If you have ever seen an evolutionary tree before, you know that biological entities share relationships with one another. Over time, with much research conducted in the field, it has been theorized that all organisms on the earth evolved from a common single-celled ancestor. Whereas once, such trees were built upon the similarities in appearance of different entities, modern phylogenetic trees (evolutionary trees) are based upon information obtained for the sequences of DNA and proteins found in different organisms (Lodish et al. 2016).
Another way of looking at this is to consider that over time, despite the fact that the patterns in which biological molecules are assembled to form functioning cells and organisms have changed over time, the same basic kinds of biological molecules have been conserved over time. And by time, I mean over billions of years, during which the process of evolution occurred, and continues to occur today (Lodish et al. 2016).
One of the things that we have learned, more recently, is that deoxyribonucleic acid or DNA for short is what genes are composed of. DNA itself is responsible for two things primarily: (1) defining biological structure and (2) maintaining the integration of cellular function. Genes, then, encode proteins. Proteins have the responsibility of doing two things: (1) making up cell structures and (2) carrying out cellular activities. Sometimes mutations arise, which transform biological structure and function of an organism, providing, random variation, due to changes made to the structure and organization of genes. Most of the time, mutations do not have a noticeable effect on the function that a gene or protein caries out. Sometimes, however, this mutation can be deleterious. Even less common is that a mutation might pose an advantage to an organism evolutionarily (Lodish et al. 2016).
Nonetheless, mutations are happening constantly. Over time, some of the small alterations that prove to be advantageous become more common. Cellular structures that are entirely new are perhaps the rarest of the occurrences we’ve discussed so far. More often, changes occur that allow the organism to function better within their environment. Sometimes mutations in DNA might alter a the function of a protein or abolish its function altogether (Lodish et al. 2016).
This may occur over time as a gene becomes randomly duplicated and a copy of that gene and its encoded protein keep their original function, but over time, the duplicate of the gene mutates, resulting in a different function for its protein. Some organisms, over time with the occurrence of evolution have undergone a complete duplication of their entire genome. Cellular organization is crucial in allowing this to happen. This is because these changes allow cells to gain new abilities with small alterations over time. Thus, like we see today, organisms that are closely related tend to have similar genes and proteins. Along with this, they also have similar cellular and tissue organizations (Lodish et al. 2016).
If this was a bit confusing for you, don’t worry. All of this leads to a more elaborate discussion. You do not need to know all of this right now. This will be a topic to which we return when we learn even more about cell biology.
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