Ribosome by kk sahu sir

RIBOSOMES
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2
CONTENTS
 INTRODUCTION
 HISTORY
 TYPES OF RIBOSOMES:
► 70S
► 80S
 ULTRASTRUCTURE OF 70 & 80S RIBOSOME
 CHEMICAL COMPOSITION
 FUNCTION OF RIBOSOME
 CONCLUSION
 REFERENCES

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INTRODUCTION
 Ribosome is a complex molecular machine
found within all living cells,that serves as the
site of biological protein synthesis.
 A ribosome is made out of RNA and
proteins, and each ribosome consists of two
separate RNA-Protein complexes, known as
the Small and Large subunits.

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DISCOVERY
 A. CLAUDE (1941), first observed and
called them as microsomes which were
actually fragments of RER.
 ROBINSON & BROWN (1953), first
discovered ribosomes, in plant cells(roots of
vicia)
 PALADE(1958), coined the term Ribosome.

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TYPES OF RIBOSOMES
 On the basis of sedimentation coefficient,
ribosomes are of two types:
(A) 70S Ribosome:
►Found in Prokaryotes.
(B) 80S Ribosome:
►Found in Eukaryotes

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DISTRIBUTION OF RIBOSOMES
 The ribosomes are present in both Prokaryotic and
eukaryotic cells.
Prokaryotic Cells
►Ribosomes are found freely scattered in the
cytoplasm.
Eukaryotic Cells
►Ribosomes are found freely in cytoplasm matrix
and also attached to outer surface of the Rough
endoplasmic reticulum (RER) and Nuclear
envelope (NE).
►Ribosomes are also found in the matrix of
Mitochondria and the stroma of plastid.

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NUMBER OF RIBOSOMES
►The fact that cells typically contain many ribosomes
reflects the central importance of protein synthesis
in cell metabolism.
For example:
►In E.coli there are about 20,000 ribosomes which
account for approximately 25% of the dry weight of
the cell whereas rapidly growing mammalian cells
contain about 10 million ribosomes.

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TYPES OF
RIBOSOME

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These types of ribosomes are found in prokaryotic
cells such as Bacteria and Cyanobacteria,
Mitochondria and Chloroplast of Eukaryotic cells.
70S

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 They are larger in size than 70S ribosome. It
is also made up of two subunits (smaller 40S
and larger 60S)
80S

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ULTRASTRUCTURE OF 70S RIBOSOME
 Ribosome is a membraneless organelle which is formed of larger 50S
and smaller 30S subunits.
► Dome shaped,140-160Â in size formed of a central protuberance, a ridge,
a stalk. A valley between central protuberance and ridge.
► It has two binding sites Peptidyl or P-Site and Aminoacyl or A Site.
► It consists of about 33 different proteins a 23SrRNA sequence of about
2900 nucleotides and a 5SrRNA sequence of about 120 nucleotides.
50S

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http://science.sciencemag.org/content/289/5481/920.full

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The latest and most acceptable model based on
electron microscopy was given by J.A. Lake
(Scientific American, February, 1981)

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 Oval shaped,90-110Â in size formed of a
platform,head & base or body, head and platform
are separated by a cleft.
 Cleft is a site of codon-anticodon interaction and a
binding site for initiation factor.
 It consist of about 21 different proteins and a
sequence 16S rRNA sequence of about 1500
nucleotide.
30S

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http://www.pnas.org/content/101/35/12893

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Ultrastructure of 80S ribosome
 They are larger than 70S ribosomes.
 Sedimentation coefficient-80S and molecular
weight is 4.2×106 daltons.
 The two subunits association and dissociation
depends upon Mg2+ ion concentration.
80S

