L5 - Membranes Flashcards
Diffusion
Net movement of particles from an area of higher to lower solute concentration
NB: molecules will diffusé both ways but net Movement will be from H-L
Passive process means no…. is needed?
Energy , ATP etc.
Gas exchange surfaces are adapted for efficient diffusion. In what way?
- Thin surface- only one layer of epithelium thick = short diffusion pathway
- give gas exchange organs LARGE SA TO VOLUME
- increases rate of diffusion and temp!! ( bcos molecules have more Ek – move faster )
Another name for cell membrane
Plasma membrane
Surface membrane??
What do cell membranes contain?
- LIPIDS ( usually phospholipid as they are membrane lipids remember!) its amphipathic also !
- PROTEINS
- CARBOHYDRATES (usually attached to lipids or proteins)
Model of cell membrane : Fluid Mosaic model
EXPLAIN
- phospholipid bilayer forms :
Fatty acids x2 = tails = Hphobic
Phosphate group = heads = Philic
Protein molecules scattered like a mosaic
Nb this layer is LIQUID
- GlycoPROTEINS - some proteins attached to polysaccharide i.e. Type of carbohydrate
- GlycoLIPIDS - some lipids = attached to polysaccharide chain (carbohydrate )
Glycol is referring to carbs I think! CORRECT
- Membrane is partially permeable to small molecules
- larger molecules or ions must go through special membrane proteins i.e. Channels and carriers - Cholesterol = membrane lipid
- Flows through phospholipids
- Forms BONDS
- Decreases fluidity of membrane
- Makes it more RIGID
Osmosis
Net movement of water through a selectively permeable membrane, as it passes from an area of high water concentration to an area of low water concentration
How to molecules go past or through or transport material through CELL MEMBRANE
- small molecules diffusé or pass through easily
- larger molecules need more help - special membrane proteins called
CARRIERS & CHANNEL PROTEINS
How CARRIER proteins work
- Molécule that wants to get through etc attaches to carrier protein
- Causes a CHANGE OF SHAPE ( In what tho? ) IN CARRIER PROTEIN
- molecule released other side of membrane
- Down CG
How CHANNELS work ?
- Create PORES in the membrane to allow molecule to pass through
- Down CG
Active transport :
- ATP needed
- only works with CARRIER proteins
- forces molecules to move AGAINST their CG - think is to do with ECF & ICF?? YES
Some molecules are too big a carrier proteins can’t help them.
Alternatives?
- ENDOCYTOSIS
- cell membrane of cell surrounds a molecule
- CM piches off to form a vesicle inside the cell contains the ingested substance
ATP NEEDED
EXOCYTOSIS
What happens?
How cells secrete or get rid of substances
How it occurs :
- vesicles containing unwanted substances move away from Golgi and towards the cell membrane
- fuse with CM & release their substances outside of the cell
- note: some membrane proteins won’t go OUTSIDE the cell but will go back into the cell membrane
ATP NEEDED
Cholesterol controversy !! Which is it ???
Lecture says moderated fluidity of molecule but CPG’s say decrease fluidity of membrane
????
Membrane proteins
- What are they?
- function (4)
- Proteins part of or inserted into the membrane
- most form ALPHA HÉLICES crossing the membrane
- membrane inserted but is HPHOBIC
- functions :
- TRANSPORTERS & CARRIERS
- Anchors?
- Receptors -
- ENZYMES - bio catalysts
Fluid mosaic model - function of FLIPPASE enzymes
Causes the flipping of phospolipds in fluid mosaic model of CM
- v unfavourable & thus delta G must be pos!!
Transporters splits into
Active - ATP needed
Passive - no ATP needed
Slow process for both
- AT - aka : PUMP since ATP must be pumped
AT : vs CG
PT : with CG
Are transporters the same as carriers??
