Unit 3: Membranes Flashcards
What is the membrane structure composed of?
- Lipids (usually phospholipids)
- Sterol lipids
- Proteins
What are phospholipids like?
They have a hydrophobic tail and a hydrophilic head. The hydrophilic head is attracted to water and to other heads. The hydrophobic tail is made up of fatty acids.
Phospholipids form a bilayer (with the hydrophobic tails in the center) There is constant movement.
What are sterol lipids like?
- Fit between fatty acid chains
- keep membrane fluid
- stabilize the membrane
Ex: cholesterol (animal cells) and phytosterols (plants)
Most cholesterol we have is used to make bile
What are proteins like?
- Many different types
- Specific to cell type
Ex: integral membrane proteins and transmembrane proteins; peripheral membrane proteins
What are the membrane functions?
- Define cell – contains and separates
- Selective transport
- Enzyme activity
- Signal transduction – protein receptors (transfer message from outside to inside the cell)
- Cell adhesion – cell-to-cell links (holds all together)
- Cell recognition
- Attachment to cytoskeleton
The functions 2-7 are due to membrane proteins
What are the types of traffic across membranes?
Passive transport and active transport
What are the different types of passive transport?
- Diffusion
- Osmosis
- Facilated diffusion
What is diffusion?
The movement of particles down concentration gradient (from high concentration to low concentration)
What are examples of molecules that can diffuse through the membrane?
H20, EtOH, O2, CO2, N2, hydrophobic molecules, lipid-soluble molecules
What is osmosis?
- The passive transport of water through aquaporin (water/protein) channels and through the membrane.
- From hypotonic concentration to hypertonic concentration until isotonic concentration – from less salt concentration to more salt concentration.
What are examples of osmosis?
- Turgor pressure (plants)
- Using salt or sugar as a preservative
- Water moving into stomach (after addition of H+ AND Cl-)
- Contractile vascuoles (in some protists)
What is facilitated diffusion?
Transport of solutes across the membrane down concentration gradient via specific transport proteins (through transmembrane proteins = channels)
What are examples of facilated diffusion?
- Glucose transporter
2. Gated ion CHANNELS in membranes of neurons
What are the different types of active transport?
- ion pumps
- co-transport
- exocytosis
- endocytosis
What is transportation through ion pumps?
Moves ions across membranes, against their concentration gradient
- Maintain membrane potential – maintain electrochemical gradient (difference in charge across the membrane)
- help maintain osmotic pressure
What is active transport?
- Transport against concentration gradient (low concentration to high concentration)
- requires energy as ATP
- requires transmembrane proteins (“pumps”)
What are examples of ion pumps?
- Na+/K+ ion pump, sodium potassium pump (Na+/K+ ATPase)
- Ca++ pump, calcium pump in sarcoplasmic reticulum (muscle cells)
- Proton pump
- H+/K+ ATPase
How does the Ca++, calcium pump work?
– In sarcoplasmic reticulum (muscle cells)
Muscle contraction requires release of calcium ions for sarcoplasmic reticulum
-Ca++ stored in specialized organelles in muscle cells
-Ca++ low in cytosol
-Ca++ high in sarcoplasmic reticulum
How does the proton pump work?
- Maintains acidic environment inside lysosome
- transports H+ into, for examples, lysosome; mitochondria (ATP production)
How does the H+/K+ ATPase (H+/K+ exchager) work?
Moves H+ into the lumen
What is co-transport?
- Movement of ion down its concentration gradient
- is coupled to movement of “transported” molecule against its gradient
- Both molecules move through the same transport protein
- Transport of 2 molecules through the same transport protein (1 is down gradient and 1 is against gradient)
What are examples of co-transport (aka secondary transport)?
- Symport
2. Antiport
What is symport?
-both molecules (coupled molecules) move in the same direction
What are examples of symport?
Plant cell uptake of sucrose coupled to H+ diffusion
-Sucrose transport – H+ down gradient, sucrose against gradient
