Membranes I Flashcards
What are the 4 barrier functions of membranes?
> prevent metabolite loss
protect against unwanted outside molecules
capacitor - stores electrical chemical energy
- creates electrochemical gradient
important for energy production + electrical signalling
What do plasma membranes need to be able to allow cells to do?
Receive info
Import + export info
What are the functions of membrane proteins?
>selective permeability > maintain ionic composition > maintain cytoplasmic pH > control cytoplasmic osmotic pressure > sense enviro > anchor cytoskelton > mediate cell-cell + cell-ECM interactions > carry out membrane requiring enzymatic reactions
What pH are most cells at?
7.2
What are the specialised water channels in plasma membranes called?
aquaporins
What % of hepatocytes does the plasma membrane make up?
2%
What type of molecules are lipids?
Amphipathic
- have hydrophobic + hydrophilic regions
How large are most membranes?
How many can fit into 1mm?
5nm
200,000
It is energetically favourable for lipids to form what?
Why is this?
Sealed compartments
No hydrophobic edges in contact w/ water
Describe the structure of glycerophospholipds
3 C glycerol
- 2 C ester linked to fatty acids
- 1 C linked to P
What can vary on lipids?
What do these variations give?
The head group
Different properties to the lipid e.g. charge
What are the other types of lipids found in membranes? Give examples.
Glycoplipids - sphingolipids
Sterols - cholesterol
Phospholipids -Glycerophospholipids + sphingolipids
Why isn’t it energetically favourable for a polar head to flip to the other leaflet?
Requires a polar molecule to move through a hydrophobic environment
Why is membrane fluidity important?
NOT energetically favourable for poor head to flip between leaflets
Allows for interactions to occur
- receptors need to move for dimerisation + signalling
What are the 4 factors that affect membrane fluidity?
> Temp
Saturation of acyl chains
Length of acyl chains
Cholesterol
How does acyl chain saturation affect fluidity?
Saturated = straight chains pack better
Unsaturated = double C bond
- kinked chain
How does cholesterol affect fluidity?
Decreases fluidity
- rigid ring structure aids packaging of lipids
Describe lipid distribution
Not random
Asymmetry
Some lipids only found on 1 leaflet e.g. cytoplasmic leaflet
Diff membranes have…?
Diff lipid compositions
- > diff properties
- > diff functions
Why are there so may diff lipids?
> important effects on fluidity, curvature, fusion properties
signalling molecules in regulating cell function
cell interactions
effect activity of membrane proteins
Describe the structure of cholesterol
No P
V small polar head group
- rest of molecule is hydrophobic
How is cholesterol distributed?
Evenly between the 2 leaflets
What are membranes permeable to?
Small, uncharged polar molecules
Sall, hydrophobic molecules
What are membranes impermeable to?
Solutes + ions
Large, uncharged polar molecules
What are the 3 types of membrane proteins?
Integral MPs
Peripheral MPs
Lipid anchored MPs
What % of all ORFs encode membrane proteins?
20-30%
Which type of amino acids are best suited to being in a hydrophobic core?
Non-polar/hydrophobic
Why are peptide bonds energetically unfavourable for hydrophobic regions?
Polar
How is the polar nature of peptide bonds overcome?
2ndary strutcure:
H bonds form between -ve carbonyl O2 and +ve amide H
= neutralises charge
Forms alpha helices + beta pleated sheets
