Biological Membranes Flashcards
Range of Plasma Membrane Functions
- Serves as a selective barrier
A. Allow fat soluble molecules to enter
B. Block entrance of large, water-soluble
molecules - Regulate
1. signaling
2. Intracellular transport
3. Nutrient entrance
4. Waste Expulsion
5. Cell recognition
6. Action Potential Conductance
Cell Membrane Composition
- Lipids [phospholipids and cholesterol]
- Proteins [channels, receptors, embedded proteins]
- Carbohydrates [Glycoproteins that coat and signal]
Fluid Mosaic Model
Theory that explains structure and function of the semipermeable phospholipid bilayer
Compounds that Readily Commute b/w the Membrane Bilayer
- Phospholipids
- Lipid Rafts
- Proteins
- Lipids [w/ help of Flippases]
Lipid Rafts
Cluster of identical lipids with or without associated proteins that participate in cell-signalling by serving as attachment points for other biomolecules.
Flippases
Enzymes that aid phospholipid transportation across the two membranes of plasma membrane in an active transport process
Membrane Components
- Lipids
I. Phospholipids
II. Fatty Acids and Triacylglycerols
III. Sphingolipids
IV. Cholesterol and steroids
V. Waxes - Proteins
I. Integral proteins
1. Transmembrane proteins
A. Channels
B. Receptors
1. Ligand-gated
2. G-coupled
C. Transporters
2. Embedded Proteins
II. Membrane-Associated/Peripheral Proteins - Carbohydrates
I. Glycoproteins
Fatty Acids
I. One of the lipid components of plasma membrane
II. Consist of 2 varieties
A. UnSaturated
I. fat with at least 1+ double bond
II. Fluid at room T
III. Imparts fluidity to plasma membrane
IV. Meagerly synthesized in the body,
mostly ingested
B. Saturated
I. Fully saturated fatty acid
II. Solid at room T
III. Decreases fluidity of plasma membrane
IV. Main Component of animal fats
V. Unhealthy type of fat
2 Essential Unsaturated Fatty Acids in Humans
- Alpha-Linolenic Acid
2. Linoleinic Acid
TriacylGlycerols
I. Energy storage in humans
II. Composed of 3 [saturated or unsaturated] fatty acids bound to a glycerol molecule through esterification
GlyceroPhospholipid
I. Preliminary component of plasma bilayer
II. Is composed of 2 fatty acids and one phosphate head
III. Gives rise to
1. Micelles
2. Liposome
3. Bilayer membrane
IV. Function as
1. Structural molecules
2. Second messengers
3. As attachment points for water soluble
components such as choline
Waxes
I. Hydrophobic constituent of plasma cell membrane in plants, not animals
II. Impart stability & rigidity to cell membranes
III. Have high melting point due to long fatty acid chain and alcohol
IV. Provide waterproofing
Transmembrane Proteins
Proteins that completely pass through the lipid bilayer
i. e.
1. Transporters
2. Channels
3. Receptors
Embedded Proteins
Proteins that only associate with either the cytoplasm or with the extracellular surface of the lipid bilayer
Integral Proteins
Combination of embedded and transmembrane proteins
Membrane Associated Proteins
Proteins that associate with the lipid bilayer through lipid rafts or through electrical interactions
ex. G proteins
pg. 262
Cell Junctions
I. Pathways in between neighboring cells that enable their communication
II. Types:
1. Tight Junctions
2. Gap Junctions
3. DesmosomesTight Junctions
Paracellular Junctions that prevent solute and solution leakage b/w cells
-Highly effective in epithelial tissues, bladder, intestines and kidneys where leakage prevention is necessary to proper organ functioning
Gap Junctions
I. Junctions b/w cells that allow direct flow of water and solutes b/w cells
***Do not permit protein movement b/w cells
II. Effective in tissues that involve Action Potential Propagation
Desmosomes
Junctions in b/w cells that permit water and solute flow in between cells
- anchor inside the cell’s cytoskeleton
- are found in cells that undergo much stress
1. skin cells
2. Intestine cells
Membrane Transport
1. Passive Transport
A. Simple diffusion
B. Osmosis
C. Facilitated Diffusion
2. Active Transport
3. Endocytosis
A. Pinocytosis
B. Phagocytosis
4. ExocytosisImpact of Thermodynamics on Membrane Transport
–Spontaneous—[-H or enthalpy]—passive—-driven by
concentration gradient—-inc rate with inc T
–Nonspontaneous—-[+H]——-Active——driven by
intracellular energy sources—–rate may or may not
increase with inc T
Simple Diffusion
Process that involves movement of nonpolar, freely permeable particles down their gradient across the plasma membrane
Osmosis
A subcategory of simple diffusion that involves movement of water among neighboring cells depending on their solute concentration.
**Relative solute concentration of a given cell
compared to its neighboring cell or surrounding
can be:
1. Hypotonic
2. Hypertonic
or 3. . Isotonic
***Osmosis can be measured by Osmotic pressure
Osmotic Pressure
A Colligative Property
Pressure associated with osmosis that results from influx of water into a hypertonic cell
****Pi=iMRT*****in units of atm
i=van’t hoff factor
R= ideal gas constant
T= absolute temperature in kelvin
Van’t Hoff Factor
of particles to which a molecule divides after desolving in a solution
Colligative Property
Physical property of a solution that relies on concentration of a solute as opposed to its chemical identity
i. e.:
1. Freezing point depression
2. Boiling point elevation
3. Vapor pressure depression
4. Osmotic pressure
Facilitated Diffusion
Passive transport of otherwise impermeable particles across the phospholipid bilayer through
1. Carriers
&
2. Channels
Carriers
Transmembrane proteins, open to only one side of the lipid-bilayer at a time, that bind substrates and carry them through an occluded state and a conformation change before releasing them across the bilayer
Occluded State
A state of a carrier protein induced by binding and conformational change of a substrate where the carrier is not exposed to either side of a phospholipid bilayer
Channels
Proteins with either open or close conformations that allow diffusion of particles across the membrane
Active Transport
Membrane Transport that involves intracellular energy usage
Types:
1. Primary Active Transport
2. Secondary Active Transport
A. Symport—same direction movement
B. Antiport—opposite movement
Primary Active Transport
Transport that involves direct power provision for particle transports across the membrane through a Transmembrane AtPase
Ex. Source of Energy: ATP
Used in maintaining neurogons*
Secondary/Coupled Active Transport
Transport that couples a spontaneous process to a nonspontaneous process to provide a source of energy for the nonspontaneous rxn/process
Used in kidneys*
Pinocytosis
Endocytosis of liquid or dissolved particles triggered by their binding to the cell surface
Phagocytosis
Endocytosis of solid particles [ex. bacteria]
Exocytosis
Fusion of secretory vesicled compounds to the membrane of cells followed by their release in the extracellular region
Specialized Membranes
- Membrane Potential
- Mitochondrial Membrane [outer membrane with more influx of ions and proteins and inner membrane with more restricted transport]
Membrane Potential
**Definition*****
Refers to the difference in electrical potential b/w the two membranes of a cell which results from the membrane’s ion impermeability and ion channel selectivity giving rise to dissimilar electrochemical gradients on either side of the cell
****Range****
Resting Potential: -80 to -40
Depolarized Potential: +35
*********
**Extra*******
Maintained by combined activity of ATPases & Leaking Channels that permit ion diffusion
