Biology I: yeast, Drosophila and C. elegans

Saccharomyces cerevisiae, or baker’s yeast, is a single-celled eukaryote used widely in scientific research. It is a valuable model organism because its genome has been sequenced, its genetics are easy to manipulate, and it is simple to maintain in the lab.

Scientists also use yeast because many of its proteins are similar in sequence and function to proteins in other organisms. This makes yeast a useful system for studying how a gene or protein works in higher eukaryotes, including humans.

Drosophila melanogaster, the fruit fly, is a widely used model organism in biological research. It has helped scientists make important contributions to biology for more than a century. The fruit fly is studied for its body features, life cycle, natural habitat, and diet.

Fruit flies are useful in the lab because they are inexpensive to keep and have simplified genetics. Their short generation times also make experiments faster and allow researchers to work with large sample numbers. These...

Caenorhabditis elegans is a microscopic roundworm that lives in soil and has become an important model organism in biology. Scientists have used it since the early 1970s because it has an invariant body plan, is easy to manipulate genetically, and is inexpensive to maintain.

This roundworm is studied for more than one reason. Research with C. elegans has helped scientists look at developmental biology, the forces involved in locomotion, and neural circuitry. Its short but notable history also...

Saccharomyces cerevisiae can be grown and maintained in the lab for scientific study. This yeast has helped researchers better understand cell cycle control, aging, and cell death. It is also inexpensive to grow and available in many ready-to-use strains.

Keeping yeast cultures in good condition is important for reliable experiments. The video explains how to monitor yeast population growth with a spectrophotometer, an instrument that measures how much light a sample absorbs. It also shows how...

Fruit fly colony care keeps Drosophila melanogaster healthy for lab studies. These flies are common model organisms in life science research. A working colony needs more than simple food and a container. It depends on careful husbandry and regular maintenance.

The first step is preparing the yeast- and sugar-containing media that the flies eat. The media also must be stored properly so it stays usable. The video then shows the vessels most often used to house Drosophila. It also explains how...

C. elegans care and stock handling are key to using this model organism in the lab. C. elegans has long been used to study developmental, genetic, molecular, and physical phenomena. Proper maintenance helps researchers use these worms effectively.

This page covers the basic housing and feeding needs of C. elegans. It also explains how to handle and move worms with a worm pick. Careful manipulation is important when working with small worm stocks.

The video also shows how to freeze important...

Yeast cells reproduce by budding and can also switch to sexual reproduction. Saccharomyces cerevisiae is a unicellular eukaryote, so it carries out many of the same basic biological processes seen in humans. Scientists use it as a model organism to study how cells grow and divide.

Asexual reproduction in yeast happens through budding. In this process, a new cell grows from the parent cell and then separates. Yeast also reproduce sexually, which helps create genetic variation in a population.

Drosophila life cycle stages and genetic crosses are important topics in developmental biology. Fruit flies are valuable because the molecular, cellular, and genetic bases of development are highly conserved between flies and higher eukaryotes such as humans.

Drosophila move through several stages of development. Each stage offers a different setting for developmental research. The fly life cycle also shows the main physical features and major events that occur during development.

Pattern...

C. elegans development follows a fixed pattern from one fertilized cell to a hatched larva and then to reproductive maturity. This nematode, or roundworm, is a useful model for studying how genes shape development and disease. Its predictable cell lineage and body structure gave researchers early insight at the electron microscopy level into how tissues form.

The embryo develops by setting up the major body axes and by assigning founder cells to future tissues. These founder cells give rise to...

Yeast nucleic acid extraction makes it possible to collect DNA and RNA from cultured cells. Yeast is a useful model system because it can produce large amounts of biomacromolecules, including nucleic acids.

The process starts with growing and harvesting the yeast cells. The cells are then lysed, which means they are broken open to release their contents. These early steps are common to the isolation of many biomacromolecules.

After lysis, the nucleic acids are purified by one of two methods.

Larval protein staining in Drosophila uses immunohistochemistry to show where proteins are located in tissues. This method relies on antibodies, which are proteins that bind specific epitopes, or small target regions, on the protein of interest. Because Drosophila larvae are easy to process and are transparent, some tissues can be seen without dissection.

To keep epitopes intact, the tissue must be fixed before staining. The cells also need to be permeabilized with detergents so antibodies can...

RNA interference, or RNAi, is a method for reducing the activity of a target gene. It works by introducing double-stranded RNA, or dsRNA, into an organism. The dsRNA matches a gene of interest and triggers targeted gene knockdown.

In the nematode C. elegans, RNAi is especially practical because the worms can be fed bacteria that produce the needed dsRNA. The transcript explains how this feeding method makes RNAi easy and effective in this model organism. It also shows how the bacteria and RNAi...

Yeast DNA uptake uses transformation to move foreign DNA into Saccharomyces cerevisiae cells. S. cerevisiae is a unicellular eukaryote and a common model organism in biological research. Scientists use this method to control gene expression, make genetic deletions, express recombinant proteins, and label subcellular structures.

Yeast plasmids are an important part of the process. The page explains the main features of these plasmids and how yeast cells are prepared to take up new DNA. It also...

Drosophila melanogaster embryos and larvae are often collected before biological experiments begin. They develop quickly and are easy to handle, which makes them useful for studies in developmental biology and behavior. Their growth also follows mechanisms that are similar to those in other organisms, including mammals.

Embryos are first gathered with egg-laying cups placed over agar plates. The harvested embryos are then dechorionated, which means the outer eggshell is removed. After that,...

Chemotaxis is the movement of cells or organisms in response to a chemical signal. In nature, it helps organisms find food and move away from harmful substances. It also matters at the cellular level. For example, sperm use chemotaxis to move toward an egg before fertilization.

In the lab, chemotaxis is often studied with the nematode C. elegans. These worms move toward food sources in soil, but they move away from toxins such as heavy metals, low-pH substances, and detergents. The assay shown...