The Evidence
David Shenk refers to proteins as "large, specialized
molecules that help create cells, transport vital elements, and produce
necessary chemical reactions" in footnote 18 in Chapter 1. Discuss
specific examples of how proteins interact with one another to complete a specific
task in an organism. Would these proteins be characterized as messenger,
structural component, or transport/storage proteins, or others? Refer to the
information provided with footnote 18 in Chapter 1. What purpose do these
proteins serve in the human body? With detail, describe the advantages that
organisms have by having proteins perform specific functions.
Weronika Dudkiewicz (wdudkie2@students.d125.org)
One of the most important proteins in our body is the protein hemoglobin, present in our blood and used to transport oxygen around our body. As discussed in our circulation and respiratory unit, hemoglobin is an essential protein to mammalian and reptilian life as both use this protein to deliver oxygen to the cells of the body where the oxygen can be used in cellular respiration to create ATP to do work in a cell. This protein is a quaternary protein, meaning it is actually created from 4 protein sub units (2 alpha and 2 beta). This quaternary structure of the protein thereby shows the intricate interactions that can take place between proteins in order to complete one task. The 4 subunits must all be created correctly in order to fit together, creating a complete hemoglobin molecule. In the disease sickle cell anemia one amino acid has been changed in these long sequences of proteins due to a point mutation, but just because of this one change the complete structure of the protein changes. In the beta sub unit, the chaining in one of the amino acids exposes a hydrophobic region of the subunit and due to this exposure, the hemoglobin molecules tend to form chains instead of staying separated from one another (Campbell 84). These chains of hemoglobin molecules are unable to hold as much oxygen as normal, healthy, dissociated hemoglobin molecules can and therefor lead to dangers in an organism. Those with sickle cell anemia run the danger of killing off many of their body cells, since when a cell is not exposed to oxygen for long periods of time it will eventually die. As explained in the A.D.A.M. Medical Encyclopedia, those with sickle cell anemia run the risks of complications like "Blindness/vision impairment, Brain and nervous system (neurologic) symptoms and stroke, [and] Death" (from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001554/). It is due to this one change of an amino acid in a protein that completely changes the structure of the protein and thereby preventing the correct functioning of hemoglobin. And since this is a genetic mutation there are few lasting cures. A.D.A.M. Medical Encyclopedia says how "Bone marrow or stem cell transplants can cure sickle cell anemia. However, they are current not an option for most patients" (from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001554/). The cures suggested are attempting to bypass the patient’s faulty genes that mess up the primary structure of the beta sub unit by inserting cells that will create healthy hemoglobin molecules from donors who have functioning hemoglobin molecules. In a well-functioning hemoglobin molecule, each subunit holds an atom of iron, and because oxygen has the ability to bond with this iron atom held by the hemoglobin, the hemoglobin is able to transport oxygen molecules throughout the body. The separate subunit proteins in hemoglobin work together, since only when each subunit is shaped correctly can hemoglobin work efficiently in red blood cells holding the maximum amount of oxygen molecules and transporting them through the circulatory system. Since hemoglobin is used in the transport of oxygen is defined as a transport protein.
ReplyDeleteAnother protein interaction that is important to life is the interactions between the many proteins found near the DNA of cells. All cells need to copy their DNA when they divide and in order to do this proteins are used to not only copy the DNA, but also unravel and hold the DNA in place. In the nucleus of all eukaryotes there are many proteins that work together in order to successfully copy an organisms DNA in preparation for mitosis. One of the first steps in the copying of genetic material is the job of a protein called helicase which unravels double stranded DNA, exposing the nitrogen bases so another protein, primase, can attach an RNA primer to the now exposed nitrogen bases. Farther down the DNA strand a protein called topoisomerase works to relive the stress created in the DNA strand when it is being unwound by helicase. If topoisomerase were not to function correctly then the helices would snap the DNA by putting too much stress on it and an organisms DNA would be unable to be copied. Other proteins like single strand binding proteins must also interact as it holds the two single stranded DNA segments apart. Then DNA polimerase I and III attach DNA nucleotides to the primer and DNA ligase follows up binding the spaces between 3' ends and 5' ends of DNA (Campbell 315-317). All these proteins must interact with each other to complete the crucial task of copying a cell’s DNA. Without the very specific jobs done by each protein, a cell’s DNA would mutate at huge rates or the cell’s DNA may not be able to be replicated at all. This would prevent life from regenerating itself and thereby kill off life. Most of these proteins mentioned are actually enzymes as they speed up the reactions of binding and splitting of nucleotides with the exception of single strand binding proteins which are structural proteins as the hold DNA strands in place and do not facilitate a reaction.
ReplyDeleteThe advantage of having proteins interact with each other and perform specific job is the fact that in order form life to exist it must not only keep homeostasis within itself and be able to pass on traits that it has developed. David Shenk also describes how "Certain types of proteins are formed, which become other cells and tissues and ultimately make us who we are" (Shenk 26). Proteins are one of the most basic building blocks of life and in order to exist, the proteins an organism has must function correctly and must do their specific task. As in my example of the effects of what happens when a protein is not created correctly leading to sickle cell anemia, if a protein does not function correctly it can result in the death of an individual.
When studying proteins one off the main themes of biology to relate to is the relation between structure and function. In a protein, the entire function of the protein is based off of the proteins structure. If the protein is not functioning right it is most likely due to a mistake mad when forming the protein. The example of the single mistake in amino acids made when forming hemoglobin leading to sickle cell anemia is a great example, as it shows only small changes in the structure of a protein, like the switching of a single amino acid, can lead to huge changes in a person’s body.
-Kyle Nelson (kynels21@gmail.com)