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MCB 2010L FINAL EXAM 2024/2025 WITH 100% ACCURATE SOLUTIONS
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MCB 2010L FINAL EXAM 2024/2025 WITH 100% ACCURATE SOLUTIONS
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MCB 2010L FINAL EXAM 2024/2025WITH 100% ACCURATE SOLUTIONS
What is the purpose of extracellular enzymes? - Precise Answer ✔✔break down molecules to import
into cell
(Bacteria obtain nutrients (carbon and energy sources) from their surrounding environment. Some
macromolecules (lipids, complex carbohydrates, large proteins) are too large to pass through the
bacterial cell wall)
Define: Hydrolytic enzymes - Precise Answer ✔✔the enzymes produced by certain bacteria to break
down large macromolecules
Define: Hydrolysis - Precise Answer ✔✔the process by which Hydrolytic enzymes use water to break
down large macromolecules into smaller components (fatty acids, monosaccharides, amino acids, etc.)
Define: Extracellular enzymes - Precise Answer ✔✔when hydrolytic enzymes are excreted out of the cell
into the surrounding media they are referred to as extracellular enzymes
What enzyme breaks down starch? - Precise Answer ✔✔α-Amylase: breaks polysaccharide to individual
α-glucose subunits, used to hydrolyze amylose (linear form) and amylopectin (branched form); and
Oligo-1,6-glucosidase - used to hydrolyze amylopectin only; end result is also an α-glucose subunit
What media is used to detect starch hydrolysis? - Precise Answer ✔✔Starch agar - beef extract, soluble
starch and agar
What reagent is used to detect the presence of starch? - Precise Answer ✔✔iodine
,If starch has been hydrolyzed, what results are observed? - Precise Answer ✔✔Blue or dark brown color
in agar from iodine so microbial growth revealed as clearing around growth.
Starch hydrolysis test results - Precise Answer ✔✔Clearing around growth: Amylase is present +
No clearing around growth: No amylase is present −
What is the starch hydrolysis result is consistent with the growth of Escherichia coli? Bacillus cereus? -
Precise Answer ✔✔E. Coli - growth, no clear zone, no amylase present
B. cereus - growth, clear zone, amylase present
What enzyme breaks down urea? What products are formed? - Precise Answer ✔✔Urea (product of
decarboxylation of certain amino acids) can be broken down by urease to form 2NH3 + CO2 (ammonia
and carbon dioxide)
What media is used to detect urea hydrolysis? - Precise Answer ✔✔Urea broth (or agar as in class) -
urea and a trace (.0001%) of yeast extract
What is the pH indicator associated with Urea media? - Precise Answer ✔✔Phenol red is included in the
medium (turns red or pink above 8.4 - alkalinization occurs)
If urea has been hydrolyzed, what results are observed? - Precise Answer ✔✔Pink: Rapid urea
hydrolysis; strong urease production +
Orange or yellow: No urea hydrolysis; organism does not produce urease or cannot live in broth −
What urea hydrolysis result is consistent with the growth of Escherichia coli? Proteus mirabilis? - Precise
Answer ✔✔E. coli - orange colored, urease not present or can't live in broth
P. mirabilis - bright pink, urease present
The urease hydrolysis test is used to differentiate between what families of bacteria? - Precise Answer
✔✔This test is used to differentiate organism based on their ability to hydrolyze urea with enzyme
urease. Urinary tract pathogens from the genus Proteus may be distinguished from other enteric
bacteria by their rapid urease activity. Proteus is gram -; rod shaped and an opportunistic UTI
, Define casein. - Precise Answer ✔✔Casein - milk protein molecule that gives milk its white color; when
broken down it loses its white opacity and becomes clear
What enzyme breaks down casein? - Precise Answer ✔✔Casease - an enzyme that some bacteria
produce to hydrolyze the milk protein casein
What media is used to detect casein hydrolysis? - Precise Answer ✔✔Milk agar - an undefined medium
containing pancreatic digest of casein, yeast extract, dextrose, and powdered milk.
If casein has been hydrolyzed, what results are observed? - Precise Answer ✔✔When milk agar is
inoculated with a casease-positive organism, secreted casease will diffuse into the medium around the
colonies and crate a zone of clearing where the casein has been hydrolyzed. Casease negative organisms
do not secrete casease and thus do not produce clear zones around the growth.
If casein has been hydrolyzed, what results are observed? Give an example of each. - Precise Answer
✔✔Clearing in agar: Casease is present - ex. B. cereus +
No clearing: Casease is absent - ex. E. coli -
Define gelatin. - Precise Answer ✔✔Gelatin - protein derived from collagen - a component of vertebrate
connective tissue
What enzyme breaks down gelatin? - Precise Answer ✔✔Gelatinase - comprise a family of extracellular
enzymes produced and secreted by some microorganisms to hydrolyze gelatin; subsequently the cells
take up individual amino acids and use them for metabolic purposes
What media is used to detect gelatin hydrolysis? - Precise Answer ✔✔Nutrient Gelatin - simple test
medium composed of gelatin, peptone, and beef extract; differs from other solid media in that the
solidifying media is also substrate for enzymatic activity; gelatinase positive organisms will liquefy the
medium
If gelatin has been hydrolyzed, what results are observed? Give example of each. - Precise Answer
✔✔Gelatin is liquid (control is solid): Gelatinase is present - ex. S. aureus +
Gelatin is solid: No gelatinase is present - ex. E. coli −
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