If we want to discuss about DNA, of course we need to know what is DNA first? Who is the inventor? What is it? Or the elements in it. So let's see my discussion this time DNA.

Understanding DNA

DNA is a nucleic acid that stores all the unique biological information of every living creature and some viruses.

DNA stands for deoxyribonucleic acid. DNA comes from three main words of deoxyribo, and nucleid acid (nucleic acid). The meaning of the word deoxyribo is the sugar that loses its oxygen atom, while the meaning of the word nucleic acid is a molecule that contains genetic information. (wikipedia)

credit

The chemical structure is a complex macromolecule composed of three molecules, namely pentose sugar (deoxyribose), phosphoric acid, and nitrogen base. The DNA nitrogen base is composed of purines, adenine and guanine, and pyrimidines, thymine and cytosine.

The main role of the DNA molecule is the long-term storage of information. DNA is often compared to a set of blueprints or recipes, or codes, as it contains instructions needed to build other components of the cell, such as proteins and RNA molecules. The DNA segment that carries this genetic information is called a gene, but another sequence of DNA that has a structural purpose, or is involved in regulating the use of genetic information.

DNA can replicate that is forming a copy of itself. Each DNA strand contains a specific base sequence. Each base is also connected by sugar molecules and phosphates. When the base forms a rung (horizontal), then the sugar and phosphate molecules form a vertical part of the ladder.

Inventors of DNA Structures

James Watson

Speaking who discovered the structure of DNA for the first time was James Watson, Francis Crick and Maurice Wilkins. James Watson is an American citizen born in 1928 who at the age of 18 received a Ph.D. in Zoology from Indiana University. While Francis Crick is a 1916-born British citizen who is very interested in physics, chemistry and mathematics. James Watson and Francis Crick began working together to determine the structure of DNA in 1949 at the Cavendish Laboratory in Cambridge. And Maurice Wilkins is a New Zealand scientist who received her Ph.D. in Physics. In 1950-1952, Wilkins collaborated with Raymond Gosling and Rosalind Franklin in an attempt to determine the structure of DNA using X-rays. Armed with the results of his collaboration with Franklin that Wilkins then start cooperation with Watson and Crick in determining the structure of DNA that is now known as Double Helix. All three were awarded the Nobel Prize in 1962 in the field of Medicine for their work (DNA Dual Helix structure) in 1953.

The properties of DNA

DNA has several properties that include the following:

1. DNA is a chromosome material as a carrier of genetic information, through the activity of cell division.
2. The amount of DNA constant in every cell type and species. Constant in a fixed sense and unchanged. For example The amount of DNA in cats is different from the amount of DNA in Dogs. Likewise with the amount of DNA in humans and primates differ in number.
3. The content of DNA in a cell depends on the nature of the ploidy (genome) of the cell or the number of chromosomes in the cell.
4. Thickness 20 Å (Amstrong) and the length of thousands of Å (1 Å = 10 ^ -10 meters).
5. Can replicate, ie form a derivative or copy themselves. Replicated DNA (child DNA) has a base sequence identical to that of a parental double helix (parent DNA).
6. In cells of prokaryotic organisms (bacteria), single-chain DNA. In eukaryotic cells, DNA is a double helix.
7. At temperatures approaching the boiling point or at an extreme pH (less than 3 or more than 10), DNA denatures (opens). If the environment is restored, DNA can re-form a double helix, called renaturation.

DNA function

DNA also has benerapa functions that can be clarified as follows:

1. The function of DNA as a cell inherited material
DNA or deoxyribonucleic acid is a substance that can be inherited in all cells. The exact DNA replicates (multiplying) during each generation of cells.
At the time of cell division, copies identical to parental DNA are distributed to each child cell. Thus, DNA provides instruction for all future generations of single cells and whole multicellular organisms.

