymes and what are some bacterial enzymes? Where are enzymes found in a cell? Describe a catalyst. What are cofactors? What are some conditionsthat can affect the functions of enzymes? I. Metabolism: the sum of all the chemical reactions that occur in an organism (and there are a few thousand different chemical reactions going on in a typical cell) A. Anabolic reactions i. Involves in the building up of biological molecules (DNA, proteins, lipids, polysaccharides, and precursor molecules) ii. Produce the complex molecules that cytoplasm is made ofiii. Associated with growthiv. Consume energy in the form of ATP B. Catabolic reactionsi. Release energy that is used to produce ATP ii. Involved in the breaking down of complex molecules to yield simple molecules that the cell can use as synthetic raw material II. Enzymes- The biological catalysts of biochemical reactions A. Most enzymes are proteins but there are some RNA molecules with catalytic activityB. Enzymes are made by living cells and are absolutely required for growth. Impairmentof enzymes (sometimes just one) can cause death of a cell (or a drastic change In its activity)C. An enzyme destabilizes chemical bonds in the substrates (reactants) and promotes formation of the activated complex, a state that is in between the substrates and the products D. A typical enzyme can make a reaction go 100 million times faster E. Typical cells have about 2000-3000 different enzymesF. The lock and key model for enzyme activity refers to the need for structural compatibility b/w the substrate and the enzyme.


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UIUC MCB 100 - Exam 2 Study Guide

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