Intracellular Compartments and Transport Flashcards
Advantages of organelles
“House” chemical reactions: sequester damaging molecules, keep reactions together
Membrane: create gradient for H+ motive force, regulation
Organelle anchorage
Held in place by cytoskeleton
Cytosol
Contains many metabolic pathways
Protein synthesis
Nucleus
Main genome
DNA and RNA synthesis and maintenance
Nucleolus
Storage of ribosomal RNA and euchromatin
Endoplasmic reticulum
Synthesis of most lipids (smooth)
Synthesis of proteins for distribution to many organelles and to the plasma membrane (rough)
Golgi apparatus
Modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle
Lysosomes
Intracellular degradation
Endosomes
Sorting of endocytosed material
Mitochondria
ATP synthesis by oxidative phosphorylation
Chloroplasts
ATP synthesis and carbon fixation by photosynthesis
Peroxisomes
Oxidation of toxic molecules
Cajal
Area of nucleus where RNA is processed
P bodies
RNA turnover
Endomembrane system
Nucleus, plasma membrane, ER, golgi, endosomes, lysosomes/vacuoles, vesicles
Originally formed from invaginations of plasma membrane
Protein sorting
Transport through nuclear pores (nucleus proteins)
Transport across membranes
Transport by vesicles
Signal sequences
Targeting motif
Directions to where the protein is supposed to go
How to determine where protein goes
Look at signal sequence
Label w/ fluorescent antibody and see where it goes (stain organelles or proteins in organelles)
Mutate sequence and see what happens (determine correct sequence as signaling)
Nuclear envelope
Outer membrane: contiguous with ER
Inner membrane: nuclear lamina
Nuclear localization signal (NLS)
Allows nuclear protein to be transported through pores into nucleus
Nuclear pores
Openings into nucleus: selective gates
Protein with NLS is attached to transport protein
Protein swings from tangle to tangle until it reaches nucleus
Mitochondrial and chloroplast protein import
Signal sequence is recognized by receptor
Receptor diffuses- forms contact site
Unfolded protein snakes through
Protein is folded in matrix
ER Transport
Proteins destined for golgi, lysosome, plasma membrane, endosomes, or secretion enter the ER first
2 types of proteins: water-soluble (lumen or secreted) or transmembrane
Proteins are imported as they are translated
Polypeptide being synthesized directs its ribosome to ER by its signal sequence
Directing an ER polypeptide to the ER
- Signal recognition particle (SRP) binds to ER signal sequence
- SRP binds to SRP receptor in ER membrane
- Translocation channel opens
- Polypeptide snakes through channel
Soluble protein going to ER
- Signal sequence is cleaved off and polypeptide is released in lumen and folded
Transmembrane protein going to ER
- During translocation, a stop transfer sequence goes through the translocator
- Those sequences diffuse through the membrane and the signal sequence is cleaved off
Both soluble and transmembrane portions of protein going to ER
- Start transfer sequence is internal to polypeptide
- Polypeptide threads through until stop transfer sequence reaches translocator
- Transmembrane domains diffuse into membrane- neither start nor stop transfer sequence is cleaved
ER protein folding and modification
Oxidation of thiols and cysteines to fold proteins
Chaperones assist in protein folding
Unfolded protein response
Too many unfolded proteins- more chaperones and ER are made
If problem isn’t fixed, apoptosis is triggered
Vesicular transport
- ER buds off
- Buds fuse with cis side of golgi
- Travels through cisternae (folds of golgi)
- Reaches trans side of golgi
- Secretory pathway- transport vesicles take products and release them into extracellular space
- Endocytic pathway: vesicle pinches off and fuses with early endosome
- Changes to early endosome (especially increasing acidification) turn it into a late endosome, which fuses with lysosome
Clathrin
Basket shaped protein that forms coat around vesicle
Vesicle budding
- Adaptin recognizes receptor that needs to be endocytosed (change in shape of receptor by binding to cargo is recognized)
- Adaptin recruits clathrin
- Clathrin forms invagination
- Dynamin pinches off vesicle
- Clathrin and adaptin dissociate
Vesicle recognition and docking
- Rab (specific for cargo and target organelle) is recognized by tethering protein
- V-SNARE interacts with t-SNARE to pull vesicle close to target
- Membrane mixing- cargo is delivered
Secretory pathway
Delivery of cargo from ER to golgi to the cell surface for exocytosis
Cargo can be signaling proteins, extracellular matrix, etc.
Sometimes stored in secretory vesicles until needed (ex- insulin, neurotransmitters)
Pinocytosis
Cell drinking
Ingestion of plasma membrane, fluid, and small molecules
Carried out by clathrin-coated pits and vesicles (fuse with endosomes)
Phagocytosis
Cell eating
Ingestion of large particles into phagosomes
Fuses with lysosome- form phagolysosomes
Performed by phagocytic cells
Receptor-mediated endocytosis
- LDL receptors bind to LDL
- Vesicle budding
- Uncoating of clathrin
- Fusion with endosome
- Transfer of LDL to lysosome and budding off of transport vesicles carrying receptors
- Return of LDL receptors to plasma membrane
Autophagy
Self eating
Organelles and large portions of cytoplasm are engulfed by autophagosome (triggered by cell starvation or because organelles are old and no longer functioning)
Lysosomes break down contents of autophagosomes
V-type transporter
Similar to f-type ATPase, but runs in opposite direction
Gives lysosome an acidic interior
