mRNA Processing and Genetic Code

mRNA processing only occurs in eukaryotes?

True

transcription and translations occur simultaneously in…

prokaryotes

What are the three main events in RNA processing?

1. a nucleotide “cap” is covalently attached to the 5’ end

2. a poly(A) “tail” is added to the 3’ end

3. Introns are spliced out

Once steps are completed, RNA becomes a MATURE messenger RNA (mRNA)

5’ Cap roles…

-gives mRNA stability

-provides a recognition site for ribosomes to bind (for translation)

3’ PolyA tail roles…

-gives mRNA stability (longer tail = more stable)

-provides a recognition site for “exporter” proteins to bind, to export mRNA from nucleus to cytoplasm

In eukaryotic cells what happens first?

mRNAs must first be processed and transported to the cytoplasm BEFORE they are translated

what is spliceosome?

a complex made out of both proteins and small (non-coding) functional RNAs —> called snRNPs

Alternative splicing

exons kept in OR edited out to fine tune the coding information included in the final mRNA

what does alternative splicing allow?

a single gene in DNA to code for MANY different proteins simply by editing which exons are kept in the final mRNA.

exons

protein coding sequence that stay in the mRNA that actually get translated

introns

non-coding, in-between and get trashed out that don’t go into the protein

mRNA carries…

the information (“blueprint”) for the protein in its nucleotide sequence (“genetic code”)

to make our protein…

we need to TRANSLATE the nucleotide sequence to know how to build the protein’s proper amino acid sequence

how is the genetic code read?

it is read on mRNA 3 nucleotides at a time, from 5’ to 3’

each triplet of nucleotides that can be termed to a specific amino acid is callled?

codons

Translations for all the possible codon combinations use which 4 nucleotides?

A,C,U, and G

what is the Start codon called?

AUG (met)

-is always at the beginning of every new polypeptide chain

what is the stop codon?

UAA, UAG, or UGA

-no more amino acids are added and the polypeptide ends