Chapter 5 Flashcards
Cell Membrane Functions
- Protects The cell
- Controls flow of molecules in and out of the cell
- Maintains a cellular environment distinct from the extracellular space
- Senses molecules and other cells in the environment
-E.g., Different pH, nutrient concentrations, sugars, proteins, etc
Fluid Mosaic Model
- Cell Membranes are Fluid
- Phospholipids and other components are usually free to drift and rotate, not rigid - Cell Membranes are Mosaic
- Cell membrane has other molecules mixed into the phospholipids.
- Cholesterol (support), Proteins
Phospholipids
- Hydrophilic head: attracted to water
- Hydrophobic tail: repels water
- Structure: phosphate head with glycerol
- 2 tails – one saturated fatty acid, one unsaturated
- The unsaturated fatty acid is slightly curved at the bottom of the tail
Selective Permeability (Semi-Permeable)
- Lipid bilayers allow some molecules to cross, but not others
- The hydrophobic fatty acid chains act as a barrier to any charged or polar molecules (hydrophilic)
Molecules to freely cross membrane
Small, uncharged, non-polar molecules (O2, CO2 , ethanol) cross freely
- Passive Diffusion
Diffusion
- movement of solutes (molecules) down a concentration gradient
- passive, i.e. does not require energy input
- Heat energy - increases the random motion of molecules (higher temperature - more motion)
o As temperature increases, the amount of motion increases –> faster diffusion - Aim - dynamic equilibrium. (molecules still move but same number in both directions)
Concentration Gradient
Diffusion occurs:
High concentration → Low concentration
Rate of Diffusion
Size of the molecule – small molecules diffuse faster than large molecules
State of the matter – #1 gas, #2 liquids, #3 solids
Temperature – faster at high temperatures than low temperatures
Concentration gradient – the steeper (more concentrated) the gradient, the faster diffusion occurs
Osmosis
Diffusion of water
- Water will cross a membrane to even out the concentration of solutes (sugars, nutrients, etc.)
- Low → High solute concentration
- High → Low water concentration
- This is how maintains gradient
Hypertonic
- Solution that has more solutes
Hypotonic
- Solution that has less solutes
Isotonic
- Solution that has the same concentration of solutes
Facilitated Diffusion
- Small, polar or charged molecules (ions) diffuse across the cell membrane through passive transport proteins
- E.g., Calcium, Water, Glucose
- It goes with concentration gradient → no energy required
Active Transport
For large molecules that have a charge
- Active transporter proteins use energy to facilitate movement across the membrane
- Channel-forming protein against a concentration gradient
- From low to high concentration (requires energy)
- ATP is used to help cross membrane
E.g., Sodium Potassium Pump
Bulk Transport
- Large particles move across the cell membrane using membrane-bound vesicles
- Vesicles form inside cell by wrapping the phospholipid bilayer around another substance, such as a protein
- Also form when a particle touches the outside of the cell and the phospholipid sags down and around the particles
Exocytosis
- Vesicular Transport to the outside of the cell
Endocytosis
- Vesicular Transport to the inside of the cell
Passive Transporters
- Pores/ channels
Active Transporters
Pumps, use ATP
- Sodium Potassium Pump
Adhesion Proteins (CAMs)
- Attachment to other cells and to their surroundings
Communication Proteins
- Channels between adjacent cells; facilitate signalling between cells by receiving external signals
Receptor Proteins
- Bind chemical messengers outside the cell; receive and transmit signals
Enzymes
- Speed up chemical reactions
Recognition Proteins
- distinguish “self” from “non-self” for the immune system
Types of Membrane Proteins
- Passive Transporters
- Active Transporters
- Adhesion Proteins
- Communication Proteins
- Receptor Proteins
- Enzymes
- Recognition Proteins
