12 Questions
What is the function of the 5’ cap region of eukaryotic mRNAs?
Align on the ribosomes during protein synthesis and protect mRNA from degradation
What modification occurs at the 5’ end of eukaryotic mRNA's?
Addition of a structure called 7 methylguanozin cap (m7G)
How is capping initiated in eukaryotic mRNA processing?
Forming a 5’-to-5’ linkage
What is added to the 3’ end of eukaryotic mRNAs?
Poly-A tail consisting of several Adenines
What is the function of adding a poly-A tail to eukaryotic mRNAs?
Regulating both translation and mRNA stability
What are the key components of polyadenylation signals?
AAUAAA and GU-rich elements
What happens to the poly-A tails during fertilization?
They lengthen, activating the translation of stored mRNAs
What is the role of splicing in pre-mRNA processing?
Removal of introns
What is the composition of the spliceosome?
Five types of small nuclear RNAs (U1, U2, U4, U5, U6) and associated proteins
What is the role of U1 snRNPs in pre-mRNA splicing?
Binding to the 5' splice site
What occurs during the first step of pre-mRNA splicing?
The intron is cleaved and ligated to an adenine within the intron, forming a lariat-like structure.
How does the length of the poly-A tail influence mRNA translation?
It can influence translation efficiency.
Study Notes
- Polyadenylation is a post-transcriptional modification that adds a poly-A tail to the 3' end of most eukaryotic mRNAs.
- The addition of a poly-A tail helps regulate both translation and mRNA stability.
- Polyadenylation involves the cleavage of the RNA chain at a specific site, followed by the addition of a poly-A tail by a separate enzyme.
- Polyadenylation signals consist of the hexanucleotide sequence AAUAAA and upstream and downstream GU-rich elements.
- These sequences are recognized by a complex of proteins, including an endonuclease and a separate poly-A polymerase.
- The length of the poly-A tail can influence translation, and short poly-A tails are found in unfertilized eggs.
- Fertilization triggers a lengthening of the poly-A tails, which activates the translation of stored mRNAs and leads to the synthesis of proteins required for early embryonic development.
- The removal of introns by splicing is another major modification of pre-mRNAs.
- Intron-containing genes are cloned downstream of a promoter, transcribed in vitro, and then splicing reactions can be studied in vitro.
- Pre-mRNA splicing occurs in two steps: the first step involves the intron being cleaved and ligated to an adenine within the intron, forming a lariat-like structure; the second step involves the cleavage at the 3' splice site and ligation of the two exons.
- Splicing requires the recognition of specific consensus sequences by the spliceosome, which is a large RNA-protein complex.
- The spliceosome consists of five types of small nuclear RNAs (U1, U2, U4, U5, U6) and their associated proteins, which form small nuclear ribonucleoprotein particles (snRNPs).
- U1 snRNPs bind to the 5' splice site, U2 snRNPs bind to the intron branch point, and U4/U6 and U5 snRNPs form a preformed complex that joins the splicosome.
- The splicing process involves the formation of a lariat-like structure and the excision and degradation of the intron within the nucleus.
Test your knowledge of mRNA processing and cap modification in medical biology with this quiz. Explore the role and function of the 5' cap region of eukaryotic mRNAs in protein synthesis.
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