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5) Food Microbiology > 5) Saccharomyces Cerivisae > Flashcards

5) Saccharomyces Cerivisae Flashcards

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1
Q

what type of yeast is Sc?

A

budding

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2
Q

Can Sc be airborne?

A

no

it needs a vector to move

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3
Q

how many chromosomes does Sc have?

A

16

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4
Q

what is the Gay Lussac Equation?

A

180g sugar –> 92g ethanol + 88g CO2 (theoretical yield)

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5
Q

what are two forms that Sc can exist as?

A

haploid or diploid

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6
Q

what occurs to haploids and diploids when there are adequate nutrients present?

A

haploids and diploids both undergo repeated rounds of vegetative growth and mitosis

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7
Q

what happens to Sc when nutrients are depleted?

A

haploids and diploids arrest as SPC (stationary phase cells)

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8
Q

what are SPC? characteristics?

how are SPC different than proliferating/growing yeast cells

A
  • SPC = stationary phase cells
  • round and bright
  • contains more storage CHO (trehalose and glycogen) than growing cells
  • higher resistance to stresses than growing cells
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9
Q

what are the 2 mating types of haploid cells?

differentiate them.

what surface receptors do they have?

A

a: produces a pheromone “a factor”
alpha: produces “alpha factor”

each cell type has the surface receptor for the opposite mating type

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10
Q

what happens when the surface receptor on one of the mating haploid types is stimulated?

A
  1. cels stop in the G2 phase of the cell cycle
  2. cells stop proliferating and grow towards each oterh
  3. creates a “shmoo”
  4. once there is cell contact, they fuse together and form a diploid
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11
Q

diploid cells with no N will undergo ____ and ____.

what does this create?

A

meiosis and spore formulation, which results in 4 haploid spores contained in an ascus

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12
Q

what is an ascus? how does it compare to SPC?

A
  • contains 4 haploid spores after sporulation

- has higher resistance to stresses than SPC

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13
Q

Sc vegetative proliferation occurs via _____

A

budding

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14
Q

what does the cell cycle have to control processes that occur?

A

checkpoint controls, where the cell cycle doesn’t continue if some processes haven’t happened (eg. mitosis won’t happen if DNA replication has not been completed)

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15
Q

what are 4 morphogenic aspects of the yeast cell cycle

A
  1. bud site selection: in rich media, haploids bud in an axial pattern, while diploids show polar budding
  2. polarity
  3. pattern
  4. rate of growth
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16
Q

how does growth occur in yeast?

A

building materials are packed into vesicles, docked at the plasma membrane, then incorporated into the growing cells

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17
Q

differentiate the products and substrates of growing and stationary phase

A

growing phase: Sc cells ferment glucose via glycolysis to form ethanol

stationary: Sc cells use ethanol already formed via TCA and glyoxylate cycles

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18
Q

why do Sc have specific transport proteins?

A

b/c most compounds needed for Sc metabolism can’t pass through phospholipid membranes, thus they must be transported through

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19
Q

describe the breakdown of maltose by Sc

A
  1. actively transported across the cell membrane
  2. hydrolyzed by alpha-glucosidase (aka maltase) to produce 2 glucose molecules
  3. glucose is broken down in glycolytic pathway
20
Q

describe the breakdown of sucrose by Sc

A

sucrose is broken down to fructose + glucose (via invertase)

21
Q

describe the cell walls of Sc

A
  • cell walls have mechanical strength against physical damage
  • has a homogenous inner layer (plasma membrane) and a fibrillary outer layer (implanted in inner layer and emanating from cell surface)
  • composition: glucans, mannoproteins, chitin (most responsible for mechanical strength of cell wall)
22
Q

what is around 50% composition of cell wall?

A

glucans

23
Q

what are 2 types of amylases

A
  1. endoamylase: alpha amylase (breaks down alpha 1,4 links)

2. exoamylase: beta amylase (breaks down alpha 1,4 links) and gluco-amylase (Breaks down alpha 1,4 and alpha 1,3)

24
Q

what is another name for oryzae

A

koji

25
Q

what are main uses of oryzae/koji?

