Dna replication essay

Dna replication essay

Essay On Replication Of DNA,Related Documents

WebJun 8,  · Because eukaryotic genomes are quite complex, DNA replication is a very complicated process that involves several enzymes and other proteins. It occurs in three Missing: essay WebDNA replication, or DNA synthesis, is the process in which makes a copy of itself prior to cell division. Every cell needs a copy of genetic material. The cell needs an entire copy of WebDue to the hydrogen bonds being more breakable, the DNA is much easier to “unzip” for replication. In the cytoplasm you can also find tRNA. tRNA contains a 3 nucleic code on WebThe ability to reproduce is one of the most fundamental properties of all living blogger.com replication, the basis for biological inheritance, is a fundamental process occurring in all WebJan 13,  · Dna Replication Essay. DNA replication is a complex cellular function that is necessary in order to sustain life and achieve growth. Many enzymes, proteins, and ... read more

Replication produces two identical DNA double helices, each with one new and one old strand. In a sense, that's all there is to DNA replication! But what's actually most interesting about this process is how it's carried out in a cell. Cells need to copy their DNA very quickly, and with very few errors or risk problems such as cancer. To do so, they use a variety of enzymes and proteins, which work together to make sure DNA replication is performed smoothly and accurately. DNA polymerase. One of the key molecules in DNA replication is the enzyme DNA polymerase.

DNA polymerases are responsible for synthesizing DNA: they add nucleotides one by one to the growing DNA chain, incorporating only those that are complementary to the template. Here are some key features of DNA polymerases:. They always need a template. They can't start making a DNA chain from scratch, but require a pre-existing chain or short stretch of nucleotides called a primer. They proofread , or check their work, removing the vast majority of "wrong" nucleotides that are accidentally added to the chain. The addition of nucleotides requires energy. This energy comes from the nucleotides themselves, which have three phosphates attached to them much like the energy-carrying molecule ATP. When the bond between phosphates is broken, the energy released is used to form a bond between the incoming nucleotide and the growing chain.

In prokaryotes such as E. coli , there are two main DNA polymerases involved in DNA replication: DNA pol III the major DNA-maker , and DNA pol I, which plays a crucial supporting role we'll examine later. Starting DNA replication. How do DNA polymerases and other replication factors know where to begin? Replication always starts at specific locations on the DNA, which are called origins of replication and are recognized by their sequence. coli , like most bacteria, has a single origin of replication on its chromosome. Specialized proteins recognize the origin, bind to this site, and open up the DNA. As the DNA opens, two Y-shaped structures called replication forks are formed, together making up what's called a replication bubble. The replication forks will move in opposite directions as replication proceeds.

Bacterial chromosome. The double-stranded DNA of the circular bacteria chromosome is opened at the origin of replication, forming a replication bubble. Each end of the bubble is a replication fork, a Y-shaped junction where double-stranded DNA is separated into two single strands. New DNA complementary to each single strand is synthesized at each replication fork. The two forks move in opposite directions around the circumference of the bacterial chromosome, creating a larger and larger replication bubble that grows at both ends. Diagram based on similar illustration in Reece et al. How does replication actually get going at the forks? Helicase's job is to move the replication forks forward by "unwinding" the DNA breaking the hydrogen bonds between the nitrogenous base pairs.

Proteins called single-strand binding proteins coat the separated strands of DNA near the replication fork, keeping them from coming back together into a double helix. Primers and primase. DNA polymerases can only add nucleotides to the 3' end of an existing DNA strand. They use the free -OH group found at the 3' end as a "hook," adding a nucleotide to this group in the polymerization reaction. How, then, does DNA polymerase add the first nucleotide at a new replication fork? Alone, it can't! The problem is solved with the help of an enzyme called primase. Primase makes an RNA primer , or short stretch of nucleic acid complementary to the template, that provides a 3' end for DNA polymerase to work on.

A typical primer is about five to ten nucleotides long. The primer primes DNA synthesis, i. Once the RNA primer is in place, DNA polymerase "extends" it, adding nucleotides one by one to make a new DNA strand that's complementary to the template strand. Leading and lagging strands. coli , the DNA polymerase that handles most of the synthesis is DNA polymerase III. There are two molecules of DNA polymerase III at a replication fork, each of them hard at work on one of the two new DNA strands. DNA polymerases can only make DNA in the 5' to 3' direction, and this poses a problem during replication. A DNA double helix is always anti-parallel; in other words, one strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction.

