Intracellular Processes Flashcards
what are the 2 major strategies to segregate molecules?
multi component complexes and compartmentalisation into membrane-bound organelles
explain the basic process of protein synthesis necessity and where they move to and from
they need to be replenished and maintained, they’re transferred from cytosol (where they’re made) to the compartment where they’re used (organelle), newly synthesised proteins need to be targeted to the organelles
describe the process of protein compartmentalisation
protein is synthesised (starting at cytosol or on ribosomes) as a multi component complex of RNA and proteins, then proteins are dispatched to different locations in the cell (done using specific amino acid sequence ‘address codes’), once at correct location the protein enters the organelle
what are ribosomes made of, and what is their general structure?
made of proteins and rRNA, composed of 2 subunits
explain the unit of measurement used in ribosomes, and the general ribosomal formula
formula - 60S + 40S = 80S
S = Svedberg, non-linear measurement based on mass, density and shape, measured sedimentation rate (how quickly it will settle to the bottom after centrifugation)
gives 2 examples of how antibiotics target bacterial cell ribosomes
antibiotics may target decoding site or small ribosomal unit (e.g docycyline) and prevent tRNA binding or moving through ribosome
they may target peptidyl-transferase centre on large subunit (e.g erythromycin) preventing polypeptide chain elongation
how do hydrophilic proteins get into organelles?
nuclear pores (selective gates for nuclear proteins)
protein translocators (for proteins moving from cytosol to ER, mitochondria or peroxisomes)
transport vesicles (for proteins moving from the ER onwards)
how do ribosomes know to go to the ER?
signal peptides on the protein being made (specific sequence on the N-terminal amino acids)
how is signal peptide guided to ER membranes?
SRP (signal recognition particle) - in the cytosol and binds to ER signal peptide when it’s exposed on ribosome
SRP receptor - embedded on ER membrane
what happens to polypeptides once entering the ER?
polypeptide continues to be created, threaded through protein channel translocon in the ER membrane
signal peptide cleaved by signal peptidase (ER membrane)
protein in ER lumen is encapsulated into transport vesicle that ‘buds off’ and secreted from ER
describe the process of proteins passing through the golgi
carried in vesicles that fuse to become cis cisterna
according to cis maturation model, proteins move through golgi stack undergoing enzymatic modifications, labelling them for a specific cell destination
transport from golgi to other compartments carried out with transport vesicles
describe how molecules move from the golgi to the endosome/lysosome
give an example of a protein targetted in this way
directed by golgi-added address label for ‘lysosomal’ (specific sugar chain M6P)
proteins labelled with M6P bind to specific receptor in golgi membrane
initial destination = endosome (matures into lysosome)
example - hydrolase enzyme
describe some PTMs proteins go through in the golgi
glycosylation - adding sugar residues (carbs) such as M6P, intense glycosylation = proteoglycans, minor glycosylation = glycoproteins
hyperphosphorylation of tau protein is a hallmark of several neurogenerative disorders (tauopathies)
name 4 common PTMs, what they add and their function
phosphorylation (phosphate group) - alters protein activity
acetylation (acetyl group) - in histones: gene expression regulation
farnesylation (farnesyl group) - targets proteins to cytoplasmic face of plasma membrane
ubiquitination (ubiquitin chain) - targets proteins for degredation
name the 2 types of protein degredation
lysosomal and proteasomal
