azad mohammad mehdi

1. Central Dogma
Genetics lec
2E
Azad Mohammad Mehdi
,

2. DNA replication
DNA replication. The double helix is unwound
and each strand acts as a template for the next
strand. Bases are matched to synthesize the
new partner strands.
DNA replication is a biological process that
occurs in all living organisms and copies their
DNA; it is the basis for biological inheritance.
It has been suggested that Replication fork be
merged into this article or section. (Discuss)
Proposed since May 2009.

3. • In a cell, DNA replication begins at specific
locations in the genome, called "origins
Unwinding of DNA at the origin, and synthesis
of new strands, forms a replication fork. In
addition to DNA polymerase, the enzyme that
synthesizes the new DNA by adding
nucleotides matched to the template strand,
a number of other proteins are associated
with the fork and assist in the initiation and
continuation of DNA synthesis.
• . The polymerase chain reaction (PCR), a
common laboratory technique, employs such
artificial synthesis in a cyclic manner to
amplify a specific target DNA fragment from a
pool of DNA.

4. • DNA structure
• DNA usually exists as a double-stranded structure, with
both strands coiled together to form the characteristic
double-helix. Each single strand of DNA is a chain of four
types of nucleotides having the bases: adenine, cytosine,
guanine, and thymine. A nucleotide is a mono-, di-, or
triphosphate deoxyribonucleoside; that is, a deoxyribose
sugar is attached to one, two, or three phosphates.
Chemical interaction of these nucleotides forms
phosphodiester linkages, creating the phosphate-
deoxyribose backbone of the DNA double helix with the
bases pointing inward. Nucleotides (bases) are matched
between strands through hydrogen bonds to form
base pairs. Adenine pairs with thymine, and cytosine pairs
with guanine.
DNA structure

5. DNA polymerase
DNA polymerases are a family of
enzymes that carry out all forms of DNA
replication However, a DNA polymerase
can only extend an existing DNA strand
paired with a template strand; it cannot
begin the synthesis of a new strand. To
begin synthesis, a short fragment of
DNA or RNA, called a primer, must be
created and paired with the template
DNA strand.
DNA polymerase then synthesizes a
new strand of DNA by extending the 3'
end of an existing nucleotide chain,
adding new nucleotides matched to the
template strand one at a time via the
creation of phosphodiester bonds.

6. Replication process
The replication fork is a structure that forms within the
nucleus during DNA replication. It is created by helicases,
which break the hydrogen bonds holding the two DNA
strands together. The resulting structure has two
branching "prongs", each one made up of a single strand
of DNA. These two strands serve as the template for the
leading and lagging strands, which will be created as DNA
polymerase matches complementary nucleotides to the
templates; The templates may be properly referred to as
the leading strand template and the lagging strand
template.

7. Transcription (genetics)
• Transcription is the process of creating a
complementary RNA copy of a sequence of DNA.
[1]
Both RNA and DNA are nucleic acids, which
use base pairs of nucleotides as a
complementary language that can be converted
back and forth from DNA to RNA by the action of
the correct enzymes. During transcription, a DNA
sequence is read by an RNA polymerase, which
produces a complementary, antiparallel RNA
strand. As opposed to DNA replication,
transcription results in an RNA complement that
includes uracil (U) in all instances where thymine
(T) would have occurred in a DNA complement.

8. Transcription is explained easily in
4 or 5 steps, each moving like a
wave along the DNA.
• RNA Polymerase moves the transcription bubble, a stretch of unpaired
nucleotides, by breaking the hydrogen bonds between complementary
nucleotides.
• RNA Polymerase adds matching RNA nucleotides that are paired with
complementary DNA bases.
• RNA sugar-phosphate backbone forms with assistance from RNA polymerase.
• Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly
synthesized RNA strand.
• If the cell has a nucleus, the RNA is further processed (addition of a 3' poly-A
tail and a 5' cap) and exits through to the cytoplasm through the nuclear pore
complex.
• Transcription is the first step leading to gene expression. The stretch of DNA
transcribed into an RNA molecule is called a transcription unit and encodes at
least one gene. If the gene transcribed encodes a protein, the result of
transcription is messenger RNA (mRNA), which will then be used to create that
protein via the process of translation. Alternatively, the transcribed gene may
encode for either ribosomal RNA (rRNA) or transfer RNA (tRNA), other
components of the protein-assembly process, or other ribozymes]

10. As in DNA replication, DNA is read from 3' → 5' during
transcription. Meanwhile, the complementary RNA is
created from the 5' → 3' direction. This means its 5' end is
created first in base pairing. Although DNA is arranged as
two antiparallel strands in a double helix, only one of the
two DNA strands, called the template strand, is used for
transcription. This is because RNA is only single-stranded,
as opposed to double-stranded DNA. The other DNA strand
is called the coding (lagging) strand, because its sequence
is the same as the newly created RNA transcript (except
for the substitution of uracil for thymine). The use of only
the 3' → 5' strand eliminates the need for the
Okazaki fragments seen in DNA replication]
Transcription is divided into 5 stages: pre-initiation,
initiation, promoter clearance, elongation

11. Translation (biology)
In molecular biology and genetics, translation is the third stage of
protein biosynthesis (part of the overall process of gene expression). In
translation, messenger RNA (mRNA) produced by transcription is decoded by the
ribosome to produce a specific amino acid chain, or polypeptide, that will later
fold into an active protein. In Bacteria, translation occurs in the cell's cytoplasm,
where the large and small subunits of the ribosome are located, and bind to the
mRNA. In Eukaryotes, translation occurs across the membrane of the
endoplasmic reticulum in a process called vectorial synthesis. The ribosome
facilitates decoding by inducing the binding of tRNAs with complementary
anticodon sequences to that of the mRNA. The tRNAs carry specific amino acids
that are chained together into a polypeptide as the mRNA passes through and is
"read" by the ribosome in a fashion reminiscent to that of a
stock ticker and ticker tape.

12. • Translation proceeds in four phases: activation,
initiation, elongation and termination (all describing
the growth of the amino acid chain, or polypeptide that is
the product of translation). Amino acids are brought to
ribosomes and assembled into proteins.
• In activation, the correct amino acid is covalently bonded
to the correct transfer RNA (tRNA). The amino acid is
joined by its carboxyl group to the 3' OH of the tRNA by an
ester bond. When the tRNA has an amino acid linked to it,
it is termed "charged". Initiation involves the small subunit
of the ribosome binding to the 5' end of mRNA with the
help of initiation factors (IF). Termination of the
polypeptide happens when the A site of the ribosome faces
a stop codon (UAA, UAG, or UGA). No tRNA can recognize
or bind to this codon. Instead, the stop codon induces the
binding of a release factor protein that prompts the
disassembly of the entire ribosome/mRNA complex.