2. THE PROCESS BY WHICH MRNA IS USED
TO PRODUCE PROTEINS IS KNOWN AS
TRANSLATION.
OR
TRANSLATION INVOLVES “DECODING” A
MESSENGER RNA (MRNA) AND USING ITS
INFORMATION TO BUILD A POLYPEPTIDE,
OR CHAIN OF AMINO ACIDS.
3.
4. •The protein synthesis which involves the
translation of nucleotide base sequence of
mRNA into the language of amino acid
sequence may be divided into the following
stages for the convenience of understanding :-
i)Requirement of components
ii)Activation of aminoacids
iii)Protein synthesis proper
iv) Chaperons and proteins folding
v)post-translation modification
5. COMPONENTS REQUIRED:-
• The protein synthesis may be considered as biochemical factory
operating on the ribosomes.
• As as factory it depend upon the supply of raw materials to give final
product , the protein synthesis also requires many components like:-
1}AMINO ACIDS
2}RIBOSOMES
3}MESSENGER RNA (mRNA)
4}TRANSFER RNA (tRNA)
5}PROTEIN FACTORS
6. • AMINO ACIDS
1)PROTEINS are polymers of amino acids
2)from 20 aminoacids found in protein structure half of them is synthesize by man and about 10 essential
amino acids to be provided through diet.
3) protein synthesis can occur when all the amino acids needed for protein is available and if there is
deficiency is supply of aminoacids translation stop , therefore regular dietary supply is needed.
But in prokaryotes all amino acids are synthesized from in organic components.
RIBOSOMES
• 1)They are the centres or factories for protein synthesis.
• 11) Also known as workbenches.
• iii)Ribomoses are huge complex structure – 70s prokaryotes and 80s eukaryotes.
• 1v) each ribosome has 2 subunits:- one big and one small
• v)Each ribosome has 2 sites
• A site-it is for binding aminoacyl tRNA and also acceptor site.
• P site- is for binding peptidyl tRNA and also donor site
vi)POLYRIBOSOME/polysome is used when several ribosome simultaneously translate on a single mRNA.
7. Messenger RNA
(mRNA)
1)The specific information
required for the synthesis of a
given protein is present on
mRNA.
ii) The DNA passed on
genetic information in form of
codons to mRNA to translate
into a protein sequence.
Transfer RNA(tRNA)
They carry the amino acids
and hand them over to the
growing peptide chain.
8. Both ATP
and GTP
are required
for the
supply of
energy in
protein
synthesis.
ENERGY
SOURCE
S
1)Process of translation involves
a protein factors.
11) Needed for initiation
,elongation and termination of
protein synthesis.
111)More complex in eukaryotes
than prokaryotes.
PROTEIN
FACTORS
9. THE GENETIC CODE
• In an mRNA, the instructions for building a polypeptide come in groups
of three nucleotides called codons.
• Here are some key features of codons to keep in mind as we move
forward:
i}There are 61 different codons for amino acids
Ii}Three “stop” codons mark the polypeptide as finished
Iii}One codon, AUG, is a “start” signal to kick off translation (it also
specifies the amino acid methionine)
• These relationships between mRNA codons and amino acids are known
as the genetic code
10. CODONS TO AMINO ACIDS
• In translation, the codons of an mRNA are read in order (from the 5' end to the 3' end)
by molecules called transfer RNAs, or tRNAs.
• Each tRNA has an anticodon, a set of three nucleotides that binds to a matching
mRNA codon through base pairing. The other end of the tRNA carries the amino acid
that's specified by the codon.
• tRNAs bind to mRNAs inside of a protein-and-RNA structure called the ribosome.
As tRNAs enter slots in the ribosome and
bind to codons, their amino acids are linked to the
growing polypeptide chain in a chemical reaction.
The end result is a polypeptide whose amino acid
sequence mirrors the sequence of codons in the mRNA.
11.
