DNA, RNA and Chromosomes

I spent an hour or so reading the Environmental Microbiology text last night. Although its depth is deeper than what would be tested, I found it intriguing enough to read on. Since I’ve spent the money (and there are coloured illustrations, unlike ESE3401), I might as well make the best out of it and am treating it as some sort of thick hardcover graphic novel.

After concluding microbial classification, the topic moved on to genetic materials. Now everyone has heard of DNA and know that it’s essential to life. Ask anymore and you’ll probably get shrugs in return. And that includes me; so here I am, trying to clarify these terms.

DNA stands for deoxyribonucleic acid, which is quite a mouthful. Let’s begin with the last two letters (N and A) which means “nucleic acid”. Nucleic acids are macromolecules composed of chains of monomeric (from monomer: basis of polymer) nucleotides (A, C, G, etc.). Another well-known NA will be the RNA. The letter D is short for deoxyribose, a monosaccharide containing five carbon atoms, including an aldehyde functional group in its linear structure. Below we see a comparison between a deoxyribose and a ribose molecule. It should then be clear that, from observing carbon-2, the former is a deoxygenated form of the latter (thus de-oxy).

Knowing that, RNA (ribonucleic acid) is simply a nucleic acid with ribose as the backbone, while DNA has deoxy-ribose instead. To form the whole DNA, the deoxyribose is bonded sideways through phosphate groups, and bonded to the opposite chain through the bases attached to the them.

Onto the purpose of DNA. The main role of DNA molecules is the long-term storage of information: somewhat similar to a hard disk drive. It contains instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic instructions are called genes. So genes are portions of DNA that contains sequences of nucleotides (instructions).

Besides the backbone structure, RNA differs from DNA by being single-stranded and has the base uracil rather than thymine. It is transcribed from DNA by enzymes called RNA polymerases as shown below.

Messenger RNA (mRNA), a type of RNA, can carry a genetic message from the DNA to the ribosomes, which translates the expression of the genetic code from nucleic acid into proteins.

Lastly, a chromosome is an organized structure of DNA and protein found in the nucleic region. The illustration below shows how DNA forms up a chromosome, but the number of layers in between are very mind boggling indeed.

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