DNA REPLICATION
WHAT IS DNA?
DNA is a molecule that has a repeating chain of identical five-carbon sugars (polymers) linked together from head to tail. It is composed of four ring shaped organic bases (nucleotides) which are Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). It has a double helix shape and contains the sugar component deoxyribose.
THE PROCESS OF DNA REPLICATION
How DNA replicates is quite a simple process. First, a DNA molecule is “unzipped”. In other words, it splits into two strands of DNA at one end of the DNA molecule. This separation will cause a formation of a replication fork.
After the replication fork has been established the strands of DNA are ready for the next stage. On each strand is a sequence of nucleotides. These nucleotides act as a template for complementary nucleotides to bind. Hence, it is the site where the synthesis of a new complementary strand will be formed.
Because of the DNA “unzipping”, there will be two single strands of DNA. Hence, because there is two single strands of DNA, there will be two new daughter strands synthesized. However, each of these daughter cells is synthesized in different ways.
The first strand of DNA is built by simply adding nucleotides to its end. This strand grows inward towards the replication fork as the DNA molecule unzips. This strand ends with a hydroxide (OH) group and is called the 3` prime or 3`end. The enzyme that catalyzes this process is called DNA polymerase.
The second strand is built by having a polymerase jump ahead on the strand and fill in the complementary nucleotides backwards. This strand moves in the outward direction, hence away from the replication fork. The DNA polymerase for this strand starts a burst of synthesis at the point of the replication fork. The addition of nucleotides to the 3` end of a short new chain until this new segment fills in a gap of 1000 to 2000 nucleotides between the replication fork and the end of the growing chain to which the previous segment was added. Hence, this new short chain is then added to the growing chain, and the polymerase jumps ahead again to fill in another gap. Thus in short, the polymerase copies the template strand in segments about 1000 nucleotides long and stitches each new fragment to the end of the growing chain. This process of replication is referred to as discontinuous synthesis.
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...hesis proceeds at a fast pace. A protein containing 400 amino acids can be synthesized in about 20 seconds. (For more information about the role of DNA in protein synthesis, see Genetics.)
Of all the molecules that DNA could direct to be built, one might wonder why the information encoded in DNA is limited solely to the manufacture of protein. The reason is that so long as DNA can direct the making of protein enzymes, no other direction is necessary because enzymes aid in the building of all other cell molecules.
Most of the details of protein synthesis have been omitted from this discussion so that key events could be stressed. However, one procedure merits mention. Before an amino acid can be assembled into a polypeptide chain, it must first be modified to a so-called acyl amino acid, which is more reactive than an unmodified one. This important acyl conversion is powered by the energy stored in a molecule called adenosine triphosphate (ATP).
REFERENCES
Raven, P.H. and G.B. Johnson, (1988) Understanding Biology. Times Mirror/Mosby: United States
Biotech – www.accessexcellence.org/AB/WYW/wkbooks/SFTS/biography.htm
A helicase uses energy provided by ATP to uncoil the DNA template specified (Biology pg. 267). The helicase essentially divides the DNA, so that it can be able to form a replication fork in its origin of replication (Biology pg. 268). Then, Okazaki fragments are formed in the lagging strand. Okazaki fragments are defined as “DNA fragments synthesized on the lagging strand (Biology pg. 268).” Meanwhile, the leading strand is still continuously replicating (Biology pg. 268). After the lagging strand synthesis, which is when “the primase synthesizes the primers needed by DNA polymerase III”, the DNA ligase closes the gaps between the Okazaki fragments (Biology pg. 268-269). Finally, termination occurs at an opposite spot of the origin. In the final stage two daughter molecules are produced and are interlocked in a chain-like
Deoxyribo Nucleic Acid (DNA) is a chromosome found in the nucleus of a cell, which is a double-stranded helix (similar to a twisted ladder). DNA is made up of four bases called adenine (A), thymine (T), guanine (G), and cytosine (C), that is always based in pairs of A with T and G with C. The four bases of A, C, G, and T were discovered by Phoebus Levene in 1929, which linked it to the string of nucleotide units through phosphate-sugar-base (groups). As mention in Ananya Mandal research paper, Levene thought the chain connection with the bases is repeated in a fix order that make up the DNA molecu...
