What is translation, where doe

Ans 1: Translation: It is theprocess of synthesis of protein from the informationavailable on m-RNA (messenger RNA).  As clearfrom the name only here m-RNA is messenger which brings messagefrom DNA that is present in the nucleus.

Translation occur in cytoplasm with the help ofribosome ,protein and 3 different RNAs that are

• t-RNA( transfer-RNA): Transfers amino acids asper the information available on m-RNA.
• r-RNA ( Ribosomal-RNA): It makesribosome.
• m-RNA ( messenger-RNA):Receive  information from DNA and then come to cytoplasmfor synthesis of protein as per information received.

Ans2: Number of ribosomal units required fortranslation: 2 ribosomal sub units are required fortranslation but their types are different in prokaryotes andeukaryotes. Ribosomes are made up of r-RNA and proteins.

Prokaryotes: 70s ribosome madeup of 2 subunits 50s and 30s

Eukaryotes: 80s ribosome made up of 2 subunits60s and 40s

Ribosome construction in prokaryotes: In thesecells ribosomes are synthesized in cytoplasm as they lack membranebound cell organelles that are present in eukaryotes.

Ribosome construction in Eukaryotes: Ineukaryotes r-RNA (except 5s r-RNA) and proteins joins in thenucleolus to form ribosomal subunits , for that ribosomal proteinscomes from cytoplasm to nucleolus through nuclear pores. Later inthe cytoplasm these two subunits assembles to form a functional 80sribosome.

Ans 3: Both P-site and A-site are present onthe ribosome.

P-site: It is the abbreviated form ofpeptidyl site. Growing polypeptide chain ispresent in this site.

A-site: It is the abbreviated form ofacceptor site. This site can also be called asarrival site of incoming t-RNA having desiredamino acid.

Ans 4: m-RNA acts as a template for thesynthesis of protein.

• m-RNA comes from nucleus to cytoplasm carrying massage fromDNA.
• With the help of amino acyl t-RNA synthetaseenzyme first amino acid that is alwaysmethionine  loads on the t-RNA.

Initiation: It has following steps:

• small sub unit of ribosome binds to the m-RNA and scan it forthe AUG codon that is the start codon.
• As soon as small sub unit of ribosome finds the AUG codon itattaches there and met-tRNA having methionine amino  acidattaches on m-RNA (with anticodon UAC that pairs with codon AUG).
• At this point large sub unit of ribosome assembles with smallsub unit thus forms complete ribosome.
• Large subunit has 3 sites A-site (acceptor site) , P-site(peptidyl site) and E site that is exit site.
• m-RNA along with met- t RNA and ribosome sub units forms theinitiation complex. Now elongation phase will start.

Elongation: Following are the steps:

• New t-RNA having amino acid as per next available codon willcome and bind with anti codon on  A-site
• Now peptide bond will form between methionine and new aminoacid. In this way dipeptide will form.
• Ribosome will move one codon ahead and empty t-RNA will go toE-site and removed from ribosome.
• Then new A-site will become free for new t-RNA with aminoacid
• same step repeat untill it reaches stop codon.

Termination:

Termination occurs once ribosome reaches stop codon that UAA,UAG, UGA. At this point popeptide chain will release fromribosome.

This is generalized translation of prokaryotes andeukaryotes.