protein synthesis in prokaryotes.

1. SUBMITTED TO
MR.M.SURYANARAYANA SIR.
PRESENTED BY:
AKKI YAMUNASRIVALLI
PHARM-D 1ST YR
ROLL NO: 13
BROWNS COLLAGE OF
PARMACY.

2.  The conventional concept of the central dogma of
life which in essence is “DNA makes the RNA makes
protein” i.e. DNA undergoes self replication and then
transforms to RNA which finally forms the
PROTEINS, which are the building blocks of the
body.

3. The word protein synthesis in actual sense is the
formation of the proteins. This formation of proteins
is done the involvement of 2 processes namely the
transcription and the translation.
TRANSCRIPTION: (DNA→RNA)
The genetic information stored in the DNA is
expressed through RNA.This process is regulated by
DNA.
TRANSLATION: (RNA→PROTEINS)
It is the biosynthesis of the protein or the
polypeptide chain. This process is regulated by
mRNA.

5. The “anticodon” is a codon that is
complimentary to the codon
present in the mRNA molecule.
 Single RNA strand with about
75-90 nucleotides.
 Highly specific in nature.
Carries an specific amino
acid and an anti-codon on
either sides.
 During translation, it acts as
a physical link between
mRNA and the amino acid.
 Formation of essential
codon-anticodon base pair.
Hence this is most
important the component of
the translation.

6.  The mRNA carries a
specific sequence of
nucleotides in triplets as
codons responsible for the
synthesis of a specific
protein molecule.
 The mRNA is the final
product of transcription
in prokaryotic cells which
needs no post
transcriptional
modification.
 Vital component of
translation.

7.  Present in both prokaryotes and eukaryotes.
 2 subunits: large subunit & small sub unit.
 They are associated by Mg+2.
 Sites on ribosome:
A-site =amino acyl tRNA
binding site
P-site =peptidyl tRNA
binding site
E-site =exit site
mRNA binding site
(only in small subunit)

9.  Acts as correspondence between a sequence of
nucleotide bases and a sequence of amino acids.
 Genetic information is coded as codon(3 nucleotides).
 Language of nucleotides :
Adenine (A)
Guanine (G)
Cytosine(C)
Uracil (U).
 Always written and read
from 5’ to 3’.

10.  The genetic information stored in DNA is passed on to the
RNA and ultimately expressed in the language of proteins. It
is a RNA-directed synthesis of a polypeptide chain.
 This translation process may be divided into the following
stages:
I. ACTIVATION OF AMINO ACIDS
II. INITIATION
III. ELONGATION
IV. TERMINATION
 The components required are:
a. Amino acids
b. Types of RNA
c. Protein translation factors
d. ATP and GTP.

11.  t-RNA charging.
 For the tRNA to be charged in should undergo
reactions with the tRNA charging machinery. It
involves 2 steps:
1)Adenylation of amino acid:
ATP+amino acid→ [Aminoacyl adenylic acid] +
pyrophosphate
2)Transfer of the adenylated amino acid to the trna :
Aminoacyl adenylic acid+tRNA → Aminoacyl-tRNA +
adenylic acid
The above 2 reactions are catalysed by the enzyme
named ‘AMINO-ACYL tRNA transferase”.

12. 1)A small ribosomal subunit binds to a molecule of
mRNA. In a prokaryotic cell, the mRNA binding site
on this subunit recognizes a specific nucleotide
sequence on the mRNA just upstream of the start
codon. An initiator tRNA, with the anticodon UAC,
base-pairs with the start codon, AUG. This tRNA
carries the amino acid methionine (Met).
2)The arrival of a large ribosomal subunit
completes the initiation complex. Proteins called
initiation factors (not shown) are required to bring
all the translation components together. GTP
provides the energy for the assembly. The initiator
tRNA is in the P site; the A site is available to the
tRNA bearing the next amino acid.
 30s subunit,50s subunit ,mRNA,f-met tRNA with an anti
codon(start codon),initiation factors (IF3, IF2, IF1).

13.  Requirements: Functional 70S ribosomes, Aminoacyl-tRNAs
specified by codons, Elongation factors (EF-Tu and EF-G),GTP.

14.  Requirements: Functional 70S ribosomes Termination
codon in mRNA Polypeptide release factors (R1, R2, R3)
1)When a ribosome reaches a
stop codon on mRNA, the A
site of the ribosome accepts a
protein called a release factor
instead of tRNA.
2)The release factor hydrolyzes
the bond between the tRNA in
the P site and the last amino acid
of the polypeptide chain. The
polypeptide is thus freed from the
ribosome.
3)The two ribosomal
subunits and the other
components of the
assembly dissociate.

15. An mRNA undergoing translation at various sites
by different ribosomes simultaneously(at a time).

16.  Newly formed Polypeptide chains float freely in cytoplasm, fold
spontaneously and join with other polypeptides to form the final
proteins.
 Often translation is not sufficient to make a protein functionally
active. hence they are to be modified by adding up with other
molecules such as sugars, lipids, phosphates etc.
 The changes which convert them into the active ones are the post
transitional modifications. Some of them are:
1. Trimming 7. Methylation
2. Phosphorylation 8. Carboxylation
3. Glycosylation 9. Iodination
4. Hydroxylation 10. Palmitoylation etc.
5. Disulfidebondformation
6. Proteolytic modification

17.  Chaperones are proteins that prevent faulty folding during protein
synthesis.
 These play role in the assembly &proper folding of synthesized proteins.
 They belong to large family proteins called “heat shock proteins”(HSP’s)
 They are inducible by conditions that cause unfolding of newly
synthesized proteins. (E.g.:- elevated temperature).
 They bind unfolded and aggregated proteins & show ATPase activity &
ADP, ATP which has important role in effecting folding.
 They can reversibly bind to hydrophobic regions of unfolded proteins &
folding intermediates.
 E.g. :- BIP (immunoglobin heavy chain binding protein)
 Calnexin; PDI(Protein Disulfide Isomerase)
 PPI (Peptidyl Prolyl cis – trans - Isomerase)
 Several translational factors also posses chaperone activity.They are IF-
2, EF – Tu & EF – G. They assist co-translational folding.

18.  Many antibiotics & toxins work by inhibiting protein
biosynthesis. They act at different stages of protein
biosynthesis. Usually in prokaryotes the protein
synthesis is blocked by the antibiotics but where as
in eukaryotes protein synthesis is not affected.
 Some of such inhibitors are:
1.Streptomycin 6.Diatheria toxin
2.Sparsomycin 7.Tetracycline
3.Alpha sarcin 8.Chloramphenicol
4.Erythromycin 9.Tunicamycin.
5.Puromycin

19. Any
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