MVU6 MEMBRANES - 1 Flashcards
end of the ubiquitination lecture and membranes (41 cards)
is it possible that a polypeptide sequence is not degraded by the proteasome?
yes, if it doesnt have lysines
how many proteins in total do the cutting in a proteasome?
6
what do AAA family ATPases do?
unfold proteins till primary structure
why do proteins need to be in primary structure before entering proteasome?
because the ring is very narrow
what is the function of the Ub receptor?
increases efficiency of targeting
on the outside of the cap
recognises the polyUb tail
selects only the K48 chains
protects against premature DUB activity
what are the two types of Ub receptors and what do they do?
- Intrinsic receptors: the cap subunit Rpn10 and Rpn13 bind polyUb
- extrinsic (shuttling) Ub receptors
separate from the proteasome
bind polyUb through Ub-associated domain (UBA)
have a Ub like domain (UBL) that is recognised by the cap
recognise poly UB proteins and bring them to the proteasome
what is the unfoldase protein called?
Rpt 1-6
what is the DUB protein called?
Rpn8/11
what happens when the Ub receptors recognise the tail?
conformational change and the tail is removed
what happens in the proteasome core?
cavity inside is small and narrow
proteins have to stay unfolded
3 active subunits in each beta ring, 6 in total
one cuts basic AAs, one cuts at acidic AAs, and one cuts at hydrophobic AAs
what happens after the proteins are cut?
peptides diffuse out and are digested into amino acids by peptidases
what defines the cell?
the membrane
what is the secretory pathway?
a transport system between several types of organelles in the cell surface
synthesis of proteins and proteins at the ER
traffic through the GA, to the plasma membrane
internalisation through endosomes, to degradation in lysosomes
some organelles (mitochondria) are not connected in the secretory pathway
what are characteristics of the lumen of secretory organelles?
the interior of the lumens is continuous with each other and the extracellular space
the lumental environments are similar to the extracellular space (blood plasma) and different from the cytosol
what do vesicles do?
bud from one organellar membrane and fuse with another without releasing contents to the cytosol
closed till they reach the target
what type of environment is the cytosol?
reducing
what type of environment is the lumenal/extracellular fluid?
oxidising
what functions do biological membranes fulfill?
provide enclosure to cells and to organelles within cells
allow regulated transport of materials between compartments
provide sites within cells for biochemical reactions (accumulate certain types of molecules)
photosynthesis, oxidative phosphorylation, metabolism of biological molecules
support contacts with the environment outside cells (cell motion, cell recognise other cells, cell fusion)
transmission of signals from exterior to interior of cells
what are properties of membranes?
form hydrophobic barriers between aqueous compartments within cells
flexible and can be folded into different shapes
selectively permeable to small hydrophobic molecules, but not to larger or charged/polar molecules
specialised protein complexes control the movement of impermeable molecules across membranes
can store energy as concentration gradients
- voltage (nerve cells)
- pH, potassium, sodium, calcium gradients
what are membranes made of?
lipid molecules and membrane proteins
how are lipids organised?
into a bilayer, polar on each side and hydrophobic in the middle
what can membrane proteins do in the fluid bilayer?
membrane proteins can rotate and diffuse laterally in the bilayer
they cannot flip
what are the major lipids in membranes?
phospholipids - in all membranes
glycolipids - only at plasma membranes (not in ER or GA)
cholesterol
other types with special functions
all have polar and hydrophobic sections
what does lipid composition determine?
physical properties of the membrane
mobility (diffusion rotation) and curvature, thickness
