RNA and the genetic code

Messenger RNA (mRNA)

Carries the information specifying the amino acid sequence of the protein to the ribosome. mRNA is transcribed from template DNA strands by RNA polymerase enzymes in the nucleus of cells. Then, mRNA may undergo a host of posttranscriptional modifications prior to its release from the nucleus.

Codon

Three-nucleotide segments

Monocistronic

each mRNA molecule translates into only one protein product.

Polycistronic

starting the process of translation at different locations in the mRNA can result in different proteins.

Transfer RNA (tRNA)

Responsible for converting the language of nucleic acids to the language of amino acids and peptides. Each tRNA molecule contains a folded strand of RNA that includes a three-nucleotide anticodon. To become part of a nascent polypeptide in the ribosome, amino acids are connected to a specific tRNA molecule; such tRNA molecules are said to be charged or activated with an amino acid.

Ribosomal RNA

Integral part of the ribosomal machinery used during protein assembly in the cytoplasm. Many rRNA molecules function as ribozymes; that is, enzymes made of RNA molecules instead of peptides. rRNA helps catalyze the formation of peptide bonds and is also important in splicing out its own introns within the nucleus.

Wobble position

For the amino acids with multiple codons, the first two bases are usually the same, and the third base in the codon is variable. Wobble is an evolutionary development designed to protect against mutations in the coding regions of our DNA.

Silent or degenerate

Mutations in the wobble position

Point mutation

Affects on e of the nucleotides in a codon

Expressed mutations

Point mutations that affect the primary amino acids sequence of the protein.

Missense mutation

a mutation where one amino acid substitutes for another

Nonsense mutation

a mutation where the codon now encodes for a premature stop codon (also known as a truncation mutation)

Frameshift mutation

Occurs when some number of nucleotides are added to or deleted from the mRNA sequence.

Alternative splicing

For some genes in eukaryotic cells, the primary transcript of hnRNA may be spliced together in different ways to produce multiple variants of proteins encoded by the same original gene. By utilizing alternative splicing, an organism can make many more different proteins from a limited number of genes.