A. UNDERSTANDING THE DEFINITION OF DNA
DNA or Deoxyribonucleic Acid is a repository of
genetic information that carry information that can be derived. Inside the
cell, DNA is one of two types of nucleic acids that are important for the body.
Analogous double helix DNA is a polymer composed of nucleotides, each
nucleotide consists of three components: a nitrogenous base, a pentose sugar or
deoxyribose and a phosphate group. Each person has a unique DNA. DNA can be
found in the cell nucleus and in mitochondria. Inside the cell nucleus, strands
of DNA form a unity called chromosomes. DNA contained in the chromosomes. Every
normal human cells have 46 chromosomes consisting of 22 pairs of somatic
chromosomes and one pair of sex chromosomes. One human cell have an estimated
50,000 to 100,000 genes that are two times more than the bacteria in general.
 |
| DNA |
In prokaryotes, the DNA is not separated from other
cell components. In eukaryotes, DNA binds to the protein, forming a complex
component called chromatin.
Less than 0.1% of the total DNA contained in the
mitochondria within cells. The genetic information encoded by mitochondrial
less than 20,000 base pairs of DNA. Genetic information in the human haploid
chromosome encoded by approximately 3 x 109 (3 billion) alkali to 40,000 pairs
of genes. DNA and protein synthesis in the mitochondrial system is more or less
similar to the bacterial system, where there is no membrane that covers the
organelle.
DNA can replicate and multiplies, it will happen in
cell division process, so that each new cell will have the same DNA as the old
cell.
B. THE CHARACTERISTICS OF DNA
The following illustrates the characteristics of DNA:
- In the living body, the number of alkali that make up DNA has a different sequence and length
- The number A equal to the number of T and G equals C.
- It is the Molecules of life
- Nitrogen consist alkaline purines (A and G) as well as alkaline Pyrimidines (S and T)
- Nucleotides formed of bonds between the sugar, phosphate, and nitrogenous bases. Nucleotides play a role in a large number of biochemical processes.
C. THE FUNCTIONS OF DNA
Here are some of the functions of DNA:
DNA can be inherited (genetic) in all cells, DNA
accurately replicates for each cell generation. When a cell divides, a copy of
which is identical to the parental DNA distributed to each daughter cell. DNA
provides instructions for all future generations of a single cell and whole
multicellular organisms.
DNA controls cell activity, determine the synthesis
of enzymes and other proteins. catalyze proteins and regulate metabolic
reactions, provide the raw material for the cell structure, allowing the
movement of the cell, interacting with the environment and other cells, and
control cell growth.
Genes are units of information in DNA, each gene
determines the amino acid sequence of a particular protein, Carries a gene that
contains the information that determines the type of protein to be synthesized,
when the cell types where and how much the amount of protein to be synthesized.
Thousands to millions of different genes required to make all the proteins that
are important in a cell.
- As an autocatalyst or ability to replicate itself
- As a Hetero Catalyst or the ability to synthesize other compounds
- Forming RNA for genetic continuity processes in the living body
D. THE STRUCTURE OF DNA
The discovery of the double helix structure of DNA by
James Watson and Crick (1953) has opened up the meaning of replication,
transcription and translation of genes. DNA included in a class of organic
molecules called nucleic acids. Nucleotides are interconnected by a
phosphodiester bond between a nucleotide phosphate and sugar in the next
nucleotide. Each nucleotide consists of three groups of molecules, namely:
- 5-carbon sugar (2-deoxyribose)
- Nitrogen bases which consists of four different types, class purine adenine (adenine A) and guanine (G guanini), and members of the pyrimidine, which are cytosine (cytosine C) and thymine (thymine T)
- Phosphate group, which is bound to the carbon-5 deosiriboksa.
Sugar and phosphate alternately form the
"backbone" long chain like nucleotide called polynucleotide. Both
ends of polynucleotides differ from each other making it a polar molecule. The
ends are designed according to the number of carbon on the sugar. Phosphate
groups at the 5 and the hydroxyl group at the 3.
 |
| DNA STRUCTURE |
In 1953, Frances Crick and James Watson discovered a
molecular model of DNA as a double-stranded helical structure, or better known
as the Watson-Crick double helix. DNA is a polynucleotide macromolecule polymer
composed of repeated nucleotides, double structured, forming double helix DNA
and consists of a pair of polynucleotides and twisting to the right.