2. The function of DNA in controlling cell activity
DNA in controlling cell activity is done by determining the synthesis of enzymes and other proteins.
As is well known, proteins are a class of molecules with the greatest variety of cellular functionalities, proteins serve as catalysts and regulate metabolic reactions, provide raw materials for cell structure, and enable movement, interact with other environments and cells, and control cell growth and division.

3. The function of DNA as a collection of information units
The gene, which is a fragment of functional fragments in DNA, functions in determining the amino acid sequence of a protein. Many genes, whether thousands or millions of different genes are needed to make all the important proteins in a cell.

DNA structure

Broadly speaking, the characteristics of DNA structure are double helices composed of nitrogen bases Adenine, Guanin, Timin and Cytosine, and are polymers of nucleotide monomers (phosphate - deoxyribose sugars - nitrogenous bases).

The DNA structure is a double helix composed of two interconnected polynucleotide strands by a weak hydrogen bond. The hydrogen bond is formed between two nitrogen, purine and pyrimidine bases, which are paired together. Adenine (purine base) is paired with thymine (pyrimidine base) connected to the double bond, while Guanin (purine base) is paired with cytosine (pyrimidine base) connected to triplicate.

Here are the molecular structures of Adenin and Guanin, and Timin and Cytosine.

credit

The nitrogen base is connected to a deoxyribose sugar in the DNA backbone. The deoxyribose sugar is a modification of the ribose sugar, a sugar with 5 carbon atoms, in which the number 2 carbon atom loses its oxygen atom. Therefore, the sugar is called de-oxy which means loss of oxygen.

Here is the deoxyribose sugar structure found in the molecular structure of DNA:

credit

In the DNA backbone chain, deoxyribose sugar is then connected to a phosphate group, precisely on the number 5 carbon atom of deoxyribose sugar, as shown below:

credit

Thus, the three components are nitrogenous bases, deoxyribose sugars and phosphate groups forming a molecule which is then called Nucleotides. In addition to nucleotides, we also recognize the term nucleoside, which lies the difference between nucleoside and nucleotide is the presence or absence of phosphate groups. If the phosphate group is removed, it is called nucleoside. Thus, nucleotides are a combination of nucleosides plus phosphate groups. The combination of various nucleotides will form a polymer called polynucleotide.

Here is the structure of Nucleotides and Polynucleotides in the structure of DNA:

credit

And the polymer is formed by the bonding that occurs between the phosphate group on one nucleotide with deoxyribose sugar in the nearby nucleotide. The bonding occurs precisely between the phosphate group and the number 3 carbon at the deoxyribose sugar. The bond is called the phosphodiester bond.

credit

Finally, the formed polinucleotides have a direction, which is actually known as polarity, ie from 5 to 3 or from top to bottom. Figures 5 and 3 are actually numbers on the numbering of carbon atoms in deoxyribose sugars.

Structure of DNA Helix

From the above structure, two different Polyukoototes are joined together and connected to the hydrogen bonds (weak) between two nitrogenous bases in which the purine base is paired with a pyrimidine base to form a double helical structure called a helical DNA structure. So, here's a picture of a double helical DNA structure:

credit

DNA replication

The process of DNA replication is a complex problem, and involves a series of proteins and enzymes that collectively assemble nucleotides in a predetermined order. In response to the molecular signals received during cell division, these molecules replicate DNA, and synthesize two new strands using existing strands as templates or 'prints'. Each produces two, identical DNA molecules composed of one new strand and one of the old DNA.

Therefore the process of DNA replication is referred to as semi-conservative. The sequence of events occurring during prokaryotic DNA replication has been described in several replications below.

1. Initiation

credit
DNA replication begins at a specific location called the origin of replication, which has a specific sequence that can be recognized by proteins called DNA initiators. They bind the DNA molecules at the origin, thus loosening up for the assembly of other proteins and enzymes essential for DNA replication. An enzyme called a helicase is recruited to a location for the unwinding of a helical in a single groove.

