Lecture 3: Saccharomyces Cerevisae

Question 1

What is fungus?

Answer 1

any group of spore producing organisms feeding on organic matter, including molds, yeast, mushrooms and toadstools

Question 2

what is a mold?

Answer 2

is afungusthat grows in the form ofmulticellular filaments calledhyphae.[1][2]In contrast, fungi that can adopt a single-celled growth habit are calledyeasts.

Question 3

what is a yeast?

Answer 3

a microscopic fungus consisting of single oval cells that reproduce by budding, and are capable of converting sugar into alcohol and carbon dioxide.

Question 4

most widely studied organism in molecular and cell biology, characterized as a species of budding yeast

Answer 4

Saccharomyces Cerevisae

Question 5

S cerevisae can exist in what two forms? expand on this

Answer 5

haploid or diploid

Question 6

Sc is known for its ability to utilize _______ in the formation of ____ and other by products

Answer 6

carbohydrates in the formation of ethanol

Question 7

when nutrients become depleted, both haploids and diploids arrest as _____

Answer 7

stationary phase cells.

Question 8

how are stationary phase cells different from proliferating cells? (3)

Answer 8

• morphologically and biochemically distinct; round and bright and contain much higher levels of storage carbohydrates (trehalose and glycogen)
• increased resistance to a number of stresses and environmental conditions when compared to growing cells.
• growing cells also ferment glucose via glycolysis whereas stationary phase cells use the ethanol formed in earlier stages via the TCA and glyoxylate cycles

Question 9

haploid cells can exist in one of two mating types ___ or ___

Answer 9

a or alpha

Question 10

each cell type has a surface receptor for the opposite mating type. explain what happens when the surface receptor is stimulated?

Answer 10

1. the cells arrest in the G1 phase of their cell cycle. the cells no longer proliferate but start growing towards eachother –> shmoo shape
2. fusion = diploid formed
3. diploids starved of nitrogen undergo meiosis and spore formation
4. 4 haploid cells are formed and contained in an ascus

Question 11

T or F: an ascus has greater resistance to environmental factors than stationary phase cells

Answer 11

True

Question 12

what happens when spores are returned to a rich environment?

Answer 12

they will germinate and commence growth as haploid cells

Question 13

Sc vegetative proliferation occurs via ____

Answer 13

budding

Question 14

Mitosis will not happen if DNA replication has not been completed. This is an example of what mechanism in the cell cycle?

Answer 14

checkpoint controls; the progression of the cell cycle is prevented if certain necessary measures have not taken place

Question 15

what are the morphogenic aspects of the yeast cell cycle?

Answer 15

1. bud site selection
2. polarity
3. patten
4. rate of growth

Question 16

where does yeast growth take place in the cell? explain the process

Answer 16

where the new cell wall material is and where the cell wall remodeling enzymes are delivered.

The building materials are packed into vesicles, dock at the plasma membrane and then incorporated into the growing cell.

Question 17

what happens to the cell cycle when nutrients are depleted?

Answer 17

• Cell cycling stops and the cells are arrested in a stationary phase
• In stationary phase, cells use the ethanol formed in earlier stages via TCA and glyoxylate cycles.

Question 18

Carbon metabolism: most compounds required for Sc metabolism are not able to pass through the phospholipid membrane, and therefore must be transported via specific transport proteins. What 2 compounds are an exception to this rule?

Answer 18

glycerol and ethanol, they can easily diffuse acros the cell membrane.

Question 19

some carbohydrates specifically disaccharides undergo what process in order to be taken up by the cell?

Answer 19

they undergo extracellular hydrolysis by secreted invertase or galactosidase and the resultant hexoses are taken up by the cell.

Question 20

explain the process of maltose metabolism

Answer 20

maltose is actively transported across the cellular membrane and then hydrolyzed via the alpha glucosidases (aka maltase) into 2 glucose molecules

The glucose is then catabolized via the glycolytic pathway

Question 21

explain the process of sucrose metabolism

Answer 21

sucrose can be hydrolyzed into fructose 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 hexoses can easily be taken up by hexose transporters

Question 22

glucose and hexoses are further catabolized by ____ via what process?

Answer 22

pyruvate via glycosis

Question 23

T or F: No net oxidation occurs in the process of carbon metabolism

Answer 23

True

Question 24

Explain the cell structure of Sc and its importance

Answer 24

The cell wall offers mechanical strength against physical damage and plays a major role in morphogeneisis.