This makes it necessary for the two new strands, which are also antiparallel to their templates, to be made in slightly different ways. One new strand, which runs 5' to 3' towards the replication fork, is the easy one. This strand is made continuously, because the DNA polymerase is moving in the same direction as the replication fork. This continuously synthesized strand is called the leading strand. The other new strand, which runs 5' to 3' away from the fork, is trickier. This strand is made in fragments because, as the fork moves forward, the DNA polymerase which is moving away from the fork must come off and reattach on the newly exposed DNA. This tricky strand, which is made in fragments, is called the lagging strand. The small fragments are called Okazaki fragments , named for the Japanese scientist who discovered them.

The leading strand can be extended from one primer alone, whereas the lagging strand needs a new primer for each of the short Okazaki fragments. The maintenance and cleanup crew. Some other proteins and enzymes, in addition the main ones above, are needed to keep DNA replication running smoothly. One is a protein called the sliding clamp , which holds DNA polymerase III molecules in place as they synthesize DNA. Topoisomerase also plays an important maintenance role during DNA replication. This enzyme prevents the DNA double helix ahead of the replication fork from getting too tightly wound as the DNA is opened up. It acts by making temporary nicks in the helix to release the tension, then sealing the nicks to avoid permanent damage.

Finally, there is a little cleanup work to do if we want DNA that doesn't contain any RNA or gaps. The RNA primers are removed and replaced by DNA through the activity of DNA polymerase I , the other polymerase involved in replication. The nicks that remain after the primers are replaced get sealed by the enzyme DNA ligase. Summary of DNA replication in E. Let's zoom out and see how the enzymes and proteins involved in replication work together to synthesize new DNA. Illustration shows the replication fork. Helicase unwinds the helix, and single-strand binding proteins prevent the helix from re-forming. Topoisomerase prevents the DNA from getting too tightly coiled ahead of the replication fork. DNA primase forms an RNA primer, and DNA polymerase extends the DNA strand from the RNA primer.

DNA synthesis occurs only in the 5' to 3' direction. On the leading strand, DNA synthesis occurs continuously. Helicase opens up the DNA at the replication fork. Single-strand binding proteins coat the DNA around the replication fork to prevent rewinding of the DNA. Topoisomerase works at the region ahead of the replication fork to prevent supercoiling. Primase synthesizes RNA primers complementary to the DNA strand. DNA polymerase III extends the primers, adding on to the 3' end, to make the bulk of the new DNA. RNA primers are removed and replaced with DNA by DNA polymerase I.

DNA replication in eukaryotes. The basics of DNA replication are similar between bacteria and eukaryotes such as humans, but there are also some differences:. Eukaryotes usually have multiple linear chromosomes, each with multiple origins of replication. Most of the E. coli enzymes have counterparts in eukaryotic DNA replication, but a single enzyme in E. coli may be represented by multiple enzymes in eukaryotes. Most eukaryotic chromosomes are linear. Because of the way the lagging strand is made, some DNA is lost from the ends of linear chromosomes the telomeres in each round of replication. Explore outside of Khan Academy.

Do you want to learn more about DNA replication? Check out this scrollable interactive from LabXchange. Sort by: Top Voted. Want to join the conversation? Log in. The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a spiral staircase. The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase. DNA molecule is a polymer which is composed of several thousand pairs of nucleotide monomers. Union of several nucleotides together leads to the formation of polynucleotide chain.

Nucleotides are also known as nitrogenous bases or DNA bases. Nitrogenous base are of two types, viz. pyrimidines and purines. Thus, in DNA there are four different types of nitrogenous bases, viz. adenine A , guanine G , cytosine C and thymine T. In RNA, the pyrimidine base thymine is replace by uracil. The purine and pyrimidine bases always pair in a definite fashion. Adenine will always pair with thymine and guanine with cytosine. Adenine and thymine are joined by double hydrogen bonds while guanine and cytosine are joined by triple hydrogen bonds. However, these bonds are weak which help in separation of DNA strands during replication. This is a pentose sugar having five carbon atoms. The four carbon atoms are inside the ring and the fifth one is with CH 2 group.

