Cell biology
Membranes
• The plasma membrane defines a cell
• Provides shape and strengthens
• Intracellular communication
• Exchange of substances
• Cell growth and mobility
• Lipids, proteins and sterols
• Selective barrier
• Bilayer
• Noncovalent interactions
• Fluid
Phospholipids
• Hydrophobic tail, hydrophilic head
• 1 phosphate, 1 glycerol, 2 fatty acids
• Phospholipids and sphingolipids- majority of dell membrane
• Self organization; two tails bilayer, micell one tail
Sterols
• Cholesterol
• Stabilizes and stiffens membrane
Fluidity
• Depends on composition
• Saturated- compact, less fluid
• Unsaturated- not compact, fluid
• Cholesterol affects fluidity
• Stiffer membrane, thicker,
• Fewer free spaces, less water
• Rafts- enriched in cholesterol and
Saturated lipids
• Rafts facilitate protein-protein interactions
Membrane proteins
• Properties to cell membrane
• Transmembrane
• Peripheral
• Carbohydrate level on the surface- protection
Membrane transport
• Selective permeability of membrane
• Passive transport
, • Carbohydrate level on the surface- protection
Membrane transport
• Selective permeability of membrane
• Passive transport
○ No energy required
○ Simple diffusion or via channels
• Active transport
○ Costs energy
○ Via transporters
○ Transport of essential substances
against their concentration gradient
Facilitated diffusion
• Passive transport down electrochemical
gradient via transport proteins
• Channels
• Carriers/transporter
Three modes of active transport
• ATP-driven primary active transport-
• Coupled transporter- secondary active transport
• Light driven
• Transporters can be divided in 3 types
○ Uniporters- ATP proton pump
○ Symporters- glucose (with Na+)
○ Antiporters Na/K pump
• Ion channels - gated
• Different ways to open and close gate
Membranes
• The plasma membrane defines a cell
• Provides shape and strengthens
• Intracellular communication
• Exchange of substances
• Cell growth and mobility
• Lipids, proteins and sterols
• Selective barrier
• Bilayer
• Noncovalent interactions
• Fluid
Phospholipids
• Hydrophobic tail, hydrophilic head
• 1 phosphate, 1 glycerol, 2 fatty acids
• Phospholipids and sphingolipids- majority of dell membrane
• Self organization; two tails bilayer, micell one tail
Sterols
• Cholesterol
• Stabilizes and stiffens membrane
Fluidity
• Depends on composition
• Saturated- compact, less fluid
• Unsaturated- not compact, fluid
• Cholesterol affects fluidity
• Stiffer membrane, thicker,
• Fewer free spaces, less water
• Rafts- enriched in cholesterol and
Saturated lipids
• Rafts facilitate protein-protein interactions
Membrane proteins
• Properties to cell membrane
• Transmembrane
• Peripheral
• Carbohydrate level on the surface- protection
Membrane transport
• Selective permeability of membrane
• Passive transport
, • Carbohydrate level on the surface- protection
Membrane transport
• Selective permeability of membrane
• Passive transport
○ No energy required
○ Simple diffusion or via channels
• Active transport
○ Costs energy
○ Via transporters
○ Transport of essential substances
against their concentration gradient
Facilitated diffusion
• Passive transport down electrochemical
gradient via transport proteins
• Channels
• Carriers/transporter
Three modes of active transport
• ATP-driven primary active transport-
• Coupled transporter- secondary active transport
• Light driven
• Transporters can be divided in 3 types
○ Uniporters- ATP proton pump
○ Symporters- glucose (with Na+)
○ Antiporters Na/K pump
• Ion channels - gated
• Different ways to open and close gate
