Ribosomes are complex cellular structures found in the cytoplasm and endoplasmic reticulum of cells that translate genetic code from messenger RNA into chains of amino acids known as proteins. They are composed of two subunits - a smaller subunit that binds to mRNA and decodes its genetic information, and a larger subunit where amino acids are added together. Ribosomes exist in both prokaryotic and eukaryotic cells, varying slightly in size between the two, and play an essential role in protein synthesis by reading mRNA sequences and assembling polypeptide chains.

1. RIBOSOME

2. RIBOSOME
Definition:
 A ribosome is a complex cellular mechanism
used to translate genetic code into chains of
amino acids.
 Long chains of amino acids fold and function
as proteins in cells.

3. FUNCTION OF A RIBOSOME:
 The function of a ribosome in any cell is to produce
proteins.
 Proteins are used in almost all cellular functions; as
catalysts they speed the time of reactions, as fibers
they provide support, and many proteins function in
specific tasks, like contracting muscle cells.
 All proteins start as deoxyribonucleic acid, or DNA.
 A special protein, RNA polymerase, is an enzyme
that recognizes sequences in the DNA, binds to
them with the help of other proteins, and creates a
new information molecule which can travel from the
nucleus to the cytosol of the cell.

4.  The strand of ribonucleic acid (RNA)
produced by RNA polymerase is processed
on its way out of the nucleus, and areas of
the RNA that do not code for proteins are
removed.
 The molecule is now known as a messenger
RNA or mRNA.
 Every mRNA is made of 4 different nucleic
bases, known as nucleic acids.
 The base pairs are “read” in series of threes,
making up codons

5.  Each codon specifies a specific amino acid.
 All life on Earth uses the same 20 amino acids,
and the codons used to call for those amino
acids are nearly universal.
 The codon that starts all proteins is “AUG”.
 This stands for the sequence of nucleic bases:
adenine, uracil, and guanine, respectively.
 A special RNA molecule that can bind to amino
acids, known as a transfer RNA or tRNA,
recognizes this sequence and binds to it.
 This particular tRNA carries a methionine amino
acid.
 Depending on the protein being built, the next
amino acid could be any one of the twenty.

6. STRUCTURE:
 Ribosomes are made of proteins and ribonucleic
acid (abbreviated as RNA), in almost equal
amounts.
 It comprises of two sections, known as subunits.
 The tinier subunit is the place the mRNA binds and
it decodes, whereas the bigger subunit is the place
the amino acids are included.
 Both subunits comprise of both ribonucleic acid and
protein components and are linked to each other by
interactions between the proteins in one subunit
and the rRNAs in the other subunit.
 The ribonucleic acid is obtained from the nucleolus,

7. The structures of ribosomes include:
 Situated in two areas of the cytoplasm.
 They are seen scattered in the cytoplasm and
a few are connected to the endoplasmic
reticulum.
 Whenever joined to the ER they are called the
rough endoplasmic reticulum.
 The free and the bound ribosomes are very
much alike in structure and are associated
with protein synthesis.
 Around 37 to 62% of rRNA is comprised of
RNA and the rest is proteins.

8.  Prokaryotes have 70S ribosomes respectively
subunits comprising the little subunit of 30S and
the bigger subunit of 50S.
 Eukaryotes have 80S ribosomes respectively
comprising of little (40S) and substantial (60S)
subunits.
 The ribosomes seen in the chloroplasts &
mitochondria of eukaryotes are comprised of big
and little subunits composed of proteins inside a
70S particle.

9.  Share a center structure which is very much
alike to all ribosomes in spite of changes in its
size.
 The RNA is arranged in different tertiary
structures.
 The RNA in the bigger ribosomes is into
numerous continuous infusions as they create
loops out of the center of the structure without
disturbing or altering it.
 The contrast between those of eukaryotic and
bacteria are utilized to make antibiotics that
can crush bacterial disease without damaging
human cells.

11. RIBOSOMES SIZE:
 Ribosomes comprise of two subunits that are
suitably composed and function as one to
translate the mRNA into a polypeptide chain
amid protein synthesis.
 Due to the fact that they are made from two
subunits of differing size, they are a little longer
in the hinge than in diameter.
 They vary in size between prokaryotic cells and
eukaryotic cells.
 The prokaryotic is comprised of a 30s
(Svedberg) subunit and a 50s (Svedberg)
subunit meaning 70s for the entire organelle
equal to the molecular weight of 2.7×106
Daltons.

12.  Prokaryotic ribosomes are about 20 nm (200
Å) in diameter and are made of 35%
ribosomal proteins and 65% rRNA.
 Not withstanding, the eukaryotic are amidst
25 and 30 nm (250–300 Å) in diameter.
 They comprise of a 40s (Svedberg) subunit
and a 60s (Svedberg) subunit which means
80s (Svedberg) for the entire organelle which
is equal to the molecular weight of 4×106
Daltons.

13. LOCATION:
 Ribosomes are organelles located inside the animal,
human cell, and plant cells.
 They are situated in the cytosol, some bound and
free-floating to the membrane of the coarse
endoplasmic reticulum.
 They are utilized in decoding DNA (deoxyribonucleic
acid) to proteins and no rRNA is forever bound to the
RER, they release or bind as directed by the kind of
protein they proceed to combine.
 In an animal or human cell, there could be up to 10
million ribosomes and numerous ribosomes can be
connected to the equivalent mRNA strand, this
structure is known as a POLYSOME.

14. ROLE IN PROTEIN SYNTHESIS:
 Even before an mRNA is translated, a cell must
invest energy to build each of its ribosomes.
 In E. coli, there are between 10,000 and 70,000
ribosomes present in each cell at any given time.
 A ribosome is a complex macromolecule composed
of structural and catalytic rRNAs, and many distinct
polypeptides.
 In eukaryotes, the nucleolus is completely specialized
for the synthesis and assembly of rRNAs.
 Ribosomes exist in the cytoplasm in prokaryotes and
in the cytoplasm and rough endoplasmic reticulum in
eukaryotes.

15.  Mitochondria and chloroplasts also have their
own ribosomes in the matrix and stroma, which
look more similar to prokaryotic ribosomes (and
have similar drug sensitivities) than the
ribosomes just outside their outer membranes in
the cytoplasm.
 Ribosomes dissociate into large and small
subunits when they are not synthesizing
proteins and reassociate during the initiation of
translation.
 In E. coli, the small subunit is described as 30S,
and the large subunit is 50S, for a total of 70S
(recall that Svedberg units are not additive).
 Mammalian ribosomes have a small 40S

16.  The small subunit is responsible for binding
the mRNA template, whereas the large
subunit sequentially binds tRNAs.
 Each mRNA molecule is simultaneously
translated by many ribosomes, all
synthesizing protein in the same direction:
reading the mRNA from 5′ to 3′ and
synthesizing the polypeptide from the N
terminus to the C terminus.
 The complete mRNA/poly-ribosome structure
is called a polysome.

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