UNIT-I
Protein Synthesis
R.KAVITHA,M.PHARM
LECTURER
DEPARTMENT OF PHARMACEUTICS
SRM COLLEGE OF PHARMACY
SRM UNIVERSIYT
KATTANKULATUR
Why Protein is so important?
• It is the essential structural part of every cell
• It controls every biological process in the form of enzymes
• How they are synthesised???
• The production of a protein molecule by a cell is the result of a two part process. Transcription
Translation
The transfer of genetic information from DNA to mRNA is known as transcription.
DNA is transcribed to mRNA in the nucleus
and mRNA is translated into Protein in the
cytoplasm
Transcription
The first part of the process, called
transcription, occurs in the nucleus and
involves messenger RNA (mRNA) being
produced that is complementary to a
specific DNA sequence
Translation
The second part of the process, called translation,
occurs in the cytoplasm and results in the synthesis
of a specific protein molecule from the genetic
information carried by the mRNA.
Transcription –
Components
1.
2.
3.
A template Activated precursors RNA polymerase
A template
Usually a double stranded DNA out of the two strands, only one strand is transcribed.
Activated precursors
• Four ribonucleoside triphosphates
RNA polymerase
The robonucleoside triphosphates are joined together by the enzyme
RNA polymerase
with the elimination of pyrophosphate (PPi)
RNA polymerase
• RNA Polymerase consists of a core enzyme and a σ (sigma factor). The core enzyme consists of four peptide chains, α , β, β, ώ
• The enzyme itself is ineffective in transcribing DNA strands. • When combines with σ factor it is enable to transcribe the sense strand
RNA polymerase
RNA Polymerase
The Process
• 1. Initiation
• 2. Elongation
• 3. Termination
Initiation
• The start signals on DNA are called promoters.
• All promoters are AT rich regions, situated about 10
bases before the initiation site. This region has a
common sequence of TATAATG and commonly
known as TATA Box.
• The σ factor recognizes the start signal on DNA and
it directs the binding of the enzyme to the promoter
region of DNA.
Initiation
• The start of transcription takes place at the initiation site which consists of one to two bases .
• The binding of RNA polymerase to DNA results in local unwinding of DNA double helix. • A short segment of DNA now opens up. Synthesis of mRNA begins on one of the two strands of ds DNA. • The first base in RNA is always a purine either G or A.
INITIATION
Elongation
• Chain elongation takes place by addition of activated ribonucleoside triphosphates. ( ATP, UTP,GTP, CTP).
• For each nucleotide added to the growing RNA chain, a pyrophosphate is given off. This is rapidly hydrolysed to inorganic phosphate (Pi). • Elongation takes place in 5’ 3’ direction.
Elongation
Elongation
• Elongation of RNA chains takes place by means of the core enzyme, which moves along the DNA template.
• After commencement of chain elongation, the sigma factor dissociates from the core enzyme and can be reused.
Termination
• RNA synthesis can be terminated by two types of mechanisms. • In the first type RNA polymerase reads an extended poly(A) sequence on DNA, resulting in an RNA transcript with a terminal poly U sequence. • In the second type termination factor or rho factor causes the release of transcribed RNA molecules
Rho independent
termination
Termination
Connecting Concepts
The Basic Rules of Transcription
let’s pause to summarize some of the general
principles
of bacterial transcription.
The Basic Rules of
Transcription
• 1. Transcription is a selective process;
only certain parts of the DNA are
transcribed.
• 2. RNA is transcribed from single-stranded
DNA.Normally, only one of the two DNA
strands—the template strand—is copied
into RNA.
The Basic Rules of
Transcription
• 3. Ribonucleoside triphosphates are used
as the substrates in RNA synthesis. Two
phosphates
are
cleaved
from
a
ribonucleoside triphosphate, and the
resulting nucleotide is joined to the 3’-OH
group of the growing RNA strand.
The Basic Rules of
Transcription
• 4. RNA molecules are antiparallel and
complementary to the DNA template strand.
Transcription is always in the 5’ 3’ direction,
meaning that the RNA molecule grows at the
3’ end.
The Basic Rules of
Transcription
• 5.
Transcription
depends
on
RNA
polymerase—a complex, multimeric enzyme.
RNA polymerase consists of a core enzyme,
which is capable of synthesizing RNA, and
other subunits that may join transiently to
perform additional functions.
The Basic Rules of
Transcription
• 6. The core enzyme of RNA polymerase
requires a sigma factor in order to bind to
a promoter and initiate transcription.
The Basic Rules of
Transcription
• 7. Promoters contain short sequences
crucial in the binding of RNA polymerase
to DNA; these consensus sequences are
interspersed with nucleotides that play no
known role in transcription.
The Basic Rules of
Transcription
• 8. RNA polymerase binds to DNA at a
promoter, begins transcribing at the start
site of the gene, and ends transcription
after a terminator has been transcribed.