RNA Processing 3d'

Summary

The lecture covers transcription, RNA processing, and alternative splicing. It explains how alternative splicing produces different mRNAs and proteins from the same gene in various cell types. The lecture also touches on the regulatory mechanisms involved in splicing, like repressor proteins, and introduces microRNAs (miRNA) and small interfering RNAs (siRNA) that regulate translation. Additionally, ribosome structure and function are discussed, along with their role in translation. The lecturer briefly reviews the transcription of rRNAs and tRNAs, emphasizing the importance of RNA processing in gene expression and protein synthesis.

Takeaways

• 🔬 Alternative splicing allows for different mRNAs and proteins to be produced from the same gene in different cell types.
• 🧬 Alpha-tropomyosin gene is an example where smooth muscle cells and striated muscle cells produce different mRNAs due to alternative splicing.
• ⛔ Repressor proteins can regulate alternative splicing by preventing certain exons from being included in the final mRNA.
• 🧩 Different types of alternative splicing lead to variations in protein structures between different cells.
• 🎯 miRNA (microRNA) and siRNA (small interfering RNA) regulate gene expression through RNA interference, affecting translation by binding to mRNA.
• 🛠 siRNA is double-stranded, then becomes single-stranded before binding to target mRNAs, helping to regulate or degrade them.
• ⚙️ Ribosomes are the sites of translation and are composed of both proteins and rRNAs. Prokaryotic ribosomes have a 70S size, while eukaryotic ribosomes are 80S.
• 📏 Ribosomal subunits are measured in Svedberg units (S), which are based on how molecules sediment during centrifugation.
• 🔄 Ribosomes contain large and small subunits, and these subunits differ between prokaryotes and eukaryotes in terms of their protein and rRNA compositions.
• 📚 Transfer RNAs (tRNAs) are involved in translation, contain anticodons to match mRNA codons, and have an acceptor stem where amino acids are attached.

Q & A

What is alternative splicing and how does it relate to mRNA production?

Alternative splicing is a process where pre-mRNAs can be spliced differently, leading to the production of different mRNAs from the same gene. This usually occurs in different cell types and results in the production of slightly different proteins.

Can you provide an example of how alternative splicing affects mRNA and protein production?

The Alpha-actinin gene serves as an example where in smooth muscle cells, splicing leads to one mRNA, while in striated muscle cells, a different mRNA is produced. This results in the production of slightly different proteins in each cell type.

What role do regulatory proteins play in alternative splicing?

Regulatory proteins, such as repressor proteins, play a role in alternative splicing by preventing certain exons from being spliced together, thus influencing which mRNAs are produced and ultimately which proteins are synthesized.

How do miRNAs and siRNAs function in RNA interference?

miRNAs and siRNAs are small non-coding RNAs that participate in RNA interference. They regulate translation by binding to mRNA, preventing it from being translated through various mechanisms, such as cleaving the mRNA or slowing down translation.

What is the significance of the Nobel Prize mentioned in the script in relation to RNA interference?

The Nobel Prize was awarded to scientists who discovered and utilized RNA interference as a tool, highlighting the importance of miRNAs and siRNAs in gene regulation and their impact on cellular processes.

What are ribosomes and how are they related to RNA?

Ribosomes are cellular structures composed of proteins and rRNA that facilitate the process of translation. They are made up of large and small subunits, each containing different types of rRNA and proteins.

How do prokaryotic and eukaryotic ribosomes differ in size and composition?

Prokaryotic ribosomes are 70S in size, composed of a 50S large subunit and a 30S small subunit, while eukaryotic ribosomes are 80S, with a 60S large subunit and a 40S small subunit. The composition includes different rRNAs and proteins in each subunit.

What is the function of the 16S rRNA in ribosomes?

The 16S rRNA in prokaryotic ribosomes plays a crucial role in the initiation of translation by binding to the Shine-Dalgarno sequence on mRNA, facilitating the recruitment of the ribosome to the mRNA.

How are rRNA genes transcribed and processed in prokaryotes and eukaryotes?

In prokaryotes, rRNA genes are part of a single transcription unit that is cleaved to generate the three mature rRNAs. In eukaryotes, the 28S, 18S, and 5.8S rRNAs are part of the same transcription unit, processed in the nucleus to produce the mature rRNAs, with the 5S rRNA being transcribed separately.

What is the role of tRNA in protein synthesis?

tRNA, or transfer RNA, is involved in translation by carrying specific amino acids to the ribosome. Each tRNA has an anticodon that pairs with the corresponding codon on the mRNA, ensuring the correct amino acid is added to the growing polypeptide chain.

How does the structure of tRNA contribute to its function in translation?

tRNA has a cloverleaf structure with an anticodon loop that pairs with mRNA codons, an acceptor stem where the amino acid is attached, and other structural features that facilitate its role in translation by ensuring correct amino acid pairing and ribosome binding.