Question

What is the difference between P-site and A-site of a ribosome?

Answer 1

Ribosomes are minute particles that serve to synthesise proteins composed of RNA and related proteins. Many cellular functions, such as repairing damage or directing chemical processes, need proteins.

Complete answer:
Protein synthesis takes place in ribosomes. It takes place by two processes.
i) Transcription: In transcription, the DNA changes to mRNA. The mRNA further moves from the nucleus to the cytoplasm.
ii) Translation: It takes place in the ribosome.The mRNA attracts the tRNA which forms amino acid. A protein is a long peptide chain which is decoded by the ribosome. The ribosome has mainly two important sites at which the synthesis of peptide chains takes place.

P-site	A-site
P-site or the peptidyl site is the second binding site for tRNA in the ribosome.	A-site or the aminoacyl site is the first binding site for tRNA in the ribosome.
Initiation of the peptide synthesis starts at the P site.	The A site accepts the incoming tRNA bound to an amino acid
The binding of tRNA to the P-site creates codon-anticodon interaction.	The A-site has the anticodon for the corresponding codon.
De-acylation of tRNA takes place in the P- site.	Acylation of tRNA takes place in the A-site.
P-site carries the growing peptide chain.	A-site binds to the incoming amino-acylated tRNA.

Note: The Human codes for 20 amino acids. The AUG is called the start codon which codes for amino acid called Methionine. The UAA, UAG, UGA are called the non-sense or stop codons which stops the amino acid synthesis. They do not code for any amino acid. The E-site of the ribosome is called the Exit site which holds the deacylated tRNA.