Lecture 3: Saccharomyces Cerevisae Flashcards
What is fungus?
any group of spore producing organisms feeding on organic matter, including molds, yeast, mushrooms and toadstools
what is a mold?
is afungusthat grows in the form ofmulticellular filaments calledhyphae.[1][2]In contrast, fungi that can adopt a single-celled growth habit are calledyeasts.
what is a yeast?
a microscopic fungus consisting of single oval cells that reproduce by budding, and are capable of converting sugar into alcohol and carbon dioxide.
most widely studied organism in molecular and cell biology, characterized as a species of budding yeast
Saccharomyces Cerevisae
S cerevisae can exist in what two forms? expand on this
haploid or diploid
Sc is known for its ability to utilize _______ in the formation of ____ and other by products
carbohydrates in the formation of ethanol
when nutrients become depleted, both haploids and diploids arrest as _____
stationary phase cells.
how are stationary phase cells different from proliferating cells? (3)
- 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
haploid cells can exist in one of two mating types ___ or ___
a or alpha
each cell type has a surface receptor for the opposite mating type. explain what happens when the surface receptor is stimulated?
- the cells arrest in the G1 phase of their cell cycle. the cells no longer proliferate but start growing towards eachother –> shmoo shape
- fusion = diploid formed
- diploids starved of nitrogen undergo meiosis and spore formation
- 4 haploid cells are formed and contained in an ascus
T or F: an ascus has greater resistance to environmental factors than stationary phase cells
True
what happens when spores are returned to a rich environment?
they will germinate and commence growth as haploid cells
Sc vegetative proliferation occurs via ____
budding
Mitosis will not happen if DNA replication has not been completed. This is an example of what mechanism in the cell cycle?
checkpoint controls; the progression of the cell cycle is prevented if certain necessary measures have not taken place
what are the morphogenic aspects of the yeast cell cycle?
- bud site selection
- polarity
- patten
- rate of growth
where does yeast growth take place in the cell? explain the process
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.
what happens to the cell cycle when nutrients are depleted?
- 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.
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?
glycerol and ethanol, they can easily diffuse acros the cell membrane.
some carbohydrates specifically disaccharides undergo what process in order to be taken up by the cell?
they undergo extracellular hydrolysis by secreted invertase or galactosidase and the resultant hexoses are taken up by the cell.
explain the process of maltose metabolism
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
explain the process of sucrose metabolism
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
glucose and hexoses are further catabolized by ____ via what process?
pyruvate via glycosis
T or F: No net oxidation occurs in the process of carbon metabolism
True
Explain the cell structure of Sc and its importance
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%
