Saccharomyces cerevisiae

This tiny living thing is called yeast.

It is very small. You can find it on ripe fruit like grapes. It also lives in the bark of oak trees.

Yeast helps us make bread and drinks. It works by changing sugar. This is how it helps food grow.

One yeast cell can make a new cell. It grows a little bump called a bud. Then the new cell pops off. This helps the yeast grow fast. It is a busy little life!

Meet *Saccharomyces cerevisiae*.

This is a type of yeast. People call it baker's yeast or brewer's yeast. It is a tiny living thing made of just one cell.

You can find it in nature on ripe grapes. It also lives in the bark of oak trees.

Yeast is very useful to humans. It helps make bread and beer. It does this through fermentation. This is a way that yeast changes sugar.

Scientists study yeast to learn about life. They use it to study how cells work. Some proteins in humans were first found in yeast.

How does yeast grow? It uses a way called budding. A small bump grows on the side of the cell. This bump is called a bud.

The bud grows until it is almost as big as the parent. Then, the two cells split apart. This allows the yeast to grow very fast. In the right place, the population can double every 100 minutes!

Meet *Saccharomyces cerevisiae*, a tiny living thing known as yeast.

Most people know it as baker's yeast or brewer's yeast. It is a single-celled fungus that is very important to humans. For a long time, people have used it to make bread and beer.

Scientists also love studying it in labs. It is a model organism, which means it is a tool used to understand how cells work. By studying yeast, researchers found many proteins that are also important in human biology. These include parts of the cell that help it grow and send signals.

This yeast grows through a process called budding.

To start, a small bump begins to grow on the side of the parent cell. This bump is called a bud. Inside the cell, a special ring made of proteins helps the two cells pull apart. At the same time, a new wall called a septum forms between them. The bud grows until it is nearly the same size as the parent.

Once the process is done, the daughter cell separates from the mother. In the right conditions, these tiny cells can double their whole population every 100 minutes!

Humans have been working with yeast for a very long time. In ancient times, people did not know about tiny germs called microbes. They used mixtures of wild yeast and bacteria to make food. This often made things taste very sour. Around the 15th century, beer makers discovered that boiling the liquid killed the bad bacteria. This allowed the good yeast to grow instead. By the 1800s, bakers started getting their yeast from brewers. This helped them make much sweeter breads.

As time went on, making yeast became a big industry. In 1879, Great Britain began using special large vats to grow yeast. Later, in the United States, machines called centrifuges helped collect the yeast.

During World War II, a company named Fleischmann's made a new kind of dry yeast. This yeast was special because it did not need a refrigerator. It could stay good on a shelf for a long time. In the 1970s, another company called Lesaffre created instant yeast. This made baking even faster and easier for people everywhere.

You can find this yeast living in the wild, too. It often lives on the skin of ripe grapes. It can also be found on the bark of oak trees. Since yeast cannot fly through the air, it needs a ride to move around. Some social wasps help carry the yeast from place to place. The yeast lives inside the wasps as they travel. This helps the yeast find new places to grow and thrive in nature.

*Saccharomyces cerevisiae* is a species of single-celled fungal microorganisms. It is widely known by common names like baker's yeast, brewer's yeast, or ale yeast. This organism is essential to human history because it drives fermentation. Fermentation is the process where yeast converts sugars into other substances.

In biology, it is a critical eukaryotic model organism. Scientists use it to study how cells function at a molecular level. It is often compared to *Escherichia coli*, which is the standard model bacterium. By studying yeast, researchers have discovered many proteins that are also found in humans. These include signaling proteins and enzymes that process other proteins.

The biology of *S. cerevisiae* is quite complex. The cells are typically round or ovoid in shape. They usually measure between 5 and 10 micrometers in diameter.

One unique feature is the presence of Berkeley bodies. These are specialized structures involved in specific secretory pathways. The organism also has two distinct mating types, labeled *a* and *alpha*. When these two types meet, they undergo genetic recombination. This process creates new combinations of chromosomes. This ability to combine genes makes yeast a powerful tool for biologists. They can use the mating pathway to study signal transduction, which is how cells respond to their environment.

Reproduction in yeast occurs through a process called budding. This is a form of asexual reproduction where a new cell grows from the parent.

The process involves several coordinated steps. First, a bud begins to form on the parent cell during the late G1 phase. This is part of a process called cytokinesis, which is the division of the cell. Inside the cell, an actomyosin ring (AMR) begins to constrict. The AMR is made of actin and myosin II molecules. As this ring pulls inward, a primary septum (PS) begins to grow. The primary septum is a structure made of chitin that forms a new cell wall. These two events are interdependent. If the ring or the septum is disrupted, the division fails.

When the process is finished, the daughter cell separates. The daughter is typically two-thirds the size of the mother cell.

*S. cerevisiae* can exist in two different life forms: haploid and diploid. Haploid cells are asexual and undergo mitosis to grow. Under high stress, these cells will generally die. Diploid cells are the preferred form for many processes. They also undergo mitosis, but their cell cycle rate can differ from haploid cells. When diploid cells face stress, they can undergo sporulation. This is a sexual process called meiosis. It results in the production of four haploid spores. These spores can then mate to start the cycle again. This sexual cycle allows for "genome renewal." This means the yeast can purge harmful mutations that build up during asexual reproduction.

In the wild, yeast cells have specific habitats. They are most commonly found on the skin of ripe grapes. They can also live in the bark of oak trees throughout the year. Because yeast cells are not airborne, they need a way to travel. Social wasps, such as *Polistes dominula*, act as vectors. The yeast can live inside the intestines of these wasps. The wasps help move the yeast to new locations.

Research shows that the wasp intestine actually encourages yeast to mate. This environment promotes the formation and germination of spores.

History shows how humans have mastered yeast production. In ancient times, people used wild mixtures of bacteria and yeast. This often resulted in very acidic foods. Around the 15th century, brewers discovered that boiling the wort killed unwanted bacteria. This allowed the yeast to flourish without acid-making bacteria. In the 19th century, bakers began using yeast from brewers to make sweeter breads. The Vienna Process was developed in 1846 to improve yeast harvesting and grain milling. Later, the work of Louis Pasteur helped scientists culture pure strains. By the 20th century, industrial tools like centrifuges allowed for mass production.

During World War II, Fleischmann's developed granulated dry yeast for the military. This version did not require refrigeration and had a long shelf-life. In the 1970s, Lesaffre introduced instant yeast, which is now widely used.

Understanding the nutritional needs of yeast is vital for science. All strains can grow on glucose, maltose, and trerose. However, they cannot grow on lactose or cellobiose. They require specific elements like phosphorus, sulfur, and metals such as magnesium and zinc. Most strains also need biotin and pantothenate to grow fully. This requirement for biotin actually helped scientists isolate and study the vitamin. In a medical context, antibodies against *S. cerevisiae* are found in many patients. They appear in 60–70% of people with Crohn's disease. They are also found in 10–15% of patients with ulcerative colitis. These markers help doctors differentiate between different types of inflammatory bowel diseases.