Ribosomes are large complex molecules found in all living cells that are the site of biological protein synthesis. They consist of two subunits that come together during protein translation. Ribosomes along with transfer RNA (tRNA) help translate protein-coding genes in messenger RNA (mRNA) into proteins. The process of protein synthesis begins with transcription of DNA to mRNA, which is then translated into proteins with the help of ribosomes and tRNA. Translation occurs as the ribosome moves along the mRNA, facilitating the binding of tRNA to the mRNA and the formation of peptide bonds between amino acids, eventually resulting in a completed protein chain.

1. RIBOSOME
T.Rajeshwari
Maris Stella College

2. Introduction
• It is a large & complex molecule.
• Found in all living cells prokaryote &
eukaryote.
• That serves as the primary site of biological
protein synthesis.
• Ribosome was first observed in 1953s by
romanian cell biologist george emil palade
using a electrone microscope.

3. George emil palade (1953)

4. • In prokaryote free form in cytoplasm &
protoplasm
• In eukaryote free in cytoplasm inside the cell
attach to the outer membrane in endoplasmic
reticulum

5. STRUCTURE
• It is without cell membrane.
• Two subunits are attach by a different angles.
 Large subunit
 Small subunit
The subunits of the ribosome are synthesized by
the nucleolus.

8. • The subunits of ribosomes join together
when the ribosomes attaches to the
messenger RNA during the process of
protein synthesis.
• Ribosomes along with a transfer RNA
molecule (tRNA), helps to translate the
protein-coding genes in mRNA to proteins.

9. Ribosome Function
• Ribosome basically a protein factory. Subunits
each have role in making of proteins
• Tounderstand exactly what each subunit
does, it’s necessary to walk through protein
synthesis step by step

10. Protein synthesis
• Process starts from DNA
through “transcription”
• “Translation” is where
ribosome comes in.
Translation occurs when
protein formed from code
on mRNA
• Ribosome carries out the
translation of the
nucleotide triplets

11. Protein synthesis
• Chart - visual image of
transcription and
translation in protein
synthesizing
• DNA and RNA have
nucleotides that
determine kind of
protein
• 3 nucleotides = 1 amino
acid of a protein

12. Ribosome and RNA
• mRNA with code for proteins located at 30S subunit
• tRNAs responsible for carrying amino acids to mRNA.
Each tRNA has own nucleotide triplet which binds to
matching triplet on mRNA, ex., tRNA with code AAA
(triple adenine) would match up with mRNA that has
code UUU (triple uracil)

13. Initiation:
The first phase of translation
• Translation begins when
mRNA attaches to the 30S
• tRNA comes and binds to
mRNA where nucleotide
code matches
• This triggers 50S binding
to 30S. 50S is where all
tRNAs will bind. Now we
move on to elongation

14. Elongation:The second phase
• Two binding sites on
50S: A site and P site,
which aid in continuing
translation
• First tRNA connected at
A site. Now moves to P
site as another tRNA
approaches
• Second tRNA binds to A
site

15. Elongation
(continued)
• Peptide bond forms
between amino acids of
tRNAs (methionine and
proline)
• First tRNA now
detached from its
amino acid, and it
leaves ribosome.
Second tRNA still has
proline and methionine
attached

16. Elongation
(continued)
• The tRNA left now
moves to P site.
Ribosome ready to
accept another tRNA
and continue process
• Each tRNA adds another
amino acid to growing
peptide chain (thus
“elongation”)
• Eventually process has
to finish, however

17. End of
translation
• Ribosome was moving
along nucleotide
triplets one by one
• Ribosome reaches “stop
codon,” peptide chain
finished. Last tRNA
leaves ribosome,
leaving behind
completed peptide

18. End of translation
(continued)
• Ribosome separates
from mRNA
• Ribosome subunits also
separate, and will
remain this way until
another mRNA comes
along to restart the
process

19. Thank you