In order to do this a polymer of DNA “unzips” into its two strands, a coding strand (left strand) and a template strand (right strand). Nucleotides of a molecule known as mRNA (messenger RNA) then temporarily bonds to the template strand and join together in the same way as nucleotides of DNA. Messenger RNA has a similar structure to that of DNA only it is single stranded. Like DNA, mRNA is made up of nucleotides again consisting of a phosphate, a sugar, and an organic nitrogenous base. However, unlike in DNA, the sugar in a nucleotide of mRNA is different (Ribose) and the nitrogenous base Thymine is replaced by a new base found in RNA known as Uracil (U)3b and like Thymine can only bond to its complimentary base Adenine. As a result of how it bonds to the DNA’s template strand, the mRNA strand formed is almost identical to the coding strand of DNA apart from these
After the initiation process is complete, amino acids begin to be added to the polypeptide in a three step process known as elongation. First, the mRNA codon in the A site pairs with the anticodon of an incoming tRNA molecule. Next, the polypeptide separates from the tRNA in the P site and attaches to the amino acid that was carried by the tRNA in the A site. The ribosome catalyzes formation of the bond. Finally, the P site tRNA leaves the ribosome and the ribosome moves the tRNA in the A site to the P site with its attached polypeptide. A new tRNA is then able to bind to the A site to start the elongation process over again. Eventually, a stop codon will reach the A site signaling the amino acid to stop translation
Protein synthesis first begins in a gene. A gene is a section of chromosome compound of deoxyribonucleic acid or DNA. Each DNA strand is composed of phosphate, the five-carbon sugar deoxyribose and nitrogenous bases or nucleotides. There are four types of nitrogenous bases in DNA. They are (A)denine, (G)uanine, (T)hymine, (C)ytosine and they must be paired very specifically. Only Adenine with Thymine (A-T) and Guanine with Cytosine (G-C).
Protein synthesis consists of two main steps: transcription and translation. The DNA is found inside of the nucleus and there in the nucleus a copy of one side of the DNA strand is made, this is the messenger RNA or mRNA. After this the mRNA travels through the cytoplasm with the DNA copy and arrives at the ribosomes. The mRNA then goes through the ribosome three bases at a time. A transfer RNA molecule or tRNA then bring the correct amino acid to match the codon. The amino acids then link together to form a long chain of proteins, making amino acids the building blocks of
Precise chromosomal DNA replication during S phase of the cell cycle is a crucial factor in the proper maintenance of the genome from generation to generation. The current “once-per-cell-cycle” model of eukaryotic chromosome duplication describes a highly coordinated process by which temporally regulated replicon clusters are sequentially activated and subsequently united to form two semi-conserved copies of the genome. Replicon clusters, or replication domains, are comprised of individual replication units that are synchronously activated at predetermined points during S phase. Bi-directional replication within each replicon is initiated at periodic AT-rich origins along each chromosome. Origins are not characterized by any specific nucleotide sequence, but rather the spatial arrangement of origin replication complexes (ORCs). Given the duration of the S phase and replication fork rate, adjacent origins must be appropriately spaced to ensure the complete replication of each replicon. Chromatin arrangement by the nuclear matrix may be the underpinning factor responsible for ORC positioning. The six subunit ORC binds to origins of replication in an ATP-dependent manner during late telophase and early G1. In yeast, each replication domain simply contains a single ORC binding site. However, more complex origins are characterized by an initiation zone where DNA synthesis may begin at numerous locations. A single round of DNA synthesis at each activated origin is achieved by “lic...
For this process to begin, the genome of the strand of DNA must form a specific pattern. If a line was draw down the very center of the DNA sequence, every base of the same distance away from the center line must be matching based pairs. To illustrate this concept, a diagram bound to the same rule with ten base pairs would have matching base pairs at numbers 5 and 6, 4 and 7, 3 and 8, 2 and 9, and 1 and 10.
