DNA REPLICATION

DNA Replication

DNA Replication

Introduction

DNA is nucleic acids that are made up of long units of called nucleotides. A nucleotide consists of three parts, a nitrogenous base, a sugar, and a phosphate group. Each nucleotide is represented by an A, T, G, or C to stand for the type of nitrogenous base that particular nucleotide contains. The nitrogenous bases that are contained in DNA are adenine, thymine, guanine, and cytosine. The sugar group that is attached to the sugar-phosphate backbone is deoxyribose. Each nucleotide will link to another corresponding nucleotide in the DNA molecule, A with G, T with C, etc. (Alberts, 2002, 154) These linkages form what seem to resemble the rungs of a ladder. Moreover, DNA molecules are a double-helix structure, in that, the rungs of the ladder appear to be twisted.

DNA Replication

DNA duplicates in a process called DNA replication. This process involves the separating of a DNA molecule into two different strands and starts at specific sites of the double helix called origins of replication. Each of these strands serves as a template to assemble a new, complementary strand. The result of DNA replication is two identical double-stranded molecules of DNA. This process is called semi-conservative replication, and yields a new double-helix DNA molecule consisting of a single strand of old DNA, with one single strand of a newly replicated DNA. Throughout replication, the DNA helicase unwinds the DNA helix, which then forms a Y-shaped replication fork. (Alberts, 2002, 154) The single stranded DNA binding proteins then attach to each strand of the uncoiled DNA to help maintain their separation. A group of enzymes also help the DNA replication process by breaking and rejoining the double helix, which allows the twists to unravel and prevents the formation of knots. DNA polymerase attaches nucleotides to the 3' end of the strand. Another enzyme called DNA ligase attaches the two strands back together.

The structure of RNA differs from the structure of DNA in the many ways. One way in which DNA and RND differ is the sugar in the nucleotides sequence. The sugar is an RNA molecule is ribose, not deoxyribose as in DNA. In addition, the thymine nucleotide does not occur in RNA, in RNA the thyamine nucleotide is replaced by uracil. When base pairing occurs in RNA, uracil pairs with adenine instead of thymine. Finally, unlike DNA, RNA is single-stranded and does not have a double-helix formation. The structure of RNA is either linear (for mRNA), "clover-leaf shaped" (for tRNA), or globular (for rRNA). (Berg, 2002, 365)

In addition to differing structurally, DNA and RNA also differ functionally. Instead of containing hereditary information like DNA, RNA manages basic functions that are essential for life. The three different kinds of RNA: mRNA, tRNA, and rRNA each perform a specific function that is key to the survival of all organisms that uses them.

Messenger RNA, called mRNA, provides the instructions for assembling amino acids into a polypeptide chain. Transfer RNA, tRNA, delivers amino acids to a ribosome for their addition into a growing ...