MCB2004 Exam 2 Review Guide Lecture 9 Microbial Growth Microbial growth increase in the number of cells 1 Cell elongates and DNA is replicated 2 Cell wall and plasma membrane begin to grow inward 3 Cross wall forms completely around divided DNA Microbial growth is exponential Bacterial Growth Curve 1 2 Lag phase intense activity preparing for population growth but no increase in population Log phase logarithmic or exponential increase in population a Growth in this phase due to reproduction by binary fission bacteria or mitosis yeast 3 Stationary phase period of equilibrium microbial deaths balance production of new cells 4 Death phase population is decreasing at a logarithmic rate Physical Requirements 1 Temperature min growth temperature optimal growth temperature max growth temperature a Psychrophiles 10 20 b Psychrotrophs 0 30 c Mesophiles 10 50 d Thermophiles 40 70 e Hypothermophiles 65 110 2 pH a 6 5 7 5 b Molds and yeasts 5 6 3 Osmotic pressure 4 Irradiation Chemical Requirements 1 Carbon 2 Nitrogen a Hypertonic environments cause plasmolysis i If the concentration of solutes is higher in the surrounding medium than in the cell hypertonic water tends to leave the cell Growth of the cell is inhibited b Facultative halophiles require high osmotic pressure 3 Sulfur 4 Phosphorus 5 Trace elements 6 Organic growth factors a Vitamins amino acids purines pyrimidines Chemotrophs Phototrophs 1 Chemoheterotrophs most bacteria use organic compounds 2 Chemoautotrophs use inorganic compounds 1 Photoheterotrophs use organic compounds 2 Photoautotrophs use inorganic compounds Forms of oxygen reactive oxygen species free radicals peroxide anion hydroxyl radical Inoculum introduction of microbes into medium Complex media extracts and digests of yeasts meat or plants Agar complex polysaccharide Used as solidifying agent for culture media in Petri plates slants and deeps Generally not metabolized by microbes Liquefies at 100 C solidifies at 40 C Selective media suppress unwanted microbes and encourage desired microbes Differential media make it easy to distinguish colonies of different microbes Pure culture streak plate viable count use samples that have 25 250 colonies Most Probable Number Test count positive tubes Estimating Bacterial Numbers by Indirect Methods Turbidity Direct Counts Indirect Counts Turbidity Metabolic activity Dry Weight Plate Count Filtration MPN Direct Microscopic count Dry weight Lecture 10 Control of Microbial Growth Increase Growth Make fermented food Make medicine Decrease Growth Prevent food spoilage Prevent disease occurrence Industrial products Recycle waste Biological control Prevent contamination in medical and in microbiological laboratories Sterilization kills off all microbes including endospores Commercial sterilization used to kill of clostridium botulinum in canned foods Disinfection destruction of devastative pathogens called antisepsis on living tissue Sanitization treatment to lower microbial counts for safe public health levels Actions of microbial growth agents alteration of membrane permeability damage to proteins damage to nucleic acids Bacterial populations die at a constant logarithmic rate Depends on number of microbes environment time of exposure microbial characteristics Moist heat denatures proteins Autoclave steam under pressure Pasteurization reduces spoilage organisms and pathogens Equivalent treatments 63 C for 30 min high temperature for a short time 72 C for 15 sec ultra high temperature 140 C for less than 1 sec Only thermoduric organisms survive Dry heat sterilization kills by oxidation flaming incineration hot air sterilization Hot air 170 C for 2 hours Autoclave 121 C for 15 min Physical methods for microbial control filtration low temperature refrigeration deep freezing lyophilization freeze dry desiccation prevents metabolism osmotic pressure causes plasmolysis high pressure denatures proteins For filtration use HIPA filters Radiation damages DNA Ionizing radiation x rays gamma rays electron beams Nonionizing radiation UV Chemical methods of microbial control concentration of disinfectant organic matter pH time Evaluating a disinfectant use a dilution test disk diffusion method Types of disinfectants phenols i e Lysol bisphenols i e hexachlorophene Triclosan These disrupt plasma membranes Biguanide i e chlorhexidine used for surgical hand wash and preoperative skin prep Iodine tinctures in aqueous alcohol Iodine iodophors in organic molecules These alter protein synthesis and membranes Chlorine bleach chloramine oxidizing agents Types of disinfectants alcohol ethanol isopropanol Denatures proteins and dissolves lipids Heavy metals Ag Hg Au Oligodynamic reaction Denatures proteins a Inactivate proteins by cross linking with functional groups Chemical sterilants 1 Aldehydes 2 Gaseous sterilants a Ethylene oxide b Denature proteins Chemical food preservatives 1 Organic acids Inhibit metabolism a b Sorbic acid benzoic acid calcium propionate c Control molds and bacteria in foods and cosmetics 2 Nitrate prevents endospore germination commonly in meat products such as ham and bacon 3 Antibiotics a Nisin and natamycin prevent spoilage of cheese Most resistant to microbial control prions Least resistant viruses with lipid envelopes Lecture 11 Microbial Genetics Genotypes the genes of an organism Phenotypes expression of the genes Base pairing and DNA replication double helix A with T C with G held together by hydrogen bonds Backbone is deoxyribose phosphate Strands are antiparallel Polarity 5 3 DNA replication is semiconservative 1 Enzymes unwind the parental double helix 2 Proteins stabilize the unwound parental DNA 3 The leading strand is synthesized continuously by DNA polymerase 4 The lagging strand Okazaki fragments is synthesized continuously Primase an RNA polymerase synthesizes a short RNA primer which is extended by DNA polymerase 5 DNA polymerase digests RNA primer and replaces it with DNA 6 DNA ligase joins the discontinuous fragments of the lagging strand DNA is copied by the DA polymerase in the 5 3 direction PCR to make multiple copies of a piece of DNA enzymatically Used to clone DNA for recombination amplify DNA to detectable levels sequence DNA diagnose genetic disease detect pathogens Transcription DNA is transcribed to make RNA mRNA rRNA and tRNA 1 RNA polymerase binds to the promoter and DNA unwinds at the beginning of a gene 2 RNA is synthesized by complementary base pairing of free nucleotides with the nucleotide
View Full Document
Unlocking...