Yeast and Molds Flashcards
The difference between fungus, yeast and mold
Fungus: They reproduce by spores; can be yeast, a mold, or a mushroom. Umbrella term
Yeast: Eukaryotic microbe, that is a single cellular
Mold: Multicellular, eukaryotic
What is Saccharomyces cerevisiae
where it is used?
- S. cerevisiae is a species of budding yeast
- Saccharomyces is from Greek and literally translates into “sugar-mold”
- It is instrumental to winemaking, baking, and brewing
Why it is said that S. cerevisiae is the analog of E.coli?
Where S.cerevisiae is naturally found
- It is one of the most intensively studied model organisms in molecular and cell biology (it’s the E. coli of the eukaryotes)
- In nature Sc is generally found on the surfaces of ripe fruits
The size of S.cerevisiae, implications
How many chromosomes
- It’s very big! 5-10um in diameter and cannot be airborne (it needs a vector to move)
- Sc has 16 chromosomes
What is Gay-Lussac Equation?
How S.cerevisiae is related to it?
- Sc is known for its ability to utilize carbohydrates in the formation of ethanol and other by-products
- In the Gay-Lussac Equation (below) 180g sugar is converted to 92g Ethanol and 88g CO2
- However, this is theoretical, and normally yields are 90 - 95% of theoretical
C6H12O6 —–> 2CH3CH2OH + 2CO2
Explain the whole potential life cycle of the budding yeast
Sc can complete its lifecycle just with diploid or haploid
Diploid: 2 of each chromosome
Both haploid and diploid can enter the stationary phase when lacking resources. When a lot of food-> division
Stationary phase with reinforced cell walls, but they are still not a spore-forming cell
Two types of haploid cells: cells, alpha cells, they can mate communicating through pheromones, they grow towards each other (shmoos) when diffuse-> diploid. When there is not enough nitrogen in the environment (not just sugars) it sporulates
Ascus is more hardy then the basic cell wall and the stationary phase
Talk in specifics about the stationary phase of S.cerevisiae
How it is related to food fermentation
–Stationary phase cells are morphologically and biochemically distinct from proliferating yeast cells
–They are round, and bright and contain much higher levels of storage carbohydrates (trehalose and glycogen) than proliferating cells
–Stationary phase cells also have an increased resistance to a number of stresses and environmental conditions when compared to growing cells
- When nutrients are depleted, cell cycling stops and the cells are arrested in a stationary phase
- Growing Sc cells ferment glucose via glycolysis to form ethanol. In Stationary phase cells use the ethanol formed in earlier stages via the TCA and glyoxylate cycles
You want to terminate your reaction on time, so you have an optimal ethanol content, kind of as in vinegar fermentation
When diploid cels will decide to enter haploid phase
When there is not enough nitrogen in the environment (not just sugars) it sporulates
•Diploid cells that are starved of nitrogen will undergo meiosis and spore formation
How vegetatative proliferation of Sc is called? How it is controlled? What is the difference between budding in haploid and diploid cells? What are other morphogenic aspects of the yeast cell cycle?
- Sc vegetative proliferation occurs via budding
- The cell cycle comprises several checkpoint controls where the progression of the cell cycle is prevented if certain necessary processes have not taken place
–Mitosis will not happen if DNA replication has not been completed
•There are several morphogenic aspects of the yeast cell cycle:
–Bud site selection: in rich media haploids bud in an axial pattern where diploids show polar budding
–Polarity
–Pattern
–Rate of growth
- Since yeast has a cell wall, growth can only occur where new cell wall material and cell wall remodeling enzymes are delivered.
- These building materials are packed into vesicles, dock at the plasma membrane, and then incorporated into the growing cell
Can Sc pass most compounds for their metabolism through their membrane? if not , then how? what are the exceptions?
- Most compounds required for Sc metabolism are not able to pass through the phospholipid membrane, and therefore must be transported via specific transport proteins
- Ethanol and Glycerol are exceptions to this rule and can diffuse easily across the cell membrane
Do Sc usually uptake disaccharides? What is particular about yeast carbohydrate metabolism?
- Some carbohydrates, specifically disaccharides, undergo extracellular hydrolysis by secreted invertase or galactosidase, and the resultant hexoses are taken up by the cell
- Yeast has an astounding 38 identified carbohydrate transport systems, that transport things like: glycerol, inositol, hexoses, maltose, sucrose, trehalose, lactate, and pyruvate (0.6% of its genome)
Why maltose is important to yeasts? How it is metabolized?
