Transport Across Cell Membranes Flashcards
Fluid Mosaic model of membrane structure
Molecules within member and can move laterally (fluid) e.g. phospholipids
Mixture of phospholipids, proteins, glycoproteins and glycolipids
Phospholipid bilayer components
Hydrophilic phosphate heads - attracted to water (orientate to aqueous environment either side of membrane
Hydrophobic fatty acid tails - repel water (orientate to interior of membrane)
Embedded proteins (intrinsic or extrinsic)
Channel and carrier proteins (intrinsic)
Glycolipids
Glycoproteins
Glycolipid - (lipids with polysaccharide chain attached)
Glycoproteins - (proteins with polysaccharide chain attached)
Cholesterol
Binds to phospholipid hydrophobic fatty acid tails
Components of the cell membrane (4)
Phospholipid bilayer
Inverted proteins
Glycoproteins and glycolipids
Cholesterol
What does the fluid Mosaic model of membrane structure explain?
How molecules can enter and leave a cell
How does the phospholipid bilayer allow molecules to enter or leave a cell?
Allows simple diffusion of nonpolar small/lipid soluble molecules (e.g. water oxygen)
Restricts movement of larger/polar molecules
How do you channel proteins allow molecules to enter or leave a cell?
Allow movement of water soluble/polar molecules/ions down a concentration gradient (facilitated diffusion)
How do you carrier proteins allow molecules to enter or leave a cell?
Allow the movement of molecules against a concentration gradient using ATP (active transport)
Features of the plasma membrane that adapt for its other functions (4)
Phospholipid bilayer
Phospholipid bilayer is fluid
Surface proteins
Cholesterol
How does the cell membrane being a phospholipid bilayer adapt for another function?
Maintains a different environment on each side of the cell (compartmentalisation of the cell)
How does the phospholipid bilayer being fluid adapt it for another function?
Can bend into different shapes for phagocytosis/to form vesicles
How do the surface proteins (extrinsic glycoproteins/glycolipids) adapt the cell membrane for another function?
Cell recognition
Act as antigens/receptors
How does cholesterol adapt the phospholipid bilayer for another function?
Regulates fluidity
Increases stability
What is cholesterol not present in?
Bacterial cell membranes
What is the role of cholesterol?
Makes the membrane more rigid/stable/less flexible
By restricting lateral movement of molecules making up the membrane (e.g. phospholipids)
Binds to fatty acid tails of phospholipids causing them to pack more closely together
Simple diffusion across the membrane
Net movement of small, nonpolar molecules (e.g. oxygen and carbon dioxide) across a selectively permeable membrane comment down a concentration gradient
Passive, no ATP required
Factors affecting rate of simple diffusion
SCD
Surface area
Concentration gradient
Diffusion distance (thickness of surface)
Facilitated diffusion across cell membranes
Net movement of larger/polar molecules (e.g. glucose) across a selectively permeable membrane, down a concentration gradient
Through a channel or carrier protein
Passive, no ATP required
Factors affecting rate of facilitated diffusion
Surface area
Concentration gradient (until the number of proteins is the limiting factor as all are and use/saturated)
Number of channel or carrier proteins
Carrier proteins transport…
Transport large molecules, protein changes shape when the molecule attaches
Channel proteins transport…
Large/polar molecules through its pore
Some are gates (open and close) eg. Voltage gated sodium ion channels
Specificity associated with channel and carrier proteins
Different carrier on channel proteins facilitate the diffusion of different specific molecules
Active transport across cell membranes
Net movement of molecules/ions against a concentration gradient
Using carrier proteins
Using energy from the hydrolysis of ATP to change the shape of the tertiary structure and push the substances through
Factors affecting the rate of active transport
PH, Temperature (affect tertiary structure of carrier protein)
Speed of carrier protein
Number of carrier proteins
Rate of respiration (affects ATP production)
Classic example of co-transport
Absorption of sodium ions and glucose by cells lining the mammalian ileum
Explain the cotransport of sodium ions and glucose
- Sodium ions are actively transported out of epithelial cells lining the ileum, into the blood, by the sodium potassium pump. Creating a concentration gradient of sodium (high concentration of sodium in lumen than epithelial cell)
- Sodium ions and glucose move by facilitated diffusion into the epithelial cell from the lumen, via a co-transporter protein
- Creating a concentration gradient of glucose – high concentration of glucose in epithelial cell then blood
- Glucose moves out of the cell into the blood by facilitated diffusion through a protein channel
Movement across membranes by osmosis
Net movement of water molecules across a selectively permeable membrane down in water potential gradient
Passive
Factors affecting rate of osmosis
Surface area
Water potential gradient
Thickness of exchange surface (diffusion distance)
How much cells be adapted for transport across that internal or external membranes?
Increase in surface Sarah
Increase the number of channel proteins or carrier proteins
Water potential
Potential of water molecules to diffuse out of or into a solution
Pure water has highest water potential
Adding solutes to a solution low as water potential (becomes more negative)
