Biological Membranes Flashcards
Cell Plasma Membrane
Semi-permeable phospholipid bilayer selectivity is mediated by channels and carriers (Water soluble). The membrane permits fat soluble compounds through
Proteins & Signaling Areas in the Membrane
Embedded in the bilayer to act as cell receptors during signal transduction and maintain overall cellular activity
Phospholipids
Move rapidly in the plane of the membrane through simple diffusion
Lipid Rafts
- Primary component of cell membranes that provide structure
- Phosphate group serves as the attachment point for other water soluble biomolecules
- Secondary messenger in signal transduction
Membrane Components
(Most plentiful) - Lipids - Proteins - Carbohydrates - Nucleic Acids (Least plentiful)
Unsaturated Fatty Acids
Impart fluidity to the membrane
Glycerophospholipids
Used for membrane synthesis
Cholesterol
- Imparts fluidity to the membrane
- Synthesizes steroids
- Provides stability by linking adjacent phospholipids and occupying the space between them
Waxes
- Serve an extracellular function in protection and waterproofing
- Provide stability / rigidity within the nonpolar tail region of the membrane
Transmembrane Proteins
Pass completely through the lipid bilayer
Embedded Proteins
Interior (cytoplasmic) OR Exterior (Extracellular) proteins on the surface of a cell
Peripheral Proteins
They are transporters, channels and receptors bound with the lipid bilayer, lipid rafts or other transmembrane and embedded proteins
Carbohydrates
- Hydrophilic
- Attached at extracellular side
- Function in signaling and molecule recognition
Receptors
(De)Activate transporters for facilitated diffusion or active transport
Cell Adhesion Molecules (CAMs)
Cell-Cell junctions that allow cells to recognize each other and contribute to proper cell differentiation and development
Gap Junctions
- Direct Cell-Cell communication
- Connexons permits water / solutes movement
Tight Junctions
Prevent solutes from leaking into intracellular space via a paracellular route. They create a physical link between cells to form a waterproof seal
Desmosomes
Bind adjacent cells by anchoring to their cytoskeleton
Hemi-Desmosomes
Attach epithelial cells to underlying (basement membranes)
Simple Diffusion
- Passively move from a High [ ] Gradient —> Low [ ] Gradient until equilibrium is achieved
- Does not require a transporter
- Substrates move directly across membrane
Ex: Small, nonpolar molecules like O2 and CO2
Osmosis
- Moves from Low [ ] Gradient —> High [ ] Gradient
- Diffusion across a selectively permeable membrane
- Move H2O Only
Hypotonic Solution
Lower concentration of solution outside the cell, [Solutes] increase in the cell, Resulting in a net flow of water into the cell (cell will swell, increase in size)
Hypertonic Solution
Higher concentration of solution outside of the cell, [Solutes] decrease in the cell, Resulting in a net flow of water out of the cell (cell will shrink, decrease in size)
Isotonic Solution
Equimolar [Solutes] inside and outside of the cell, resulting in no net flow of water
Osmotic Pressure Equation
Osmotic Pressure - iMRT
i = Van't Hoff Factor (# of molecules that a compound dissociates into) M = Molarity of solution R = Ideal gas constant T = Temperature
Facilitated Diffusion
- Moves from High [ ] gradient —-> Low [ ] gradient
- Transport proteins facilitate movement
- Carriers will open 1 side of the membrane at a time
- Channels are exposed to both sides of the membrane when open
Passive Transport
- Positive Entropy (S) - increases
- Negative Free Energy (G) - Spontaneous
- Does not require energy
Active Transport
- Positive Free Energy (G) - Nonspontaneous
- Moves [ ] against the gradient
Primary Active Transport
- Uses ATP Hydrolysis (or another energy molecule) to directly transport molecules across the membrane.
- May involve Transmembrane ATPase
Secondary Active Transport
- One molecule moves down the [ ] gradient which releases energy to move a different molecule up it’s [ ] gradient
Endocytosis
Cell membrane invaginates and engulfs material to bring into cell
Pinocytosis
Fluids and dissolved particles are engulfed by the cell membrane and brought into the cell
Phagocytosis
Large solids and bacteria are engulfed by the cell membrane
Exocytosis
Secretory vesicles fuse with the membrane, releasing materials from the inside of the cell into the extracellular environment
Na+ and K+ Pump
- 3 Na+ out and 2 K+ in
- Leak channels (more K+) allows ions to permeate through the cell membrane
- Both maintain a stable resting membrane potential
Outer Membrane Mitochondria
- Highly permeable
- large pores move ions and small proteins
Inner Membrane Mitochondria
- Contain Cristae (foldings)
- Restricted Permeability
- Encloses matrix
Osmotic Pressure
- Colligative Property
- Pressure applies to a pure solvent to prevent osmosis, and is related to the [ ] of the solution
Symport (Active Transport)
Transport mechanism that moves two compounds simultaneously across a cell membrane in the same direction, one compound being transported down a concentration gradient and the other against a gradient
Antiport (Active Transport)
Cell membrane transport mechanism that transports two molecules at once through the membrane in opposite directions.
Countertransport (Active Transport)
Simultaneous transport of two substances across a membrane in opposite directions, either by the same carrier or by different carriers that are biochemically linked to each other.
