Cellular transport Flashcards
How is the CSM ‘fluid’ & ‘mosaic’
aka Describe the fluidity of the components of a cell membrane and explain how membrane fluidity
FLUID: phospholipid & protein molecules in constant motion, move laterally,
evident from the random distribution of saturated and unsaturated phospholipids
MOSAIC: Diverse protein types present, random arrangement (scattered in membrane)
structure of FA in
Cold environment vs hot environment
Cold:
- Higher proportion of unsaturated FA
- Phospholipids packed less closely
-> so as to remain fluid, not freeze
Hot:
- HIgher proportion of saturated FA
- Phospholipids packed more closely
- > Ensures less fluid to remain intact
Explain how membrane fluidity
is influenced by temperature and membrane composition.
- Separates cell contents from external env.
- Compartmentalisation
Regulates membrane fluidity
1. degree of saturated fatty acids
- Length of fatty acid chains
Shorter FA , increased fluidity, less extensive hydrophobic interaction
Longer FA, decreased fluidity, more extensive
hydrophobic interaction
Explain how cholesterol resists changes in membrane fluidity with temperature change.
Characteristic of cholesterol:
Amphipathic
Fn: Regulate membrane fluidity, at high temp, presence of cholesterol
High temp-> Prevents from too fluid
Low temp -> Prevents close packing
Unsaturated fatty acids -> C=C double bond which causes kinks
Prevent adjacent phospholipids from coming close together, hence preventing the membrane from being frozen at low temperature.
Distinguish between peripheral and integral membrane proteins.
Peripheral/extrinsic:
1. BOUND, not embedded
bounded indirectly by interactions w intergral/intrinsic proteins directly by interactions w polar lipid heads
- **Charged, polar amino acid residue, bound via H & ionic bonds
Integral/intrinsic
1. Embedded Either partly/fully span membrane
**Transmembrane protein -> fully span CSM
- Held by hydrophobic & hydrophilic interactions
List six major functions of membrane proteins.
WITHIN CELL
1. Compartmentalisation
**Isolate enzymes & rxts, high conc, fast RoR
CSM/EXTERNAL
2. Formation of transport vesicles
**Seperate cell contents from external env.
+ control exchange of substances across membrane
- Cell to communicate w external env.
- Cell to cell recognition
- Adhesion of cells -> form tissue
- Atatchement to cytoskeleton & extracellular matrix
Explain the role of membrane carbohydrates in cell-to-cell recognition.
Short oligosaccharides (<15sugars)
- Covalently bonded to proteins & lipids:
Glycoproteins, Glycolipids
Solely on extracellular face (for recognition & adhesion)
Explain how hydrophobic molecules cross cell membranes.
Diffuse across directly
Differentiate between active and passive transport across the membrane.
Passive: FD, SD, osmosis
Active: Active tpt, bulk tpt
SD: only for non-polar & uncharged due to hydrophobic region (acts as barrier)
FD: net movememnt down conc. gradient
- Polar & Charged moleq via channel & carrier proteins
Osmosis: net movement of H2O moleq via PP membrane
Hypertonic - high wp
Hypotonic - low wp
Isotonic - both sides same wp
AT: By pumps, against conc. gradient via hydrolysis of ATP-> induces conformational change in tpt protein
Bulk: Exocytosis/endocytosis
- Movement of vesciles along microtubules
Phagocytosis: Engulf solids via pseudopodia
Pinocytosis: Cell invaginates forming vesicle around extracellular fluid
Channel vs Carrier vs Pump
Channel:
- Multiple molecules
- may/may not undergo conformational change
- FD, passive, no ATP
- down conc. gradient
Carrier: similar to channel but
Binds 1/ v few moleq at a time, only a few molecules across membrane/s
+ Undergoes conformational change
Pump
Binds to 1/ v few moleq at a time, only a few across membrane
AT via ATP, against conc gradient
pump
Describe difference of unsaturated C=C (kink) & saturated C-C fatty acid (no kink)
Increases distance between phospholipid molecules, thus allowing membrane to
remain fluid / prevents membrane from freezing at low temperatures
Describe how R groups (of polypeptides/amino acids) [sec. structure] interact
+ How they react w phospholipids
the five polypeptides are held together by bonds between R-groups
ionic bonds, hydrogen bonds, disulfide bonds, hydrophobic interactions
hydrophilic / charged / polar R-groups of amino acids interact with phosphate head of phospholipid
hydrophobic R-groups of amino acids interact with fatty acid tails / hydrocarbon tails
of phospholipid
Explain why it is important that the channel protein completely spans the cell surface
membrane.
/explain why channels are requires for ions to pass through membranes
- ions are charged
- unable to traverse across the hydrophobic fatty acids of the phospholipid bilayer
- channel of the protein lined with hydrophilic amino acids -> allow ions to pass across the membrane
4.
Describe how insulin is released across the membrane.
- Insulin is packaged into a secretory vesicle at the trans face of Golgi body
- vesicle moves towards CSM
- Membrane of the vesicle fuses with CSM to release insulin via exocytosis.
Suggest why there are no channels for insulin release across the membrane.
- Insulin ->protein, too large to pass thru the channel proteins
- If large enough for large molecules, cell contents would leak out
