Introduction
Yeast
is a unicellular, eukaryotic microorganism belonging to the kingdom Fungi. The
most commonly used yeast species in biotechnology is Saccharomyces
cerevisiae. Yeast serves as an important model organism and expression host
due to its simple cellular organization, rapid growth, non-pathogenic nature,
and well-characterized genome. Because yeast combines features of both
prokaryotic and eukaryotic systems, it occupies a unique position in molecular
biology and biotechnology.
Structural
Organization of Yeast Cell
Yeast
cells are typically oval or spherical in shape and range from 5–10 µm in size.
Being eukaryotic, yeast cells possess a true nucleus enclosed by a nuclear
membrane. The nucleus contains linear chromosomes associated with histone
proteins. The cell wall is rigid and mainly composed of glucans, mannans, and
chitin, providing structural support and protection. Internally, yeast cells
contain membrane-bound organelles such as mitochondria, endoplasmic reticulum,
Golgi apparatus, vacuoles, and ribosomes, similar to higher eukaryotic cells.
This cellular complexity allows yeast to perform advanced cellular processes
not possible in bacterial systems.
Genome
Organization and Gene Expression
The
yeast genome is relatively small (approximately 12 Mb) and has been completely
sequenced. Most yeast genes contain introns, which are accurately removed
during mRNA processing by the splicing machinery. Interestingly, yeast introns
contain specific conserved sequences necessary for proper splicing, which
differ from those found in higher eukaryotes. Yeast efficiently carries out
transcription, RNA processing, and translation, making it a valuable system for
studying eukaryotic gene regulation.
Yeast in
DNA Cloning and Transformation
In
yeast, foreign DNA is commonly introduced using spheroplast transformation. In
this method, the cell wall is enzymatically removed to form spheroplasts, which
can take up DNA in the presence of calcium ions and polyethylene glycol (PEG).
After DNA uptake, the spheroplasts regenerate their cell wall and begin normal
growth. Yeast artificial chromosomes (YACs) and yeast plasmids (YEp, YIp, YRp,
YCp) are widely used cloning vectors capable of carrying large DNA inserts.
Post-Translational
Modifications
A
major advantage of yeast over bacterial systems is its ability to perform
post-translational modifications. Yeast can carry out proper protein folding,
disulfide bond formation, glycosylation, and removal of signal peptides from
precursor proteins during secretion. These modifications are essential for the
biological activity of many eukaryotic proteins.
Role of Yeast
in Biotechnology
Yeast
plays a crucial role in modern biotechnology. It is extensively used for the
production of recombinant proteins such as insulin, vaccines (e.g., hepatitis B
vaccine), enzymes, and hormones. Yeast is also used in metabolic engineering,
bioethanol production, functional genomics, and drug screening. Due to its
genetic tractability, yeast is a preferred model organism for studying cell
cycle regulation, aging, signal transduction, and gene expression.
Conclusion
Yeast
is an ideal eukaryotic host for genetic manipulation and recombinant protein
production. Its simple structure, fast growth, ability to perform
post-translational modifications, and safety make it indispensable in
biotechnology and molecular biology research, especially at the CSIR-NET and
advanced academic level.
Yeast –
CSIR NET Revision Notes
1. General Features
- Yeast is a unicellular
eukaryotic fungus
- Commonly used species: Saccharomyces
cerevisiae
- Size: 5–10 µm, oval or
spherical
- Non-pathogenic
and GRAS (Generally Recognized As Safe)
- Rapid growth rate
(generation time ~90 min)
2. Cell Structure
- True nucleus
with linear chromosomes
- Cell wall:
glucans, mannans, chitin
- Organelles present:
- Mitochondria
- Endoplasmic reticulum
- Golgi apparatus
- Vacuole
- Similar to higher eukaryotic cells
→ ideal model system
3. Genome & Gene
Expression
- Genome size: ~12 Mb
- Fully sequenced genome
- Genes contain introns
- Efficient splicing machinery
- Yeast introns have conserved
splicing signals
- Accurate transcription &
translation
4. DNA Uptake &
Transformation
- Foreign DNA introduced via spheroplast
transformation
- Cell wall removed enzymatically → spheroplast
- DNA uptake aided by:
- Ca²⁺ ions
- Polyethylene glycol (PEG)
- Cell wall regenerates after DNA
uptake
5. Yeast Cloning
Vectors
- YEp
– Yeast episomal plasmid
- YIp
– Yeast integrative plasmid
- YRp
– Yeast replicative plasmid
- YCp
– Yeast centromeric plasmid
- YAC
– Yeast artificial chromosome (large inserts)
6. Post-Translational
Modifications (Key Advantage)
- Protein folding
- Disulfide bond formation
- Glycosylation
- Removal of signal peptides during
secretion
- Advantage over bacterial systems
7. Role in
Biotechnology
- Recombinant protein production
(e.g., insulin, vaccines)
- Hepatitis B vaccine production
- Metabolic engineering
- Bioethanol production
- Functional genomics &
proteomics
- Drug screening & disease
modeling
8. Why Yeast is
Preferred (Exam Point ⭐)
- Eukaryotic system with simple
genetics
- Fast growth like bacteria
- Performs post-translational
modifications
- Safe & cost-effective
- Large DNA insert capacity (YACs)
9. CSIR-NET Tips
(Memory Points)
- Type:
Eukaryote
- Transformation:
PEG + Ca²⁺
- Special feature:
PTMs
- Best vector:
YAC (large DNA)
