Download REPLICATION A DNA molecule separates into two template strands

REPLICATION
A DNA molecule separates into two
template strands. New nucleotides align
with and bind to the nucleotides of the
existing strands forming two DNA molecules
that are identical to the original DNA
molecule.
The DNA polymerase needs to know what it
has to copy.
Replication takes place during the S process
of cell’s cycle.
TRANSCRIPTION AND TRANSLATION
DNA in the cell nucleus carries a genetic code, which consists of sequences of adenine (A),
thymine (T), guanine (G), and cytosine (C) (Figure 1). RNA contains uracil (U) instead of
thymine.
To make RNA, DNA pairs its bases with those of the “free” nucleotides located in the nucleous
(Figure 2).
Messenger RNA (mRNA) then travels to the ribosomes in the cell cytoplasm, where protein
synthesis occurs (Figure 3).
mRNA pairs with triplets of nucleotides from tRNA (for example, U, G and C pair with adenine,
cytosine and guanine) to create an amino acid. A chain of amino acids synthesize a protein,
which is released to perform its task in the cell or elsewhere in the body.
SEVERO OCHOA
He was a scientist who discovered the polynucleotide-phospgorilase in
1955. This enzyme synthesizes (builds) the RNA messenger (mRNA) in the
nucleous of a cell. The mRNA is in charge of the synthesis of proteins of
the cell.
Thanks to this discovery he could create, for the first time, ARN molecules
taking its basic components, the nucleotides. A year later, one of his
students will synthesise DNA using this enzyme, whose name was
changed to ARN polimerase. Both of them received the Nobel Prize in
Physiology and Medicine in 1959.
The enzyme has very important for scientists, which could understand
and re-create translation, the process in which the hereditary information
contained in genes is translated with the help of RNA mediators, and be transformed into
enzymes that determine the functions and character of each cell.
DNA FORENSIS
In a crime scene you can found DNA in blood, semen, saliva, hair… Extracted DNA is compared
to suspects DNA, taken from blood. DNA profile analysis study the polymorphic (exclusive in
each human) regions of human DNA.
Restriction enzymes (endonuclease) cut DNA into pieces of different specific lengths. This
length depends on the code of the enzyme and DNA (because it is different for every person).
Then they are poured in the agarose gel, which has a positive and a negative charged side. As
they are polarized (they are negative due to the phosphate in the backbone), they move
towards the positive side. The ones that are shorted run faster and reach farther distances.
DNAs are denatured (the helix of DNA are unzipped) while still in the agarose gel by
submerging it in a basic solution. Single strands of DNA, they are stacked to a nylon
membrane. Then, probes (a single locus probe is a DNA or RNA sequence that is able to
hybridize) are added. The DNA strands form duplex formations by paring themselves with this
probe sequences.
These hybrids are incubated in a radioactive solution.
When they join, the nylon is cleaned. The unbound probe
is washed away, so that the only radioactivity remaining in
the membrane is associated with the target DNA.
The washed nylon is placed next to a sheet of X-ray film in
a light container. The X-Ray film records the locations of
radioactive decay. Results can be compared now.
PCR (POLIMERASE CHAIN REACTION)
A technique used to make numerous of copies of a specific segment of DNA quickly
and accurately. A machine designed to carry out PCR reactions can complete many
rounds of replication, producing billions of copies of a DNA fragment, in only a few
hours. The polymerase chain reaction enables investigators to obtain the large quantities
of DNA that are required for various experiments and applications in molecular
biology, forensic analysis, evolutionary biology, and medical diagnostics.
The PCR technique is based on the natural processes a cell uses to replicate a new DNA
strand. Only a few biological ingredients are needed for PCR. The discovery of a heatstable DNA polymerase called Taq, an enzyme isolated from the thermophilic
bacterium Thermus aquaticus, which inhabits hot springs made it able to make PCR,
because it is stable at high temperatures. The most important component is the template
DNA, the DNA that contains the region to be copied, such as a gene. The only
information needed for this fragment to be replicated is the sequence of two short
regions of nucleotides (the subunits of DNA) at either end of the region of interest.
These two short template sequences must be known so that two primers—short
stretches of nucleotides that correspond to the template sequences—can be
synthesized. The primers bind to the template at their complementary sites and
serve as the starting point for copying. Also needed are free nucleotides used to build
the new DNA strands and a DNA polymerase, an enzyme that does the building by
sequentially adding on free nucleotides according to the instructions of the template.
The process is the following: PCR is a three-step process that is carried out in repeated
cycles. The initial step is the denaturation or separation, of the two strands of the
DNA molecule. This is accomplished by heating the starting material to temperatures of
about 95° C (203° F). Each strand is a template on which a new strand is built. In
the second step the temperature is reduced to about 55° C (131° F) so that the primers
can anneal to the template. In the third step the temperature is raised to about 72° C
(162° F), and the DNA polymerase begins adding nucleotides onto the ends of the
annealed primers. At the end of the cycle, which lasts about five minutes, the
temperature is raised and the process begins again. The number of copies doubles
after each cycle. Usually 25 to 30 cycles produce a sufficient amount of DNA.