BSC 300 2023 TM_Lecture #13_Moving proteins into membranes and organelles Part II_In Class Lecture Slides
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What are the major topics covered in the lecture on protein transport?
• Targeting of Proteins to Mitochondria and Chloroplasts • Targeting of Peroxisomal Proteins • Transport Into and Out of the Nucleus These topics are discussed in Chapter 13, pages 602-621.
What is required for the delivery of proteins and lipids to organelles?
• Organelle-specific function • Growth and replication of organelles • Cell division Each daughter cell requires a complement of these structures.
What initiates the protein sorting process?
Initiation of protein translation on ribosomes in the cytoplasm This is with the exception of some proteins produced directly in the mitochondria or chloroplasts.
What is a sorting signal in protein transport?
A unique amino acid sequence recognized by cellular proteins for delivery or retention Typically a continuous stretch of 4-60 amino acids.
Proteins must _______ to enter mitochondria and chloroplasts.
unfold This is necessary for their import into the organelles.
What are the three energy inputs required for protein import into the mitochondrial matrix?
• Cytosolic Hsp70 • Matrix Hsp70 • H+ electrochemical gradient These inputs facilitate the translocation and folding of proteins.
What is the N-terminal matrix-targeting sequence?
A sequence that directs proteins to the mitochondrial matrix It is typically composed of 20–50 amino acids with an amphipathic α-helical conformation.
What are the three pathways to the inner mitochondrial membrane from the cytosol?
• Path A: CoxVa • Path B: ATP synthase subunit 9 • Path C: ATP/ADP antiporter Each pathway has distinct characteristics for protein import.
What is the role of FG-nucleoporins in the nuclear pore complex?
They fill the central channel with a gel-like matrix This matrix allows diffusion of small molecules but blocks unchaperoned translocation of proteins larger than 40 kDa.
What is required for nuclear import of proteins larger than 40 kDa?
• Nuclear-localization signal (NLS) • Nuclear transport receptors • Ran G-proteins • Localized Ran-GEFs and GAPs These components facilitate the transport through nuclear pore complexes.
What is the function of importin in nuclear transport?
Recognizes proteins with an NLS and facilitates their import into the nucleus The importin/cargo complex binds to fibrils on the outer rim of the pore.
What is the nuclear-export signal (NES)?
A leucine-rich region that facilitates the export of proteins from the nucleus It is recognized by exportin 1 in the nucleoplasm.
What is the PTS1-directed import of peroxisomal matrix proteins?
Involves a C-terminal peroxisomal-targeting sequence recognized by a cytosolic receptor This targets proteins for transport to the peroxisome lumen.
What are the six compartments of chloroplasts?
• Outer membrane • Inner membrane • Thylakoid membranes • Inner membrane space • Stroma • Thylakoid lumen Each compartment plays a role in the chloroplast’s function.
What is the SRP-dependent pathway for transporting proteins to chloroplast thylakoids?
• Translocation through Toc and Tic • Cleavage of the N-terminal stromal-import sequence • Binding of thylakoid-targeting sequence by SRP-related proteins This pathway is crucial for the import of proteins into the thylakoid lumen.
True or false: Peroxisomal membrane proteins contain the same targeting sequences as peroxisomal matrix proteins.
FALSE They are imported by different pathways.
What is the role of the heterodimeric NXF1/NXT1 nuclear export receptor complex?
Binds to mRNA-protein complexes (mRNPs) This complex facilitates the export of mRNA from the nucleus.
How does the NXF1/NXT1 complex diffuse through the nuclear pore complex (NPC)?
By transiently interacting with FG nucleoporins FG nucleoporins are proteins that line the nuclear pore and assist in transport.
What is the function of the RNA helicase (Dbp5) in the cytoplasm?
Uses ATP energy to remove NXF1 and NXT1 from the mRNA This process is crucial for recycling the export receptors.
What is the purpose of the Ran-dependent import process?
Recycles free NXF1 and NXT1 proteins back into the nucleus This ensures a continuous supply of export receptors for mRNA transport.
What types of molecules are exported from the nucleus to the cytoplasm?
• Proteins • tRNAs • Ribosomal subunits These molecules are essential for various cellular functions in the cytoplasm.
What is a Ran-independent mechanism for nuclear export of mRNAs?
A method of exporting mRNAs that does not rely on the Ran protein This mechanism provides an alternative pathway for mRNA export.
What is the topic of the next lecture?
Vesicular Traffic, Secretion and Endocytosis This topic will cover processes related to cellular transport and secretion.
What is the reading assignment for the next session?
Chapter 14: 622-641 This chapter likely contains relevant information on vesicular traffic and related processes.