L5 Membranes Flashcards
What are the five macromolecules that make up the plasma membrane and describe their function
Carbohydrates - cell identity
Proteins - transport
Cholesterol - fluidity
Phospholipids - form selectively permeable barrior
What are the functions of the plasma membrane
Transport - protein channels, pumps, carriers
Communication - protein receptors
Metabolism - protein enzymes
Structure - cytoskeleton proteins ( create cell junction)
Self identify markers - proteins that protect ( prevents autoimmunity)
Concentration gradient
Drives molecules down/ with concentration
(Passive process)
High ➡️ low
What is a passive process? Active?
Passive process = no energy required
Active = requires energy (ATP)
What are the 2 membrane transports?
Driving force and ATP
————— powers protein pumps ( driving molecule up concentration)
ATP
What 2 things effect a molecules pathway through a membrane?
- Molecule size
- small molecules =pass
- large molecules = not pass w/o transporter (pore, channel) - Molecule polarity
- Nonpolar = pass
- polar = transporter
Simple diffusion
Random movement of molecules
Net diffusion
Directional movement of molecules ( driven by concentration gradient)
Channel- mediated facilitated diffusion
- “facilitated” by proteins that form channels/ pores
Each channel has specificity
Ex. Ion channels
What are the 4 types of ion channels.
- Always open
- Voltage gated - switch in membrane charge
- Ligand gated - need neurotransmitter to open
- Mechanically gated - gated ion channels
Carrier- mediated facilitated diffusion
Molecules cross plasma membrane by protein carriers
Mechanism for : Carrier- mediated facilitated diffusion
- Molecule blinds w/ specificity to protein carriers (glucose, amino acids)
- Binding = shape change of carrier protein ➡️ molecule transported and released
- Released molecule = shape change back to original shape of protein carrier
What mechanism of water is used when cells need to move lots of water quickly?
Aquaporins - channel specifically for water
Primary active transport (pumps)
Uses ATP to phosphorylate transport protein
3 types : Na+/K+ pump , ca+ pump & protein pump
List the steps of the mechanism for Na+ / k+ pump
- 3 Sodium bind w/ specificity
- Activation of ATPase site
- Pump is phosphorocated
- Protein changes shape & sodium ions released
- Potassium binds
- Phosphate is released (@ ATPase site)
- Shape change back to original shape & potassium ions released
Secondary active transport and 2 sub parts
Energy is stored in Na+ concentration gradient ➡️ moving Na+ into cell &
Co-transport = same direction (down concentration)
Counter- transport = opposite direction (up concentration)
Osmosis
Net diffusion of water through a selectively permeable membrane
What molecules will promote osmosis and what will NOT promote osmosis?
Will = o2, co2, cholesterol
Not = h2o, Na+, glucose (c6H12O6)
What is Tonicity?
Comparison of solute concentration between 2 solutions
Hypertonic
One solution has more active solute than other
Hypotonic
A solution has less active solute than other solution
Isotonic
Active solute is the same on both sides
Osmolarity means
Measure of concentration of osmotically active solutes
What are osmotically active solutes?
Solutes that don’t easily cross the plasma membrane
What is the set point for the parameter osmolarity?
300 mOsm
What does cremation mean?
To shrink
What does lysis mean?
To burst (the cell membrane)
Epithelial transport
Transport across sheets of epithelial cells (membranes)
What three transport mechanisms are required for epithelial transport?
- Na+/ K+ pump
- secondary (active) transport
- carrier mediated facilitated diffusion (passive)
What is the purpose of bulk transport?
It allows large molecules to cross the membrane
What does intercellular signaling mean?
Happens b/w cells where one cell releases a messenger molecule and it binds to a receptor on another cell
Define ligand
Anything that binds to a protein with specificity
Endocytosis vs exocytosis
Endocytosis = captures substrate/ particle from outside and brings it into cell
Exocytosis = out of cell ; release contents out of the cell
What are the three types of Endocytosis and how are they different?
Phagocytosis- “to eat” - engulfs small part
Pinocytosis - “pinch close - closes lightly
Receptor- mediated endocytosis- ligand binding to receptor
Where can receptors be located in the cell?
The cytoplasm ( cytosol)
Plasma membrane
Nucleus
Define signal transduction
Events between activation of receptor (binding of ligand ➡️ receptor) and the response by the cell
Define Autocrine ( intercellular signaling)
Communication that acts on its self
Paracrine (intercellular signaling)
Acts on neighboring cell
Endocrine (intercellular signaling)
Released by endocrine gland into blood
Synaptic signaling (intercellular signaling)
Released by neuron ➡️ synapse ➡️ acts on adjacent nerve/muscle/gland
Neuroendocrine (intercellular signaling)
Released by neuron into blood ➡️ acts on target cell
Receptor location is based on ———
Polarity (solubility) of ligand
What happens after messanger molecule binds to receptor?
Signal concentration converts ligand binding event ➡️ intercellular signal altering behavior of cell
What is membrane potential
Measure of charge difference (mv) across membrane
What is resting membrane potential (RMP) in humans?
-70mv
What causes the -70mv RMP?
- Na+/k+ pump (3 Na+ out & 2 k+ in)
- more k+ leak channels than Na+ channels
- large negatively charged proteins
What is the value of Na+ equilibrium?
60mv
What is the value for K+ equilibrium potential?
-90mv
Is k+ or Na+ responsible for the generation of the RMP? Why?
K+ is responsible for RMP due to :
- having more k+ leak channels than Na+ leak channels
- RMP closer to k+ equilibrium potential
- membrane is more permeable to k+ than Na+
Explain 3 important functions that the Na+/k+ pump plays in cells
- Creates/ maintains ion gradients (RMP)
- Creates Na+ gradient for secondary active transport
- Prevents osmotic damage
