Dna Replication Essay Example
Dna Replication Essay Example
Dna Replication DNA replication is a complex cellular function that is necessary in order to sustain life and achieve growth. Many enzymes, proteins, and other molecules work together to ensure that genetic information is replicated efficiently, quickly, and accurately. Without any one of these components, replication would be very limited in its efficacy. DNA is comprised of two strands of complementary nitrogenous bases (adenine & thymine, guanine & cytosine), five-carbon sugars (either ribose or deoxyribose), and phosphate groups. Dna Replication Essay Example. The strands of DNA are arranged in a double-helix array and are held together with hydrogen bonds.
The semiconservative replication model is used to depict replication. In this model, each new double helix has one old strand and one new strand. This is yet another way in which accuracy is ensured. Because the shape of the DNA molecule is extremely important to its functionality, care must be taken to ensure that all parts of the molecule remain in their appropriate space during replication, and that no part of the strand is broken. To replicate DNA, the two strands must first be separated from one another. The first enzyme used in this process is called helicase. Dna Replication Essay Example.
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Helicases use the energy from ATP molecules to unwind the three-dimensional double helix. While the strand is unwinding, topoisomerase enzymes (such as gyrase) prevent the strands from being winded into a supercoil due to the torque produced by the separating action. Since each strand is comprised of complementary base pairs that have a high affinity to hydrogen-bond with one another, single-stranded binding proteins (SSBs) are attached to the strands to keep them from reattaching to one another. Once the strands are separated, work can begin to construct two new complementary strands that will ultimately attach to the existing DNA strands to form new complete DNA sequences. DNA polymerase III is the active enzyme that builds the new complementary strands. DNA polymerase III is a DNA-dependent enzyme.
As such, a template (the existing separated strand) must be present to generate the new strand. DNA polymerase III requires a primer to begin its action. The primer used is a short RNA sequence with a 3′ hydroxyl group that is formed by an enzyme known as primase. This primer is usually about ten nucleotides in length and is complementary to the existing DNA strand. DNA polymerase always works in the same direction: from the 5′ end to the 3′ end.
Since DNA polymerase III always works in the 5′ to 3′ direction, and DNA strands are complementary, this gives rise to a few minor issues that must be dealt with. The strand in which DNA polymerase can move in the same direction as gyrase (with the replication fork) is known as the leading strand. Dna Replication Essay Example. As the strand is unwound, DNA polymerase III can easily begin to replicate the strand, as the replication fork is already moving in the 5′ to 3′ direction. Dna Replication Essay Example. The complementary strand is known as the lagging strand. The replication fork is necessarily moving in the 3′ to 5′ direction on this strand.
On this strand, numerous primer sequences are inserted so that the DNA polymerase III can backtrack to build the new sequence as the strand is unwound. The DNA sequences between these primers, which are 1000 to 2000 nucleotides long, are known as Okazaki fragments. Once DNA polymerase III has replicated the fragments, the need arises to remove the RNA primer sequences and fuse the portions of the new strand together. The first critical enzyme used to do this is known as DNA polymerase I. This enzyme removes the primer sequence with the crucial 3′ hydroxyl group and synthesizes complementary DNA to fill in the gaps left by the primers.
After this is completed, yet another enzyme known as ligase is used to join the fragments. This enzyme works by forming a phosphodiester bond between the 3′ hydroxyl of the new strand and the 5′ phosphate group found on the Okazaki fragment. Using each enzyme to perform a specific function, DNA is successfully replicated. Science Essays.
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 The first discovery Chagraff made was that the amount of adenine present in all DNA molecules is equal to the amount of thymine.  The second discovery Chagraff made was that the amount of guanine was equal to the amount of cytosine.  The third discovery Chagraff made was that the amount of adenine plus thymine often differs greatly from the amount of guanine plus cytosine. HOW THE IMAGE OF DNA WAS FIRST DISCOVERED After Chagraff’s discoveries, two British scientists by the name Rosalind Franklin and Maurice Wilkens were able to apply his observations. Thus, these two scientists were the first ones to discover the image of what a DNA molecule actually looked like in three-dimension. How these scientists manage to obtain the image of a DNA molecule was by the use of “x-ray crystallographic analysis”. In this process, DNA molecules are bombarded with a x-ray beam. These x-rays encounter atoms, which in turn causes their paths to bent or diffract. The pattern created by the sum of total of these diffractions are then captured on a photographic film. The pattern is then interpreted into the image of the molecule through careful analysis. Thus, because of this research it led to the first theory and model structure of DNA. MAURICE WILKENS Maurice Wilkens was born in the year 1916 and is a British. Dna Replication Essay Example.
