Process Description DNA Revised

7/30/2019 Process Description DNA Revised

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The Process of DNA Replication

Nicole M. Celani

ENG 202 C

Section 017

10/22/2012

Audience: Professor Mateer


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Audience and Scope of Description

The purpose of this description is to describe the process of how DNA, our genetic

information, is replicated and transferred among cells. This description lays outthe major steps that occur during DNA replication in Chronological order. After

reading this description the audience will have a better understanding of how all

cells in the body can contain the same DNA.

The anticipated audiences for this description are individuals with little to no

knowledge of how DNA is replicated. This process description can be placed

online and in textbooks for individuals to develop a more comprehensiveunderstanding of DNA replication.


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Introduction to DNA Replication

Did you know all the cells in your body contain the exact same DNA that was

deposited by your mother and father? Have you ever wondered how this couldeven be achieved? This phenomenon is made possible by the process of DNA

Replication. The following description will give you a better understanding of

how this process works. The replication of DNA is a biological process in whichDNA is copied and allows for inheritance of genetic information.


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The Structure of DNA

DNA, Deoxyribonucleic acid, is a

double stranded helix. A doublestranded helix is coiled structure with

the two strands linked with hydrogen

bonds. This creates a spiral structure

that can be best seen in Figure 1.

The inside of DNA is made up of four

nucleotides. The four nucleotides that

pair together in DNA are Adenine,

Guanine, Cytosine and Thymine. These

nucleotides can also be referred to as

base pairs. The nucleotides are heldtogether by hydrogen bonding.

The outside of the helix is connected

using a sugar-phosphate structure to

hold the molecule in place.

The two strands of DNA run anti-parallel, reverse order, to one another to

allow enzymes to synthesize two

strands of DNA from one strand of

DNA. Figure 2 indicates this anti-

parallel nature by showing one side

running 5-3 and the other side running

3-5.

One DNA molecule can be separated to

create two new DNA molecules. Thisdivision allows for the inheritance of

DNA from one cell to another. Figure 2

shows the overall structure of DNA.

Figure 1: The overall structure of

DNA replication

Figure 2:The four nucleotides of DNAand the outside held together using a

Sugar-Phosphate structure.


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DNA Replication

DNA replication is the process in which DNA can be copied. In order for genetic

information to be passed on to all cells, this process is essential. DNA replicationcan be broken down into the following four major steps.

STEP 1:Splitting the Two Strands of DNA

In order to split the DNA an enzyme called DNA Helicase is introduced

to the cell as seen in figure 3. This enzyme breaks the hydrogen bonds

between the nucleotides. Breaking the two sides of DNA apart allows for

the individual strands to be made into new DNA molecules.

The exact point on the DNA molecule where replication is occurring is

called the Replication Fork. The Origin of Replication is where the

replication process actually began.

Figure 3: Helicase is an enzyme that is used to

split the double helix of DNA. The Helicasemolecule is located at the Replication Fork.


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STEP 2: Starting the Polymerization of the new strands

To continue building the DNA molecules, modifications must be made toeach of the separated strands. These alterations are essential because

enzymes cannot simply attach and begin to polymerize without a starting

point.

The starting point is created by the addition ofRNA primers. RNA

Primase is the enzyme that attaches the RNA primers to each separated

strand and creates a start point for replication. Figure 4 shows the RNA

primer added to one strand of the separated DNA molecule.

Figure 4: The RNA primer has been addedto the strand by RNA Primase.


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STEP 3:Elongation of the New DNA Strands

The elongation of the new strands begins with an enzyme called DNApolymerase. DNA polymerase adds the complimentary nucleotides to

the original strands of DNA thus elongating the new DNA molecule as

seen in Figure 5.

The anti-parallel structure of DNA creates a leading and lagging strand

as seen in Figure 5. The leading strand can be synthesized by DNA

polymerase continuously, whereas the lagging strand must be

synthesized in pieces as seen in Figure 6. These pieces are called

Okazaki fragments.

DNA replication is a semi-conservative process because the new DNA

molecules contain one half from the original strand and the other half

will be newly synthesized.

Figure 5: The enzyme DNA polymerase is usedto synthesize the new strands by a semi-

conservative method.

Figure 6: Okazaki fragments originate on the

lagging strand due to the inability to continuouslyreplicate this strand.


