Membranes Flashcards
Selective permeability
Hydrophobic (nonpolar) molecules cross the membrane easily through dissolution in hydrophobic region
Hydrophilic (polar) molecules and ions do not move across easily (moved by transport proteins)
Types of membrane movement
Active transport
Passive transport
Diffusion
Facilitated diffusion
Active transport
Transport requiring energy (ATP)
Membrane pumps and carrier proteins
Moving against concentration gradient
Passive transport
No energy required
Moving with the concentration gradient
Diffusion
net movement of molecules from high to low concentration until equilibrium is reached
Spontaneous process that increases entropy
Facilitated diffusion
Channel proteins and carrier protons
Allow diffusion to occur more easily
Osmotic concentration
Total solute concentration of a solution
Osmotic equilibrium
Equal concentrations of solute on both sides
No net movement
Concentration gradient
Graded change in the concentration of a substance over some distance
Osmosis
Diffusion of water across a selectively permeable membrane
Tonicity
The ability of the surrounding solution to cause a cell to gain or loose water
Isotonic solution
Solution has the same concentration as inside of the cell
Hypertonic solution
Solution has a greater osmotic concentration than the cell
Hypotonic solution
Solution has a lower osmotic concentration than the cell
Isotonic solution in animals
Normal
Isotonic solution in plants
Flaccid
Hypertonic solution in animals
Crenulated/shriveled
Water diffuses from cell to solution
Hypertonic solution in plants
Plasmolyzed
Water diffuses out of cell
Cell membrane pulls away from the cell wall
Hypotonic solution in animals
Lysed
Water diffuses into the cell
Hypotonic solution in plants
Turgid (normal)
Water diffuses into the cell increasing turgor (water) pressure
Osmoregulation
Adaptations for the control of water balance
Contractile vacuole in protists
Fluid mosaic model
Comprised of phospholipid bilayer
Mosaic mixture of lipids, proteins, and carbohydrates
Selectively permeable
Fluidity
How are phospholipids held together
Weak hydrophobic interactions
Fluidity
The ability for components of a cell membrane to move
Protein complexes
Specialized patches of proteins that travel together in the membrane
Lipid rafts
Specialized patches of lipids that travel together in the membrane
Cholesterol
Steroid imbedded in the cell membrane
Cholesterol function
Acts as a buffer against temperature changes
Keeps the membrane
Saturated fatty acids
Straight chained, no double bonds, tight (non-fluid) phospholipid arrangement
Unsaturated fatty acids
Bent chain with double bonds, creates space for a fluid phospholipid arrangement
Variations in cell membrane structure
Changes membrane fluidity via lipid content and proportion of saturated vs unsaturated fatty acids as an evolutionary response to different environmental factors
Integral proteins
Go through the membrane
Transmembrane protein
Type of integral protein that crosses the entire membrane
Integral protein structure
Hydrophobic interior regions consisting of stretches of 20-30 amino acids in an alpha helix structure
Peripheral proteins
Loosely bound to the surface of the membrane or resting on integral proteins
Membrane protein functions
Transport
Enzymatic activity
Cell to cell recognition
Intercellular joining
Cell structure
Transport proteins
Provides hydrophilic channel across the membrane
Proteins are very specific with what they allow through (size and charge)
Channel proteins
Carrier proteins
Aquaporins
Membrane pumps
Signal transduction
Process in which a cell signal is converted to a cellular response as a signaling molecule attaches to a receptor to change shape
Cell to cell recognition
Polysaccharides serve as tags allowing cells to recognize like cells so they develop properly and organize into tissues (recognize like cells) and provide immunity (reject unfamiliar cells)
Cell structure
Attachment of proteins to cytoskeleton and extracellular matrix
Glycoprotein
Carbohydrates with a protein
Glycolipids
Carbohydrates with a lipid
Channel proteins
Passive transport
Proteins that allow molecules or ions to diffuse through the membrane
Ion channels
Channel proteins that transport ions
Gated channels
Channel proteins that open and close in response to a stimuli (chemical or electric)
Aquaporins function
Channel proteins that transport water
Aquaporins structure
Consist of 4 identical polypeptide subunits each forming a channel
Carrier proteins
Active and passive transport
Change conformation as they move substances
Membrane pumps
Active transport carrier proteins
H⁺ pump
Pumps H⁺ out of cell to create a positively charged extracellular side which can be used for cell work
Main electrogenic pump for plants, fungi, and bacteria
Electrogenic pump
Pump that creates a voltage difference across a membrane by redistributing ions
Voltage
Electrical potential energy
Membrane potential
Voltage across membrane
Cytoplasmic side is negative in comparison to the EC side
Causes certain ions to be favored in passive transport
Negative cytoplasm favors positive cations
Electrochemical gradient
Osmotic gradient plus charge gradient that helps govern diffusion as substances always diffuse along this gradient (only sometime along only osmotic gradient)
Cotransport
Substance that has been pumped across the membrane can carry another substance with it as it diffuses back
Bulk transport
Transport across the plasma membrane that requires energy
Endocytosis and exocytosis
Exocytosis
A large vesicle fuses with the cell membrane to move molecules to outside of cell
Endocytosis
Membrane forms a large vesicle around molecules outside the cell to pull them inside
Types of endocytosis
Phagocytosis
Pinocytosis
Receptor
Phagocytosis
Movement of particles into the cell
Pinocytosis
Movement of fluid into the cell via coated vesicles
Receptor
Mediated endocytosis
Movement of specific molecules into the cell that first bind to receptors (taking in everything else but ensuring the specific molecule)
