Genes

​Articles about the recent outbreak of the Covid19 often includes mention that this simple virus has its 15 genes tied to it’s mRNA.  I am pretty sure that RNA was not mentioned (or I wasn’t paying attention) in my college genetics course in 1960.  I recall teaching my secondary class in biology in 1963- and 1964 in Sarawak that the genes in the nucleus of the cell controlled the cell biology, but I could not explain how.  I became fascinated to learn of DNA and its interaction with mRNA and protein manufacturing in cells.  Lots has been learned since the 60’s and there is a lot more to come. Certainly, most of the younger readers of this blog have been educated on this but, as a review for some of the ‘oldies’ I will try to summarize.

Corn genes, like in all plants and animals, are organized in the nucleus in chromosomes.  Corn has 10 pairs and humans have 23 pairs.  Each chromosome of the diploid part has one strand of DNA from the male parent and one from the female parent.  Corn has 30,000 to 40,000 genes spread across the 10 chromosomes.  DNA code are a string of nucleic bases (adenine, cytosine quinine and thymine) attached to a sugar (deoxyribose).  The sequence of these four becomes a significant factor in the ultimate expression the gene.

When called upon to transcribe the gene, a molecule called RNA (ribonucleic acid) is constructed by transcribing the DNA of the gene, using its codes for the sequence of nucleic bases.  The gene has a start and stop code to stop the transcription.  This newly formed RNA molecule, now called mRNA (messenger RNA) migrates through the nuclear membrane into the cytoplasm of the cell.

mRNA enters the cell ribosome, a small organelle of the cell.  The mRNA now become translation RNA (tRNA). Each set of 3 consecutive nucleic baes signal for a specific amino acid to be attached within the ribosome creating a long string which becomes a protein.  The specific arrangement of the aminos acids dictate the potential action of the protein as an enzyme in cell activity.  This enzymatic activity becomes most important determinant of the cells, and therefore the organism’s, behavior.

Many viruses, such as the one causing Covid-19, have relatively few genes, no DNA, that is coded to invade human cells, codes for the ribosome to produce the protein that allows formation of the virus spike to penetrate the cell.  The host cell thus produces more of the virus.

The response of the corn plant to its environment is ultimately tied to those small DNA codes in every living cell of the corn plant.