Cell membranes Flashcards
What is the phospholipid bilayer?
Hydrophilic heads and hydrophobic tails (fatty acids)
Permeable by diffusion to non polar (CO2) and lipid soluble (vitamin K)
Barriers to charged particles (ions) and polar molecules (glucose)
HOWEVER: H2O because it is very small
What is cholesterol?
Controls stability and fluidity of the phospholipid bilayer
The more kinks (unsaturated) cholesterol is the more fluid it becomes
Increase cholesterol = increase stability = less fluid
What are the roles of the cell membrane?
- Separates cell contents from environment
- Regulates transport of nutrients in and out of cells
- Receptor sites
- Recognition - have built in protein-based antigens, which enable cells to recognise other and to trigger an immune response
What is the fluid mosaic model?
Fluid because: phospholipid molecules move around each other within a layer relative to one another
Mosaic because: proteins embedded between the phospholipids vary in shape, size and pattern
What is an extrinsic protein?
- on either side of the bilayer
- provide structural support
- form recognition sites by identifying cells
- form receptor sites for horn attachment
What is an intrinsic protein?
- extend across the bilayer
- provide structural support
- some are carrier proteins - active transport or diffusion of water soluble substances and large polar molecules
- some are channel proteins - molecules act as hydrophilic pores lined with polar groups for diffusion of water soluble molecules and ions
- usually small but highly selective, each protein only allowing specific molecules or ions through
What is a glycoprotein?
Protein + carbohydrate = glycoprotein
Phospholipid + carbohydrate - glycolipid
Function: cell to cell communication, cell to cell recognition, hormone reception
How do membranes react to heat?
- When temperature increases, the molecules that make up the membrane gain more kinetic energy and move faster
- This causes the membrane to become more fluid (molecules are more free to move) and therefore more permeable for pigments and solutes in the innermost compartment
What is diffusion?
Movement of molecules from a region of high concentration to a region of low concentration, down a concentration gradient
- lipid soluble molecules, O2, H2O, CO2
How does temperature affect diffusion?
Increasing temperature = increases kinetic energy = diffusion rate increases
How does the conc gradient affect diffusion?
Increases conc gradient = increases rate of diffusion
How does surface area affect diffusion?
Increased surface area = increases rate of diffusion
How does thickness of membrane affect diffusion?
The thicker the membrane = slower the rate of diffusion
How does diffusion distance affect diffusion?
The shorter the difference = the great the diffusion rate
How does size of molecule affect diffusion?
Smaller molecules diffuse more quickly
How does lipid solubility affect diffusion?
The more lipid soluble = faster the rate off diffusion
What is facilitated diffusion?
Passive transfer (no ATP) of molecules or ions down a concentration gradient, across a membrane, by protein carrier molecules in the membrane
What are hydrophilic channel proteins?
- Molecules with pores lined with polar groups
- Each protein is specific and will only allow one type of ion through (specific shape)
- Channels can be gated
What are carrier proteins?
- Allow specific large polar molecules to pass through the membrane
- A particular molecule will attach to the protein at its binding site and causes the protein to change shape, and releasing the molecule through the membrane
What is active transport?
Movement of ions and other molecules across the membrane via carrier proteins, substances can be moved from a low concentration to a high concentration against a concentration gradient, requires ATP
What is the mechanism of active uptake?
- The molecule or ion combines with a specific carrier protein on the outside of the membrane
- ATP transfers a phosphate group to the carrier protein on the inside of the membrane
- The carrier protein changes shape and the molecule or ion across the membrane, to the inside of the cell
- The molecule or ion is released into the cytoplasm
- The phosphate ion is released from the carrier molecule back to the cytoplasm and recombines with ADP to form ATP
What are the processes involving active transport?
- Protein synthesis
- Muscle contraction
- Nerve impulse transmission
- Absorption of mineral salts by plant roots
- Reabsorption of glucose in kidneys
What is co transport?
Type of facilitated diffusion, brings molecules and ions into cells together on the same transport molecule/transports 2 substances in the same direction e.g sodium-glucose co-transport
What is bulk transport?
Transport of substances into the cell. Uses ATP to provide energy to move membrane to form vesicles to contain substance as it enters cell
E.g: phagocytosis, pinocytosis, exocytosis
