lec 8-9 cell compartments and communication

Question 1

importance of compartments

Answer 1

provide local environments for specific metabolic functions

Question 2

phosphoglycerides

Answer 2

2 long chain fatty acids

one unsaturated CC bond causing kink

Question 3

amphiphilic molecules

Answer 3

polar and non-polar molecules in phospholipid bilayers

Question 4

different phospholipid head groups…

Answer 4

determine properties

Question 5

longer hydrocarbon chains..

Answer 5

stronger interactions

less fluidity

Question 6

decreased temperature of phospholipid bilayers…

Answer 6

tighter packing

crystal formation

Question 7

cholesterol

Answer 7

sits in gaps caused by kinks in chain
form steroid rings
regulate fluidity

Question 8

effect of cholesterol on membrane

Answer 8

partly immobilises hydrocarbon chains

decreases mobility and permeability of the membrane

Question 9

formation of compartments

Answer 9

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

Question 10

phospholipid translocators

Answer 10

membrane-bound enzymes

catalyse ‘flip-flop’ of individual phospholipids across sides of bilayer

Question 11

3 mechanisms of protein movement between compartments

Answer 11

gated channels
translocators
vesicles

Question 12

translocators

Answer 12

directly unwind and pull proteins across membrane from cytosol

Question 13

vesicles

Answer 13

load and off-load cargo to different compartments via membrane fusion

Question 14

NPC

Answer 14

nuclear pore complex

Question 15

5 subunits of NPC

Answer 15

annular
lumenal
ring
fibrils
nuclear basket

Question 16

function of NPC

Answer 16

helps transport large molecules between nucleus and cytoplasm

barrier between nucleus and cytoplasm preventing harm to nuclear genetic material

Question 17

nuclear localisation signals

Answer 17

positively charged amino acid sequence

tag proteins for import into cell nucleus

Question 18

how are nuclear localisaton signals recognised

Answer 18

by nuclear import receptors directly or indirectly

using adaptor proteins karyopherins/importins

Question 19

Ran

Answer 19

small GTPase protein - molecular switch

Question 20

how is Ran switched off

Answer 20

GTPase activating proteins (GAPs)

Question 21

Ran.GDP

Answer 21

lots found in cytosol
do not bind to Karyopherins
free for import of cargo

Question 22

when do karyopherins cross the nuclear pore complex

Answer 22

when Ran.GDP is bound to cargo

Question 23

what happens when Ran.GDP binds to cargo

Answer 23

karyopherins cross NPC
cargo is exchanged for Ran.GTP
Ran.GTP-karyopherin complex is transported back out to cytosol

Question 24

2 active spaces in mitochondria

Answer 24

matrix

inter-membrane space

Question 25

Chaperone proteins

Answer 25

bind to synthesised proteins and prevent folding | hold them as polypeptides

Question 26

what do signal sequences form before they bind to protein translocator complexes

Answer 26

ampiphilic alpha-helices with +ve charged clusters on one side

Question 27

protein translocator complexes

Answer 27

TOM - transporter out of mitochondrial membrane TIM - transporter into mitochondrial membrane

Question 28

TOM complex

Answer 28

binds to signal sequence facilitates transport across outer membrane using ATP hydrolysis chaperones dissociate

Question 29

TIM complex

Answer 29

sequence binds after interaction with TOM complex

Question 30

what drives initial translocation of +vely charged residues to the mitochondrial matrix

Answer 30

the mitochondrial membrane potential

Question 31

once the sequence has bound to TIM complex

Answer 31

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

Question 32

inter membrane proteins have hydrophobic region...

Answer 32

stops TIM from translocating protein through inter-membrane space

Question 33

inter-membrane proteins have second signal sequence..

Answer 33

transports back from matrix to inter-membrane space via OXA translocator

Question 34

transport into chloroplasts

Answer 34

GTP and ATP used to get photo stem proteins across the double membrane H+ gradient used for crossing thylakoid membrane

Question 35

why is transport into endoplasmic reticulum different

Answer 35

it is a co-translational mechanism the others are all post-translational

Question 36

signal recognition particle

Answer 36

N-terminal amino acid sequence recognises and targets specific proteins to the ER composed of many proteins and RNA large hydrophobic pocket - methionine

Question 37

using microbiology to study protein translocation

Answer 37

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

Question 38

using biochemistry to study protein translocation

Answer 38

in vitro translated protein (labelled with radioactivity) is incubated with and without organelles

Question 39

why is cell communication necessary

Answer 39

cell organisation control output signals interpreting input signals

Question 40

examples of signalling molecules

Answer 40

``` nucleotides small molecules steroids proteins fatty acids dissolved gases ```

Question 41

examples of nucleotide signalling molecules

Answer 41

cAMP | NADPH

Question 42

nitric oxide on smooth muscle

Answer 42

relaxes smooth muscle increased blood flow erection

Question 43

paracrine secretion signalling

Answer 43

``` molecule released into extracellular environment acts locally on neighbouring cells signal molecule rapidly taken up specific reaction initiated signal doesnt diffuse far ```

Question 44

synaptic signalling

Answer 44

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

Question 45

synapse-synapse

Answer 45

short range

Question 46

axons

Answer 46

long range signalling

Question 47

endocrine signallign

Answer 47

long range signalling anywhere in body hormone released into bloodstream low conc of hormone in blood - binds with high specificity/affinity to receptor

Question 48

gap junction signalling

Answer 48

direct communication allow transfer or small molecules and inorganic ions cytoplasmic filled channels connecting cells

Question 49

indirect signal communication into a cell

Answer 49

signal binds to cell surface receptor inducing conformational change

Question 50

ion channel coupled receptors

Answer 50

rapid synaptic signalling voltage gated channels undergo conformation change upon ligand binding removes charged residues from channel allowing ion influx

Question 51

GPCR

Answer 51

7 transmembrane domains on receptors ligand binds and conformational change to trimeric G proteins 1 subunit dissociates and activates enzyme

Question 52

enzyme couple receptors

Answer 52

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

Question 53

where does phosphorylation mostly occur

Answer 53

serine and threonine residues of amino acids

Question 54

signals can be amplified

Answer 54

``` one molecule activates one receptor cascade initiated kinase activity amplifies signal effector proteins activated ```

Question 55

positive feedback mecahnisms

Answer 55

out put stimulates its own production

Question 56

signal speed depends on..

Answer 56

how the cell receives the signal

Question 57

examples of how fast signal speed is created

Answer 57

binding of neurotransmitter ion channel phosphorylation of a protein protein present in cell already - secretion

Question 58

examples of how slow signal speed is created

Answer 58

when gene expression is involved | e.g. cell growth, differentiation