Transcription and RNA

Finished transcripts are modified in 3 ways before they exit the nucleus:

Step 1: ___- Adding a modified guanine

Step 2: ___- Adding -AAAAAAA

Step3: ___- ‘Stitching’ the gene together

5’ capping : polyadenylation (3’ poly A tail) : gene splicing

Step I : 5’ Capping:

-Adding of modified __ to the 5’ end of the transcript (nucleotide is attached via __ triphopsphate bridge

-5’ Cap is needed for __ of translation (making protein) and it __ the transcript

-guanine : 5’ to 5’

-initiation : stabilizes

Step II: Polyadenylation:

-Adding of multiple adenine (poly-A tail). The poly-A tail increases __

-mRNA with little or no poly-A tail is quickly __

stability : degraded

Eukaryotic RNA must undergo further ___ in addition to the 5’ cap and poly(A) tail

processing

Eukaryotic RNA typically has noncoding sequences called __ that are interspersed in the coding sequences. The coding regions between introns are called __

introns : exons

Introns must be __, and exons stitched together to generate a functional mRNA molecule

removed

Small nuclear ribonucleoprotein particles ( snRNA - “__” ) form the core of a complex called a __, which carries out RNA splicing in the cell

-The spliceosome recognizes sequences common to introns, and cuts out the intron via a __ structure. The … structure involves a ‘branch point adenine

snurps: splicesome

-lariat

Intron Splicing by Lariat Structure: The 5’ end of the intron bonds to the __ position of the ribose of the adenine to form a lariat structure (the yellow loop). The __ of the exon joins with the 5’ end of the next exon to form a continuous __region

2’ OH : 3’ OH : coding

Why Would Cells Evolve __?

1.Transcripts can be spliced in several different ways to produce a variety of proteins from a single transcript (__ splicing) - i.e. many proteins can come from one gene

2.___ is much more likely with introns, which has probably led to many chimeras (combinations) of existing proteins; many current proteins resemble ‘patchworks’, which supports this theory (i.e. new proteins are more likely to be created)

Introns : alternative : Genetic Recombination

Export from the Nucelus

Mature mRNA is exported from the __ to the cytoplasm. Nuclear pores recognize the binding proteins associated with the poly(A) tails and 5’ cap. __ (e.g. introns) are not exported and are

nucleus : Waste RNA

mRNA Lifespan and Degradation

mRNA is eventually degraded after use by __. The lifespan of a transcript varies according to the mRNA __ and the type of __ is exists in

RNases : sequence : cell

mRNA Lifespan and Degradation

Bacterial mRNA lifespans can be as short as __ but Eukaryotic mRNA exists from ~30 min to __. In general, mRNA that code low-level proteins have __ lifespans, while those that code for high-level proteins (e.g. B-globin) last longer (e.g. 10h)

3 min : 10h : short

From RNA to ___

Recall the genetic code where _ nucleotides code for __ amino acids. A set of three nucleotides (known as a __) codes for a single amino acid. There are __ possible codons (4 x 4 x 4)

Protein : 4 : 20 : codon: 64

Each transcript has three possible __ frames. This is because mRNA is decoded by groups of three __. Each … frame produces a different protein. Generally there is only one ‘correct’ reading frame

reading : nucleotides

Translation from genetic code to protein requires the help of __ RNA (tRNA). tRNA are __ nucleotides long with an amino acid attachment site (top) and an __ site (bottom)

transfer: 80 : anticodon

When a tRNA is coupled to its specific amino acid, it is said to be ‘__’. There are twenty individual __ that link each type of amino acid to tRNA molecules

charged : aminoacyl-tRNA synthetases

may be acc