Intracellular Processes Flashcards
describe the concept of compartmentilisation in cells
different organelles carry out different and specific functions
e.g. cytosol - where proteins are made
80s=
60s + 40s
s in ribosome measurement
= svedberg
a non-linear measurement depending on mass, density and shape; measures the sedimentation rate
what does the main antibiotic of bacterial cells target
the decoding site located on the small ribosomal subunit
(prevents tRNA binding or moving through ribosome)
methods of movement
nuclear pores - selective gates for nuclear proteins
protein translocators - from cytosol into ER, peroxisomes
transport vesicles - ER onwards
sorting of proteins
1- signal peptides ‘tells’ protein to go to ER
- N-terminal amino acid
2- signal-recognition particle (SRP) in the cytosol binds to ER signal when exposed
3- SRP receptor embedded on ER membrane
4- SRP binds to the signal peptide on ribosome
5- SRP receptor on ER binds to SRP on the ribosome/ polypeptide chain
6- holds the ribosome in place so the polypeptide chain feeds through protein channel into ER as it is produced
protein trafficking (movement to and through Golgi apparatus)
1- protein in vesicles as it reaches the cis cisternae
2- modified (by enzymes) and packaged into vesicles to go to target location
3- proteins are sorted in trans Golgi network
same target network = same location
arrangement of Golgi apparatus
closest to ER -> farthest
cis cisternae; medial cisternae; trans cisternae; trans Golgi network
movement occurs in waves (cis maturation model)
exocytosis
‘stop translocation’ on c-terminal
proteins remain anchored to the ER membrane
vesicles from ER then fuse with plasma membrane
movement to lysosome
determined by side chain ((monose-6-phosphate (M6P))
M6P binds to specific receptor in Golgi
initial destination is endosome, which matures into a lysosome
e.g. hydrolase
protein modification
-necessary for delivery to target destination
- specific sugar molecules are added to a core oligosaccharide (attached to protein) (act as signal, M6P, glycosylation)
receptors have domains that extends through trans-Golgi membrane (molecules become associated with trans-Golgi membrane
after the vesicle docks + fuses at target destination; molecule released; signal is removed (e.g. M6P); receptors are sent back to Golgi for re-use
post translational modifications
PHOSPHORYLATION - alters activity of protein (hyperphosphorylation of Tau protein is a hallmark for several neurogenerative disorders (taupathies))
ACETYLATION - in histones (gene expression)
FARNESYLATION - targets proteins to cytoplasmic face of plasma membrane
UBIQUITINATION - targets proteins for degradation
targets of protein degredation
old, faulty or foreign cells
lysosomal protein degradation
targets long half-life; membrane/ extracellular
lysosomal enzymes (lipases, nucleases, protease (pH 4.8))
>20 hrs (autophagy)
membrane proteins brought by endocytosis; extracellular proteins via receptor-mediated endocytosis; pathogenic proteins via phagocytosis
proteasomal protein degradation
targets short half-life; key metabolic enzymes/ defective proteins
in the cytosol at proteasomes = cylindrical protein complexes
‘walls’ made from protease enzymes shield the active site
protein ‘stoppers’ at either end - have to open to allow protein in
ATP-dependant
SPECFIC SEQUENCE: PEST - rich in Proline, Glutamic acid, Serine + Threonine
proteins are covalently tagged with ubiquitin in 3-step process
1- shutting proteins take ubiquinated protein -> proteasome
2- tagged proteins recognised, unfolded and translocated (peptides)
3- peptides extruded + digested by cytosolic peptidases
