ch 15 Flashcards
(48 cards)
What is the difference between a Nuclear Localization Sequence (NLS) and a Signal Sequence?
NLS sends proteins into the nucleus and uses Ran-GTP to release protein inside nucleus. Protein often folded
Signal Sequence sends proteins into other organelles and uses ATP/GTP, protein often unfolded
T/F: Some signal sequences have more important structural features than specific amino acids sequences
True
How does the organelle recognize the signal sequence and allow the protein in?q
The organelle has a receptor that recognizes the signal sequence and allows to cross the organelle’s membrane using ATP and a protein channel/transporter
What is the signal sequence for import into ER?
2nd longest, look for bunch of Leu.
Signal sequence for retention in lumen of ER?
KDEL (Lys-Asp-Glu-Leu) (LAGLEU)
Signal sequence for import into mitochondria
N-terminus, very long bunch of Arg
Signal sequence for import into Nucleus
Series of Lys (KKK)
Signal for export from nucleus
Met - Leu - Leu- Phe (MET DELULU BAE) not all together
Signal sequence for import into peroxisomes
Ser-Lys-leu (SKL) South korea L
Which organelle does the nucleus’s outermembrane connect into?
the ER
Selective gate that goes through both membranes of the nucleus, allows stuff in and out depending on the molecule, tightly regulated.
Nuclear Pore
How do small vs large molecules (proteins) go through nuclear pores
Small Molecules: freely diffuse
large molecules: require a Nuclear Localization Signal that is read by nuclear transport receptors to specifically enter nucleus
What is a nuclear localization signal and what is it used for?
A short stretch of Lys and Arg that is read by nuclear transport receptors to specifically enter molecule into the nucleus.
Is transport through nuclear pores passive or active?
Active, requires energy to move proteins across membrane against gradient
Do proteins remain folded or unfolded when going through nuclear pores?
Fully folded
What is Ran?
A type of GTPase that regulates the transport of proteins through nuclear pores
RanGTP and RanGDP, which one is inside nucleus and outside? Explain functions of each
RanGTP = Inside Nucleus, binds to protein with NLS coming into nucleus, helps release protein inside nucleus
RanGDP = Outside Nucleus, hydrolyzed from GTP to GDP to release proteins outside nucleus
Explain the steps for proteins to enter nucleus through nuclear pores
- Protein with NLS attaches to Nuclear Transport Receptors in the cytoplasm
- Transport Receptor carries protein through nuclear pore into the nucleus
- RanGTP binds to transport receptor, causing a conformational change that releases protein inside nucleus
- Receptor goes back to cytoplasm
What prevents protein misfolding during transport and helps refold proteins once inside organelle?
Chaperonins/Chaperone Proteins
Explain how proteins are transported across mitochondrial and chloroplast membranes. use the following vocabulary: N terminal sequence, import receptors, protein trans locator (TOM and TIM) mitochondrial matrix, Chaperonins.
Protein binds its N-terminal sequence to import receptors on outer membrane, protein travels through import receptor protein and also goes through protein translocator in outer membrane (TOM) and then the inner one (TIM), protein is unfolded. Once inside mitochondria matrix, signal is cleaved off and protein is refolded with chaperonins.
What are the 2 kinds of proteins transferred from cytosol to ER? explain each and what do both have?
- Soluble Proteins: transferred completely to ER lumen during synthesis, destined to be secreted outside cell or to another organelle (not mitochondria)
- Transmembrane Proteins: halfway in ER membrane, destined to reside in ER or membrane of another organelle/plasma membrane
both have a N-termines signal to direct to ER
What do proteins need if they want to stay in the lumen of the ER?
C terminal signal (KDEL)
if a protein does not have an ER signal sequence, where does it gO?
it’s synthesized in the cytosol using free ribosomes instead of the ER and will stay there.