A
  • east asian cuisine

- ferment soy beans, soy sauce, miso, breaks down rice starches into sugars for sake

26
Q

what is oryzae

A
  • fungus that secretes amylases that extracellularly degrades starches
27
Q

how does A.oryzae form a hyphae

A
  • asexually produces a conidium spore at the tip of a specialized hypha, capable of growing into a new multicellular organism
  • if conditions are right, the conidium will swell and grow into a germ tube to form the hyphae
28
Q

what is a hyphae?

A

individual secretions partitioned by septa

constitutes multicellular filamentous fungi

29
Q

what is a hyphal tip

A

highly metabolically active

where growth of the fungi occurs from

30
Q

how do A. oryzae cells communicate between each other?

how is this related to woronin bodies?

A

through the pore in the middle of septum

if cell damage is detected, woronin bodies will plug the pore to prevent danger to the entire organism

31
Q

A. oryzae secretes amylases that do what?

A

extracellularly degrades starch

32
Q

what is Spitzenkorper?

what does it do?

A

organelle present in the hyphal tip region; involved in accumulation and secretion of vesicles that contain secretory enzymes
- vesicle is then endocytosed right after fusion with cell membrane; then recycled for incorporation into new secretion vesicles. This is imp for sustaining high levels of amylases

33
Q

what is a conidiophore? what is its mechanism?

A
  • a special cell designed to produce conidium to spread the mold
  • nutrients are passed from the hyphae into the budding conidia
  • when conditions are right, the conidium prepares to germinate by swelling
  • vacuoles involved in autophagy appear and grow to aid in the physical extrusion of cytoplasm at tips of the germ tubes
34
Q

what is geotricum candidum?

A

rapid growing mold that prevents unwanted mold growth in moist cheeses

35
Q

what is penicillium candidum

A
  • produces fuzzy white mold on surface of bloomy rind cheeses
  • includes Brie, Camembert, Coulommiers, French goat cheeses
  • different strains can produce different flavours
36
Q

what is penicillium roqueforti

A
  • creates colored veins and surfaces

- major contributor to flavour in blue cheeses

37
Q

describe why a symbiotic mix of MO is needed

A
  • LAB usually needs nutrients that are provided by yeasts and molds
  • difference in O2 requirements: molds and AAB are on the surface (aerobic) while LAB and yeasts are internal (anaerobic)
38
Q

what are main ingredients in Sake?

A

H2O
rice
koji
yeast

39
Q

what is the function of koji in sake?

what is aded after koji?

A

koji: converts starches in rice into sugars

LAB: colonizes sugars and grows for a second stage of fermentation, which kills wild yeast and prepares the solution for the fermentation by the brewing yeast

40
Q

what is Fukuyama Pot vinegar?

A

traditional japanese rice vinegar

- rice + koji is added into a large pot and laid in an open air field

41
Q

what rxns occur in the production of Fukuyama Pot vinegar?

A
  1. saccharification
  2. alcohol fermentation
  3. acetic acid fermentation
  4. lactic acid fermentation
42
Q

what is milk kefir?

A

fermented beverage inoculated with kefir grains that harbor LAB, AAB, yeast and sometimes molds

43
Q

what are characteristics of kefir grains?

A
  • white, elastic, opaque, cauliflower shaped

- consists of water and water-insoluble kefiran (extracellular polysaccharide produced by LAB)

44
Q

how are kefir cultures usually started?

A

via back slopping

45
Q

what is kefiran? what are characteristics? describe composition.

A
  • main EPS produced in kefir grains
  • heteropolysaccharide
  • composed by equal proportions of glucose and galactose
  • mainly produced by Lactobacillus kefiranofaciens. But adding Saccharomyces sp. to the culture improves net quantity of kefiran
46
Q

where are live kefir MO mostly found?

A

at exterior of kefir grains

5) Food Microbiology (21 decks)

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