new stuff Flashcards
importance of compartments
provide specific local environments
3 types of protein sorting
gated
transmembrane
vesicular
gated transport
protein sorting
between cytosol and nucleus
small molecules can diffuse through
Active transport of macromolecules
loading of cargo using Ran.GDP to cross the NPC
karyopherin.Ran.GTP complex
transmembrane transport
between cytosol, mitochondria, plastids (chloroplasts) peroxisomes and ER
requires translocator proteins
post-translational transport
between cytosol and mitochondria, plastids and perxosiomes
co-translational transport
between cytosol and ER
transmembrane transport from cytosol to mitochondria
proteins held as polypeptides by chaperone proteins (Hsp70 family)
TOM complex- used to cross outer membrane, dissociation of chaperones
TIM complex - used to enter matrix, Hsp70 bidnds, ATP hydrolysis, Hsp60 folds proteins correctly
mitochondrial membrane potential is driving force
vesicular transport
between ER and golgi
between golgi and early/late endosomes
from golgi to cell exterior
G-actin
globular actin
can be present as a free monomer
transitions into F-actin under nucleotide hydrolysis and actin binding proteins (ABPs)
actin
2 stranded helical polymer
most abundant protein in most eukaryotic cells
most protein-protein interactions
actin cortex
lies underneath plasma membrane
provides strength and shape to lipid bilayer
actin based cell surface projections
filopodia
used for cell movement and actin-based motility of pathogens
actin cytoskeleton
provides asymmetry to cells
e.g. seen in budding yeast cells
Microtubules are used for
long range transport
cell migration
actin polymerisation at plus end causes protrusion of leading edge
contraction of back edge caused by interaction with myosin
actin in cytokinesis
actin and myosin make up contractile ring - belt that constricts to separate two daughter cells
intermediate filaments
desmosomes - cell junctions nuclear lamina (mechanical support/cell division)
basis of muscle contraction
actin interaction with myosin
G proteins
guanine nucleotide binding proteins
family of proteins
more than 700 in humans
transmit signals to cell interior
G protein strucuture
7 transmembrane domain receptor
serpentine - polypeptide chain threads in and out bilayer
ligand binds to g protein
causes 3D conformational change
GEF
GAP
guanine nucleotide exchange factor
gtpase activating protein
induce GTP/GDP exchange
regulators of g proteins
multidomain proteins regulated by extracellular signals and localised cues
may be potential therapeutic targets for drug development
Gi and Gs
effect adenyl cyclase activity
targets for medical toxins eg cholera
transmembrane proteins are usually linked to
enzymes on their cytosolic side
e.g. kinases
roles of phospholipase C (PLC)
liver - vasopressin - glycogen breakdown
smooth muscle - Ach - muscle contraction
Rhodopsin
light activated GPCR in eye (in rods of retina)
advantages of GPCR
most common method of cellular signalling
allows amplification of signals
works synergistically to produce correct response
G proteins have pivotal function
molecular transducing elements that couple membran receptors to their molecular effectors
Gq pathway
PLC activated
PLC cleaves phospholipid
PIP2 cleaves into DAG and IP3
IP3 released into cytosol and binds to receptors (e.g. Ca channels in ER) - cytosolic Ca conc increases
DAG remains membrane bound and activates PKC with Ca causing phosphorylation cascade
monomeric G proteins
used in cytoskeleton and vesicle trafficking
first discovered in virus causing rat sarcoma tumours
called Ras
ras
small GTPase
regulates cell differentiation and proliferation
relayes signals from kinase receptors to the nucleus
G proteins can directly bind and activate ion channels
seen in neurons and some heart muscle cells
e.g. GPCRs bind Ach
can influence membrane potential
called muscarinic receptors
GAPs
determine rate of GTP hydrolysys
terminate signalling
types of polarity
dorsal/ventral
anterior/posterior
left/right
EPP
epithelial polarity programme
apical surface
faces externally
permeable to water soluble molecules
SA can increase
basolateral surface
impermeable
faces internally to blood supply
why is cytoplasmic polarity required
to generate different cell progenes for tissue morphogenesis
why is membrane polarity required
for crucial vectorial transport function s
apical and basolateral surfaces of epthelium
separated by tight junctions
different lipid/protein compositions
