Yeast

Question 1

what is the Latin name for baker’s or budding yeast?

Answer 1

Saccharomyces cerevisiae

Question 2

what is the Latin name for fission yeast?

Answer 2

Schizosaccharomyces pombe

Question 3

what is the equation of yeast fermentation?

Answer 3

C6H12O6 —> 2CO2 + 2C2H5OH + 2ATP

Question 4

what is the CO2 from yeast fermentation used for?

Answer 4

to make bread rise

to add fizz to drinks

Question 5

what happens to yeast when it is starved of a source of nitrogen?

Answer 5

When deprived of a source of nitrogen, yeast undergoes meiosis to produce four haploid games as a tetrad of spores enclosed within an ascus. The spores germinate when provided witha rich food source. They mate with each other to produce diploid cells.

Question 6

what is contained within a tetrad?

Answer 6

two gametes of the a type and two of the α type

Question 7

how is mating type controlled?

Answer 7

Mating type is controlled by genes at the single locus MAT. Haploids have either the MATa or the MATα allele. The MATa and MATα alleles determine mating type by controlling expression of pheromones and receptors. Diploids are heterozygous at the MAT locus.

Question 8

define ‘shmoo’

Answer 8

a cellular bulge that is produced by a haploid yeast cell as a response to a pheromone from the opposite mating type

Question 9

define ‘auxotrophic’

Answer 9

unable to synthesise a particular compound required for its growth; cannot grow on a synthetic minimal medium without the addition of required nutrients

Question 10

define ‘prototrophic’

Answer 10

having the nutritional requirements of the normal/wildtype; can grow on a synthetic minimal medium

Question 11

describe the process of cloning a specific gene

Answer 11

1. wildtype genomic DNA is digested using a suitable restriction endonuclease
2. mix and ligate wildtype genomic DNA restriction fragments and the restriction digested shuttle vector
3. transformants can be screened for the wildtype phenotype by selection on a minimal medium without lysine, before being transferred into E. coli for amplification

Question 12

describe the process of testing candidate genes

Answer 12

1. find a restriction site in the candidate gene
2. ligate in a known yeast marker gene eg. KanMX4 which gives resistance to the drug G418
3. cut out the whole complex using suitable restriction enzymes
4. transform into yeast
5. yeast will attempt to repair the bare ends of the transformed DNA by recombining with a homologous sequence
6. wildtype LYS2 gene is replaced by lys2::KanMX4 complex, giving the cell resistance to G418 but knocking out the gene conferring resistance to lysine
7. test that the phenotype is unable to grow without lysine

Question 13

what is a complementation test and what is it used for?

Answer 13

a complementation test verifies that the transformed gene is the same as the wildtype;
if the resulting double mutant does not grow without lysine, it is the same gene; if it does grow without lysine, they are different genes

Question 14

why is yeast a good model organism?

Answer 14

well-characterised
genetically simple
rapid growth and breeding
easy to manipulate
many yeast genes are homologous to human genes

Question 15

what is the industrial use of this cloning method?

Answer 15

used to scale up the industrial production of drugs; cheaper drugs for widespread distribution

Question 16

give an example of a drug produced by this cloning method

Answer 16

Artemisinin, an expensive anti-malaria drug from the plant Artemisinia, can be produced cheaply by this method