The structure resembles a rope ladder with sugar
phosphate as its backbone formed "the ladder" and the alkali pairs
form the " rigid rungs". DNA molecules are twisted to form a helix
with 10 bases each helix bend.
Both strands of the DNA molecule paired with
complementary alkali pairs (resulting from the formation of hydrogen bonds
between specific pairs). Each nucleotide in one strand pairs with a specific nucleotides
(complementary) on the other strands.
variation of DNA found in a linear sequence of base
pairs in the whole molecule. Amazing circuit formed in DNA molecules whose
length can reach thousands to millions of base pairs. The structure of nucleic
acids stabilized by sugar-phosphate chains, base pairing, base stacking
(hydrophobic) and ionic interactions.
E. DNA REPLICATION
Replication is the event of DNA synthesis.
Replication or mold (identical copies) is a key feature of DNA. Each DNA
molecule provides the mold itself to replicate. Each strand serves as a
template for synthesizing a new complementary DNA strand. An enzyme called DNA
polymerase synthesizes DNA nucleotides conect each new pair to the end of the
third strand of DNA that is growing.
At each DNA molecule children, the parental DNA
strand (old) was retained to pair with the newly synthesized strand. Such
replication pattern refers to a pattern semiconservatively. Instead, this
pattern will produce entirely new DNA molecules. DNA replication is very fast
and accurate. It is estimated that about 500 nucleotides replicated every
second and it is estimated there is an error in one billion base pairs (bp). This
is amazing considering the size of the eukaryotic genome (about 3 billion bp
DNA) within a cell nucleus.
When a cell divides by mitosis, each new product
contains Full DNA and are identical to the parent. Thus, the DNA must be
accurately replicated before division begins. DNA replication can occur with
the synthesis of new nucleotide chains of nucleotides long chain. Base pair
complementation process generates a new DNA molecule that has the same length
as DNA template. The possibility of replication can be done via three models.
- The first model is a conservative model, namely two long DNA chain remain unchanged, serves as a template for two new DNA chains.
- The second model is called Semiconservative models, two separate long DNA chain and new chain synthesized with the principles of complementation in each of the long DNA chain.
- The third model is the model dispersive, that some parts of the long DNA chain used sebgai template for the synthesis of new DNA chain.
Below is an illustration of DNA replication that
occurs:
 |
| TYPES OF DNA REPLICATION |
The Semiconservative mode is the best model for DNA
replication process. This replication can be done by all organism, prokaryotic or
eukaryotic. Replication differences between prokaryotes to eukaryotes is depend
on the type and amount of enzyme that is involved, as well as the speed and
complexity of the Replication process. In eukaryotic organisms, replication
events occur before the mitotic division, precisely in the synthesis phase of
the cell division cycle.
The mechanism of DNA replication was first observed
in a bacterium Escherichia coli. A similar process occurs in eukaryotes.
Replication begins when specific proteins recognize and bind to a spesific site
in chromosomes called a replication source. There are many sources of linear
eukaryotic chromosomes. Replication runs on the structure of the replication
fork. Each fork moving in one direction. Some processes keep going at the
replication fork. Mounting bases with strands of mold parental determine the
nucleotide sequence of each new strand DNA. Complementary nucleotide linked to
the 3 'end of the new strand by a DNA polymerase molecule, which moves along
the mold. Thus, the new DNA are always synthesized in the 5 to 3. Elongation
their continuous replication fork, a new strand extended continuously in the direction
5 to 3 forks move. It is called directional strand synthesis.
Lagging strand synthesis illustrate the mechanism of
discontinuous elongation, occurs in the unfocused template strand. Because the
template strand is antiparallel, a new strand will be formed on the direction of 3 to 5 which is not the direction determiner.
 |
| DNA REPLICATION |
There are several important enzymes involved in DNA
replication, namely:
1. Complex Replication
Enzymes
The replication process involves a lot of different
enzymes. Replication complex is formed when a miraculous different enzymes join
the DNA polymerase.
2. The enzyme
in the replication fork:
- DNA helicase, release the parental DNA strands and the replication complex
- Single strand binding protein, binds to a separate parental reinforced or repaired
- RNA primase, start the de novo synthesis of each fragment pkazaki on the lagging strand. Primase synthesizes short primer RNA that is complementary to the DNA template newly displayed. RNA primer provides the necessary “3 end” so that DNA polymerase can start adding DNA nucleotides
3. Exonuclease,
between the RNA primer serves rid fragment
4. DNA ligase,
serves to combine fragments okazaki each other to extend the new DNA strand.
