1. RIBOSOMES
Department of Genetics and Plant Breeding
FACULTY OF AGRICULTURE
BIRSA AGRICULTURAL UNIVERSITY
KANKE, RANCHI – 834 006 (JHARKHAND)
ANJANI KUMAR
Registration No:- A/BAU/5129/2017
Sub:- Molecular Cell Biology (MBB-503)
2. Introduction
Cell have tiny granular structures
known as ribosomes
That serve as the primary site of
biological protein synthesis
They are not membrane bounded
They are the only organelle found
in prokaryotic cell
Found in both Prokaryotes &
Eukaryotes
3. Discovery
Ribosomes were first seen in cellular
homogenates by dark-field microscopy in the
late 1930s by Albert Claude who referred to
them as “microsomes.”
First observed in the mid-1950s by Romanian-
American cell biologist George Emil Palade,
using an electron microscope, as dense
particles or granules
Ribosomes were discovered by Robinson and
Brown (1953) in plant cells and by Palade
(1955) in animal cells.
Palade (1955) also coined the term of
ribosome. Source: Ribosomes: Discovery, Occurrence and
Functions- M. Manisha
https://en.wikipedia.org
4. Number
Quantity of ribosomes vary depend upon
the type of cell e.g.,
Escherichia coli = 20,000
Yeast= 200000
Quantity depends upon the physiological
ability of cell to produce proteins
6. Origin
In prokaryotes Completely cytoplasmic
23S,16S & 5S rRNA are transcribed by
specific segments of nucleoid.
23S & 5S rRNA associates with cytoplasmic
proteins to form 50S subunit.
16S rRNA alongwith their proteins
form 30S subunit.
In eukaryotes Partly nucleolar & partly cytoplasmic in origin
Nucleolar organising region transcribes 45S nucleolar RNA
(precursor of 5.8,28,18S rRNAs)
5S rRNA is transcribed from the r-DNA lying adjacent to NOR.
7. On the basis of location ribosomes are
divided into two types:
Free ribosomes
Bounded ribosomes
Types
On the basis of sedimentation coefficient,
ribosomes are of two types:
70S Ribosomes:
80S Ribosomes:
Found in prokaryotes
Found in cytoplasm of eukaryotes
8. Free Ribosomes
These ribosomes are found freely dispersed in the cytosol
They are involved in the synthesis of proteins that work inside the
cytosol
They vary in number depending upon the functionality of the cell types
and its need to synthesize proteins
Bounded Ribosomes
They are found attached to the surface of Endoplasmic reticulum making
them “Rough Endoplasmic Reticulum”
The proteins assembled in these ribosomes are either transported to the outside of
the cell or are included in the cell membrane
Contd…
9. Structure
A ribosome has two main constituent elements
Protein = 25-40%
RNA = 37-62%
Two main subunits are present i.e.,
A larger subunit
A smaller subunit
10. Various Component of 70S & 80S Ribosomal Subunit
Ribosome Sources Whole Ribosome Small Subunit Large Subunit
Prokaryote 70S 30S (16S rRNA
+ 21Protein)
50S (23S & 5S
rRNA +
34Protein)
Eukaryote 80S 40S (18S rRNA+
30 Protein)
60S (28S,5.8S &
5S rRNA + 40
Protein)
(Source: De Robertis & De Robertise, Jr. 1987)
Cell and Molecular Biology
11. Svedberg Unit (S)
The large and small subunit of ribosome are
named according to the velocity of
sedimentation when subjected to centrifugal
forces
The unit used to measure sedimentation
velocity is Svedberg(S)
Named after inventor of ultracentrifuge
Theodor Sevdberg
The sedimentation velocity is a function of a
particles molecular weight, size, volume and
shape
13. The large and small subunits undergo association and
dissociation during each cycle of translation
14. Views of 3-D structure of the ribosome including three bound tRNAs
15. Each mRNA can be translated simultaneously by multiple
ribosomes
16. Domains of Ribosomes
There are two domains of Ribosomes
Translational Domain
The region responsible for translation is called the
Translational domain
Both subunits contribute to this domain, located in
the upper half of the small subunit and in the
associated areas of the large subunit
Exit Domain
The growing peptide chain emerges from
the large subunit at the exit domain
This is located on the side of the subunit
https://www.google.co.in
18. Function
Translation of genetic information encoded in nucleotide bases
of DNA into amino acid sequence of proteins
This is also known as “gene expression”
Translation
The two ribosomal subunits join to translate the mRNA into proteins
Steps
Initiation
Elongation
Termination
21. The Nobel Prize in Chemistry 2009
"for studies of the structure and function of the ribosome"
Venkatraman Ramakrishnan
1/3 of the prize
United Kingdom
Thomas A. Steitz
1/3 of the prize
USA
Ada E. Yonath
1/3 of the prize
Israel
Weizmann
Institute of
Science
Rehovot, Israel
MRC Laboratory of
Molecular Biology
Cambridge, United
Kingdom
Yale University New
Haven, CT, USA; Howard
Hughes Medical
Institute