With the recent development of transparent Zebrafish, allowing scientists to directly view its internal organs, and observe processes like tumor metastasis and blood production after bone-marrow transplant, it seems appropriate to describe Zebrafish as a model organism. Read more »

Phenol extraction is a commonly used method for removing proteins from a DNA sample, e.g. to remove proteins from cell lysate during genomic DNA preparation. It’s commonly used, but not commonly understood.

If you want to know how it works so you can show off to all of your friends… read on. Read more »

Continuing with the recent theme on model organisms, there is the nematode (roundworm) Caenorhabditis elegans. This organisms is particularly useful owing to the fact that it has very defined development patterns involving fixed numbers of cells, and it can be rapidly assayed for abnormalities. Further, strains are cheap to breed and can be frozen. When subsequently thawed they remain viable, allowing long-term storage. Because the complete cell lineage of the species has been determined, C. elegans has proven especially useful for studying cellular differentiation.
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Another popular model organism is the African Clawed Frog, Xenopus laevis, which is extremely useful for studying development and cellular physiology, owing to its particularly large and easy manipulable oocytes and embryo.
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As noted in the previous post on Model Organisms, Dictyostelium discoideum is a popular model for studying fundamental aspects of cell-cell communication and chemotaxis. This is a soil-living social amoeba grows as separate, independent cells that interact to form multicellular structures when challenged by adverse conditions such as starvation. Up to 100,000 cells signal each other by releasing the chemoattractant cAMP and aggregate together by chemotaxis to form a mound that is surrounded by an extracellular matrix. This mechanism for generating a multicellular organism differs radically from the early steps of metazoan embryogenesis. However, subsequent processes depend on cell-cell communication in both Dictyostelium and metazoans. Many of the underlying molecular and cellular processes appear to have arisen in primitive precursor cells and to have remained fundamentally unchanged throughout evolution. Basic processes of development such as differential cell sorting, pattern formation, stimulus-induced gene expression, and cell-type regulation are common to Dictyostelium and metazoans. Read more »

The term “model organism” is often used in research, to describe species that are extensively studied to understand particular biological phenomena. We say “model,” because there is usually the expectation that discoveries made in the organism model will be representative of related taxonomic groups. In particular, model organisms are widely used to explore potential causes and treatments for human disease when human experimentation would be unfeasible or unethical. For instance, a it may be difficult or impossible to visualize cellular processes in mammalian embryos; and the manipulation of human subjects is tightly regulated for obvious reasons. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.
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In the early 1950’s so many new enzymes were being discovered in the burgeoning field of biochemistry that enzyme nomenclature was in danger of getting out of hand. With no guidelines on how to name enzymes, researchers simply chose their own. Some enzymes were given names, like diaphorase or Zwischenferment, that conveyed nothing about the reaction they catalyzed and enzymes with similar function were given names that implied they were different. It was all very confusing and clearly if the situation continued it would be disastrous for our attempts to study enzymes. Read more »

….statistics. The very word strikes fear into the heart of many a biologist (including me). In an article published earlier this year, Cumming and co-workers of La Trobe University, Melbourne gave a very useful rundown of common mistakes made when using statistical error bars in biology and suggested a number of rules that should be adhered to when presenting data in this way, especially in publications. The article provides a quick taster of their advice, which helps to make things seem a little less scary.

Two types of error bars are commonly used in biology. Descriptive error bars used to describe a data set and inferential error bars used to determine which conclusions can be justifiably drawn from a data set. These are summarized in the table on the right, which is taken from the paper. Read more »

Alkaline lysis was first described by Birnboim and Doly in 1979 (Nucleic Acids Res. 7, 1513-1523) and has, with a few modifications, been the preferred method for plasmid DNA extraction from bacteria ever since. The easiest way to describe how alkaline lysis works is to go through the procedure and explain each step, so here goes.

1. Cell Growth and Harvesting

The procedure starts with the growth of the bacterial cell culture harboring your plasmid. When sufficient growth has been achieved, the cells are pelleted by centrifugation to remove them from the growth medium. Read more »

It takes a real effort to keep your basic knowledge of molecular and cell biology fresh, in addition to everything else you have to do. Wouldn’t it be great to if there was a place where you could find easy-to-read articles that allow you to brush-up on those basics in just a couple of minutes?

…I hope you said “yes”, because this is the aim of my “The Basics:” series of articles, which I will be bringing to you periodically (Feel free to let me know whether you think this is a good or bad idea either in a comment or by hitting the “contact” button above). This article explains the basics of DNA ligation. I hope you find it useful. Read more »