This has three OH groups on 1, 3 and 5 carbon positions. Hydrogen atoms are attached to carbon atoms one to four. In RNA, the sugar ribose is similar to deoxyribose except that it has OH group on carbon atom 2 instead of H group. The phosphate molecule is arranged in an alternate manner to deoxyribose molecule. Thus there is deoxyribose on both sides of phosphate. The phosphate is joined with carbon atom 3 of deoxyribose at one side and with carbon atom 5 of deoxyribose on the other side. A combination of deoxyribose sugar and nitrogenous base is known as nucleoside and a combination of nucleoside and phosphate is called nucleotide. Thus, a nucleotide is a nucleoside with one or more phosphate groups covalently attached to it. Nucleosides differ from nucleotides in that they lack phosphate groups.

The four different nucleosides of DNA are deoxyadenosine dA , deoxyguanosine dG , deoxycytosine dC , and deoxythymidine dT. The DNA backbone is a polymer with an alternating sugar-phosphate sequence. Depending upon the nucleotide base per turn of the helix, pitch of the helix, tilt of the base pair and humidity of the sample, the DNA can be observed in four different forms namely, A, B, C and D. The comparison of A, B and Z forms of DNA is presented in Table The minor groove is wide and shallow which is accessible to proteins, but information content is lower than major groove.

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In this essay we will discuss about:- 1. Definition of DNA Replication 2. Mechanism of DNA Replication 3. Evidences for Semi-Conservative DNA Replication 4. Models for Replication of Prokaryotic DNA. Each half then serves as a template for nucleotides available in the cells which are joined together by DNA polymerase. The nucleotides are guanine, cytosine, adenine and thymine. DNA replication or DNA synthesis is the process of copying a double-stranded DNA molecule. This process is important in all known forms of life and the general mechanisms of DNA replication are the same in prokaryotic and eukaryotic organisms.

The process by which a DNA molecule makes its identical copies is referred to as DNA replication. In other words, it is the process of duplicating the DNA to make two identical copies. The main points related to DNA replication are briefly presented below. The process of DNA replication takes place during cell division. The DNA replication takes place during S sub stage of interphase. In prokaryotes, DNA replication is initiated before the end of the cell cycle. Eukaryotic cells can only initiate DNA replication at the beginning of S phase. In humans and other eukaryotes, replication occurs in the cell nucleus, whereas in prokaryotes it occurs in the cytoplasm.

Prokaryotes have only one active replication site, but eukaryotes have many. The existing DNA is used as a template for the synthesis of new DNA strands. It is possible that during replication on strand of DNA can replicate continuously and the other discontinuously or in piece. The continuously replicating strand is known as leading strand and the discontinuously replicating strand is known as lagging strand. When one strand of DNA replicates continuously and other discontinuously, it is called semi-discontinuous replication.

Earlier it was thought that DNA replicates discontinuously. But now it is believed that DNA replication is semi-discontinuous. Short segments of nucleotides are synthesized in the lagging strand of DNA as a result of discontinuous replication. These are called Okazaki after the name of discoverer. Okazaki fragments are about 1, bases in length in prokaryotes, and bases in eukaryotes. The process of DNA replication takes place under the control of DNA polymerase. In other words, the process is catalized by the polymerase enzyme. In eukaryotes, four types of polymerase enzymes, viz. alpha, delta, gamma and epsilon are used.

DNA Polymerase alpha and delta replicate the DNA. The alpha is associated with initiation, and delta extends the nascent strands. DNA polymerase epsilon and beta are used for repair. DNA polymerase gamma is used for replication of mitochondrial DNA. In prokaryotes [E. coli], there are three major DNA polymerases: DNA polymerase I, II and III. DNA poly I is found in the highest concentration of all DNA polymerases; it is involved in DNA repair and assists with primary DNA replication. DNA poly II is exclusively involved in repair. DNA poly III is the major DNA polymerase.

Currently, six families of polymerases A, B, C. D, X, Y have been discovered. At least four different types of DNA polymerases are involved in the replication of DNA in animal cells POLA, POLG, POLD and POLE. The synthesis of one new strand takes place in and that of other in opposite direction. The replication may take place either in one direction or in both the directions from the point of origin. When replication proceeds in one direction only, it is called unidirectional replication. When the replication proceeds in both the directions, it is called bidirectional replication. Based on the direction, the replication may be unidirectional or bidirectional. On the basis of continuity, the replication may be continuous or discontinuous. The point of initiation of DNA replication is known as origin.

The progress of replication process is measured from the point of origin. In prokaryotic cells the rate of replication is bases per second. In eukaryotic cells the rate of replication- is 50 bases per second. Eukaryotes have to 3, times more DNA than prokaryotes. There are three models which explain the accurate replication of DNA. These are: i dispersive replication, ii conservative replication, and iii semiconservative replication Fig. According to this model of replication the two strands of parental DNA break at several points resulting in several pieces of DNA. Each piece replicates and pieces are reunited randomly, resulting in formation of two copies of DNA from single copy.

