The Cell Wall of Prokaryotic Cells - Essay Example

THE ESSENTIAL FEATURES OF PROKARYOTIC REPLICATION Institute The essential features of prokaryotic replication Cells are mainly differentiated into two classifications namely prokaryotic cells and eukaryotic cells. There are many differences in these two types of cells as well as the genetic processes that they undergo. Much research has been done on analyzing the genetic process in the prokaryotic cells and this paper will focus upon the prokaryotic cells with regard to the important features of replication in these cells. The prokaryotic cells are small in diameter and their size ranges from 1 till an average of 5 micrometer. The genetic material of prokaryotic cells is distinct in its own way. The DNA of these cells does not lie within a nuclear envelope and this DNA is also not bounded to histones. A distinct structure where the DNA is present in the prokaryotes is present which is known as nucleoid. These cells also possess only one chromosome which is folded many times for it to fit into the prokaryotic cells. Mitotic division is absent and thus mitosis is not a feature of prokaryotic cells. Specialized cell structures which are surrounded by membranes like mitochondria and lysosomes are also not present in the prokaryotes. The size of the ribosomes in these cells is small and is 70 S. The cell wall of prokaryotic cells is stiff due to the presence of peptidoglycans. Replication is a process whereby new genetic material is formed with the copying of the parent genetic material. It is basically the formation of daughter DNA from the parental DNA strand. It is considered to be a process for the production of offspring and this process needs to be carried out in a much regulated manner to maintain the stability of the gene line so that mutations do not occur as they can serve to produce grave consequences. Prokaryotic replication has mainly been studied and understood by carrying out extensive research on the organism E. coli which is a bacterium. This replication has served to open ways for understanding the mechanisms that occur during the process of replication in eukaryotes as this process is more complicated in the eukaryotic cells. The DNA in prokaryotes is basically round and it has two strands. The initiation point where the replication begins is termed as ori which stands for origin of replication. In different prokaryotes there are different oris which are basically the points where certain double stranded DNA specific proteins attach to certain DNA sequences which are repeated. In E. coli the DnaA which is a specific protein comes and binds to the oriC which is the origin of replication. It is at this point that the unwinding of the double stranded DNA starts to occur. There are many important steps that are required during the separation of the two strands of DNA for replication and the formation of the replication fork. The replication fork is basically the proceeding path on which the replication of the strands is taking place. A very interesting fact about this replication is that it occurs on both strands at the same time in opposite directions and as replication is taking place on two strands, there are two replication forks. The replication fork is maintained by four mechanisms. The first is the action of the enzyme DNA helicase which functions to separate the strands. The simultaneous action of the single strand binding proteins is also present. They have an important role to serve as they impede the separated strands from joining again during the process of replication as well as guard these single strands from the actions of enzymes that may break them down. Another enzyme which is known as topoisomerase also assists in the process of replication by avoiding and preventing the formation of coils which may occur during the separation of the parent DNA strands. DNA gyrase is an example of a prokaryotic topoisomerase. Primers are also important because they can only serve to start the formation of the process of replication and without primers, enzymes cannot start this process. An example of a common primer is RNA oligonucleotide. This primer is formed by the action of the enzyme RNA polymerase. DNA polymerases are the enzymes which assist in forming the DNA that are present on the daughter strands. There are many different kinds of DNA polymerases with their specialized functions. The bacterium E. coli which is used to study shows the presence of three types of DNA polymerases which are known as Pol I, Pol II and Pol III. The DNA polymerases have a very important property that they function only in the direction of 3’ to 5’. As a result of complementary base pairing the daughter strand produced by the DNA polymerases is in the 5’ to 3’ direction. The DNA sequences that are added to the strand that is being formed require substrates. This requirement is fulfilled by the deoxyribonucleoside triphosphates. Complementary base pairing occurs with regard to the template strand. There is the release of pyrophosphate with the addition of every single nucleotide base. This pyrophosphate is acted upon by pyrophosphatase which releases energy and assists in the carrying out of this process. The DNA polymerases also have an important property of processivity. This enables them to be attached to the template of the DNA strand from which the daughter strand is being formed throughout the process of replication. This is an important property because it assists in increasing the efficiency of the process because the enzyme remains attached to the strand and does not separate and then rejoin again and again for adding a DNA nucleotide to the newly forming strand. It rather keeps on adding the nucleotide continuously. Pol III is the DNA polymerase in E. coli that is associated with the function of processivity. Pol II acts in proofreading the newly formed daughter strand of the DNA during the process of replication and mends and corrects any errors in the strand. Another important feature of replication is that there are two strands present during the process. One is the leading strand that is copied continuously and the other one is the lagging strand that is formed in fragments. This is because the DNA polymerase can only act in the 3’ to 5’ direction so it acts straight on one of the strands in the direction of the replication fork. On the other strand, small fragments are formed known as Okazaki strands on which the DNA polymerase acts opposite the direction of the replication fork. Pol I DNA polymerase is the enzyme involved in joining these Okazaki fragments and forming one complete strand. The process of replication ends at a point exactly opposite to the point of origin of replication which is referred to as the termination point. A single strand of DNA requires more than 4 million nucleotides for its synthesis. This process of replication of a single strand occurs in about 40 minutes. This formation of duplication of DNA which is known as replication is a “semi-conservative” process. This term implies to the fact that each newly formed DNA strand pairs with one of the parental strand. Hence the parental strands are not broken down and their sequences stay the same that is they are conserved but this is semi conservation because the two strands do not exist together and each strand is joined to a new daughter strand. References Top of Form BROOKS, G. F., BUTEL, J. S., MORSE, S. A., & JAWETZ, E. (2004). Jawetz, Melnick, & Adelbergs medical microbiology. New York, N.Y., Lange Medical Books/McGraw-Hill, Medical Pub. Division. Top of Form LEVINSON, W. (2008). Review of medical microbiology and immunology. New York, McGraw-Hill Medical. Top of Form LIEBERMAN, M., MARKS, A. D., & SMITH, C. M. (2009).Marks basic medical biochemistry: a clinical approach. Philadelphia, Wolters Kluwer Health/Lippincott Williams & Wilkins. Bottom of Form Top of Form MURRAY, R. K., GRANNER, D. K., & RODWELL, V. W. (2006). Harpers illustrated biochemistry. Stamford, Conn, Appleton & Lange. Bottom of Form Bottom of Form Bottom of Form Read More