lec 8-9 cell compartments and communication Flashcards
importance of compartments
provide local environments for specific metabolic functions
phosphoglycerides
2 long chain fatty acids
one unsaturated CC bond causing kink
amphiphilic molecules
polar and non-polar molecules in phospholipid bilayers
different phospholipid head groups…
determine properties
longer hydrocarbon chains..
stronger interactions
less fluidity
decreased temperature of phospholipid bilayers…
tighter packing
crystal formation
cholesterol
sits in gaps caused by kinks in chain
form steroid rings
regulate fluidity
effect of cholesterol on membrane
partly immobilises hydrocarbon chains
decreases mobility and permeability of the membrane
formation of compartments
sheets of bilayers form enclosed compartments
hydrocarbon tails avoid water
energetically favourable
lipid rafts - bring proteins together to interact with each other - caused by addition of cholesterol
phospholipid translocators
membrane-bound enzymes
catalyse ‘flip-flop’ of individual phospholipids across sides of bilayer
3 mechanisms of protein movement between compartments
gated channels
translocators
vesicles
translocators
directly unwind and pull proteins across membrane from cytosol
vesicles
load and off-load cargo to different compartments via membrane fusion
NPC
nuclear pore complex
5 subunits of NPC
annular lumenal ring fibrils nuclear basket
function of NPC
helps transport large molecules between nucleus and cytoplasm
barrier between nucleus and cytoplasm preventing harm to nuclear genetic material
nuclear localisation signals
positively charged amino acid sequence
tag proteins for import into cell nucleus
how are nuclear localisaton signals recognised
by nuclear import receptors directly or indirectly
using adaptor proteins karyopherins/importins
Ran
small GTPase protein - molecular switch
how is Ran switched off
GTPase activating proteins (GAPs)
Ran.GDP
lots found in cytosol
do not bind to Karyopherins
free for import of cargo
when do karyopherins cross the nuclear pore complex
when Ran.GDP is bound to cargo
what happens when Ran.GDP binds to cargo
karyopherins cross NPC
cargo is exchanged for Ran.GTP
Ran.GTP-karyopherin complex is transported back out to cytosol
2 active spaces in mitochondria
matrix
inter-membrane space
Chaperone proteins
bind to synthesised proteins and prevent folding
hold them as polypeptides
what do signal sequences form before they bind to protein translocator complexes
ampiphilic alpha-helices with +ve charged clusters on one side
protein translocator complexes
TOM - transporter out of mitochondrial membrane
TIM - transporter into mitochondrial membrane
TOM complex
binds to signal sequence
facilitates transport across outer membrane using ATP hydrolysis
chaperones dissociate
TIM complex
sequence binds after interaction with TOM complex
what drives initial translocation of +vely charged residues to the mitochondrial matrix
the mitochondrial membrane potential
once the sequence has bound to TIM complex
translocation of +vely charged residues to mitochondrial matrix
ATP hydrolysis releases Hsp70 from polypeptide and drives the rest of the import
Hsp60 folds proteins correctly
inter membrane proteins have hydrophobic region…
stops TIM from translocating protein through inter-membrane space
inter-membrane proteins have second signal sequence..
transports back from matrix to inter-membrane space via OXA translocator
transport into chloroplasts
GTP and ATP used to get photo stem proteins across the double membrane
H+ gradient used for crossing thylakoid membrane
why is transport into endoplasmic reticulum different
it is a co-translational mechanism
the others are all post-translational
signal recognition particle
N-terminal amino acid sequence recognises and targets specific proteins to the ER
composed of many proteins and RNA
large hydrophobic pocket - methionine
using microbiology to study protein translocation
identify sequence to target specific protein
fuse sequence to reporter gene e..g GFP
express it in cells
mutageneiss alters single amino acids to determine which structural elements are important
using biochemistry to study protein translocation
in vitro translated protein (labelled with radioactivity) is incubated with and without organelles
why is cell communication necessary
cell organisation
control output signals
interpreting input signals
examples of signalling molecules
nucleotides small molecules steroids proteins fatty acids dissolved gases
examples of nucleotide signalling molecules
cAMP
NADPH
nitric oxide on smooth muscle
relaxes smooth muscle
increased blood flow
erection
paracrine secretion signalling
molecule released into extracellular environment acts locally on neighbouring cells signal molecule rapidly taken up specific reaction initiated signal doesnt diffuse far
synaptic signalling
secretion of chemical into synaptic space as a result of electrical impulse
very rapid and specific signal
high conc. of hormone - low affinity of receptor for binding
synapse-synapse
short range
axons
long range signalling
endocrine signallign
long range signalling
anywhere in body
hormone released into bloodstream
low conc of hormone in blood - binds with high specificity/affinity to receptor
gap junction signalling
direct communication
allow transfer or small molecules and inorganic ions
cytoplasmic filled channels connecting cells
indirect signal communication into a cell
signal binds to cell surface receptor inducing conformational change
ion channel coupled receptors
rapid synaptic signalling
voltage gated channels undergo conformation change upon ligand binding
removes charged residues from channel allowing ion influx
GPCR
7 transmembrane domains on receptors
ligand binds and conformational change to trimeric G proteins
1 subunit dissociates and activates enzyme
enzyme couple receptors
1 transmembrane domain - forms a dimer
activates catalytic domain
tyrosine receptors
autophosphorylation of cytosolic sites on receptor - triggers other pathway 0 creates docking sites downstream
where does phosphorylation mostly occur
serine and threonine residues of amino acids
signals can be amplified
one molecule activates one receptor cascade initiated kinase activity amplifies signal effector proteins activated
positive feedback mecahnisms
out put stimulates its own production
signal speed depends on..
how the cell receives the signal
examples of how fast signal speed is created
binding of neurotransmitter ion channel
phosphorylation of a protein
protein present in cell already - secretion
examples of how slow signal speed is created
when gene expression is involved
e.g. cell growth, differentiation