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CHEMICAL COMPOSITION
 Ribosome consists of 60-65% Rrna Ribosomal protein (35-
40%).There is no lipid content in ribosomes.
 In all, 21 proteins were isolated in smaller subunit (30S)
of E. coli ribosome. These are designated as SI to S21.
 Similarly, in larger subunit (50S) of E. coli ribosome, 31
different proteins are designated as LI to L34 (due to early
misassignment, these are not designated LI to L31).
 50S Subunit- 23S rRNA, 5S rRNA
 30S Subunit- 16SrRNA
70S

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 In eukaryotes, however, there are 33 proteins in the
smaller subunit (40S) and 45 proteins in larger
subunit (60S).
 60S Subunit- 28S rRNA, 5S rRNA, 5.8S rRNA
 40S Subunit- 18S rRNA
80S

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SITES OF RIBOSOME
 Ribosome contains 3
discrete sites:
(i) Peptidyl site
(P site)
(ii) Aminoacyl site
(A site)
(iii) Exit site
(E site)

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FUNCTION OF RIBOSOMES
 As protein factories: The ribosomes are the site of protein
synthesis and also provide necessary enzyme for translation.
 Free and attached ribosomes: free ribosomes synthesize
structural and enzymatic proteins for use inside the cell.the
attached ribosomes synthesise protein for transport.

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 mRNA: Ribosomes has tunnel for mRNA so
that it can be translated properly.
 Enzymes and Factors: ribosomes provide
enzymes(peptidyl transferase) and factors for
condensation of Amino acids to form
polypeptide.
 rRNA: ribosomes contain rRNAs for
providing attachment points to mRNA and
tRNA.

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 All the following sites has ribosomes except
a) nucleus
b) mitochondrion
c) chloroplast
d) cytoplasm
Ans a
 2. Ribosomes are present in
a) Eukaryotes only
b) Eukaryotes and prokaryotes
c) Prokaryotes only
d) Eukaryotes, prokaryotes and viruses
Ans b
3. In 70S ribosomes, ‘S’ stands for
a) SI unit
b) Solubility factor
c) Svedberg unit
d) all of these
Ans c
 4. 80 S ribosomes occur in
a) Eukaryotic cells of animals
b) Eukaryotic cells of animals and plants
c) Both Eukaryotic cells and prokaryotic cells
d) all of these
Ans b

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 5. The subunits of 80S ribosome include
a) 40S and 50S
b) 30S and 50S
c) 40S and 60S
d) 20S and 60S
Ans c
 6. Which of the following ions are required for binding of ribosomal subunits
a) Na+
b) Mg++
c) Mn++
d) Fe++
Ans b
 7. 70S ribosome occur in
a) viruses
b) prokaryotes
c) prokaryotes and eukaryotic plant cells
d) All of these
Ans b
 8. The larger and smaller subunit of 70S ribosome is
a) 50S and 30S
b) 30S and 40S
c) 40S and 20S
d) 20S and 50S
Ans a

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 9. Ribosomes are made up of
a) RNA only
b) RNA and proteins
c) RNA, DNA and proteins
d) Nucleic acids, proteins and lipids
Ans b
 10. Polysomes are
a) multiple units of ribosomes
b) attachment of many ribosomes to a common mRNA
c) attachment of many mRNA to a common ribosomes
d) lysosomal aggregations
Ans b
 11. The rRNA subunits of 70S ribosome are
a) 23S in larger 50S ribosomal subunit and 16S and 5S rRNA in smaller 30S ribosomal subunit
b) 23S and 5S in larger 50S ribosomal subunit and 16S rRNA and 5S in smaller 30S ribosomal
subunit
c) 28S and 5S in larger 50S ribosomal subunit and 16S rRNA in smaller 30S ribosomal subunit
d)23S and 5S in larger 50S ribosomal subunit and 16S rRNA in smaller 30S ribosomal subunit
Ans d
 12. Chloramphenicol inhibits
a) bacterial ribosomes
b) plant ribosomes
c) both a and b
d) animal ribosomes
Ans a

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REFERENCES
 .
https://byjus.com/biology/ribosomes/

Ribosome by kk sahu sir

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