- Maltose is an important carbon source for yeast during brewing and bread-making
- Maltose is actively transported across the cellular membrane, and then hydrolyzed via 𝝰-glucosidase (AKA maltase) into two glucose molecules
- The glucose is then catabolized via the glycolytic pathway
How sucrose metabolism occurs in yeast?
- Sucrose can be hydrolyzed into fructose and glucose by Sc by an enzyme called invertase
- Sc has a cytoplasmic invertase that requires uptake of the sucrose before catabolism, and an invertase in the periplasmic space
- If sucrose is catabolized in the periplasmic space the resultant hexoses can easily be taken up by hexose transporters
- Glucose and hexoses are further catabolized to pyruvate via glycolysis
The result is ethanol and CO2
What is the cell wall structure of yeasts? Why it is important? What compounds make it more strong
- The cell wall of Sc offers mechanical strength against physical damage and plays a major role in morphogenesis
- The cell wall consists of a homogenous inner layer (plasma membrane) and a fibrillar outer layer implanted in the inner layer and emanating from the cell surface
- Glucans compose approximately 50% of the cell wall, while mannoproteins make up 40% and Chitin accounts for the remaining 10%
- Chitin is largely responsible for the mechanical strength of the cell wall
What is Aspergillus oryzae? Why there can be trivia questions related to it? What is its metabolism/ food
- A. oryzae (also known as koji) is used mainly in East Asian cuisine to ferment soybeans, make soy sauce, miso, and break down rice starches into sugars for making sake
- Trivia: It is Japan’s “National Fungus” even though it was discovered in China and imported into Japan
- It secretes a selection of amylases that extracellularly degrade starch
How does Aspergillus oryzae looks like (morphology) ? How does it spread? Is it one organism?
- A. oryzae is a filamentous fungi
- A conidium is a spore that is produced asexually by A. oryzae fungi at the tip of a specialized hypha that is capable of growing into a new multicellular organism
- If the conditions are right the conidium will swell and eventually grow into a germ tube that will eventually form the hyphae
- The hyphae are the individual sections that are partitioned by septa and constitute multicellular filamentous fungi
- The growth of the fungi occurs via extension of a highly metabolically active hyphal tip
- There is a pore located in the middle of each septum that allows for communication between cells
- If one cell is killed or damaged it presents a danger to the entire organism, Woronin bodies are grouped near the septum and will plug the pore if it detects cell damage
How does A.oryzae secrete so much amylase? What is the organelle?
- A. oryzae secretes a selection of amylases that extracellularly degrade starch
- A. oryzae contain a specific organelle called a Spitzenkorper that is present in the hyphal tip region and is involved in the accumulation and secretion of vesicles that contain secretory enzymes
- Secretion of enzymes happens very quickly
- The secretion vesical is then endocytosed immediately after fusion with the cell membrane, and is then immediately recycled for incorporation into new secretion vesicles
- This recycling is critical for sustaining high levels of amylases by A. oryzae
What is condiophore? Speak about its function and metabolism
- The conidiophore is a special cell that is designed to produce conidium to spread the mold
- Nutrients are passed from the hyphae and up into the budding conidia
- When conditions are right the conidium prepares to germinate. The first step is to swell
- Vacuoles involved in autophagy begin to appear and grow, and aid in the physical extrusion of the cytoplasm at the tips of the germ tubes
What types of organisms are there in wine? soy sauce? kefir? tofu? whisky?
What organisms are used for sake (specific types), how Kino type sake is different?
- In making sake koji is used to convert the starches in rice into sugars
- In certain varieties of Sake (Kimoto-type) LAB can colonize the sugar and grow for a second stage of the fermentation
- This kills wild yeast which prepares the solution for the fermentation by the brewing yeast
Why Fukuyama pot vinegar is famous? what is happening there in terms of fermentation?
- Fukuyama pot vinegar is a traditional Japanese rice vinegar
- Rice and koji are added without additional microorganisms to a loosely capped large pot and laid in an open-air field
- Three reaction steps occur sequentially (and partially in parallel)
–Saccharification
–Alcohol fermentation
–Acetic acid fermentation
–Lactic acid fermentation
