A straight forward presentation on saccharomyces cerevisiae: genome, Existence in haploid & diploid cell form. hope you will find it helpful

1. Naren yadav

2.  this yeast is used for winemaking, baking and brewing
 It is one of the most intensively studied eukaryotic model
organisms in molecular and cell biology
 There are two forms in which yeast cells can survive and
grow: haploid and diploid
 Why it is preferred organism for genetic research?
1. simple life cycle
2. Alternating haploid and diploid phases
3. short generation time, and easy to-identify meiotic products

3.  Haploid S. cerevisiae has 16 linear chromosomes.
 Each chromosome contains:-
1. One centromere /kinetochore
2. Two termini consisting of longer subtelomeric repeats
3. Followed by short telomere repeats at the very ends
4. Multiple origins of replication spaced approximately 30–40 kb
 Chromosomes are packaged into nucleosomes consisting of the
core histones H2A, H2B, H3, and H4.

5.  Pulse-field gel electrophoresis, which separates intact yeast
chromosomes, produces molecular “karyotypes” of the yeast
genome.
 Chromosome I, about 235 kb in length smallest one.
 Chromosome XII is the largest; its size varies between about 2060
and 3060 kb because of a variable number of tandem ribosomal
RNA genes (rDNA).

6.  The total genetic map length, a function of the frequency of
meiotic recombination, is about 4400 cM. With an average of
3 kb/cM.
 Total genetic map of yeast is extraordinarily long compared to
the genetic map of other fungal organisms.

7.  6000 and 6500 genes
 2000 have no known function, known as orphan genes
 To predict the number of genes that code for proteins from
the number of open reading frames (ORFs) identified in the
yeast genomic DNA sequence
 2,60,000 ORFs were identified assuming a length of 2–99
amino acids.
 About 1,14,000 ORFs assuming a length of 15–99 amino acids.

8. Among the protein-coding genes, introns occur in only 4% to 5%
of all yeast genes.
274 tRNA genes.
71 small nucleolar RNAs.
5 small nuclear RNAs that function in intron splicing, a few RNAs
of unknown function, and three RNAs that serve as functional
subunits of the enzymes RNase P, endoribonuclease MRP, and
telomerase.

9.  yeast genome is composed of unique, nonreiterated DNA
sequences.
 Approximately 75% of the genome is transcribed into RNA.
 Reiterated DNA sequences:-
1. 100–200 copies of rDNA
2. tRNA genes
3. subtelomeric repeats
4. Transposable elements
5. 385 solo LTRs

10.  Yeast cells can proliferate both as haploids (1n, one
copy of each chromosome) and as diploids (2n, two
copies of each chromosome).
 Haploid cells have one of two mating types: a or α
(alpha).
 Two haploid cells can mate to form a zygote; since
yeast cannot move, cells must grow towards each
other (shmoos).
 In Conditions such as nutrient depletion, Diploid cell
can undergo meiosis to produce four haploid spores:
two a spores and two α spores.

11.  'a' cells produce ‘a-factor’, a mating pheromone which
signals the presence of an a cell to neighbouring α cells. &
alpha cell produces alpha -factor & form conjucation duct.
 These phenotypic differences between a and α cells are
due to a different set of genes being actively transcribed
 a cells activate genes which produce a-factor and produce
a cell surface receptor (Ste2) which binds to α-factor and
triggers signaling within the cell. a cells also repress the
genes associated with being an α cell Similarly, α cells
result in production of (ste3) receptor.

12.  The different sets of transcriptional repression and
activation which characterize a and α cells are caused
by the presence of one of two alleles of a locus called
MAT: MATa or MATα located on chromosome III.
 The MATa allele of MAT encodes a gene called a1,
which in haploids direct the transcription of the a-
specific transcriptional program (such as expressing
STE2 and repressing STE3) which defines an a cell.
 The MATa allele of MAT encodes a gene called a1,
which in haploids direct the transcription of the a-
specific transcriptional program (such as expressing
STE2 and repressing STE3) which defines an a cell.

13.  Like the differences between haploid a and α cells,
different patterns of gene repression and activation
are responsible for the phenotypic differences
between haploid and diploid cells.
 In addition to the specific a and α transcriptional
patterns, haploid cells of both mating types share a
haploid transcriptional pattern which activates
haploid-specific genes (such as HO) and represses
diploid-specific genes (such as IME1). Similarly,
diploid cells activate diploid-specific genes and
repress haploid-specific genes.

14. BUDDING

15. YEAST FISSION

18. Thank you