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STEP 4: Termination of DNA Replication

The last step in DNA Replication is termination. Termination can be

broken down into three separate procedures.

I. Termination begins when the lagging strands Okazakifragments are glued together using an enzyme called DNA

ligase. This creates two separate functioning molecules of

DNA.

II. Next in termination, telomeres are added to the end of DNAmolecules. Every time DNA divides a portion of the telomere

is degraded and this functions to prevent unlimited divisions of

DNA. When the telomere is fully degraded, the DNA becomesnon functional. Telomerase is the enzyme that adds these

segments to the DNA.

III. Finally, mistakes are commonly made during DNA replicationby adding the wrong nucleotides. These errors must be repaired

by an enzyme called DNA nuclease. DNA nuclease serves to

cut out the wrong nucleotides and replace them with the correct

ones.

Finally, DNA replication is complete and two functioning DNA

molecules are created. The culminating products of DNA replication can

be seen in Figure 7.

Figure 7: Okazaki fragments are glued

together using DNA ligase and errors areremoved using DNA nuclease. This allows

for two complete strands of DNA.


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Conclusion of DNA Replication

DNA replication starts with a single molecule of DNA. A series of enzymes

catalyze reactions on a single DNA molecule to allow for the synthesis of twoindividual molecules of DNA. DNA Helicase separates the two strands and breaks

the hydrogen bonds between the base pairs. Next, RNA Primase adds RNA

primers to the separated DNA strands. This allows for DNA polymerase to

polymerize the new molecules of DNA. The leading strand is made continuously

and the lagging strand is made in fragments due to the anti-parallel structure of

DNA. DNA Ligase connects the lagging strands Okazaki fragments together and

creates two cohesive DNA molecules. The two strands are then checked for errorswith DNA nuclease and partitioned into two separate cells.

Replication of DNA allows for all organisms on earth to pass on their genetic code,

making life possible. DNA replication allows for humans to begin as one single

cell and develop into a trillion celled organism, all containing the same genetic

information.


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Glossary of Important Terms

DNA- Deoxyribonucleic acid is the genetic material that carries all the genes of all

organisms on earth.

DNA Helicase- An enzyme that splits the double strands of a DNA helix molecule.

DNA ligase- An enzyme that is used to glue the Okazaki fragments together. This

is done to make the lagging strand on continuous DNA molecule.

DNA Polymerase- DNA polymerase adds the complimentary nucleotides to theoriginal strand of DNA, thus elongating the new DNA molecule.

Double Helix- A double stranded helix is coiled structure with the two strandslinked by hydrogen bonds.

Enzymes- Enzymes are molecules that catalyze reactions within the cell. All

enzymes have the ending suffix -ase to designate that it is an enzyme.

Hydrogen Bonds- Hydrogen bonds are week bonds between any element and

hydrogen. These bonds are week and can be broken easily but in numerous

numbers can be very strong.

Lagging Strand of DNA- The lagging strand of DNA is one half of the separated

DNA molecule that must be re-primed continuously and synthesized in fragments.

Leading Strand of DNA- The leading strand is one half of a separated DNAmolecule that can by synthesized continuously by DNA polymerase.

Nucleotides- Structures that form the basic structural unit of nucleic acids such as

DNA. Nucleotides are located on the inside of DNA.

Okazaki Fragments- Fragments that result on the lagging stand of DNA due toDNAs anti-parallel structure.

Origin of Replication- The start position for replication on a DNA molecule

Replication Fork- The position on the molecule where DNA replication is

occurring at any given time.


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RNA Primase- RNA Primase attaches RNA primer to the individual strands of

DNA when the helix has been split into two halves.

RNA primer- RNA primers is a small attachment that is added to the individualhalves of a DNA molecule to allow for synthesis of new DNA.

Telomerase- An enzyme that adds Telomeres to the end of DNA molecules.

Telomeres- Molecular attachments present at the end of DNA molecules.

Telomeres function to prevent unlimited divisions of DNA molecules because they

are degraded continuously after each DNA division.


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List of Illustrations

FIGURE 1:

DNA Replication and Synthesis. 2011. Oracle Education Foundation Copyright Agent, Redwood

Shores. Web. 22 Oct 2012.

FIGURE 2:

File:DNA chemical structure.svg. 2011. Wikipedia,the free encyclopediaWeb. 22 Oct 2012.

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Process Description DNA Revised