Snapshot: What is DNA?

DNA (deoxyribonucleic acid) is the way that living beings store the information that determines how they look and function. Think about DNA as the blueprints, or instructions, for life. All life forms – humans, cats, dogs, trees, and bacteria – all contain DNA. Your DNA is what carries the information that decides your specific traits, like what color eyes you have or if you will be tall or short. All the information in your DNA is unique to you. No one else in the world has the exact same DNA as you, unless you have an identical twin. You do share about fifty percent of your DNA with your biological parents, because the information stored in DNA is transmitted from generation to generation. This is why you look a little bit or a lot like your parents.

The reason that traits, like having blue eyes or being short, run in families is because they are transmitted in genes, which are the functional units of DNA.  Genes work on a very small scale, providing instructions to the cells of your body so they know what they need to make to do their jobs. While normal changes in the DNA can influence physical characteristics, like eye color, sometimes abnormal changes in the DNA may cause individuals to develop a disease. This is the case for hereditary ataxias. The abnormal DNA changes (called “mutations”) make it so cells no longer do their jobs well. Although we live with the same DNA information all our lives, it may take years or decades for a disease to manifest. As with genes for eye color, the genes causing a disease can be transmitted across generations. This explains why families are more likely to have relatives with the same type of ataxia.

Cartoon drawing of DNA moleculue next to an image of a ladder
Cartoon of DNA (Left), Photo of a ladder (right)

So, that is what DNA does, but what does it actually look like? DNA forms a double helix, think of it as a twisted ladder. The sides of the DNA ladder are made up of sugars, specifically “deoxyribose” units, and phosphate groups, and the rungs of the ladder are made up of bases. There are four bases, adenine, thymine, guanine, and cytosine, or A, T, C, and G for short. In the DNA ladder, each rung is made up of two bases forming a pair, either A and T or C and G. The instructions for life are “written” into our DNA using these bases, sometimes called the “genetic code”. The language of the genetic code has a lot fewer letters than our alphabet, just A, T, C, and G, but together these four bases write every instruction for every function and characteristic of every living thing that has ever existed in the form of genes.

If you would like to learn more about DNA, take a look at this BBC article.

Snapshot written by Dr. Laura Bowie, edited by Dr. Judit M Perez Ortiz.

 

 

Snapshot: What are Purkinje cells?

Purkinje cells are important neuronal cells located in the outer layers of the cerebellum. The cerebellum is part of the brain that is primarily known for controlling sense of balance and movement but can also influence learning, memory, and mood.

Purkinje cells receive lots of information from other neurons through their large and highly branched processes called dendrites (Figure 1, see below). This information is processed in large oval cell bodies of Purkinje neurons and is transmitted from Purkinje neurons through their axons, another type of neuronal process, to other neurons residing deep within the cerebellum.

Left, drawing of purkinje neuron. Right, image of a tree
Figure 1. Drawing of Purkinje cell by Spanish scientist Ramon y Cajal illustrating large and beautiful dendrites (bottom of dendrite labeled with d, top labeled by arrow) and axon (labeled with a). Information flows from top to bottom in this image, where Purkinje neurons receive input in the dendrites, process it in the cell body, and transmit it to other neurons through the axon (a). Photo of tree is on the right for comparison.

Purkinje cells look a lot like trees. The dendrites are like the leaves and branches, the cell body is like the tree trunk, and the axon is like the roots. Information starts at the top and goes to the bottom. This information processing ensures balance and accuracy of movements.

Because of these important roles, dysfunction or loss of Purkinje cells often leads to problems with balance and movement. Indeed, a loss of normal Purkinje neuron function appears to be very important for the development of ataxia.

Many researchers study different inherited ataxias by expressing mutant proteins in Purkinje cells in mouse models of these diseases. For example, the first mouse model created for spinocerebellar ataxia type 1 (SCA1), called ATXN1[82Q], expresses mutant Ataxin-1 only in Purkinje neurons. These mice develop balance and movement deficits and were critical for increasing our understanding of how Purkinje neurons influence how SCA1 progresses.

If you would like to learn more about Purkinje cells, take a look at this Encyclopaedia Britannica article.

Snapshot written by Dr. Marija Cvetanovic, edited by Dr. David Bushart