Think So
Channels i.e. Ion channels - what type of process is allowed - fast or slow - types of ion channels -
- ONLY ALLOW FACILITATED DIFFUSION ( passive diffusion)
- fast
- 2 types : voltage gated - open/close due to membrane potenitial changing - AP’s etc
& - ligand gated ion channels - open/close due to ligands binding to them
At: active transport can be further subdivided into :
Check this re lecture notes
Primary - driven by ATP
Secondary - driven by a transport of ATP
PRIMARY :
- Na+/ K+ ATPase pump
- 3 Na out & 2 K in
- Vs CG
But DIGOXIN inhibits this process
- Meaning Na CG is reduced
- Meaning concentration of Ca inside the cell increase
(NB; Ca needed for muscle contraction)
- used to treat heart failure ; heart can contract faster
SECONDARY :
- Energy produced in same way ( Na / K pump etc)
- but this energy is used to drive other transport reactions in same : SYMPORT or opposite: ANTIPORT direction
Eg symporters glucose & AA uptake in gut
Antiporters : Na + & Ca 2+ antiport In heart!
Primary active transport
How does it occur
YouTube video animation v good!!
Picture the diagram,
- ECSurface of cell where Na + conc is higher than K+
- Na / K ATPase pump
-ICS of cell where K = higher conc than Na
Process :
- 3 Na & 1 ATP attach to pump
NOTE ; 3 Na join on side where there is less Na and more K ; NB
- ATP — ADP & Pi
- 3 Na join pump
- ADP is released
- this causes pump where Na ions are to change shape and thus Na moves towards outside of cell against its conc grad
- then 2 K ions attach to pump
- Pi is released
- causes pump To change shape & K is released into cell vs gradient
- continuous process
How does secondary AT occur?
Picture the image: same as PAT but there’s GLUCOSE &; another pump/ transporter aswell as normal pump.
( think it’s just a carrier protein as it changes shape when Na & glucose go in)
- Glucose is pumped into the cell along with Na ion
- energy is needed for this to occur (AS we are moving glucose VS its CG)
- the energy is provided by the sodium gradient ( which occurs due to ATP - IN primary active transport)
- thus it’s not directly from ATP that glucose is pumped vs it’s conc grad
- Na is then pumped back out of cell by PAT
- etc.
- since Glucose & Na go In same direction SYMPORTER protein
Opposite? ANTIPORTER protein
Receptors
- Special proteins that attach to ligands (signalling molecules ) &; produce a cellular response
- function of receptor will usually have changed
Eg of ligands
ligands; signalling molecules that bind to receptors
- Hormones
- Cytokines
- Neurotransmitters - Ach ?
Types of receptors and ex.
Cell surface receptors - Ligand gated ion channels ( NB : IC only support facilitated diffusion ) - enzyme coupled receptors - G protein coupled receptors
Intracellular Receptors
- bind Hydrophobic ligands
- eg. Steroid hormones like testosterone & oestrogen
- Thyroid hormone
- Vitamin D
Ligand gated ion channels that are receptors aka?
- Inotropic Receptors
- IC Coupled Receptors
GPCR - how do they work ?
Picture this:
- Receptor with an indent made for a ligand to bind easily
- alpha beta &; gama subunits attached to the receptor
- ADP is attached to the alpha subunit ; NB NB NB NB
- Once ligand binds all subunits move away
- GDP—- GTP
- alpha subunit moves away with GTP = ACTIVATED
- once ligand is removed alpha uses its own phosphorylation activity - GTP—–GDP & Pi
- subunits return to to the receptor
What activated G proteins can do:
- Can stimulate enzymes that produce second messengers
- they can AMPLIFY signals
- eg cAMP stimulates protein kinases (enzymes) &; thus they can phosphorylate various substances
- this can cause change in gene expression or metabolic regulation
Enzyme coupled receptors
How it occurs in receptor tyrosine kinase for eg
nb video - YOUTUBE
- Switched on by ligands binding
- often leads to DIMERISATION
( 2 polypeptides bond )
Receptor tyrosine kinase
- receptor that has tyrosine attached (AA) along polypeptide chain
- has kinase activity – can cause phosphorylation
Process:
- ligand binds to the receptor (2)
- causes a changé In shape
- 2 polypeptides aggregate
- ATP —-ADP & Pi
- Pi is added to each tyrosine
- relay inactive protein binds to tyr & Pi - cause A cellular response
