Transfer RNA (t-RNA): Transfer RNA (tRNA) has clover leaf structure in two dimension and L- shaped structure in 3 dimension. tRNA is 73 to 94 ribo-nucleotides in length. A tRNA molecule consists of 5’ phosphate terminal, an acceptor arm that ends in CCA terminal at 3’, D loop which often contains dihydrouridine, anticodon loop, and T arm which has where is pseudouridine. CCA sequence is important as it is important for recognition of tRNA and is also site of attachment of amino acid.Structure of t RNA are given below in Figure 30.3

Figure 30.3 :Structure of T RNA

 

Each t-RNA is specific to amino acid that it carries it in CCA arm. There are 30-45 different tRNA in prokaryotes and 50 types in eukaryotes which suggest that there is more than one tRNA for single amino acid. For example for glycine there are two tRNA which are represented as and .

Ribosomes: Ribosomes are ribonucleoprotein particles that contain r-RNA and proteins.  Each ribosome is made of two subunits. In prokaryotes, mitochondria and chloroplast of prokaryotes there is 70S ribosome which is composed of 50s and 30s subunits. In E.coli, 30s subunit consist of 16s rRNA (1541 nucleotides) and 21 r-proteins and 50s subunit contains 23s rRNA (2904 ntds), 5s rRNA (120 ntds) and 31 proteins. In eukaryotes there is 80S ribosome which consists of 60s and 40s ribosomal subunit. 60s subunit consists of 28s rRNA (4718 nucleotides), the small 5s rRNA (120 nucleotides), 5.8s rRNA (160 nucleotides) and approximately 50 proteins. The 40s subunit consists of the 18s rRNA (1874 nucleotides) and 33 r-proteins. (Note:‘s’ means Svedberg’s unit of sedimentation coefficient). The 70s ribosome has three tRNA binding sites- P-site (or peptidyl-tRNA binding site), A-site (aminoacyl-tRNA-binding site), and E-site (deacylated tRNA, also called the exit site) Figure 30.4.