“Write what you know about” – Mark Twain

Good advice from a great communicator. From now on, the majority of posts will relate in some way to bacteria, especially microbial genomics. Most of the remainder of posts will be related to science communication and education.

Why bother spreading the love for the little creatures? I believe this quote from microbialgenomics.energy.gov sums it up:

By some estimates, microbes make up about 60% of the earth’s biomass, yet less than 1% of microbial species have been identified. Because most do not cause disease in humans, animals, or plants and are difficult to culture, they have received little attention. Identifying and harnessing their unique capabilities will offer us new solutions to longstanding challenges in environmental and waste cleanup, energy production and use, medicine, industrial processes, agriculture, and other areas. Scientists also are starting to appreciate the role played by microbes in global climate processes, and we can expect insights about both the biological underpinnings of climate change and the contributions of microbes to earth’s biosphere. Their capabilities soon will be added to the list of traditional commercial uses for microbes in the brewing, baking, dairy, and other industries.

There is so much we don’t know about microbes. However, we are beginning to understand their enormous adaptability. Whether it is 30,000 feet above the ground or two miles beneath it, bacteria can inevitably survive. I will now focus on getting the word out about the little guys who can’t speak for themselves.

Microbes can be used in soil cleanup
Microbes can be used in soil cleanup (Photo credit: Wikipedia)

What is in a genome?

English language svg version of Image:Plasmid ...
English language svg version of Image:Plasmid (numbers).svg Description : This image shows a line drawing of a bacterium with its chromosomal DNA and several plasmids within it. The bacterium is drawn as a large oval. Within the bacterium, small to medium size circles illustrate the plasmids, and one long thin closed line that intersects itself repeatedly illustrates the chromosomal DNA. (Photo credit: Wikipedia)

I first have to apologize. The mission of this blog is to inform those who are curious about science and nature. My ADD gets the best of me sometimes and I digress towards more policy and advocation.

So…what is in a genome? A broad question with lots of answers. Let’s start with the ‘simple’ example of a genome; bacteria. Unlike humans, and other animals, bacteria have only one true chromosome which is circular. Many bacteria, however, have extra DNA not on the chromosome. This extra DNA is also circular and usually called a plasmid. Many bacteria have several plasmids, and some even have very large plasmids called cosmids.

There is not a lot of room within a bacterial cell, so there is not a lot of ‘junk’ DNA in its chromosome. If an average gene is 1000 base pairs (bp), then a 7 Mbp (7,000,000 bp) genome usually has about 6500 genes. This means bacteria pack a big punch in a small size cellular blueprint. Other than genes, bacteria contain DNA elements that help regulate what and when genes are actively transcribed into RNA to produce functional proteins. Promoters are areas of DNA upstream of genes that are attractive places for some proteins to interact with. Some proteins activate gene transcription while other repress transcription. This ensures only the proteins needed by the cell are being produced since making and degrading unneeded proteins costs energy.

What about plants and animals?

I’ll leave plants out since I’m not knowledgeable enough to write about them. Animals have very elaborate genomes. The number of chromosomes vary for each organism and are not circular. For simplicity, I will discuss humans. Humans have pairs of each chromosome that are identical except for the pair that determine a persons sex. Even identical chromosomes are essentially different in the characteristics of individual genes (see dominant and recessive alleles). Strands of DNA are wrapped around proteins known as histones which interact to compact the size of the chromosome.

The major chromatin structures.
The major chromatin structures. (Photo credit: Wikipedia)

Human genes have MANY ways of being regulated. The histones themselves can undergo modification by enzymes that affects how compact they are and how attractive they are to proteins regulating gene transcription. Like bacteria, human gene transcription can be regulated by promoters. However, unlike bacteria, these genes will not totally be used to make a protein. Human genes are composed of introns, regions not translated into a protein, and exons, regions that are translated into protein. Human messenger RNA is processed after transcription which removes intron sequences leaving only exons that will be shuttled out of the nucleus for protein synthesis. To make this more complicated, during processing, many genes can undergo something called alternative splicing. This means as mRNA is being processed, even some exons can be removed resulting in different versions of a protein! 

Other elements can regulate gene transcription besides promoters. Animals have DNA elements called enhancers and insulators that may or may not be located close to actual genes. Enhancers and insulators can intricately interact to regulate gene expression.

Français : Organisation de l'ADN en chromosome...
Français : Organisation de l’ADN en chromosome National Human Genome Research (USA) (Photo credit: Wikipedia)


I will leave it at this. I hope you enjoyed my little ramble about genomes. Let me know what you think…please…