Transport across cell membranes Flashcards
What’s the cell surface membrane made of?
Phospholipid bilayer
Name the components of the cell surface membrane
- Phospholipid bilayer
- Glycoproteins
- Glycolipids
- Channel protein
- Carrier protein
Function of phospholipid bilayer
Acts as a barrier to separate the inside of a cell from its outside environment
Function of glycoproteins
Proteins which act as recognition sites and antigens
Function of antigens
Act as little ‘flags’ on surface of cells, allowing body to detect foreign cells
Function of glycolipids
- Act as recognition sites
- Helps maintain membrane stability
- Helps cells attach to each other and form tissues
Function of channel proteins
Allow charged substances to diffuse through the membrane
Function of carrier proteins
Involved in facilitated diffusion to move ions from a high to low concentration
Function of cholesterol
Restricts movement to provide stability
Why’s the membrane described as a fluid mosaic model?
- Molecules can move freely
- Contains many types of molecule
Define diffusion
Net movement of particles from an area of high to low concentration until equilibrium is reached
Define simple diffusion
Movement of small, non-polar molecules through the phospholipid bilayer
Define facilitated diffusion
Movement of large, polar molecules through channel or carrier proteins
Difference between channel and carrier proteins
- Substances pass right through channel proteins
- Binding of substance alters tertiary structure of carrier protein, allowing molecule to enter cell
Define active transport
Movement against the concentration gradient using carrier proteins, requiring ATP hydrolysis
What forms ATP?
ADP + Pi (phosphate molecule)
Define co-transport
The coupled movement of substances across a membrane via a carrier protein
Absorption of glucose via the ileum process
- Sodium ions and glucose molecules are co-transported from the lumen to the epithelium
- Sodium ions are actively transported into the blood via a carrier protein, Potassium ions are pumped into epithelium from blood (ensures favourable concentration gradient is maintained)
- This ensures that glucose can be absorbed into the blood
- Glucose moves into the blood via facilitated diffusion through a channel protein
What’s the lumen?
Space inside the small intestine
What’s the epithelium?
Cells that line the small intestine
Define osmosis
Movement of water across selectively permeable membrane from a high to low water potential
Define water potential
Water concentration
Define isotonic
When water potential is balanced on both sides
Adaptations in cell membrane
- Increase in surface area (more molecules can be transported across the membrane)
- Increase in number of channel or carrier proteins (more polar molecules can be transported across membrane)