• consists of an homogeneous 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%

Question 25

chitin is largely responsible for what property of the Sc cell wall?

Answer 25

mechanical strength

Question 26

Define Aspergillus oryzae

Answer 26

filamentous fungi, it secretes a selection of amylases that extracellularly degrade starch into glucose

Question 27

Explain the life cycle of Aspergillus oryzae

Answer 27

simply; 1.conidium,

2. if conditions are right –>swollen conidium, 3. germling tube and then differentiated hyphae

Question 28

what is a conidium?

Answer 28

a spore that is produced asexually by A oryzea fungi at the tip of a specialized hypha that is capable of growing into a new multicellular organism.

Question 29

what is the hyphae of aspergillus oryzae?

Answer 29

individual sections that are partioned by septa and constitute multicellular filamentous fungi

Question 30

the growth of the fungi occurs via ______

Answer 30

extension of a highly metabolically active hyphal tip

Question 31

what is the purpose of the the pore located in the middle of each septum in a. oryzae?

Answer 31

communication between cells

Question 32

Define woronin bodies

Answer 32

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

Question 33

present at the hyphal tip region and is involved in the accumulation and secretion of vesicles that contain secretory enzymes

Answer 33

Spitzenkorper

Question 34

what happens when the secretion vesicle by a oryzae fuses with the cell?

Answer 34

it is endocytosed immediately and then recycled into a new secretion vesicle. recycling is critical for sustaining high levels of amylases.

Question 35

what is the conidiophore in a.oryzae?

Answer 35

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.

Question 36

Geotrichum Candidum

Answer 36

a rapid growing mold that prevents unwanted mold growth in moist cheeses. several varieties exist

Question 37

Penicillium Candidum

Answer 37

Produces the fuzzy white mold on the surface of bloomy rind cheeses like brie and camenbert

Question 38

Penicillium Roqueforti

Answer 38

creates the colored veins and surfaces and is major contributor to the flavor in blue cheeses including Gorgonzola, roquefort and stilton. various strains = colors (grey, green and blue)

Question 39

Several traditional fermentations rely on symbiotic mix of yeast, mold, LAB and AAB. explain their interactions, compare and contrast.

Answer 39

1. LAB = require high nutrients
2. yeast and molds provide nutrients to LAB
3. in traditional fermentations mold and AAB are usually on the surface while LAB and yeasts are internal. LAB and yeasts are anaerobic and mold and aab are aerobic.

Question 40

traditional japenese alcoholic drink

Answer 40

sake contains 18-20% ABV

Question 41

explain the process of making sake (3 main steps)

Answer 41

water +rice + kojii + brewing yeast.

1. kojii is used to convert the starches in rice to sugars.
2. In certain varieties LAB colonize the sugars and grow for a second stage of fermentation.
3. this kills the wild yeast which prepares the solution for the fermentation by the brewing yeasts.

Question 42

explain the process of making Fukuyama Pot vinegar

Answer 42

1. rice and cojii are added without additional microorganisms to a loosely capped large pot and laid in an open air field.
2. three rxns occur sequentially; saccharification, alcohol fermentation, acetic acid fermentation and lactic acid fermentation.

Question 43

what are kefir grains and what is their function?

Answer 43

they are white, elastic and cauliflower shaped. they consists of water and water insoluble kefiran that is extracellular polysaccharide that is produced by the LAB.

Question 44

what type fermentation method is used to a start culture of milk kefir? explain

Answer 44

via back slopping since they increase after each fermentation. Back slopping is defined as the adddition of the product of a previously successful fermentation to start a new one.

Question 45

what is the main EPS produced in kefir grains?

Answer 45

kefiran, a heteropolyssacharide composed by equal proportions of glucose and galactose

Question 46

How is kefiran produced?

Answer 46

by Lactobacillus kefiranofaciens. additions of saccharomyces sp to the culture improves the net quantity of kefiran

Question 47

LAB in kefir include

Answer 47

Lactobacillus, Lactococcus, Streptococcus and Leuconostoc

Question 48

Yeasts in kefir include

Answer 48

Saccharomyces, Kazachstania, Kluyveromyces, Torulaspora, Pichia, Lanchancea and Yarrowia

Question 49

The live kefir microorganisms are predominantly found ……

Answer 49

exterior of kefir grains

Question 50

explain the life cycle of SC

Answer 50

1. it can replicate diploid and haploid
2. diploid
3. sporilate to form ascus
4. germinate = haploid
5. ascus = most resistant
6. go back