basics of membrane transport-

Question 1

what do kinases and phosphatases do?

Answer 1

kinase - phosphorylate, activate signal transuction pathways

phosphatase - remove phosphate, dephosphorylate, shut down signalling pathway

Question 2

what does a signal tranduction cacde leas to?

Answer 2

amplification of orignal signal

Question 3

what adaption would a cell have to detect a signal at LOW CONC?

Answer 3

the cell surface receptors would be HIGH AFFININTY and coupled to an amplification system to activate the signalling systems

also SPECIFICITY, reversible on/off non covalent bond , able to saturate

Question 4

name some examples of how cell can respond to cell signals

Answer 4

• alter metabolism e.g glygcogen metabolism
• excitation to propogate nerve impulse
• grow + divide e.g. GF response, mitogenesis
• cell death (programmed) apoptosis
• alter GENE expression e.g IgM synthesis

Question 5

outline a simple signal cascade

Answer 5

cortisol is able to freely cross the plasma membrane (hydrophobic) to the glucocorticoid cytosolic receptor.
GR is a TF so is able to move to the nucleus and alter gene transcription.

Question 6

what would a ligand bind to if it was hydrophilic?

Answer 6

If hydrophilic then molecule can’t cross lipid membrane

So require cell SURFACE receptors with a extracellular ‘ligand’ domain to couple

Question 7

describe ways to turn receptor on/off

Answer 7

use GTP and GDP proteins

use phosphorylation/kinases

Question 8

name some examples of secondary receptors

Answer 8

2nd messengers allow amplification of signals
cyclic AMP -> PKA

PLC -> IP3

Question 9

briefly describe active transport

Answer 9

Process where you can pump ions across a membrane using ATP. Can use a variety of transporters+channels
- co transporter
- ligand gated
- voltage gated
- mechanically gated

Question 10

how are Na2+, Ca2+, K+ channels structurally similar?

Answer 10

have 6 transmembrane domain helixes
all have S4 voltage sensor subunit around 70kD

Question 11

how would a ligand enter a cell if it was charged?

Answer 11

well the lipid bilayer is IMPERMEABLE to charged ions
therefore there is a need for ion channels (and pumps/transporters)

Question 12

what molecule is calcium (signalling) regulated by?

Answer 12

calmodulin!
which exposes the hydrophobic residues of calcium =changes conformation so signal cascade can continue

active site of receptors become active and can target effector protein (PKA)

Question 13

where is calcium stored?

Answer 13

biggest store is ER
also cytosolic, golgi, secretory vesicles
mitch temporarily

Question 14

describe strucutre of calmodulin

Answer 14

has 2 domains joined by a flexible linker and each domain has 2 EF hands that can bind to one calcium molecule each

EF hands found on many binding proteins

Question 15

off mechanisms in calcium signalling

Answer 15

SERCA pump
NCX changer
Ca buffers and chaperones

problems in these can lead to pathologies!

Question 16

what does the SERCA pump do?

Answer 16

pumps the Ca2+ from cytosol to the ER/SR lumen using ATP

Question 17

what does calsequestrin do?

Answer 17

it is a buffer protein within SR and bind to calcium
helps to pump calcium out against a concentration gradient

Question 18

what inhibits SERCA

Answer 18

b-adrenergic stimulation results in phosphorylation of phospholambin
which inhibits SERCA

Question 19

how does the sodium-calcium exchanger work? (NCX)

Answer 19

3 sodium IN CELL, 1 calcium out of cell so helps with calcium efflux

this exchanger is electrogenic and creates a current in response membrane potential

Question 20

why is NCX better than ATPases?

Answer 20

NCX works quicker than ATPases and at higher concentrations

Question 21

what is an agonist and an antagonist

Answer 21

agonist ACTIVATES receptor

antagonist INHIBITS the receptor

Question 22

what is likely to happen if a mitogenic signal is not turned off

Answer 22

mitogenic signal = growth and divide

if not switched off -> uncontrolled cell division -> cancer/tumour

Question 23

how do specific calcium codes differ?

Answer 23

the frequency, amplitude and duration of caclium osscilations determine the end result of selective intracellular activation processes

Question 24

what is the normal physiological range cytosolic and extracellular calcium

Answer 24

extracellular - 1.4mMol
intracellular 100nMol at rest
so calciuim has one of the largest ioninic gradients

Question 25

name some regulatory machinery for calciuim

Okay but how regulate

Answer 25

calcium pumps
ATP ases and exchangers like PMCA, SERCA
na/ca exchanger

STIM 1 and Orai1 CRAC channels as well for SOCE to replenish ouur stores of calcium

Question 26

how can intracellular calcium levels be induced

Answer 26

stimuli bind to receptors on cell surface, leads to second messenger levels rising of
inositol triphosphate -ip3
cyclic adp robdoe
naadp (Nicotinic acid adenine dinucleotide phosphate)????????

Question 27

how does calcium maintain its low intracellular/cytocsolic conc?> (100nmol)

Answer 27

1. using pumps and exchangers
2. sequeste/store calcium in SR, ER, mitch
3. chelating calcium, having it bound to proteins

Question 28

how can calcium be put into its stors?

Answer 28

SERCA pumps are located on the membrane of endo/sarcoplasmic reticulum to store calcium

there are also mitochondrial uniporters (although mitch store is temporary)

Question 29

which receptors are present on the ER?

Answer 29

Ip3 receptors and ryanodine receptors which mediate calcium release from the Stores

Question 30

how do non excitable cells become activted

e.g Pancreatic Acinar Cells

Answer 30

they do not have voltage gated ion channels so cannot generate an AP, rely on a second messenger
= calcium release from intracellular stores, which can then activate processes like granular secretion as seen in PAC

Question 31

how can we replenish the ER store ?

Answer 31

via store operated calcium entry
use the STIM1 ER membrane proteins which respond to low calcium in ER and interact with plasma membrane to TO ACTIVATE ORAI proteins and activate the CRAC channels
calcium entry then moves through the ER pump to remain in ER

in very toxic high intracellular calcium, we can inhibit this oligomerisation of STIM1

Question 32

what can a mutation in PMCA2 result in

Answer 32

is linked to deafness, ataxia (lack of coordination), motor imbalance

Question 33

what is function of serca pump?

Answer 33

pumps calcium from cytosol into lumen of ER/SR using atp
> removes cytosolic calcium

Question 34

how is serca pump regulated

Answer 34

phosphorylation of phospholambin inhibits SERCA and is under beta-adrenergic stimulation

Question 35

what does the sodium calcium exchanger do? (NXC)

Answer 35

3 sodium inside cell
1 calcium outside of cell
> allows calcium efflux to occur

Question 36

where are NXC usually present? What is the advantage

Answer 36

in cells with lot of calcium channels like cardiac myocytes, smooth muscle, renal, pancreatic

they work quicker than ATP-ases especiallly at higher concentrations

Question 37

generally speaking how would elevated calcium levels result in pathology

Answer 37

high cytosolic calcium can detabilize zymogen granules and expand and rupture

this releases digestive enzymes like trypsin and result in cell death -> may spread to neighbouring cells = inflammation

Question 38

what could be some causes of elevated calcium channels

Answer 38

bile acids
alcohol metabolites
drugs like aspariganases

Question 39

what is the issue with CRAC channels

Answer 39

CRAC channels on plasma membrane open to replenish the ER store

but this can EXACERBATE THE PROBLEM

Question 40

where can EF hands be found?

Answer 40

they able to sense calcium
> calmodulin has 2 EF hands so 4 binding sites
> STIM1/2 have EF too to sense ER store of calcium