Yeasts are omnipresent, eukaryotic, single-celled organisms that belong to the fungus kingdom. They are estimated to have originated hundreds of million years ago and constitute about 1% of the total fungal population. Around 1500 species of yeasts are currently known. The most common examples of yeast include Saccharomyces cerevisiae, Candida albicans, Blastomyces and Histoplasma.
They are unicellular fungi that contain the same organelles as found in a mature eukaryotic cell such as nucleus, endoplasmic reticulum, mitochondria, vacuole and cytoskeleton. It is a prolific organism that plays significant roles in food, pharmaceutical and beverage industries.
The cell wall of yeasts is made up of glycoproteins, polysaccharides like chitin and mannoproteins. The vacuoles in the yeast cell occupy around 20% of the cell volume and are important for breaking down proteins, storing nutrients and maintaining homeostasis.
Mitochondria in yeasts play a similar role as in plant and animal cells. They are the source of energy for growth, respiration and homeostasis. ATPs are produced in yeast mitochondria by the process of oxidative phosphorylation.
The endomembrane system of the yeast cell consists of ribosomes, Golgi apparatus and endoplasmic reticulum. The system is involved in sorting, packaging and transporting molecules to other parts of the cell.
The cells of Saccharomyces cerevisiae have a smooth, moist, flat and dull or glistening appearance. They are creamish in colour and no true hyphae are found. A typical yeast cell is about 0.075 mm in diameter and can grow in various egg-shaped or spherical filamentous forms.