Yeast Flashcards
(113 cards)
1
Q
what is yeast
A
unicellular fungi that reproduce by budding
2
Q
how many yeast genera are there
A
around 100
3
Q
how are the yeast genera divided
A
into around >700 species
4
Q
what is yeast used as a model for
A
higher organisms
5
Q
are yeasts pathogenic
A
some are
6
Q
what is yeast cytology
A
different species vary in shape, size and colour
7
Q
what is budding
A
replication
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)
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
10
Q
how many times do cells bud
A
cells only bud a finite number of times (age+die)
11
Q
how does yeast respire
A
anaerobic and aerobic
12
Q
what is yeast used for
A
fermentation
13
Q
what products can be made by yeast fermentation
A
beer is a by-product of yeast growth on wort
14
Q
what is the yeast fermentation reaction
A
C6H12O6 –> 2C2H5OH + 2CO2
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
16
Q
what temperature is yeast stored at in cultivation
A
- 196 degrees C
17
Q
why is yeast stored at -196 degrees C in cultivation
A
provides a stable environment
no genetic changes
18
Q
what are the two types of propagation
A
batch
fed batch
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
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
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)
22
Q
what is flocculation
A
ability of yeast cells to adhere to each other, form clumps, is a reversible process
23
Q
why is flocculation important
A
cells need to be dispersed in wort during active fermentation
24
Q
what is ADY
A
active dried yeast
25
when are cells non-flocculated
when dispersed
26
what happens when cells are non-flocculated
more able to use sugar efficiently
27
when is yeast flocculated for the second time int he fermentation process
need to form a crop at the end of fermentation, separate from 'green beer'
yeast is flocculated, provides natural means of clarifying beer
28
what does flocculation involve
interactions between adjacent yeast surfaces
| yeast cells have receptor sites in cell surface, have lectin projections, can stick into receptor sites of other cells
29
what is calcium needed for in flocculation
interactions between adjacent cells is a calcium-mediated process
30
what happens when the lectin projections stick to receptor sites of other cells
clumps become so heavy, sediment out of beer
31
what is flocculence
inherent genetic property of yeast strain
32
are brewing strains flocculent
most brewing strains are moderately flocculent
33
what determines flocculation
flocculation genes - depends if clumping characteristic on/off
34
what causes yeast to de-flocculate
sugars block the receptor sites
| cause de-flocculation
35
why do yeast cells de-flocculate
ensure cells dispersed at start of fermentation
36
what does yeast separation from beer allow
yeast to be recovered, reused
37
why does yeast quality deteriorate over time
oxidation, osmotic stress
end of fermentation nutritional and ethanol stress
cold shock
stresses occur over re-pitchings, eventually disregarded
38
what is yeast responsible for the production of
made as a result of amino acid metabolism:
- ethanol and higher alcohols
- aldehydes
- esters
vicinal diketones (e.g. diacetyl)
39
what amino acid requirements do yeast have
different yeast strains have different amino acid requirements, can cause different flavour profiles
40
what is the start point for a lot of yeast flavour development
keto acid pool
41
what are keto acids decarboxylated by, to form
CO2 decarboxylates it
| forms aldehyde
42
what is aldehyde reduced to
fatty acetyl CoA
| higher alcohol
43
what does acetyl CoA form
ester
44
what is diacetyl created by
yeast
45
when is diacetyl removed
removed by yeast near end of fermentation
46
what pathway is diacteyl part of
valine synthetic path
47
when is fermentation deemed complete
when diacetyl levels below flavour threshold
48
how do lager and ale differ
different yeast strains
49
which strains are 'top cropping'
ale
50
how can ale strains be made to flocculate down
in large cylindro-conical fermenters
51
which strains are 'bottom cropping'
lager
52
what causes bottom cropping
flocculation properties cause strains to sink
53
how do bottom and top cropping differ
require different growth requirements e.g. temperature
54
what is cell envelope made of
cell wall
periplasm
cell membrane
55
what can pass through cell envelope
leaky molecules
56
what is the cell wall made of
mannoproteins
beta-glucans
(chitin too)
57
what is the beta-glucan for in cell wall
rigidity
58
what is constantly replaced in cell wall
mannoproteins and beta-glucans
59
why is yeast cell wall constantly changing
in response to external stimuli
| e.g. nutrients
60
can yeast cell wall permanently change
can adopt permanent change over time
61
what is after the cell wall
periplasm
62
what is the periplasm
gap between cell wall and cell membrane
