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Physiology of Microbes > Yeast > Flashcards

Yeast Flashcards

1
Q

what is yeast

A

unicellular fungi that reproduce by budding

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2
Q

how many yeast genera are there

A

around 100

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3
Q

how are the yeast genera divided

A

into around >700 species

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4
Q

what is yeast used as a model for

A

higher organisms

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5
Q

are yeasts pathogenic

A

some are

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6
Q

what is yeast cytology

A

different species vary in shape, size and colour

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7
Q

what is budding

A

replication

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8
Q

what happens in budding

A

after DNA has been replicated a daughter cell is made, grows out of the side of the mother cell
mother gets bud scar on cell surface (chitin rich)

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9
Q

how are the mother and daughter distinguishable

A

birth scar on the daughter where there is less chitin

mother cells are distinct to daughter cell

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10
Q

how many times do cells bud

A

cells only bud a finite number of times (age+die)

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11
Q

how does yeast respire

A

anaerobic and aerobic

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12
Q

what is yeast used for

A

fermentation

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13
Q

what products can be made by yeast fermentation

A

beer is a by-product of yeast growth on wort

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14
Q

what is the yeast fermentation reaction

A

C6H12O6 –> 2C2H5OH + 2CO2

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15
Q

what is yeast cultivation

A

yeast is stored under liquid nitrogen

yeast taken out at start of propagation process, grown in lab on liquid medium to increase cell number

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16
Q

what temperature is yeast stored at in cultivation

A
  • 196 degrees C
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17
Q

why is yeast stored at -196 degrees C in cultivation

A

provides a stable environment

no genetic changes

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18
Q

what are the two types of propagation

A

batch

fed batch

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19
Q

what is pitching

A

in the start of fermentation yeast takes up sugars, nutrients, oxygen and presents in wort
uses this to divide initially aerobically
once oxygen used, switch to fermentation pathway

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20
Q

what happens at the start of yeast fermentation

A

start fermentation yeast population divided 2/3 times, makes carbon dioxide it bubbles up through centre of vessel, causes yeast to move in circular way, so yeast in contact with beer

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21
Q

what happens in yeast fermentation as wort sugars used

A

CO2 made decreases

yeast accumulates at bottom of vessel, remains till fermentation complete (sugar utilization, flavour problem)

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22
Q

what is flocculation

A

ability of yeast cells to adhere to each other, form clumps, is a reversible process

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23
Q

why is flocculation important

A

cells need to be dispersed in wort during active fermentation

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24
Q

what is ADY

A

active dried yeast

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25
Q

when are cells non-flocculated

A

when dispersed

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26
Q

what happens when cells are non-flocculated

A

more able to use sugar efficiently

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27
Q

when is yeast flocculated for the second time int he fermentation process

A

need to form a crop at the end of fermentation, separate from ‘green beer’
yeast is flocculated, provides natural means of clarifying beer

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28
Q

what does flocculation involve

A

interactions between adjacent yeast surfaces

yeast cells have receptor sites in cell surface, have lectin projections, can stick into receptor sites of other cells

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29
Q

what is calcium needed for in flocculation

A

interactions between adjacent cells is a calcium-mediated process

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30
Q

what happens when the lectin projections stick to receptor sites of other cells

A

clumps become so heavy, sediment out of beer

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31
Q

what is flocculence

A

inherent genetic property of yeast strain

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32
Q

are brewing strains flocculent

A

most brewing strains are moderately flocculent

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33
Q

what determines flocculation

A

flocculation genes - depends if clumping characteristic on/off

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34
Q

what causes yeast to de-flocculate

A

sugars block the receptor sites

cause de-flocculation

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35
Q

why do yeast cells de-flocculate

A

ensure cells dispersed at start of fermentation

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36
Q

what does yeast separation from beer allow

A

yeast to be recovered, reused

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37
Q

why does yeast quality deteriorate over time

A

oxidation, osmotic stress
end of fermentation nutritional and ethanol stress
cold shock
stresses occur over re-pitchings, eventually disregarded

