RNA

Biology: Cambridge International A Level, topic 6.1.7

Structure of RNA

RNA is usually single-stranded and is made of ribonucleotides that are linked by phosphodiester bonds.

A ribonucleotide in the RNA chain contains ribose (the pentose sugar), one of the four nitrogenous bases (A, U, G, and C), and the phosphate group.
Uracil (U) is a nucleotide only found in RNA. It replaces thymine and pairs with adenine.
Uracil is a pyrimidine nucleotide.
RNA base sequences are complementary to the DNA's coding sequence from which it has been copied.
If the DNA strand has a sequence AATTGCGC, the sequence of the complementary RNA is UUAACGCG.

Uracil is a pyrimidine nucleotide found only in RNA. It takes the place of the DNA nucleotide thymine.
The RNA base sequence is complementary to the DNA's coding sequence from which it has been copied.
- If the DNA strand has a sequence AATTGCGC, the sequence of the complementary RNA is UUAACGCG.

Ribonucleic acid, or RNA, is mainly involved in the process of protein synthesis under the direction of DNA.
RNA is usually single-stranded and is made of ribonucleotides that are linked by phosphodiester bonds.
There are four major types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), and microRNA (miRNA).

Messenger RNA (mRNA) carries messages from DNA, which controls all of the cellular activities in a cell.
The sequence of nucleotides in mRNA encodes biological information.
The RNA base sequence is complementary to the coding sequence of the DNA from which it has been copied.
However, in RNA, the base T is absent and U is present instead.
The mRNA is read in sets of three bases known as codons.
Each codon codes for a single amino acid. In this way, the mRNA is read and the protein product is made.

Transfer RNA (tRNA) is one of the smallest of the four types of RNA, usually 70–90 nucleotides long.
It carries the correct amino acid to the site of protein synthesis.
It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted in the polypeptide chain.
It has an anticodon, which is complementary to the mRNA codon.

Ribosomal RNA (rRNA) is a major constituent of ribosomes on which the mRNA binds.
The rRNA ensures the proper alignment of the mRNA and the ribosomes; the rRNA of the ribosome also has an enzymatic activity (peptidyl transferase) and catalyzes the formation of the peptide bonds between two aligned amino acids.