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
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
Proteins are one of the main building blocks of the body. They are required for the structure, function, and regulation of the body’s tissues and organs. Even smaller units create proteins; these are called amino acids. There are twenty different types of amino acids, and all twenty are configured in many different chains and sequences, producing differing protein structures and functions. An enzyme is a specialized protein that participates in chemical reactions where they serve as catalysts to speed up said reactions, or reduce the energy of activation, noted as Ea (Mader & Windelspecht).
Also in a PRC reaction, DNA Polymerase is made of many complicated proteins with the function of duplicating DNA before division occurs (2).
In telophase, these separate chromatids uncoil to become chromosomes. This division produces two identical cells.
The study of nucleic acids has now become a fruitful and dynamic scientific enterprise. Nucleic acids are of unique importance in biological systems. Genes are made up of deoxyribonucleic acid or DNA, and each gene is a linear segment, or polymer, of a long DNA molecule. A DNA polymer, or DNA oligonucleotide, contains a linear arrangement of subunits called nucleotides. There are four types of nucleotides. Each nucleotide has three components; a phosphate group, a sugar and a base that contains nitrogen within its structure. The sugar moiety in DNA oligonucleotides is always dexoyribose, and there are four alternative bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The phosphate groups and the deoxyribose sugars form the backbone of each DNA stand. The bases are joined to the deoxyribose sugar and stick out to the side. Both oligomers, DNA and RNA, consist of 5’->3’ phosphodiester-linked nucleotide units that are composed of a 2’-deoxy-D-ribose (DNA) or D-ribose (RNA) in their furanose forms and a heteroaromatic nucleobase (A, T, G, and C; A, U, G, C), and the resulting oligonucleotide chain is composed of a polar, negatively charged sugar-phosphate backbone and an array of hydrophobic nucleobases. The amphiphilic nature of these polymers dictates the assembly and maintenance of secondary and tertiary structures the oligonucleotides can form. In the DNA duplex structure, genetic information is stored as a linear nucleotide code. This code can be accessed and replicated. RNA, or ribonucleic acid, is another structurally related essential biopolymer. RNA differs from DNA in having the sugar ribose in place of the deoxyribos...
... the codon for the amino acid methionine is added the head of each chain.
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...
A chromosome is made up of two identical structures called chromatids. The process of nuclear division is called interphase; each DNA molecule in a nucleus makes an identical copy of itself. Each copy is contained in the chromatid and a characteristic narrow region called the centromere holds the two chromatids together. The centromere can be found anywhere along a chromosome but the position is the characteristic for a particular chromosome. Each Chromatid contains one DNA molecule. DNA is the molecule of inheritance and is made up of a series of genes. The fact that the two DNA molecules in the sister chromatids, and hence their genes, are identical is the key to precise nuclear division.
thousands of different ways to form thousands of different proteins. each with a unique function in the body. Both the amino acids manufactured in the liver and those derived from the breakdown of the The proteins we eat are absorbed into the blood stream and taken up by the cells and tissues to build new proteins as needed.... ... middle of paper ... ...denatured by boiling, their chains are shortened to form gelatine.
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.
Protein synthesis is one of the most fundamental biological processes. To start off, a protein is made in a ribosome. There are many cellular mechanisms involved with protein synthesis. Before the process of protein synthesis can be described, a person must know what proteins are made out of. There are four basic levels of protein organization. The first is primary structure, followed by secondary structure, then tertiary structure, and the last level is quaternary structure. Once someone understands the makeup of a protein, they can then begin to learn how elements can combine and go from genes to protein. There are two main processes that occur during protein synthesis, or peptide formation. One is transcription and the other is translation. Although these biological processes slightly differ for eukaryotes and prokaryotes, they are the basic mechanisms for which proteins are formed in all living organisms.
The result will be two DNA molecules, each containing an old and a new strand. Therefore, DNA replication is called semiconservative. The original strand is referred to as the template strand because it provides the information, or template, for the newly synthesized strand. DNA replication relies on the double-stranded nature of the molecule. One double stranded DNA molecule, when replicated, will become two double-stranded molecules, each containing one original strand and one newly synthesized strand. You remember that the two strands of DNA run antiparallel: one from the 5’ to the 3’, and the other from the 3’ to the 5’. The synthesis of the new DNA strand can only happen in one direction: from the 5’ to the 3’ end. In other words, the new bases are always added to the 3’ end of the newly synthesized DNA strand. So if the new nucleotide is always added to the 3’ end of an existing nucleotide, where does the first nucleotide come from? In fact, DNA polymerase needs an “anchor” to start adding nucleotides: a short sequence of DNA or RNA that is complementary to the template strand will work to provide a free 3’ end. This sequence is called a
A polypeptide chain is a series of amino acids that are joined by the peptide bonds. Each amino acid in a polypeptide chain is called a residue. It also has polarity because its ends are different. The backbone or main chain is the part of the polypeptide chain that is made up of a regularly repeating part and is rich with the potential for hydrogen-bonding. There is also a variable part, which comprises the distinct side chain. Each residue of the chain has a carbonyl group, which is good hydrogen-bond acceptor, and an NH group, which is a good hydrogen-bond donor. The groups interact with the functional groups of the side chains and each other to stabilize structures. Proteins are polypeptide chains that have 500 to 2,000 amino acid residues. Oligopeptides, or peptides, are made up of small numbers of amino acids. Each protein has a precisely defined, unique amino acid sequence, referred to as its primary structure. The amino acid sequences of proteins are determined by the nucleotide sequences of genes because nucleotides in DNA specify a complimentary sequence in RNA, which specifies the amino acid sequence. Amino acid sequences determine the 3D structures of proteins. An alteration in the amino acid sequence can produce disease and abnormal function. All of the different ways
Secondly the gene has to be cut from its DNA chain. Controlling this process are many restriction endonucleases (restriction enzymes). Each of these enzymes cut DNA at a different base sequence called a recognition sequence. The recognition sequence is 6 base pairs long. The restriction enzymes PstI cuts DNA horizontally and vertically to produce sticky ends.
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