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38
Q

what is yeast responsible for the production of

A

made as a result of amino acid metabolism:

  • ethanol and higher alcohols
  • aldehydes
  • esters

vicinal diketones (e.g. diacetyl)

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39
Q

what amino acid requirements do yeast have

A

different yeast strains have different amino acid requirements, can cause different flavour profiles

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40
Q

what is the start point for a lot of yeast flavour development

A

keto acid pool

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41
Q

what are keto acids decarboxylated by, to form

A

CO2 decarboxylates it

forms aldehyde

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42
Q

what is aldehyde reduced to

A

fatty acetyl CoA

higher alcohol

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43
Q

what does acetyl CoA form

A

ester

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44
Q

what is diacetyl created by

A

yeast

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45
Q

when is diacetyl removed

A

removed by yeast near end of fermentation

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46
Q

what pathway is diacteyl part of

A

valine synthetic path

47
Q

when is fermentation deemed complete

A

when diacetyl levels below flavour threshold

48
Q

how do lager and ale differ

A

different yeast strains

49
Q

which strains are ‘top cropping’

A

ale

50
Q

how can ale strains be made to flocculate down

A

in large cylindro-conical fermenters

51
Q

which strains are ‘bottom cropping’

A

lager

52
Q

what causes bottom cropping

A

flocculation properties cause strains to sink

53
Q

how do bottom and top cropping differ

A

require different growth requirements e.g. temperature

54
Q

what is cell envelope made of

A

cell wall
periplasm
cell membrane

55
Q

what can pass through cell envelope

A

leaky molecules

56
Q

what is the cell wall made of

A

mannoproteins
beta-glucans
(chitin too)

57
Q

what is the beta-glucan for in cell wall

A

rigidity

58
Q

what is constantly replaced in cell wall

A

mannoproteins and beta-glucans

59
Q

why is yeast cell wall constantly changing

A

in response to external stimuli

e.g. nutrients

60
Q

can yeast cell wall permanently change

A

can adopt permanent change over time

61
Q

what is after the cell wall

A

periplasm

62
Q

what is the periplasm

A

gap between cell wall and cell membrane

63
Q

what occurs at cell wall

A

site for storage e.g.glycogen and site of enzyme reactions

64
Q

what is the cell membrane like

A

highly selective

lipid bilayer with globular proteins

65
Q

what is the primary membrane

A

primary boundary between cell and environment

66
Q

what does the primary membrane have

A

has membrane proteins

67
Q

what does ATPase do

A

hydrolyse ATP
generates electrochemical gradient
gradient for protons

68
Q

what is the effect of the electrochemical gradient

A

barrier against free diffusion
transport molecules (trans-membrane ion, ATP, solute gradients)
binding site for signal molecules

69
Q

what is an invagination

A

enclosed plasma membrane droplets

leading to compartmentalisation of molecules, also used for compound secretion/excretion

70
Q

what is the cytoplasm

A

aqueous acidified fluid

71
Q

what is in the cytoplasm

A

made of dissolved, suspended macromolecules, enzymes, proteins

72
Q

what does the cytoplasm allow

A

surrounds all organelles

allows communication and transport ‘houses’ the cytoskeleton network

73
Q

what is the cytoskeleton network

A

microtubules - structural organisation for cell

74
Q

what is the cytoskeleton network important for

A

e.g. bud development, cell growth

75
Q

what is present in the outer membrane of the mitochondria

A

enzymes involved in lipid metabolism

76
Q

what is in the matrix of the mitochondria

A

has enzymes involved in fatty acid oxidation, citric acid cycle, protein synthesis and mitochondrial DNA

77
Q

what is in the inner membrane of the mitochondria

A

form cristae

contains cytochromes, proteins, ATP synthase - respiratory chain

78
Q

what is the role of mitochondria in brewing

A

aerobic

synthesis ATP during respiration (oxygen terminal electron acceptor)

