Intracellular compartments and protein sorting 1 (lecture 10) Flashcards
What is the Plasma membrane
- Outer boundary of cells,bilary
- fxn: protective barrier, has transporter, signaling
Nucleus
- Contains the genome
- principle site for DNA and RNA synthesis
Cytoplasm
- Consists of cytosol and cytoplasmic organelle
- intermediary metabolism
Enoplasmic Reticulum (ER)
- Ribosomes attached to it (rough ER), no ribosomes (smooth ER)
- Protein synthesis, lipid synthesis, protein folding, storage of calcium
Golgi apparatus
- Stacks of disc-like compartments
- site of post-translational changes on proteins and lipids, trafficking
Mitochondria
- Outer and inner membrane and matrix
- Makes ATP, signaling, cell differentiation and cell death
Lysosomes
- Contain digestive enzymes that degrade organelles and biomolecules
Peroxisomes
- Small vesicular compartments that contain enzymes used in oxidation reactions
What intracellular compartment makes up the majority of the cell
Cytosol
The cell can be divided into what 3 topological categories
- Nucleus and cytosol (communicate through nuclear pore complex)
- Organelles in secretory and endocytic pathways (ER, Golgi apparatus, endosomes, and lysosomes) (communicate through vesicles)
- Mitochondria
Nucleus and cytosol communicate through _____ complex
- nuclear pore complex
Organelles in secretory and endocytic pathways (ER, Golgi apparatus, endosomes, and lysosomes) communicat through
Vesicles
membrane ____ and ____ allows the lumen of the cell compartments to communicate with each other and with the cell exterior
Budding and fusion
Protein trafficking
- Gated transport
- Transmembrane transport
- Vesicular transport
Gated transport: between ____ and ___ through nuclear pore complexes (active transport and free diffusion)
Nucleus and cytosol
Transmembrane transport: membrane _______ directly transport specific proteins from cytosol across an organelle membrane
Protein translocators
Vesicular transport: membrane-enclosed transport intermediates move proteins between various compartments via
vesicles
Protein transfer/transport to various compartments guided by ____
sorting signals
Sorting signals on proteins are a stretch of amino acids, typically ____ residues long
15-60
Sorting signals may be localized on ___ or ___ terminus or _____
N or C terminus, within protein sequence
multiple scattered sequences in protein may form
signal patch
____ may remove signal after protein reaches final destination
signal peptidase
Protein signal sequences are both necessary and sufficient for _____
protein targeting
_________ properties of the protein signaling sequence are more important than the actual sequence
physical properties (charge,hydrophobicity)
Protein signal sequences are recognized by ______
complementary receptors
what is the protein signal sequence for importing into nucleus
- Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
- (note that there are 5 positive charges)
Nuclear transport is ____, _____ and _____
gated, bidirectional, and selective
Proteins needed in nucleus (e.g. histones, DNA and RNA polymerases, topoiserases, gene regulatory proteins) are imported from ____ where they are synthesized
cytoplasm
____ and ____ molecues synthsized in nucleus are exported to cytosol
tRNA and mRNA
Nuclear pore complexes (NPCs) perforate ____ in eukaryotes
Nuclear envelope
What si the moleuclar mass of nuclear pore complexes (NPCs)
125 million Daltons
Nuclear Pore Complexes (NPCs) are composed of ____ different proteins or ____-
30, nucleoporins
Nuclear Pore coplexes (NPCs) are arranged in ____- symmetry with one or more ______
ocagonal symmetry, aqueous pores
Nuclear envelope has ______ Nuclear pore comlexes (NPCs)
3000-4000
Nuclear Pore Complexes transport molecules in ______
both directions
Nuclear pore complexes (NPCs) transport molecuels in both directions. By means of ____ of small molecules and _____
Passive diffusion, facilitated transport
Nuclear pore complexes (NPCs) faciliate tansport by
binding of particles to fibrils extending from NPC
____ are sorting signals that direct molecules to the nucleus
- Nuclear Localization Signals (NSL)
Nuclear localization signals (NLS) are short sequences rich in _____ amino acids ____ and ____
postitivley charged amino acids lysine and arginine
Nuclar locatlization signals (NLS) are located on many different sites on protein- form ____ or ____ on surface
loops or pathes
Nuclear Localization Signals (NLS) result in ____ import of proteins into nucleus
selective
Nuclear localization signals (NLS) are recognized by
nuclear import receptors (NIRS)
Nuclar import receptors (NIRs) are ______ that bind to ____ on protein and to ______ present on fibrils that extend into cytoplasm
soluble cytosolic proteins, NLS, NPC proteins
NPC proteins have _____ which serve as binding sites for import receptors
Phenylalanine glycine (FG) repeats
Nuclear import receptors plus cargo traverse NPC by ___, ___, and ___ to adjacent Phenylalanine glycine (FG) repeats
binding, dissociating, and re-binding
Once cargo is released inside the nucleus the NIR
return to cytoplasm
Nuclear import receptors (NIRs) can either do ____ binding or ____ binding to cargo protein with help of adapter protein
direct or indirect binding
Nuclear export works similar to import but
in opposite direction
Nuclear export relies on _____ on molecules that need to go out of nucleus
nuclear export signals (NES)
For nuclear export Nuclear export signals (NES) on molecules need complementary
nuclear export receptors (NER)
NER binds to cargo present in nucleus and ____ proteins
NPC
Gradient of ____ conformational states drive nuclear transport in appriate direction
Ran
RAN-GTP binds to complex of ____ and ____. The binding causes release of cargo. Ran-GTP and ____ then leave the nucleus and return to cytoplasm. In the cytoplasm Ran-GTP is hydrolyzed by _____. The _____ is released from Ran-GDP and is ready for another cycle
import receptor and cargo, import receptor, Ran-GAP. Import receptor
Shuttle protein contain both ____ and ___. This allows them to shuttle back and forth between ___ and ___
NLS and NES. nucleus and cytosol
Steady state locatlization is dependent upon
relative rate of transport
If the rate of import is greater than export, the shuttle protein is considered ____
nuclear
Gene regulatory protein can regulate transport by turning ____ and ____ on and off. The mechanisms include ____, ____, and ______
NLS and NES. phosphorylation, proteolysis, and binding to inhibitory proteins
Feedback regulation of cholesterol biosynthesis
SREBP (sterol response element binding protein), a latent transcription regulator that controls expression of cholesterol biosynthetic enzymes, is initially synthesized as an ER membrane protein. It is anchored in the membrane by interaciton wiht another ER memabre protein, called SCAP (SREBP cleavage activation protein), which binds cholesterol. If the cholesterol binding site on SCAP is empty (at low cholesterol concentrations), SCAP changes conformation and is packaged together with SREBP to free its cytosolic domain form the membrane. The cytosolic domain then moves into the nucleus, where it binds to the promoters of genes that encode proteins involved in cholesterol biosynthesis and activates their transcription. In this way, more cholesterol is made when its concentration falls below a threshold.
