Messenger RNA processing

In eukaryotic cells where is messenger RNA (mRNA) modified?

Nucleus

which enzyme adds the 5’ G-Cap to mRNA?

Capping enzyme complex

what is the capping enzyme complex?

a group of enzymes that modifies the 5’ end

Which enzyme adds the 3’ Poly-A tail?

poly(A) polymerase

what is Poly(A) polymerase (PAP)

enzyme that catalyzes a poly A tail to end the 3’ end of RNA molecules using ATP

What are three functions of the 5’ G-Cap & 3’ Poly-A tail?

• protecting the mRNA from degradation, facilitating ribosome binding, and aiding in nuclear export.

Why do some human viruses attach A 5’ “G-Cap” & 3’ “Poly-A Tail” to their mRNA?

to replicate and ensure protein synthesis by mimicing the hosts mRNA

Which large enzyme complex splices newly made mRNA molecules?

The spliceosome

Does the splice some consist of proteins & specialized RNA molecules?

yes, Small nuclear RNAs (snRNAs)

The nucleotide sequences removed from mRNA during splicing are called—-

introns

The nucleotide sequence remaining in mRNA after splicing are called——

exons

Are mRNA molecules shorter before or after splicing?

Yes, because introns are removed during splicing leaving only exons

Which sequence in mature mRNA determine the amino acid sequence of the protein?

The codons

Some introns in mRNA splice themselves out of mRNA. RNA enzymes are called—-

ribozymes

Do your cells use alternative splicing to produce more than one version of a protein from a single gene?

Yes, one gene can give several mRNA variants

Do alternatively spliced mRNA have different combinations of exons?

Yes, can add or skip certain exons when forming the final mature mRNA

Do alternativly spliced mRNA code for proteins with different amino acids sequence & cellular functions?

Yes, because of different exon combinations it can result in protein changes.

What are some medical consequences of abnormal mRNA splicing?

• autism spectrum disorder (ASD)

• Beta-thalassemia

• Cystic fibrosis

• parkinson’s disease

• some cancers

• spinal muscular atrophy

Can abonormal splicing result in oncoproteins that increase the risk of cancer?

Yes, it can generate oncoproteins increasing the risk of cancer and progression

Exons

coding sequences that stay in the mRNA and are joined together

Introns

noncoding seqeunces that are removed during splicing

AUG

codes for methionine (start codon)

UUU

codes for phenylalanine

Ribozymes

RNA enzymes that catalzye chemical reactions