FST 114: Final

What are the properties of yeast?

single cell, non motile, require carbon source

What are the two reproductive methods of yeast?

budding and fission

What do yeast require?

small, easy assimilated carbon and nitrogen sources, vectors for dispersal

What is ploidy?

number of sets of chromosomes in a cell

Prior to 1/30/13, what was the classification of yeast regarding sexual reproduction?

must have different genus names for sporulating and non sporulating yeast

What are the features of anamorphs (yeast)?

non sporulated in lab, imperfect state

What are the features of telemorphs (yeast)?

sporulated in lab, perfect state

Currently, what was the classification of yeast regarding sexual reproduction?

can not have different genus names for otherwise identical sporulating and non sporulating yeast

What is the two molecular methods to ID yeast species?

phenotype based analysis and molecular methods

What does the molecular methods to ID identify?

species, NOT differentiating strains

How does molecular methods to ID yeast occur?

through sequencing DID2 loop of 26s rRNA gene

Why is DID2 loop used for molecular identification?

conserved among strains of the same species, variable between different species

What is utilized to bind to the D1D2 loop?

NL1 and NL4 primers for PCR amplification

What does yeast respiration yield?

CO2 and O2

What are the two mode of metabolism that yeast can be divided into?

obligate aerobes and facultative anaerobes

What is the features of obligate aerobic yeast?

no fermentation of glucose, no anaerobic growth

What is the feature of facultative anaerobic yeast?

able to utilize glucose both aerobically and anaerobically

What are the two classes of yeast carbon metabolism?

ferment in presence of oxygen and can ferment but mostly respire with oxygen

What are two main species of yeast found in food/beverage?

ascomycota and basidiomycota

How does yeast transport glucose into the cell?

facilitated diffusion with hexose transporters

What is the metabolism for majority of Basidiomycetes?

obligate aerobes

What is the branch point of the yeast metabolism? Where is it?

pyruvate, cytoplasm

For the fermentation pathway of yeast, what occurs with pyruvate?

becomes ethanol and CO2 with PDC

For the respiration pathway of yeast, what occurs with pyruvate?

becomes Acetyl CoA

What is the purpose of the fermentation pathway for yeast?

NAD+ regeneration for glycolysis

Under what conditions is the fermentation pathways used over the respiratory pathway for yeast?

oxygen is low/absent, glucose levels are very high even with oxygen

What is the first step of yeast fermentation?

glucose converted into 2 pyruvate, 2 ATP produced

What is the second step of yeast fermentation?

2 pyruvate is converted to 2 Acetaldehyde and 2 CO2

What is the third step of yeast fermentation?

Acetaldehyde is converted to ethanol and 2 NAD+ regenerated

What are the two types of regulation in the glycolytic pathway of yeast?

flux of glycolysis must be coordinated to prevent ATP consumption/production + regenerate NAD+ and coordinate transport to prevent glucose toxicity

What can glucose toxicity be a problem?

glucose is reactive moiety

What is Pfk activated by?

AMP, speeds up glycolysis

What is Pfk inactivated by?

ATP, slows down glycolysis

What is Pyk1 regulated by?

activated by Fructose-1,6P2

How many hexose transporters found in S. cerevisiae genome?

18, 7 major players

How do hexose transport operate by?

facilitated transport

What is PDC? What is its function?

pyruvate decarboxylase, converted pyruvate into acetaldehyde

What is PDH? What is its function?

pyruvate dehydrogenase, converts pyruvate into acetyl coA

Between PDC and PDH, which has the higher affinity?

PDC

What does PDC work in? Which pathway?

anaerobic conditions, fermentation for ethanol

What does PDH work in?

aerobic conditions, respiration acetyl coA

What is the Pasteur effect?

slowing of glycolysis and fermentation in the presence of oxygen, switch to respiration

Pasteur Effect:

Why does it occur?

there is different affinities between PDC and PDH

Pasteur Effect:

Why does PDC and PDH's affinity affect the metabolism?

ETC requires oxygen and can regenerate NAD+ and ATP efficiently

What is the Crabtree effect?

fermentation is preferred with high glucose levels even in the presence of oxygen

What is the feature of the Crabtree effect?

only found in ethanol producers like brettanomyces

Why is respiration not favored when there is a lot of glucose?

pyruvate and NADH buildup, need to rid pyruvate and regenerate NAD+

Why does ethanol pathway regenerate NAD+?

acetaldehyde converted to ethanol creates 2 NAD+

What is Custer's effect?

oxygen increases fermentation and sugar use, niche dominance in AAB to regenerate NAD+ through production of ethanol

What is the basis of Custer's effect with fermentation?

stalled fermentation due to NADH accumulation, ethanol production is stalled

What organisms can perform Custer's effect?

only acetic acid producers, obligately hetero-fermentative LAB

What is the result of Custer's effect?

acetaldehyde is converted to ethanol and acetic acid for the regeneration of NAD+

Custer's Effect:

What converts acetaldehyde into ethanol?

