02/20: mRNA Processing & Intro To Translation

mRNA Processing

Occurs only in eukaryotes, where mRNAs are processed and transported to the cytoplasm before translation.

Eukaryotes

Organisms whose cells contain a nucleus and organelles; mRNA processing only occurs here.

Prokaryotes

Organisms whose cells lack a nucleus; transcription and translation occur simultaneously.

RNA Processing Steps

The three main steps include adding a 5' cap, a 3' poly(A) tail, and splicing out introns.

5' Cap

A modified Guanine nucleotide that stabilizes mRNA and serves as a recognition site for ribosomes.

3' Poly(A) tail

A sequence of adenine nucleotides added to the 3' end of mRNA that provides stability and recognition for export proteins.

Introns

Non-coding regions of a gene that are spliced out during mRNA processing.

Exons

Coding regions of a gene that are expressed in the final mRNA and protein.

Splicing

The process of removing introns from the RNA transcript and joining exons together.

Alternative Splicing

The process that allows a single gene to code for multiple proteins by producing different mRNA variations.

Dscam gene

An example of a gene that can produce almost 40,000 different proteins through alternative splicing.

Translation

The process of converting the nucleotide sequence of mRNA into an amino acid sequence to form a protein.

Genetic Code

The set of rules that defines how the nucleotide sequence is translated into amino acids.

Codons

Triplets of nucleotides in mRNA that specify particular amino acids.

Start Codon

The codon AUG, which signals the beginning of translation and encodes the amino acid methionine.

Stop Codons

Codons (UAA, UAG, UGA) that signal termination of the polypeptide synthesis.

Reading Frame

The way nucleotides are grouped into codons; it must start correctly at the start codon for accurate translation.

Codon Table

A reference table used to translate mRNA codons into corresponding amino acids.

Redundant Code

A characteristic of the genetic code where multiple codons can code for the same amino acid.

UAA, UAG, UGA

The three stop codons in the genetic code that signal the end of protein synthesis.

RNA Stability

The characteristic provided by the 5' cap and 3' poly(A) tail that helps protect mRNA from degradation.

Nucleotides

The building blocks of RNA and DNA, comprising adenine, cytosine, guanine, and uracil (in RNA).

Methionine (Met)

The amino acid encoded by the start codon AUG.

Protein Synthesis

The overall process that includes transcription and translation to produce proteins.

Nucleotide Sequence

The order of nucleotides in a strand of DNA or RNA that encodes genetic information.

Transport of mRNA

The process by which processed mRNA is exported from the nucleus to the cytoplasm for translation.

Covalently Attached

Refers to the chemical bond formed during the addition of the 5' cap and 3' tail to the mRNA.