Eukaryotic mRNA Transcription and Processing

This set of flashcards covers key concepts about eukaryotic mRNA transcription, processing, and splicing including fundamental mechanisms and associated diseases.

What is the Central Dogma of Eukaryotic Biology regarding mRNA?

Transcription and mRNA modification occur in the nucleus, then mRNA is transported out for translation in the cytoplasm.

What are the important steps in mRNA processing?

5’ capping, 3’ polyadenylation, and intron splicing.

What is 5’ capping?

The addition of a modified nucleotide to the 5’ end of the mRNA.

What occurs during 3’ polyadenylation?

Cleaving at the 3’ end of mRNA and addition of a tail of multiple adenines.

What is the role of intron splicing in mRNA processing?

To remove introns and ligate exons together.

What enzyme adds guanine to the 5’ end of pre-mRNA?

Guanylyl transferase (GTase).

What is the purpose of 5’ end capping?

To protect mRNA from degradation, facilitate splicing, and enhance translation efficiency.

What is the consensus sequence for the 3’ splice site?

An 11 nt pyrimidine-rich sequence with an AG dinucleotide at the 3’ end.

What are CPSF and CStF?

CPSF is Cleavage and Polyadenylation Specificity Factors; CStF is Cleavage Stimulating Factor.

What is the function of the 3’ poly-A tail?

Protecting mRNA from degradation and facilitating export from the nucleus.

Define lariat structure in mRNA splicing.

A loop formed during splicing that connects the 5’ splice site to the branch site.

What are the two segments of eukaryotic genes?

Exons and introns.

What is alternative splicing?

The process by which a pre-mRNA can be spliced in different patterns to produce various proteins.

What is the significance of the branch point adenine?

It plays a key role in the splicing reaction, uniting the intron and leading to lariat formation.

How many human genes are estimated to exist?

Approximately 22,800.

What is one reason for the production of over 100,000 human proteins from fewer than 22,800 genes?

Alternative splicing.

Describe the fundamental process of mRNA splicing.

Involves forming a lariat, cleaving the intron, and joining the exons together.

What proteins facilitate mRNA splicing?

Spliceosomes, which consist of snRNPs (small nuclear ribonucleoproteins).

What is the main role of PolyA polymerase (PAP)?

To add adenines to the 3’ end of the pre-mRNA during polyadenylation.

What happens to the introns during mRNA processing?

They are removed and the exons are ligated together.

What is the consequence of a mutation affecting splicing in a gene, such as LMNA?

It can lead to diseases such as Hutchinson-Gilford Progeria, affecting nuclear structure.

What motif is found at the 5’ splice site?

The consensus sequence GURAGU.

What does a point mutation creating a new splicing site result in?

Aberrant splicing leading to modifications in protein structure, potentially causing disease.

How does the 5’ cap influence translation efficiency?

By helping the ribosome recognize and bind to the mRNA for translation.

What enables a single gene to generate multiple distinct proteins?

Alternative splicing, alternative promoters, and alternative polyadenylation.

Why is the stability of the poly-A tail important?

It helps control the lifespan and degradation of mRNA.

Which mechanism allows mRNA to be processed differently in various cell types?

Alternative splicing.

What contributes to the diversity of the human proteome?

The high level of alternative splicing observed in human genes.

What happens in the mRNA 5’ capping process regarding phosphates?

The gamma and beta phosphate groups are removed from the guanosine triphosphate, allowing it to join the mRNA via a triphosphate linkage.

What defines a spliceosome?

A complex of snRNA and proteins that facilitates the splicing of pre-mRNA.

What diseases are associated with defective mRNA splicing, such as in Hutchinson-Gilford Progeria?

Genetic disorders resulting from abnormal protein production due to splicing errors.

In what way can a single message from DNA lead to more than one protein product?

By employing different combinations of exons during splicing.