week 4: lecture 5 Flashcards
-Endomembrane system: structure and function Nuclear enevlope endoplasmic reticulum golgi - proteins: nucleus export inport -process of protein traffic pathway from production in RER export from the cell -structure and function lysosme vocuole endosomes (32 cards)
membrane bound ribosome proteins will end up?
- in the lumen of the endoplasmic reticulum
- golgi
- lysosomes or being secreted by secretory granules, i.e exported.
what are rich in rough ER
pancreas
Endomembrane system includes
Nuclear envelope, endoplasmic reticulum, golgi apparatus, lysosomes, various vacuoles, tiny vesicles, endosomes
what membrane surrounds nucleus
double membrane envelope.
The nuclear envelope is penetrated by pores and is continuous with the endoplasmic reticulum.
What do proteins synthesised in the cytoplasm that are targeted for the nucleus contain?
Nuclear localization signal (NLS)
What can proteins with nuclear localisation signals do?
- Bind to an NLS receptor (importin).
- Conformation of the nuclear pore complex changes as the protein passes through.
- RNAs move through the NPCs as ribonucleoproteins (RNPs) and carry nuclear export signals (NES) to pass through.
How are RNAs transported from the nucleus?
- Most RNAs exit out of the nucleus rather than coming into it.
- Generally transported as RNA-protein complexes, in which the proteins carry the nuclear export signals.
How are ribosomal RNAs transported out
Ribosomes RNAs are a special case, in that they are:
- assembled with ribosomal proteins into ribosomal subunits
- before being exported from the nucleus.
Endoplasmic reticulum
Network of membranous tubules and sacs (called cisternae) that are continuous with the outer membrane of the nucleus.
Two types of ER
rough and smooth
Rough Endoplasmic Reticulum
- Network of membranes nearest the nucleus.
- studded with ribosomes engaged in protein synthesis.
Functions of rough ER
- makes secretory proteins
- membrane factory for the cell
Pancreas has extensive rough endoplasmic reticulum meaning
cell is actively involved in protein synthesis
smooth endoplasmic reticulum
- Continuous extension of the rough ER,
- surface lacks ribosomes
- more distantly located from the nucleus.
Functions of Smooth ER
- synthesis of lipids
- metabolism of carbohydrates
- detoxification of drugs and poisons
- stores calcium ions
what are rich in smooth ER
testes
- ovaries
- liver cells
- muscle cells.
Ribosomes free in the cytosol, proteins will end up?
staying in the cytoplasm for things like glycolysis and fatty acid synthesis
2 kinds of proteins transferred from the cytosol to the ER
1) water - soluble proteins which are fully translocated across the ER membrane and are released into the ER lumen.
2) Transmembrane proteins which are only partly translocated across the ER membrane and become emedded in it.
4 components required to direct a protein to the ER:
- ER signal sequence - part of the N - terminus of protein destined for ER - signal peptide.
- Signal recognition particl, SRP
- SRP receptor on the ER membrane
- Translocation channel in the ER.
N-linked glycosylation
Most important form of post - translational modification for proteins synthesised:
-folded in the endoplasmic reticulum.
-Majority of proteins in the secretory pathway require glycolysation in order to achieve proper folding.
- The addition of an N-glycan to a protein can have several roles:
- enhancing solubility
- enhancing stability
- create labels and targets for specificity
protein sorting
process of directing each individual protein to a specific destination
ER to Golgi transport
- At the ER, proteins destined for the extracellular space or to organelles along the route are packaged into vesicles that transport them to the golgi apparatus.
-At this point, cells seem to distinguish between:
>native proteins
>nonnative proteins
-ensuring that only appropriately folded and assembled cargo protein undergo forward transport.
bulk flow
Traffic that occurs during protein sorting.
golgi apparatus cis face
receive vesicles containing ER products
