BIOL 230 Chapt. 15 Organelles and Protein Transport I

What strategies do prokaryotes and eukaryotes have for isolating and organizing chemical reactions?

biomolecular condensates/ membraneless organelles

What do prokaryotes/ eukaryotes form to isolate different proteins and molecules?

aggregates

How can you fractionate cell components?

repeated centrifugations at progressively higher speeds

Why do Eukaryotic cells need membrane enclosed organelles?

surface area to volume ratio is too small

What organelles make up the endomembrane system?

nucleus, ER, Golgi, peroxisome, lysosomes, plasma membrane

What organelles are semiautonomous?

mitochondria and chloroplasts

How do members of the Endomembrane system communicate with one another?

small vesicles

Where did the endomembrane system evolve from?

plasma membrane of an ancient archaeal via plasma membrane protrusions

Where did mitochondria and chloroplasts evolve from?

bacteria that were captured by ancestral archaeal cells

What are ribosomes? 

complexes of ribosomal RNA and protein

What does nearly all protein synthesis begin?

ribosomes in the cytosol

What is a sorting signal?

an amino acid sequence that directs proteins to the desired organelle

Do cytosolic proteins have signal sequences?

NO

What are the methods of protein transport from cytosol?

nuclear pores, protein translocators, transport vesicles

What do nuclear pores act as?

nucelar gates

What is the nuclear envelope? 

double membrane with inner and outer membranes, each a bilayer, that is continuous with the ER membrane and perforated by nuclear pores 

What do the extensive unstructured regions within proteins that line the nuclear pore form?

soft tangled meshwork inside pore that controls transport, allows small, water-soluble molecules to pass freely

What is the function of a nuclear localization signal? What do they contain?

directs a protein from the cytosol into the nucleus, contain several positively charged lysines or arginines

What is the nuclear localization signal recognized by? 

the nuclear import receptor

How do nuclear import receptors guide newly synthesized proteins to the nuclear pore?

by interacting with cytosolic fibrils

What happens during cargo delivery?

protein dissociates from the nuclear import receptor once inside the nucleus

What happens to the nuclear import receptor after it delivers its cargo? 

it exits the pore

What prevents nuclear import receptors from entering the nucleus empty handed and then returning to the cytosol carrying nuclear proteins?

hydrolysis of GTP drives nuclear transport in the appropriate direction

What is RAN?

monomeric GTPase (GTP binding protein) that mediates nuclear transport

What are the two forms of RAN?

RAN-GTP and RAN-GDP

Is RAN-GTP present in high concentrations in the cytosol or in the nucleus? 

the nucleus 

Is RAN-GDP present in high concentrations in cytosol or the nucleus?

the cytosol

What energy source fuels nuclear transport?

GTP hydrolysis

What is RAN-GAP (GTPase-activating protein)?

accessory protein that triggers GTP hydrolysis, located in cytosol 

What is RAN-GEF (guanine nucleotide exchange factors)?

protein that exchanges GDP for GTP, located in nucleus