Membrane Structure and Function Flashcards
What is the water in the body divided into?
> Intracellular fluid - 60%
ECF - 40%
- 1/3 interstital fluid and 2/3 plasma
what are the main components of the ECF?
> sodium ions
chloride ions
calcium
what are the main components of the ICF?
> potassium
proteins
low in Ca2+
what are the main functions of the plasma membrane?
1) physical isolation: ICF from ECF
2) regulation of exchange with the environment -> ions, waste, nutrient molecules
3) communication -> receptor proteins
4) electrical excitability -> nerve cells
5) structural support via cell-cell or cell-extracellular matrix junctions
What type of lipids are in the plasma membrane, and what are there basic properties?
- glycerophospholipids—> Phospholipid
- sphingolipids —–>Phospholipid
- glycolipids -> derivative of sphingolipids with a sugar attached, often receptors
- cholesterol
> amphipathic: - hydrophilic heads
- hydrophobic tails
what are the properties of cholesterol in the PM?
> precursor molecule for bile acids, steriod hormones and vit D
free cholesterol moderates membrane fluidity ( more cholesterol = more rigid, less fluid)
held in place by non-covalent, physical interactions between steroid nucleus and fatty acid tails
movement of cholesterol into and out of the membrane is possible as there are no covalent bonds
What are carbohydrates role/ structure in the plasma membrane?
> carbohydrates on cell surface only ever face the extracellular environment = signal recognition
sugars present as glycolipids, most glycoproteins
glycoproteins formed in the rER, modified by Golgi
What are the 4 different broad functions in the Plasma membrane?
1) structural proteins
2) enzymes
3) receptors
4) transporters - ion channels etc
> they move freely in the membrane or are anchored by cytoskeletal elements
> higher metabolic activity of cell = more proteins -> mitochondria
what are the 3 different structures of proteins in the plasma membrane?
1) integral membrane proteins
- penetrate lipid bilayer
- span from one side of the membrane to the other -> amphipathic
- ion channels are commonly this type
2) peripheral membrane proteins
- attached to membrane via integral proteins or by polar portions of the phospholipid heads
- on outside of cell
- enzymes
3) lipid-anchored proteins
- covalently bound to lipid tails
- inside the cell
- receptors, enzymes
describe receptors structure and functions
> membrane receptors - integral membrane proteins - carbohydrates bound to integral proteins or phospholipids > lots of things can bind to receptors: - antibodies - viral infection - hormone uptake - insulin - neurotransmitters - ACh - growth factors
what determines a molecule’s ability to permeate the membrane?
> lipid bilayer is non-polar= highly impermeable to ions (polar)
things that make it easier to permeate =
- small in size (O2, CO2, N2)
- chemical charge
eg charged molecules cannot cross, but uncharged (h20, ethanol etc) can cross
describe the variables influencing simple diffusion
- concentration gradient
- lipid solubility
- size of molecule
- membrane surface area
- membrane thickness
- composition of bilayer
- potential difference
- diffusion potential
Describe facilitated diffusion
> ‘carrier-mediated’ transport or passive diffusion
mediators are carriers, channels or pores formed by protein complexes
movement of solute occurs sown an electrochemical gradient: NO ENERGY INPUT REQUIRED
at lo solute conc. facilitated diffusion faster than simple diffusion but saturates at a higher solute conc.
Membrane channels/pores involved:
- integral membrane proteins with transmembrane units
- transport of ions is down their conc. gradient - faster than carriers or pumps but less selective
What are the three types of integral membrane proteins involved in carrier-mediated transport?
1) pore
- remains open
- aquaporin water channel
2) Channel
- has a moveable gate
- therefore is opened and closed
- all ion channels
- voltage, chemically or mechanically gated
3) carrier - active transport
- gated by two doors that are never open at the same time
- na/k atpase pump and na/glucose cotransporter
what are the different types of carrier proteins?
> change conformation to move molecules across the membrane, are never open to ECF and ICF at the same time
uniporters: transport only one type of molecule
Co-transporters: carry > 1 type of molecule
- symporters (same direction) -> glucose/Na+
- antiporters ( opposite direction)-> K+/Na+