Helicase releases hydrogen bonds between base pairs in an energy-dependent fashion. This point or region of DNA now known as a replication fork (Replication or replication fork is a structure that is formed when the DNA replicates). After the open helix, a protein called a single strand binds the protein (SSB) binds the open area and prevents them from sticking back. The replication process is thus initiated, and the replication fork is continued in two opposite directions along the DNA molecule.

2. Primary Synthesis

credit

Primary Synthesis / New Synthesis, complementary strands of DNA use existing strands as templates carried by enzymes known as DNA polymerases. In addition to replication they also play an important role in DNA repair and recombination.

However, DNA polymerase can not initiate DNA synthesis independently, and requires 3 'hydroxyl groups to begin the addition of complementary nucleotides. It is provided by an enzyme called DNA primase which is a type of DNA dependent-RNA polymerase. It synthesizes a short stretch of RNA to an existing DNA strand. This short segment is called a primary, and consists of 9-12 nucleotides. This gives the DNA polymerase platform necessary to begin copying a DNA strand. Once the primers are formed on both strands, the DNA polymerase can extend this primer into a new strand of DNA.

The opening of a DNA zipper can cause supercoiling (spiral-like disturbance) in the next fork area. This supercoil DNA is opened by a special enzyme called topoisomerase that binds to the front DNA strand of the replication fork. This creates a cut on the DNA strand in order to lighten the supercoil.

3. The leading strand synthesis

credit
DNA polymerase can add new nucleotides only to the 3 ends of the existing strand, and therefore can synthesize DNA in the 5 '→ 3' direction only. But the DNA strand goes in the opposite direction, and hence DNA synthesis on one strand can occur continuously. This is known as the strand of the guard (leading strand).

At this stage, DNA polymerase III (DNA pol III) recognizes 3 'OH ends of the primary RNA, and adds new complementary nucleotides. When the replication fork takes place, new nucleotides are added continuously, resulting in a new strand.

4. Synthesis of lagging Strand (left behind strand)

credit
In this opposite strand, DNA is synthesized intermittently by producing a series of small fragments of new DNA in the 5 '→ 3' direction. These fragments are called Okazaki fragments, which then combine to form a continuous chain of nucleotides. This strand is known as the lagging Strand since the DNA synthesis process on this strand results at a lower level.

Here, primase adds primers in some places along the open strand. DNA pol III lengthens the primer by adding new nucleotides, and falls when it encounters previously formed fragments. Thus, it is necessary to release the DNA strand, then shift further to the top to begin another RNA primary expansion. A sliding clip holds the DNA in its place as it moves through the replication process.

5. Primary Removal

credit
Even if a new DNA strand has been synthesized the primary RNA present on the newly formed strand has to be replaced by DNA. This activity is carried out by DNA polymerase I (DNA pol I) enzyme. It specifically eliminates RNA primers through its '5 → 3' exonuclear activity, and replaces them with new deoxyribonucleotides with 5 '→ 3' DNA polymerase activity.

6. Ligation

credit
And after the removal of the finished primaries the left strand still contains a gap between the adjacent Okazaki fragments. The ligase enzyme identifies and clogs the gap by creating a phosphodiester bond between the adjacent 5 'phosphate and 3' hydroxyl groups of fragments.

7. Termination (disconnection)

credit
This replication stops at a special termination site consisting of a unique sequence of nucleotides. This sequence is identified by a special protein called tus that binds to the site, thus physically blocking the helicase lane. When the helicase meets the tus protein it falls along with the single strand of the nearest binding protein.

That's more or less the discussion of DNA, this is STEM Science that is taught when we are in high school. Hopefully this science is useful for myself and for you who read it.

Reference:

http://www.belajarbiologi.com/2015/04/belajar-biologi-fungsi-dna.html
http://hedisasrawan.blogspot.com
http://www.artikelmateri.com/2016/08/dna-adalah-pengertian-struktur-fungsi-sifat-replikasi.html
http://informasitips.com/struktur-dna-bentuk-komposisi-gambar-dan-penemunya
http://www.sridianti.com/tahap-proses-replikasi-dna-7-langkah.html