Saccharomyces cerevisiae

Organization of Saccharomyces cerevisiae

- Eukaryote, ovoid - cell wall, mostly polysaccharide, resists osmotic stress - no flagella (non-motile), - Fungus: cell wall, no chlorophyll

Growth and Development of Saccharomyces cerevisiae

- Grows by Increases diameter - Develops long filaments and becomes invasive in response to nutrient deprivation

How has Saccharomyces cerevisiae adapted to the environment?

A. Live in the surface of fruit 1. easy access to food 2. no need for motility B. Have to deal with rain (changes in osmolarity) - has a cell wall C. Deal with desiccation - sporulates D. Deal with changes in environment - sexual reproduction

How does Saccharomyces cerevisiae respond to the environment?

A. change to filamentous growth (haploid only) 1. response to poor nutrition 2. allows invasion into fruit tissue B. sporulates (diploid only) 1. response to poor nutrition/dehydration 2. allows survival through rough times

What is Saccharomyces cerevisiae used in industry for?

B. Many Uses 1. brewing and baking 2. source of B vitamins and vitamin D 3. protein supplements 4. industrial production of recombinant proteins 5. biological and medical research

What are the two kinds of mating types of Saccharomyces cerevisiae?

a and alpha

What is shmooing?

extension of part of the cell wall to reach out and contact other cells as they are non-motile

What is the transcription factor that is at the end of the signal cascade initiated by a pheromone?

STE-12, initiates gene trasncription for cell wall fusion, nuclear fusion and schmooing

When does mating type switch occer?

The new bud from a mother cell has a different mating type. Only cells that have undergone a division can switch mating types

How does mating occur?

1. 2 different mating types, a and alpha 2. mating type depends on cassette in mating type locus (MAT) 3. mating type switching 1. removal of cassette in MAT locus and replacement with other cassette 2. only cells which have undergone a division will switch mating types 3. switching allows there to always be an equal number of a and cells.

What are the requirements for two cells to mate?

1. Know mating partner is near 2. Contact partner 3. Fuse cell walls 4. Fuse nuclei 5. All of this is accomplished by secreting and sensing pheromones

What are the purposes of Pheremones?

1. Know that a compatible mating partner is near 2. Conact the partner 3. Initiate shmooing 4. Fuse cell wall 5. Fuse nuclei

What are the roles of MAT locus (cassettes)?

1. MAT a has gene for the protein a1 2. MAT alpha has the gene for proteins alpha1 and alpha2. 3. alpha1 is a repressor of a-specific genes 4. a1 and alpha2 have no role in haploids, but in diploids they form a complex that represses alpha-specific genes and activates diploid specific genes

In Saccharomyces cerevisiae, how do the mating phermones work?

1. a cells produce a-factor 2. alpha-cells produce alpha-factor 3. know partner is near when sense pheromone i. a cells have alpha-factor receptor ii. alpha cells have a-factor receptor iii. receptor binds specific factor

What is Saccharomyces cerevisiae's metabolism?

A. Chemoorganotroph/Chemoorganotroph (carbon from organic molecules, energy from oxidizing of organic molecules) B. facultative anaerobe: 1. glycolysis 2. oxi/phos 3. fermentation in anoxic conditions 1. C6H12O6 = 2 C2H6O + 2 CO2 (why beer and champagne are carbonated

What is Saccharomyces cerevisiae's reproduction?

A. Haploid life cycle: divides by simple budding B. Mating, 2 different mating types, a and alpha

What is the purpose of switching mating types?

It ensures equal numbers of each mating type