Nucleic acids {ribonucleic acid}| (RNA) can have ribonuceotides. Hydroxyl groups at pentose-sugar second carbons make RNA chains unable to lie anti-parallel to each other for more than several bases, so RNA cannot make double helices. RNA can double back on itself to make hairpin loops, with short double strand at neck.
types
Ribose-nucleotide nucleic acid is for protein translation (mRNA), codon translation (tRNA), protein-synthesis sites (rRNA), and intron excision from RNA (snRNA). Specific 22-nucleotide fragments of RNA have regulatory activity.
genes
E. coli has 50 to 200 RNA genes, as do other organisms. Over 95 percent of eukaryotic RNA encodes rRNA, mRNA, and tRNA, not proteins.
RNA {messenger RNA}| (mRNA) can hold information for making proteins. mRNA is 5% of RNA and has short life. mRNA is ribonucleotide chain copied from gene.
Two or three globular RNAs {ribosomal RNA}| (rRNA) can make ribosomes for protein synthesis. rRNA is 80% of RNA. rRNA has three or four long-lived types. Ribosomes look like snowmen, with two main rRNA globules beside each other. Globular rRNAs have two adjacent binding sites for tRNAs and mRNA. Ribosomes use many proteins.
RNA {transfer RNA}| (tRNA) can transfer amino acids from cytoplasm to ribosomes, to make protein chains. tRNA is 15% of RNA.
structure
tRNA is 75 bases long and has three-leaf-clover shape. tRNA has modified bases in three locations to make tRNA hydrophobic and curve back on itself. Middle-clover-leaf tip has three ribonucleotides, which differ for different amino acids. Clover-stem tip has three ribonucleotides that bind an amino acid. Different tRNAs bind different amino acids. There are more than 40 different tRNAs.
number
Different tRNA amounts differ greatly. Low amounts can limit protein production.
codon
RNA has three-nucleotide codons. tRNA has three tip nucleotides {anticodon}. Anticodon binds to first two codon nucleotides exactly but can bind inexactly to third codon nucleotide {wobble}.
mitochondria
Mitochondria have only 22 tRNAs and use only first two codon bases.
5-Chemistry-Biochemistry-Nucleic Acid
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Date Modified: 2022.0225