| |
RIBOSOMAL RNA (rRNA) |
MESSENGER RNA(mRNA) |
TRANSFER RNA (tRNA) |
Percentage of total RNA of cell |
~ 80% |
3 to 5% |
10 to 20% |
| Sedimentation coefficient |
28S, 18S, 5.8S, 5S 23S, 16S, 5S |
8S |
3.8S |
| Number of nucleotides. |
5S RNA: 120 nucleotides.
16-18S RNA: 1,600 to 2,500 nucleotides. 23-28S RNA : 3,200 to 5,500 nucleotides |
E.coli:900 to 1,500 nucleotides |
73 to 93 nucletides |
Molecular weight. |
23S RNA: 1.1*10
30S RNA: 0.55*10 |
500,00 |
25,000-30,000 |
| Unusual bases |
Small amount of methylated bases. (E. coli: 1 per 100-150 nucleotides). |
Small amount of unusual bases. |
High content of unusual bases. (E. coli: 1 per 3040 nucleotides). |
| Site of synthesis |
Derived from nucleolar DNA. |
Synthesized in nucleus on DNA template |
Synthesized in nucleus on DNA template |
| Beginning of synthesis |
Synthesis begins at gastrulation, and increases as development proceeds. |
Some mRNA is found in the ovum. New mRNA is synthesized during early cleavage. |
.tRNA synthesis occurs at the end of cleavage stages. |
Base of relationship DNA |
No obvious base relationship to, DNA. rRNA is formed from only small sections of DNA. |
mRNA shows base relationship to DNA. It is formed from all sections of DNA. |
Same as in rRNA. |
| Function. |
Unpaired bases may bind mRNA and tRNA to ribosomes. |
Conveys genetic information from DNA of chromosomes to the ribosomes, where it takes part in protein synthesis. |
Adaptor for attaching amino acids to mRNA template |
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