MCB 2610 Lab Practical (Questions & Answers) Rated 100%

What is fermentation - Being able to grow anaerobically in the presence of a suitable organic compound, such as a sugar. Several reduced products are excreted by the cell as a way of disposing of the electrons derived from oxidation. Function and Types of hydrolytic enzymes - Hydrolytic enzymes hydrolyze (break down) complex molecules to get food that can be transported into the cell. 1. Amylase 2. Caseinase 3. Gelatinase Amylase - catalyzes starch hydrolysis. Reacts readily with iodine to produce a dark blue color. Clear zone indicates amylase production. Iodine makes the starch blue. Caseinase - Enzymes that hydrolyze milk protein (casein) into peptides and ultimately into amino acids Clear zone where caseinase is digested Catalase - An enzyme which protects cells from hydrogen peroxide - a highly reactive and toxic chemical produced as a byproduct of oxygen metabolism H2O2 in the presence of catalase will produce water and oxygen as a byproduct If catalase positive, bubbles of O2 will form when a drop of H2O2 is placed on the organism Complex media - Exact chemical composition is not known Most are made from inexpensive sources Diverse mixture of proteins (peptides), sugars, vitamins, mineralsDeath phase - Occurs if conditions remain unchanged (no new medium or environment remains stable). The cell death rate will eventually exceed any remaining cell division. Defined media - Made up of a strict list of compounds Forces organisms to synthesize necessary amino acids, nucleotides, lipids, polysaccharides, vitamins Allows scientists to characterize the versatility and limitations of an organism's metabolic capacity Defined media can be used to help define the specific requirements for a particular organism Differential media - Allows certain bacteria to be differentiated from others, typically by changing of color, production of a zone of clearing etc. Dye used for spore staining - 5% aqueous Malachite green dye Gelatinase - An enzyme that hydrolyzes gelatin, a protein derived from collagen. If gelatin is hydrolyzed, the media will become liquid General purpose media - WIll support growth of a wide range of organism Used to grow up dense cultures of bacteria, typically for experimentation How does SF select for streptococci - Streptococci lack a respiratory system, so they use fermentation. Brom cresol purple is an acid indicator that changes color when acid is produced, indicating fermentation of the glucose. Purple = negative for fermentation of glucose Yellow = positive for fermentation of glucose How is bacterial growth measured? - Using a spectrophotometer, you can measure the optical density (absorbance) over a period of time How is microbial growth defined? - Increase in population sizeIn Gram stains, why can't Gram negative bacteria retain the crystal violet? - Because Gram negative bacteria have an outer membrane and a thinner layer of peptidoglycan, which are easily depolarized and can only retain the counterstain (Safranin-pink) Lag phase - Occurs when the bacteria is transferred to a fresh growth medium. The cells must adjust to new conditions and synthesize a full complement of enzymes. Log phase - Period of tremendous growth in population. Each cell divides into two new cells; twofold exponential growth MacConkey agar - used to differentiate for coliforms and select for gram negative bacteria No growth = gram positive Growth and yellow = non coliform and gram neg Growth and pink = coliform and gram negative Gram positive bacteria are inhibited by the bile salts and crystal violet in the medium. Oxidase - Indicates presence of cytochrome c, a component of some electron transport systems When oxidized, the compound will turn blue or red. An organism that has cytochrome c will oxidize the reagent used and produce a color change = oxidase positive