CHAPTER 17 Flashcards
What is the significance of non-coding RNAs (ncRNAs) in cellular functions?
ncRNAs are abundant in cells, constituting about 80% of transcription, and perform diverse cellular functions, including binding to various molecules and forming structures like stem-loops.
Scaffold
Bind a group of proteins
Guide
Direct proteins to different sites
Alteration of Protein Function or Stability
Modify protein structure and stability
Ribozyme
Catalyze biochemical reactions
Blocker
Prevent cellular processes
Decoy
Sequester other ncRNAs
What is a protobiont and its role in the evolution of living cells?
A protobiont is a precursor to living cells, containing macromolecules that maintained a distinct internal environment and had catalytic functions, potentially leading to the emergence of RNA-based life forms.
How did the RNA world evolve to utilize DNA?
In the RNA world, RNA served both as genetic material and catalyst. The evolution of DNA provided a more stable information storage mechanism, allowing RNA to evolve modified bases and enhanced catalytic functions.
What is HOTAIR, and how does it influence gene expression?
HOTAIR is a long ncRNA that alters chromatin structure and represses gene expression by guiding histone-modifying complexes (PRC2 and LSD1) to target genes, leading to histone modification and transcription inhibition.
Describe the mechanism of RNA interference (RNAi) and its significance.
RNAi involves microRNAs (miRNAs) and small-interfering RNAs (siRNAs) that regulate gene expression by inhibiting mRNA translation or promoting degradation, playing a crucial role in defense against viruses and gene regulation.
What are microRNAs (miRNAs), and how do they regulate gene expression?
miRNAs are short ncRNAs that regulate gene expression by inhibiting translation of multiple mRNAs through partial complementarity, with up to 60% of human genes potentially regulated by them.
Explain the function of small-interfering RNAs (siRNAs).
siRNAs originate from external sources (e.g., viruses) and typically match a single mRNA perfectly. They play a role in silencing specific mRNAs and protecting against viral infections.
steps in the formation and function of the RNA-induced silencing complex (RISC).
- pri-miRNA is processed in the nucleus to pre-miRNA;
- Pre-miRNA is exported and further processed by Dicer to form siRNA;
- One strand associates with proteins to form RISC;
- RISC binds mRNA, leading to inhibition or degradation.
What role do small nucleolar RNAs (snoRNAs) play in ribosome biogenesis?
snoRNAs are abundant in the nucleolus and guide the modification of rRNAs, such as methylation and conversion of uracil to pseudouracil, facilitating ribosomal RNA synthesis and assembly.