The new DNA molecules are hybrids which have new and DNA in patches Fig. This method of DNA replication is not accepted as it could not be proved experimentally. According to this model of DNA replication two DNA molecules are formed from parental DNA. One copy has both parental strands and the other contains both newly synthesized strands Fig. This method is also not accepted as there is no experimental proof in support of this model. This model of DNA replication was proposed by Watson and Crick. According to this model of DNA replication, both strands of parental DNA separate from each other. Each old strand synthesizes a new strand. Thus each of the two resulting DNA molecules has one parental and one new strand Fig.

This model of DNA replication is universally accepted because there are several evidences in support of this mode. The semi-conservative model mechanism of DNA replication consists of six important steps, viz:. The first major step in the process of DNA, replication is the breaking of hydrogen bonds between bases of the two anti-parallel strands. The unwinding of the two strands is the starting point. The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine, whereas there are three hydrogen bonds between Cytosine and Guanine. The Helicase enzyme splits the two strands.

Synthesis of RNA primer is essential for initiation of DNA replication. RNA primer is synthesized by DNA template near the origin with the help of RNA Primase. RNA nucleotides are the primers starters for the binding of DNA nucleotides. The elongation proceeds in both directions, viz. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase a reads the template and lengthens the bubbles. The daughter strand is elongated with the binding of more DNA nucleotides.

The RNA Primers are removed or degraded by DNA polymerase I. This enzyme also catalyzes the synthesis of short DNA segments to replace the primers. The gaps are filled with the action of DNA Polymerase which adds complementary nucleotides to the gaps. The DNA Ligase enzyme adds phosphate in the remaining gaps of the phosphate-sugar backbone. Each new double helix is consisted of one old and one new chain. This is called semi-conservative replication. The termination takes place when the DNA Polymerase reaches to an end of the strands.

In other words, it is the separation of replicated linear DNA. After removal of the RNA primer, it is not possible for the DNA Polymerase to seal the gap because there is no primer. Hence, the end of the parental strand where the last primer binds is not replicated. These ends of linear chromosomal DNA consist of noncoding DNA that contains repeat sequences and are called telomeres. A part of the telomere is removed in every cycle of DNA Replication. The DNA replication is not completed without DNA repair. The possible errors caused during the DNA replication are repaired by DNA repair mechanism.

Enzymes like nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps. Similar processes also happen during the steps of DNA Replication of prokaryotes though there are some differences. Various experiments have demonstrated the semi-conservative mode of DNA replication.

Structure of the DNA and DNA Replication Questions Essay,AP®︎/College Biology

WebDue to the hydrogen bonds being more breakable, the DNA is much easier to “unzip” for replication. In the cytoplasm you can also find tRNA. tRNA contains a 3 nucleic code on WebThe ability to reproduce is one of the most fundamental properties of all living blogger.com replication, the basis for biological inheritance, is a fundamental process occurring in all WebDNA replication, or DNA synthesis, is the process in which makes a copy of itself prior to cell division. Every cell needs a copy of genetic material. The cell needs an entire copy of WebFeb 10,  · Structure of the DNA and DNA Replication Questions Essay Question 2. Non covalent bonds attach the paired bases that compliment each other. The bond WebJun 8,  · Because eukaryotic genomes are quite complex, DNA replication is a very complicated process that involves several enzymes and other proteins. It occurs in three Missing: essay WebJan 13,  · Dna Replication Essay. DNA replication is a complex cellular function that is necessary in order to sustain life and achieve growth. Many enzymes, proteins, and ... read more

This is yet another way in which accuracy is ensured. Want to join the conversation? The point of initiation of DNA replication is known as origin. Read More. Helicases use the energy from ATP molecules to unwind the three-dimensional double helix. The RNA primers are removed and replaced by DNA through the activity of DNA polymerase I , the other polymerase involved in replication. The process of DNA replication takes place under the control of DNA polymerase.

Models for Replication of Prokaryotic DNA. Transcription is carried out by an dna replication essay called RNA polymerase and proteins called transcription factors. When replication proceeds in one direction only, it is called unidirectional replication. An example of this would be when thymine connects to adenine and guanine connects to cytosine, dna replication essay. DNA replication or DNA synthesis is the process of copying a double-stranded DNA molecule. It binds