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MICROBIOLOGY 210 – LAB EXAM II QUESTIONS AND ANSWERS
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MICROBIOLOGY 210 – LAB EXAM II QUESTIONS AND ANSWERS...
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LO 22: 2 - Discuss the importance of the electron transport chain andcompare its location in prokaryotes with that in eukaryotes - ANSWER
The ETC is the final step in aerobic and anaerobic respiration, and is
responsible for the production of energy in the form of ATP
Aerobic respiration = oxygen
Anaerobic respiration = a molecule other than oxygen
This creates a proton gradient when protons (H+) are transferred across
the membrane and their are more on one side
Eukaryotes = ETC in inner membrane of the mitochondrion
Prokaryotes = ETC in the cytoplasmic membrane
LO 22:3 - Discuss the biological importance of the enzyme oxidase -
ANSWER Some common enzyme complexes that are involved in
electron transport are NADH dehydrogenase, flavoproteins,
cytochromes, iron-sulfur proteins, and quinones
Most aerobic organisms contain cytochrome c oxidase (oxidase) which
is a member of the cytochrome group.
This enzyme accepts electrons from the ETC and then transfers them to
molecular oxygen, forming water
Since some aerobes produce oxidases other than cytochrome c
oxidase, not all aerobes are oxidase positive. (this also works inversely
where some facultative anaerobes and microaerophils have cytochrome
c oxidase)
LO 22:4 - Describe the biochemical reactions in both positive and
negative oxidase test when using an oxidase test strip !!! - ANSWER To
,test for the presence of cytochrome c oxidase, a test strip is used that is
imprinted with N,N-dimethyl-p-phenylenediamine and a-naphthol !!!!
Organisms are rubbed into the pink to gray reagent band of the test strip
and allowed to stand for 30 seconds.
If the organism possesses cytochrome c oxidase, the enzyme will
oxidize and it couples the reagents to produce the product indophenol
blue - blue to purple color
If the organism does not possess the enzyme then there will be no
change in color or a slight pink color.
LO 22:5 - Identify the organisms that are typically assessed using an
oxidase test - ANSWER This test is useful for differentiating members of
the genus Enterobacteriaceae with other Gram negative rod-shaped
bacteria
LO 23:1 - Compare and contrast the various categories of organisms
based on their oxygen requirements - ANSWER Aerobes - require
oxygen as the final electron acceptor in aerobic respiration, survival is
dependent upon the presence of oxygen
Obligate anaerobes - undergo either fermentation or anaerobic
respiration meaning oxygen is not required for either process, and
survive without oxygen
Facultative anaerobes - undergo aerobic respiration, anaerobic
respiration, or fermentation depending on the conditions, and grow
better in the presence of oxygen because the energy yield is better
LO 23:2 - Discuss the types of metabolism each category of organisms
is capable of performing based on their oxygen requirements and
provide rationale for each answer - ANSWER Aerobes - contain
superoxide dismutase and catalase or peroxidase since they live in the
presence of oxygen
, Obligate anaerobes - lack both superoxide dismutase and catalase or
peroxidase meaning that if they come into contact with toxic radicals,
their cellular macromolecules will oxidize which results in cell death
Facultative anaerobes - contain superoxide dismutase and catalase or
peroxidase since they are able to grow in the presence of oxygen
LO 23:3 - Compare and contrast the terms selective, differential, and
selective and differential as they apply to microbiological media -
ANSWER Selective media - grows only one particular group of microbes
from a mixed culture, contain compounds that inhibit the growth of some
organisms while allowing the growth of others (methylene blue grows
gram-negative and not gram-positive)
Differential media - differentiates between organisms growing in a
culture, contains substances that are utilized differently by
microorganisms and allows for the differentiation between organisms
based on their particular metabolic capabilities (fermenting sugar or
lactose)
Selective and differential media - selects for specific organisms and then
differentiates between the organisms capable of growing under those
selective conditions
LO 23:4,5 - Identify the components in MacConkey agar that make it
selective and differential and describe the function of each - ANSWER
Selective - The crystal violet and bile salts inhibit the growth of Gram-
positive bacteria which means it is selective for Gram-negative bacteria
Differential - on the basis of lactose fermentation, neutral red indicator
shows if the organisms ferments lactose or not.
If it does ferment lactose, acidic by-products are released, dropping the
pH of the medium, causing the colonies to absorb the neutral red
indicator and appear pink to brick-red. The drop in pH also causes the
precipitation of bile salts, forming a hazy precipitate surrounding them.
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