79
Q

when is mitochondria redundant in brewin

A

fermentation causes decrease in oxygen so lead to anaerobic respiration for yeast

80
Q

what happens to mitochondria when anaerobic respiration starts

A

decrease number of cristae

lose efficiency = promitochondria

81
Q

what is cell trafficking

A 
moving production and construction of molecules
need to be correct site to function
-nucleus
-ribosomes
-ER
-golgi 
all involved
82
Q

what are ribosomes made of

A

RNA and protein

83
Q

where are ribosomes

A

freely suspended in cytoplasm

84
Q

what do ribosomes do

A

transfer information from DNA to participate in protein synthesis

85
Q

what happens in protein synthesis

A

proteins synthesised on ER polysomes
proteins discharged into lumen of ER, restructuring occurs (transport prep)
vesicles transport protein to golgi using cytoskeleton
another set of vesicles transport protein to appropriate site

86
Q

what is vascular morphology

A

vacuole can exist as single large compartment or series of smaller units, as both is primary storage in cell

87
Q

what is the vacuole the site of

A

site of proteolysis (contains proteolytic enzymes)

88
Q

what do proteolytic enzymes do

A

breaks proteins that are not needed

89
Q

what is fragmentation

A

single vacuole begins to dissociate as daughter cell begins to form
some of the vacuole moves to new cell, takes nutrients, reforms in mother then in daughter cell

90
Q

what are vacuole fragments a response to

A

response to fermentation stress

91
Q

when do vacuole fragments occur

A

late in fermentation

92
Q

what are some other structures in the cytoplasm

A

proteosome
lipid particles
glycoxisomes
perioxisomes

93
Q

what is a proteosome

A

large protease enzyme complexes

94
Q

what is the function of a proteosome

A

degrade damaged proteins

95
Q

what is the function of a lipid particle

A

storage vesicles for lipids for membrane synthesis

96
Q

what are glycoxisomes

A

vesicles containing catalase

97
Q

what are perioxisomes

A

vesicles containing catalase and oxidases

98
Q

how do yeasts replciate

A

divide sexually via spore production
OR
asexually via budding or fission

99
Q

how do brewing strains replicate

A

ONLY asexually

100
Q

what is yeast cell buddinf

A

replication in asmetryic manner

101
Q

what happens in the 0-8hrs of budding

A

lag phase, growth occurs very slow

102
Q

what happens in the 8-24hrs of budding

A

exponential phase, reproduction > death

103
Q

what happens in the 24-32hrs of budding

A

stationary phase, reproduction inhibited/death

104
Q

what happens in the vegetative cell cycle

A

cell initiated division

unbudded cell must be correct size to start budding

105
Q

which genes in DNA control the vegetative cell cycle

A

G1 cyclins

106
Q

what determines whether unbudded cell is right size to start budding

A

gene encoded by N1, N2, N3

dependent on the e.g. nutrients, cell size

107
Q

what happens if the environmental conditions change after cell starts budding

A

once started it continues

108
Q

what happens in the nuclear division

A

DNA fully replicated (mitosis)

109
Q

what is an aneuploid

A

can find an odd number of chromosomes (may have 3 copies of chromosome 1 and only 2 copies of chromosome 2)

110
Q

why may cytokinesis of mother and daughter cell not be completed properly

A

poor activity of chitinate enzyme

responsible for breaking chitin attaching mother to daughter

111
Q

how many times do yeast divide

A

they have a genetically predetermined number of divisions

have a finite lifespan

112
Q

what is senescence

A

when produce last daughter

permanent loss of replicative potential

113
Q

what are signs of ageing

A

increase in size as grow is linear
each time yeast cell divides, deposits chitin, production of daughter = scar
can’t let go of daughter - more likely chain formation
wrinkles

Physiology of Microbes (21 decks)

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