ADH, alcohol dehydrogenase

Is there ATP production in custer effect?

No

Custer's Effect:

What converts acetaldehyde into acetic acid?

AD, aldehyde dehydrogenase

Which enzyme is up-regulated for the Custer's effect?

aldehyde dehydrogenase

Where is the Custer's effect found in?

acetic acid producers

Why is producing ethanol not enough in Custer's effect?

isn't enough to regenerate NAD+

Why does oxygen stimulate Custer's effect?

oxygen is a terminal electron acceptor

What can acetic acid producer (i.e Brettanomyces) use as an alternative?

reduce and decarboxylate phenolic compounds to regenerate NAD+

What are the features of Phylum Basidomycta?

generalist, 48-70% GC content

What is the asexual form of Phylum Basidomycta?

anamorphic basidomycetes

What are examples of yeast in Phylum Basidomycta? Where are they found?

crypotococcus and rhodotouria, incidental in wine fermentation

What is used to stain Phylum Basidomycta and Ascomycota?

diazonium blue b

What are the features of Phylum Ascomycota?

specialist, 25-50% GC content

What is the sexual form of Phylum Ascomycota?

ascospores

What is the asexual form of Phylum Ascomycota?

anamorphic ascomytes

What are the features of Ale beer?

top fermenting yeast, fermented warm

What strain is used for Ale beer production?

saccharomyces cerevisiae, pure strain

What are the features of lager beers?

bottom fermenting yeast, fermented cold

What strain is used for lager beer?

saccharomyces pastorianus, hybrid strain

What is flocculation?

aggregation of yeast cells into clumps, settle out of beer

When is flocculation wanted?

end of fermentation

What are the two main components of beer flocculation?

mannose residue on the surface and flocculin proteins that binds to the mannose

What is feature of wild brewing/lambic style?

open top fermentation, utilizes wild yeast

Beer Processing:

What is the purpose of germination?

activate enzymes like amylase and protease from barley

Beer Processing:

What occurs during the germination step?

barley incubations in cool and humid conditions, generates rootlets and induces hydrolase

Beer Processing:

What is the purpose of drying/kilning?

dry and preserve barley to maintain enzymatic activity, moisture drops from 45% to 15%

What are the three layers of barley?

husk, aleurone, endosperm

What is in the aleurone layer of barley?

enzymes, activated during malting

What are the main starch degrading enzymes? Where are they found?

alpha and beta amylase, endosperm

What is the final step of mashing? What is the purpose?

raising the temperature to 75C, to inhibit enzymes and cause precipitation

What does the precipitant from the mashing step include?

fermentable sugar in wort

What is wort?

soluble fraction, contain 75% fermentable sugar that is consumed by yeast to make ethanol and CO2

What does the rest of the wort contain?

non fermentable nitrogen and nitrogen containing compoundsa

Why do hops produce a bitter flavor?

alpha acid

What does the beer fermentation utilize?

crabtree effect

What are the undesirable compounds of beer fermentation?

THP and diacetyl

What microbe is used in beer fermentation after saccharomyces? What are its features?

brettanomyces, non spore forming

What are beer spoilages of LAB?

acidification, EPS, diacetyl

What contributes to hop resistance in LAB? What are its features?

iso alpha and beta acids, proton ionophores, provide bitterness flavor and antimicrobial

What do the proton ionophores do?

collapse proton gradient by dragging H+ across the membrane to drain ATP and removes Mn2+

What are two common beer spoilage LABs?

pediococcus damosus and lactobacillus brevis

How can pediococcus damosus and lactobacillus brevis retain hop resistance?

pump out iso-alpha-acids, maintain PMF, replenish Mn2+

What is the feature of cacao fermentation?

occurs outside of the bean, germination is stopped by acid and OH

What are sweatings?

liquid that drains out of fermenting cocao beans and pulp

What are the cacao beans surrounded by? Why is it important?

mucilage, broken down by yeast and LAB for heat, ethanol, and acids

How do the yeast break down mucilage? What is the product?

anaerobically, ethanol and CO2

How do the LAB break down mucilage? What is the product?

aerobically, lactic acid

Where do sweatings come from?

breakdown of mucilage