63
what occurs at cell wall
site for storage e.g.glycogen and site of enzyme reactions
64
what is the cell membrane like
highly selective
| lipid bilayer with globular proteins
65
what is the primary membrane
primary boundary between cell and environment
66
what does the primary membrane have
has membrane proteins
67
what does ATPase do
hydrolyse ATP
generates electrochemical gradient
gradient for protons
68
what is the effect of the electrochemical gradient
barrier against free diffusion
transport molecules (trans-membrane ion, ATP, solute gradients)
binding site for signal molecules
69
what is an invagination
enclosed plasma membrane droplets
| leading to compartmentalisation of molecules, also used for compound secretion/excretion
70
what is the cytoplasm
aqueous acidified fluid
71
what is in the cytoplasm
made of dissolved, suspended macromolecules, enzymes, proteins
72
what does the cytoplasm allow
surrounds all organelles
| allows communication and transport 'houses' the cytoskeleton network
73
what is the cytoskeleton network
microtubules - structural organisation for cell
74
what is the cytoskeleton network important for
e.g. bud development, cell growth
75
what is present in the outer membrane of the mitochondria
enzymes involved in lipid metabolism
76
what is in the matrix of the mitochondria
has enzymes involved in fatty acid oxidation, citric acid cycle, protein synthesis and mitochondrial DNA
77
what is in the inner membrane of the mitochondria
form cristae
| contains cytochromes, proteins, ATP synthase - respiratory chain
78
what is the role of mitochondria in brewing
aerobic
| synthesis ATP during respiration (oxygen terminal electron acceptor)
79
when is mitochondria redundant in brewin
fermentation causes decrease in oxygen so lead to anaerobic respiration for yeast
80
what happens to mitochondria when anaerobic respiration starts
decrease number of cristae
| lose efficiency = promitochondria
81
what is cell trafficking
```
moving production and construction of molecules
need to be correct site to function
-nucleus
-ribosomes
-ER
-golgi
all involved
```
82
what are ribosomes made of
RNA and protein
83
where are ribosomes
freely suspended in cytoplasm
84
what do ribosomes do
transfer information from DNA to participate in protein synthesis
85
what happens in protein synthesis
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
what is vascular morphology
vacuole can exist as single large compartment or series of smaller units, as both is primary storage in cell
87
what is the vacuole the site of
site of proteolysis (contains proteolytic enzymes)
88
what do proteolytic enzymes do
breaks proteins that are not needed
89
what is fragmentation
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
what are vacuole fragments a response to
response to fermentation stress
91
when do vacuole fragments occur
late in fermentation
92
what are some other structures in the cytoplasm
proteosome
lipid particles
glycoxisomes
perioxisomes
93
what is a proteosome
large protease enzyme complexes
94
what is the function of a proteosome
degrade damaged proteins
95
what is the function of a lipid particle
storage vesicles for lipids for membrane synthesis
96
what are glycoxisomes
vesicles containing catalase
97
what are perioxisomes
vesicles containing catalase and oxidases
98
how do yeasts replciate
divide sexually via spore production
OR
asexually via budding or fission
99
how do brewing strains replicate
ONLY asexually
100
what is yeast cell buddinf
replication in asmetryic manner
101
what happens in the 0-8hrs of budding
lag phase, growth occurs very slow
102
what happens in the 8-24hrs of budding
exponential phase, reproduction > death
103
what happens in the 24-32hrs of budding
stationary phase, reproduction inhibited/death
104
what happens in the vegetative cell cycle
cell initiated division
| unbudded cell must be correct size to start budding
105
which genes in DNA control the vegetative cell cycle
G1 cyclins
106
what determines whether unbudded cell is right size to start budding
gene encoded by N1, N2, N3
| dependent on the e.g. nutrients, cell size
107
what happens if the environmental conditions change after cell starts budding
once started it continues
108
what happens in the nuclear division
DNA fully replicated (mitosis)
109
what is an aneuploid
can find an odd number of chromosomes (may have 3 copies of chromosome 1 and only 2 copies of chromosome 2)
110
why may cytokinesis of mother and daughter cell not be completed properly
poor activity of chitinate enzyme
| responsible for breaking chitin attaching mother to daughter
111
how many times do yeast divide
they have a genetically predetermined number of divisions
| have a finite lifespan
112
what is senescence
when produce last daughter
| permanent loss of replicative potential
113
what are signs of ageing
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