12. TRANSLATION PROCESS:-
• A book or movie has three basic parts: a beginning, middle, and end.
• Translation has pretty much the same three parts, but they have fancier
names: initiation, elongation, and termination.
• Initiation ("beginning"): in this stage, the ribosome gets together with
the mRNA and the first tRNA so translation can begin.
• Elongation ("middle"): in this stage, amino acids are brought to the
ribosome by tRNAs and linked together to form a chain.
• Termination ("end"): in the last stage, the finished polypeptide is
released to go and do its job in the cell.
13. • Initiation
• In order for translation to start, we need a few key ingredients. These include:
• A ribosome (which comes in two pieces, large and small)
• An mRNA with instructions for the protein we'll build
• An "initiator" tRNA carrying the first amino acid in the protein, which is almost always
methionine (Met)
• During initiation, these pieces must come together in just the right way. Together, they
form the initiation complex, the molecular setup needed to start making a new protein.
• first, the tRNA carrying methionine attaches to the small ribosomal subunit.
• Together, they bind to the 5' end of the mRNA by recognizing the 5' GTP cap (added
during processing in the nucleus). Then, they "walk" along the mRNA in the 3' direction,
stopping when they reach the start codon .
14.
15. • In bacteria, the situation is a little different. Here, the small ribosomal subunit doesn't
start at the 5' end of the mRNA and travel toward the 3' end. Instead, it attaches
directly to certain sequences in the mRNA. These Shine-Dalgarno sequences come
just before start codons and "point them out" to the ribosome.
•
16. • Why use Shine-Dalgarno sequences?
• Bacterial genes are often transcribed in groups (called operons), so one
bacterial mRNA can contain the coding sequences for several genes. A
Shine-Dalgarno sequence marks the start of each coding sequence,
letting the ribosome find the right start codon for each gene.
17. ELONGATION
• elongation is when the polypeptide chain gets longer.
• after the initiation complex has formed, but before any amino acids have been linked to make a
chain.
• Our first, methionine-carrying tRNA starts out in the middle slot of the ribosome, called the P site.
• Next to it, a fresh codon is exposed in another slot, called the A site. The A site will be the "landing
site" for the next tRNA, one whose anticodon is a perfect (complementary) match for the exposed
codon.
• Once the matching tRNA has landed in the A site, it's time for the action: that is, the formation of
the peptide bond that connects one amino acid to another. This step transfers the methionine from
the first tRNA onto the amino acid of the second tRNA in the A site.
• Once the peptide bond is formed, the mRNA is pulled onward through the ribosome by exactly one
codon. This shift allows the first, empty tRNA to drift out via the E ("exit") site. It also exposes a new
codon in the A site, so the whole cycle can repeat.
18.
19. TERMINATION
• Polypeptides, like all good things, must eventually come to an end.
• Translation ends in a process called termination.
• Termination happens when a stop codon in the mRNA (UAA, UAG, or
UGA) enters the A site.
• Stop codons are recognized by proteins called release factors, which fit
neatly into the P site (though they aren't tRNAs).
• Release factors mess with the enzyme that normally forms peptide
bonds: they make it add a water molecule to the last amino acid of the
chain.
• This reaction separates the chain from the tRNA, and the newly made
protein is released.
20. EPILOGUE: PROCESSING
• Our polypeptide now has all its amino acids—does that mean it's ready to do its job in
the cell?
• Not necessarily. Polypeptides often need some "edits.“
• During and after translation, amino acids may be chemically altered or removed. The
new polypeptide will also fold into a distinct 3D structure, and may join with other
polypeptides to make a multi-part protein.
• Many proteins are good at folding on their own, but some need helpers ("chaperones")
to keep them from sticking together incorrectly during the complex process of folding.
• Some proteins also contain special amino acid sequences that direct them to certain
parts of the cell. These sequences, often found close to the N- or C-terminus, can be
thought of as the protein’s “train ticket” to its final destination.
