Cell Membrane and Transport Across Membrane Flashcards
Functions of a biological membrane (5)
1) Defines cell’s boundaries
2) Organisation and localisation of function
3) Regulates cell contents
4) Signal Transduction
5) Mediates cell-to-cell communication and adhesion
How does the membrane’s selective permeability help in its function?
It allows desirable substances to be kept within and undesirable substances to be kept out of the cell
S->F: Definition of cell’s boundaries
The hydrophobic core of the membrane keeps cell interior physically separated from the surrounding environment
S->F: organisation and localisation of function
Molecules or structures with specific functions are embedded in membranes or localised within organelles
S->F: Regulation of cell’s contents
Proteins and other components like cholesterol embedded in the membrane help to regulate transport of substances into and out of the cell and organelles
S->F: Signal Transduction
Specific protein receptors on the outer surface of the cell membrane are crucial in detecting specific signals and triggering specific responses within the cell
S->F: Cell-to-cell communication and adhesion
Membrane proteins bind to the extracellular matrix or cell surface constituents to mediate adhesion and communication between adjacent cells
‘Fluid’ in Fluid Mosaic Model (FMM) (3)
1) * the membrane is composed of two layers, consisting of mainly phospholipids
2) Phospholipids, cholesterol and some proteins are free to move about laterally within the membrane, within (laterally) or between (flip transversely) layers
‘Mosaic’ in Fluid Mosaic Model (FMM)
proteins are randomly distributed and attached to the phospholipid bilayer, which is asymmetrical on the two lipid layers
In the FMM, the membrane is viewed as _____
a collage of proteins randomly distributed and attached to the fluid phospholipid bilayer which is free to move about laterally
Characteristics of FMM (4)
1) bilayer is asymmetrical
2) bilayer is fluid
3) unit membrane is dynamic
4) membranes are amphipathic
Asymmetry of phospholipid bilayer: Two lipid layers may differ in
(__________ __ _____ & ____)
composition/arrangement of proteins and lipids
Dynamism of membranes: Embedded proteins can float, some (________) while others are
(_________) by (_____________)
some moving freely; fixed in positions; microfilaments on the cytoplasmic face
Amphipathicity of membranes
Phospholipids have a hydrophilic phosphate head and hydrophobic hydrocarbon tail
Where do the head and tail of phospholipids face?
1) p. head face outwards into aqueous environment both inside and outside the cell
3) Hydrocarbon tails face inwards and create a hydrophobic core
Three types of lipids
1) Phospholipids
2) *Cholesterol
3) Glycolipids
Why can phospholipids move about laterally?
Hydrophobic interactions between hydrophobic fatty acid tails are weak
Why is it rare for phospholipids to flip transversely across the membrane?
Hydrophilic head must cross the hydrophobic core of the membrane to do so
Factors affecting membrane fluidity (and their relationship) (4)
1) Temperature (Temp. ↓ , MF ▼)
2) Length of fatty acid chains (length 🠕, MF ▼)
3) Degree of saturation of fatty acid chains (degree of saturation 🠕, MF ▼)
4) Amt. of cholesterol (effect on MF depends on temp.)
Effect of low temp. on MF (3)
1) KE of hydrocarbon chains decreases
2) Hydrocarbon chains are more tightly packed => stronger hydrophobic interactions between phospholipids molecules => restricted motion
3) bilayer exists in semi-solid state (less fluid)
Effect of increased fatty acid chain length on MF
Melting point increases due to increased hydrophobic interactions
Effect of saturated lipids on MF (3)
1) they have long. straight hydrocarbon chains 2) -> allows for close packing ( 🠕 hydrophobic interactions)
3) enhances membrane solidification
Effect of unsaturated lipids on MF
have kinks -> prevent hydrocarbon chains from packing closely tgt => enhances membrane fluidity
Effect of amt of cholesterol on MF (2)
it increases stability and regulates membrane fluidity in ANIMAL cells