What is Regarding cytosolic Eukaryotic gene expression false is - and explain in detail?
Ans. is 'a' i.e. N formyl Met is the first t-RNA to come into action Genetic information is stored in the chromosomes and transmitted to daughter cells through DNA replication. It is expressed through transcription to RNA (tRNA, mRNA & rRNA). Subsequently, it is translated into polypeptide chain i.e. protein synthesis.Steps of protein synthesisActivation of amino acids.InitiationElongationTerminationWe are not going into detailed steps, as it is a vast topic, so let's discuss the options one by one.Methionine having anticodon UAC is the first amino acid required in binding to the initiation codon AUG on m- RNA. In bacteria and in mitochondria the initiator t-RNA carries an N-formyl ated methionine but in eukaryotes the methionine is not formyl ated so ans. is (a).Recognition of a particular codon in an mRNA sequence is accomplished by the anticodon sequence of the tRNA and it follows the rules of complimentary and antiparallel binding, that is, the mRNA codon is read 5' - 3' by an anticodon pairing in the "flipped" (-5') orientation (when writing the sequences of both codons and anticodons, the nucleotide sequence must always be listed in the 5' - 3' order).During elongation of the polypeptide chain, the ribosome moves from the 5' end to the 3' end of the m-RNA that is being translated. This process is facilitated by elongation factors (EF-2) & requires GTP. EF-2 GTP complex is hydrolyzed to EF-2-GDP & the energy released moves the m-RNA forward by one codon.The initiation of protein synthesis starts with dissociation of 80S ribosome into 60S & 40S followed by formation of 43 S Pre initiation complex, which binds to cap structure at the 5'end of m-RNA (present in all eukaryotic cells) & moves down the mRNA until it encounters the initiator codon. But in prokaryotes there is a purine rich sequence of nucleotide bases known as the Shine - Dalgarno sequence of m-RNA. This sequence binds with complimentary sequence near 3'end of 16S r-RNA component of 30S ribosomal subunit.Other important differences in prokaryotes & eukaryotes regarding protein synthesis are:Prokaryotic mRNAs are polycistronic i.e. with several coding regions with its own initiation codon. It can produce separate species of polypeptide while eukaryotic mRNA is monocistronic i.e. codes for only one polypeptide chain.The releasing factors utilized in termination are 3 in prokaryotes RF-1, RJF-2 & RF-3 while in eukaryotes it is only one- eRF.In prokaryotes three initiation factors are known (IF-1, IF-2 & IF-3) whereas in eukaryotes there are at least 10 (designated as- elF)