The human genome contains approximately 20,000 protein-coding genes, yet it has the capacity to produce several hundred thousand
gene products. What can account for the vast difference in gene number and product number? The human genome contains approximately 20,000 protein-coding genes, yet it has the capacity to produce several hundred thousand gene products. What can account for the vast difference in gene number and product number? Alternative splicing occurs. There are more introns than exons. There are more exons than introns. Much of the DNA is in the form of trinucleotide repeats, thus allowing multiple start sites for different genes. Every gene can be read in both directions, and each gene can have inversions and translocations.
The human genome comprises of a large number of introns or no protein-coding sequence interspersed between the exons or the protein-coding sequence.
After transcription in eukaryotes, an event takes place called splicing which removes all the introns from the mRNA and joins exons and additionally alternative splicing takes place which joins together many exons in many combinations which produce a variety of processed mRNA and thus a variety of proteins.
The process of alternative splicing produces a lot more than proteins from a single gene product.
The amount of lipids stored as an energy reserve far exceeds the energy stored as glycogen since the human body is simply not capable of storing as much glycogen compared to lipids. Lipids yield 9 kcal of energy per gram while carbohydrates and proteins yield only 4 kcal of energy per gram.
