concept 17.3: eukaryotic cells modify RNA after transcription

what is the initial product of transcription

pre- RNA

primary transcript

the initial RNA strand of any gene including RNA not translated into protein

what happens to the primary transcript during RNA processing

both ends of the primary transcript are altered

what must happen before the genetic messages are sent to the cytoplasm

enzymes in the eukaryotic nucleus must modify the pre-mRNA by RNA processing

how is each end of a pre-mRNA molecule modified

the 5’ end receives a nucleotide 5’ cap and the 3’ end gets a poly-A tail (50-250 adenine nucleotides added

what are the functions of the modifications made to pre- mRNA

they facilitate the export of mRNA to the cytoplasm, protect mRNA from hydrolytic enzyme, and help ribosomes attach to the 5’ end

what are the UTRs in mRNA strand

untranslated regions and they are used for ribosome binding

what are non coding regions

they are stretches of nucleotides that lie between coding regions

introns

intervening sequences or non coding regions

exons

regions that will eventually be expressed

what does RNA splicing do to introns and exons

they remove introns and join exons and create a mRNA molecule with a continuous coding sequence

what is the use of UTRs

they do not code for amino acids but are used for ribosome binding in translation

spliceosomes

carries out RNA splicing and consist of a variety of proteins and small nuclear ribonucleoproteins

riboxymes

catalytic RNA molecules that function as enzymes and can splice RNA

what is unique about ribozymes

they are a non protein catalyst

what three properties of RNA allow it to function as an enzyme

1- it can form a 3d structure because it base pairs with itself

2- some bases in RNA contain function groups that may participate in catalysis

3- RNA may hydrogen bond with other nucleic acid molecules

alternative gene splicing

some genes can encode more than one kind of polyp0eptide, depending on which segments are treated as exons during splicing

does an organism produce more proteins or genes

produces more proteins

exon shuffling can cause what

can result in the evolution of new proteins and eventually lead to a variant