Each of the nucleotides accommodate a phosphate group, sugar group, and a nitrogen base. There is four nitrogen bases in DNA. The four nitrogen bases are; Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). Each of the bases are connected to a sugar molecule and a phosphate molecule. They are then positioned into two long strands that form a spiral called a double helix (DNA). The nitrogen bases are paired up with one another. Adenine and Thymine will always be paired with each other because of the bonds between them. Between A and T, there are two hydrogen bonds. The same goes with Guanine always being paired with Cytosine due. Between both G and C there is three hydrogen bonds. The nitrogen bases Adenine and Guanine won’t pair up with each other because, of their size. Both the nitrogen bases Adenine and Guanine are a purine base. Thymine and Cytosine are both a pyrimidine base. Adenine pairs with Thymine, and Guanine pairs with Cytosine, because they are of opposite
The use of this form of punishment of spanking has been used for the longest time. Many parents have this form of punishment towards their children to help control their child in some cases. Like in the article “Spanking” by John A Addleman he adds to this argument of how there are many parents who strongly follow this form of punishment for their children. He added that there are parents who also believe that this form of corporal punishment is not abuse “ data regarding attitudes about spanking, have found that most parents believe that corporal punishment is a non abusive manner is an acceptable form of discipline” (Addleman 1). Many may ask what kind of corporal punishment exactly is acceptable to use towards your child. The form of punishment
... the codon for the amino acid methionine is added the head of each chain.
DNA (deoxyribonucleic acid) is a self-replicating molecule or material present in nearly all living organisms as the main constituent in chromosomes. It encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. Simply put, DNA contains the instructions needed for an organism to develop, survive and reproduce. The discovery and use of DNA has seen many changes and made great progress over many years. James Watson was a pioneer molecular biologist who is credited, along with Francis Crick and Maurice Wilkins, with discovering the double helix structure of the DNA molecule. The three won the Nobel Prize in Medicine in 1962 for their work (Bagley, 2013). Scientist use the term “double helix” to describe DNA’s winding, two-stranded chemical structure. This shape looks much like a twisted ladder and gives the DNA the power to pass along biological instructions with great precision.
The first part of the process of protein synthesis is transcription - the creation of RNA based on the DNA template. First the enzyme RNA polymerase helps to unwind the DNA helix. Then the DNA is elongated. RNA polymerase binds to one strand of the DNA at the promoter sequence (a specific sequence of nucleotides on the DNA chain) and when it reaches the start signal, the formation of mRNA begins. Transcription stops when it reaches the termination signal.
Transcription is split into three stages; initiation, elongation and termination. During initiation of transcription RNA polymerase binds to the promoter and just 17 base pairs of DNA are unwound at any given time. Figure 1 shows RNA polymerase attached to the DNA strand and 17 base pairs that have been separated (Burrell, H, 2014).
During this phase the DNA aka “deoxyribose nucleic acid” clone then forms chromatin. Chromatin is the mass of genetic material that forms into chromosomes. Interphase is divided into smaller parts: G1 Phase, S phase and G2 Phase. Throughout all the phases, the cells continuously develop by producing mitochondria, endoplasmic reticulum, and proteins. The actual division occurs during the S phase bur the G phases are mainly for the purpose of growing. Starting with the G1 phase the cell grows in preparation for certain intracellular components and DNA replication. This phase makes sure the cell is prepared for the process of DNA replication. It reviews the size and environment to ensure that is it ready to go, and cannot leave the G1 until it is complete. But what happens to a cell when it is not complete and cannot exit out of the phase? It will pause and transfer to phase G0. There’s no certain time to be in this phase but it will remain until it reaches the fitting size and is in a supportive surroundings for DNA replication. It will exit either G1 or G0 and there is no other way besides these. Then the cell will advance to the next phase which is the S phase. Synthesis, or more known as S phase is the section of the cell cycle when the DNA is wrapped into chromosomes then duplicated. This is a very important part of the cycle because it grants each of them that is created, to have the exact same genetic