Question

Notes on ribosomes: site of protein synthesis : initiation,elongation,termination

Answer 1

The site of protein synthesis is the ribosome. Ribosomes are interesting structures in that they are a combination of RNA and protein. The form of RNA that is found in a ribosome is ribosomal RNA, or rRNA.

Translation occurs in three major steps: (1) initiation. (2) elongation, and (3) termination.

Initiation

During initiation, a group of proteins called initiation factors assist in assembling the ribosome around the mRNA.

Elongation

The elongation stage involves the assembly of specified amino acids into a polypeptide chain.

Termination

The process of termination begins once the end of the mRNA is reached by the ribosome.

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Answer 2

All About Ribosomes

1. Ribosomes are the only organelles that synthesis protein chains ( Amino acids ). Hence, ribosmes are known as site of protein synthesis.
2. Ribosomes are small membrane-less, granular organelles which normally occur in prokaryotes. In prokaryotes, they remain spread in the cytoplasm. This makes it an organelle. And in eukaryotes they are present over RER( Rough Endoplasmic Reticulum ) and it is also present in the organelles : Chloroplast ( in plant cells ) and Mitochondria. Since RER is itself an organelle. Hence, ribosomes are known as 'organelles within organelle'.
3. Ribosomes was first observed under the electron microscope as dense particles by George Palade in 1953.
4. Ribosomes are composed of ribosomal ribonucleic acid (rRNA) and proteins.
5. Where do ribosomes are formed ? Ans : Nucleolus.
6. The eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S. Each ribosomes has two subunits, larger and smaller subunit. The two subunits of 80S ribosomes are 60S and 40S while that of 70S ribosomes are 50S and 30S. Both 80S and 70S ribosomes are composed of two subunits.
7. Several ribosomes may attach to a single mRNA and form a chain called polyribosomes ( or polysomes ).