Orthologs Identity Than Paralogs Within Essay
The purpose of this experiment is to examine the amount of relation found in proteins recognized as homologs. In order to test our hypothesis which states that sequence identity shared among orthologous proteins is not different from the sequence identity shared among paralogous proteins, we used bioinformatic databases. We found that sequence identity of human prolactin to human growth hormone was 23.9% identical, human prolactin to pig prolactin was 78.
6% identical, and human prolactin to fish prolactin was 32.6% identical. In conclusion, we found that the sequence identity of orthologous protein hormones share a higher percentage of relatedness, especially those in class Mammalia.IntroductionFor scientist, especially those who specialize in evolution, the revolution of DNA technology has proven to be an influential factor in evolutionary research. The advancement in technology has allowed DNA to be used as a marker in the history of evolution.
It is because of this technology, like bioinformatic databases, that we can compare DNA sequences of various genes between different organism and gain information about their relationships (Harvey et. al. 1995). Molecular evolution has opened a whole new field of scientific research.
The purpose of this paper is to examine the amount of relatedness found in proteins that are classified as homologs by testing whether sequence identity among orthologous proteins is different from the sequence identity among paralogous proteins. In order to test our hypothesis which states that the sequence identity shared by protein hormones that are paralogs is not different than the sequence identity share by protein hormones that are orthologs, we used bioinformatic databases to compare human prolactin, pig prolactin, human somatotropin (growth hormone), and fish prolactin.For organisms to be homologous they must be derived from the same common ancestor (Corbacho et. al 2002). There are many different types of homologs such as: orthologs, paralogs, ohnologs, xenologs, and gametologs. The two most common homologs are orthologs and paralogs.
Orthologs are genes in different species that are similar to each other because they originated from a common ancestor. Paralogs are genes related by duplication within a genome, they typically evolve new functions (Corbacho et. al 2002), the paralogous proteins hormones in this experiment are human prolactin and human somatotropin, and the orthologous protein hormones are prolactin from the human, fish, and pig. These hormones are secreted from the anterior pituitary gland.
The anterior pituitary is a part of the endocrine system; it is composed of several cell types which create various cell populations that secrete specific hormones (Hiraoka et. al. 1991). Prolactin and growth hormone are two hormones that the anterior pituitary secretes. These hormones are closely related and are form the same family of peptide hormones (Corbacho et.
al. 2002). Although prolactin and somatotropin are hard to distinguish from one another, prolactin has a broader spectrum of biological activities in vertebrates (Li 1973). It plays a role in mammary-gland development, induces brood-patch development in a variety of species, increases weight in tadpoles, and regulates osmotic pressure in fish (Li 1973).By testing the relatedness of the hormones, we were able to determine whether paralogous hormones or orthologous hormones shared a higher percentage of sequence identity.Evolution has not only changed the physical appearance of organisms, but it has had a tremendous affect on the production and function of certain hormones.
We found that orthologous protein hormones in our experiment which are: human, fish, and pig prolactin, had a higher related identity than the paralogous proteins, human prolactin and human somatotropin. We also noticed that the related identity of the prolactin in hormone in mammals was higher than the related identity of the prolactin hormone between mammals and fish. It is well known that prolactin in mammals help promote milk production (Harvey et. al. 1995).In some fish the function of prolactin seems to be different from the function of prolactin in mammals.
In fresh-water fish, prolactin plays an important role in osmoregulation; it is even sometimes given the alternate term of paralactin (Harvey et. al. 1995). This difference may have stemmed from the evolution of fish to mammal. There is speculation that there were multiple gene duplications from the ancestral somatolactin hormone in fish to the prolactin hormone in modern day fish and mammals (Harvey et.
al. 1995). Another cause for this difference between fish and mammal prolactin may be the environment in which these two organisms live.Fish in general, with the exception of whales and dolphins which are mammals, do not feed milk to their young. The prolactin gene may have coded for milk production at a higher percentage than it did for osmotic pressure regulation, but at some point during the evolutionary change that particular code was turned off and the osmoregulating code turned on.
Another reason for the difference could be a product of natural selection. Fish that has prolactin that managed osmoregulation survived and reproduced better in their aquatic environment, causing a decrease in fish with the milk producing prolactin until there were none left.In paralogous proteins, the differences might stem from gene duplication. Growth hormone and prolactin almost act as a team, while prolactin stimulates milk production; growth hormone stimulates the growth of mammary glands in the breast (Li 1973).
The differences may be because of the function; one acts as a hormone that increases gland size, while the other acts as a hormone that increases gland production. In conclusion, we found that protein hormones that are orthologous have a higher related sequence identity than those that are paralogous.