endomembrane system Flashcards
what does the system contain
Golgi ER vesicles Nuclear envelope cell membrane
nuclear envelope/nuclear membrane consists of and can also be found in
lipid bilayer and contiguous with ER
Nuclear pores complex
regulate movement of molecules in and out of nucleus
protein that has column subunits and nuclear baskets etc
nuclear baskets
regulate size of molecules
movement of molecules direction
bidirectional - goes in both direction
molecules that can move into nucleus
building blocks for DNA and RNA synthesis
molecules for energy
molecules moving out of nucleus
ribosomal subunit synthesised by nucleus
Nuclear localisation signal (NLS)
amino acid sequence tags protein for entry into nucleus
Nuclear export signal (NES)
amino acid sequence tags protein for exit from nucleus
NPC function
allow small (5kda) molecules to move freely in and out of nucleus larger molecules move slower (>60kda) barely enter by passive diffusion
mitosis of nuclear envelope
breaks down during prophase
ER - endoplasmic reticulum - amount and function for proteins
> 50% of total cellular membrane
stores protein in lumen as well as golgi or lysosomes and delivered within ER
role of ER
protein and lipid synthesis
calcium store in cell used for signalling processes
RER - rough
covered in ribosomes for protein synthesis
transporting proteins into the ER in lumen or membrane
SER - smooth
lower proportion
for lipid synthesis
lipids bud off in vesicles and transported, fuse with membrane
co-translational protein import into ER
ribosome finds start codon and starts reading polypeptide chain
ribosome binds to ER membrane by the signal peptide (N-terminal)
ribosome continues to translate
protein is embedded into membrane
Post-translational translocation
polypeptide fully formed in cytoplasm
ribosome never binds to membrane
found in mitochondria, peroxisomes, chloroplast, nucleii
Transmembrane protein
partially translocated across membrane pores regulates movement of molecules embedded proteins and receptors peripheral proteins
peripheral proteins
proteins bound to one side of membrane
water-soluble protein
fully translocated across membrane
secreted by signal peptide and cleaved off
protein released into lumen of organelle
co-translational translocation into ER lumen
translocator in closed stated
opens when in contact with signal peptide
allow rest of polypeptide to go through
when fully translated, signal paptidase cleaves signal peptide
mature protein released and translocator closed
polysomes
single mRNA simultaneously bound by several ribosomes
moves along mRNA and translates to free up space for another ribosome to bind to make polypeptides
sucrose gradient
experimental technique
separates mRNA with different number of attached ribosomes
occurs at different times
glycosylation of protein in ER
ER have different glycosylate enzymes
glycosyl transferase within lumen of ER
