Biological Membranes Flashcards
Cell Membrane
- semipermeable phospholipid bilayer
- permits fat soluble compounds to cross easily while making larger water-soluble compounds seek alternative route
- contain proteins imbedded in the lipid bilayer that act as cellular receptors during signal transduction
Lipid Raft
- collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules
- in the phospholipid bilayer containing proteins and distinct signaling areas
- serve as roles in signaling
- travel within plane of the membrane
- moving between membrane layers can occur but is energetically unfavorable
Glycoprotein Coat
carbs associated with membrane bound proteins create this
Phospholipids
move rapidly in the plane of the membrane through simple diffusion
Flippases
Enzymes that assist in the transition between layers
Membrane components most plentiful to least plentiful
- Lipids (phospholipids, cholesterol and others most plentiful), including trans membrane proteins (channels and receptors)
- Membrane associated proteins, embedded proteins next most plentiful
- Carbohydrates including the glycoprotein coat and signaling molecules are next
- nucleic acids are essentially absent
Triacylglycerols
- also referred to as triglycerides
- storage lipids involved in human metabolic processes
- contain 3 fatty acid chains esterified to a glycerol molecule
Fatty Acids
carboxylic acids that contain a hydrocarbon chain and terminal carboxyl group
Phospholipid
- substituting one of the fatty acid chains of triacylglycerol with a phosphate group forms a polar head with nonpolar tails
- spontaneously assemble in micelles or liposomes (bilayered vesicles) due to hydrophobic interactions
- used for membrane synthesis and can produces hydrophilic surface layer on lipoproteins such as VLDLs
- primary component of cell membranes
- structural role and second messengers in signal transduction - serving as attachment points for water-soluble groups (choline) or inositol
Sphingolipid
- important part of the cell membrane
- do not contain glycerol, but are similar in structure to phospholipid with a hydrophilic region and 2 fatty-acid derived hydrophobic tails
Classes of Sphingolipids
ceramide, sphingomyelins, cerebrosides, and gangliosides
Cholesterol
- regulates membrane fluidity but is also necessary for the synthesis of all steroids
- stabilizes adjacent phospholipids and occupies the space between them preventing formation of crystal structures in the membrane
- increases membrane fluidity at lower temperatures
- decreases fluidity and helps hold membrane intact
- mole fraction, makes up about half
- Also stabilizes by cross linking adjacent phospholipids through interactions at the polar head group and hydrophobic interactions at the nearby fatty acid tails
Waxes
-class of lipids that are extremely hydrophobic
rarely found in cell membrane of animals but sometimes in cell membranes of plants
-long chain fatty acid and a long chain alcohol contributing to the high melting point
-provide both stability and rigidity in the nonpolar tail region only of membrane
serve as extracellular function in protection or waterproofing
Transmembrane Proteins
pass completely through the lipid bilayer
- integral protein
- channels or receptors
Embedded Proteins
- associated with only the interior or exterior surface of the cell
- integral protein
- catalytic activity linked to near by enzymes
Membrane Associated (peripheral) Proteins
- may be bound through electrostatic interactions with lipid bilayer, especially lipid rafts, or to transmembrane or embedded proteins, like G proteins found in G protein coupled receptors
- ex- transporters, channels, and receptors
- Signaling and are recognized molecules on the extracellular surface
Carbohydrates
- generally attached to protein molecules on the extracellular surface of cells
- generally hydrophilic so interactions between glycoproteins and water can form a coat around the cel
Membrane Receptors
- activate or deactivate transporters for facilitates diffusion and active transport
- usually transmembrane proteins
- generally proteins, but can be carbohydrate and lipid receptors
Cell Adhesion Molecules (CAM)
- comprise cell-cell junctions
- proteins that allow cells to recognize each other and contribute proper cell differentiation and development
Gap Junctions
-allow for direct cell-cell communication
- Allow intercellular transport of material and do NOT prevent paracellular transport of material
-In discontinuous branches around the cell
-often found in small bunches together
also called connexons and are formed by the alignment and interaction of pores composed of six molecules of connexin
-permit movement of water and some solutes directly between cells
-proteins NOT transferred through this
Tight Junctions
- Not used for intercellular transport of material and Do prevent paracellular trasport
- form bands around the cell
- prevent solutes from leaking into the space between cells via a paracellular route
- found in epithelial cells and function as a physical link between cells as they form a single layer of tissue
- limit permeability enough to create a transepithelial voltage difference based on differing concentrations of ions on either side of epithelium
- must form continuous band around cell to be effective
Desmosomes
- bind adjacent cells by anchoring to their cytoskeletons
- formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells
- found at interface between two layers of epithelial tissues
Hemidesmosomes
function is to attach epithelial cells to underlying structures especially basement membrane
Passive Transport
- spontaneous (-ΔG) and does not require energy
- generally increase in rate as temperature increases
Active Transport
- nonspontaneous (+ΔG) and requires energy
- may or may not be affected by temperature
- net movement of solute against its concentration gradient
- requires ATP
Simple Diffusion
- passive transport
- substrates move down their concentration —gradient directly across the membrane
- only particles that are freely permeable to the membrane are able to undergo simple diffusion
- potential energy here
Osmosis
- type of simple diffusion concerning water
- water moving from low solute to high solute
- important when solute itself is impermeable to the membrane
Hypotonic
- if concentration of solutes inside the cell is higher than the concentration of surrounding solution
- water rushes in and sometimes the cell can lyse
Hypertonic
- solution is more concentrated than inside the cell
- water rushes out and the cell shrivels
Isotonic
- solutions inside and outside the cell are equal
- prevents net movement of particles
- water continues to move but the cell will neither gain not lose water overall
Osmotic Pressure
- colligative property- physical property of solutions that is dependent on the concentration of dissolved particles but not one the chemical identity of the dissolved particles
- hydrostatic pressure exerted by the water level in the solute containing compartment will eventually oppose the influx of water so the water will only rise to the point at which it exerts a sufficient pressure to counterbalance the tendency of water to flow across the membrane
- pi= iMRT
Facilitated Diffusion
- passive simple diffusion for molecules that are impermeable to the membrane
- requires integral membrane proteins to serve as transporters or channels for these substrates
- ex- carrier or channel proteins
Carrier
- facilitated diffusion
- only open to one side of the cell membrane at any given point
- substrate binds to the transport protein, remains in the transporter during conformational change, and then dissociates
- sometimes it is in occluded state where it is not open to either side of the phospholipid bilayer
Channel
-facilitated diffusion
-may be in open or closed conformations
in open - exposed to both sides of the cell —–membrane and act as a tunnel for particles to diffuse through
Primary Active Transport
- uses ATP or another energy molecules to directly power the transport of molecules across the membrane
- involves use of transmembrane ATPase
Secondary Active Transport
- also known as coupled transport
- no direct coupling to ATP hydrolysis
- harnesses the energy released by one particle going down its electrochemical gradient to drive a different particle up its gradient
- same direction - symport
- opposite directions - antiport
- low to high solute concentration
- uses electrochemical gradient
Pinocytosis
endocytosis of fluids and dissolved particles
-Type of endocytosis
Phagocytosis
ingestion of large solids such as bacteria
-Type of endocytosis
Exocytosis
- occurs when secretory vesicles fuse with the membrane releasing material from inside the cell to the extracellular environment
- important in the nervous system and intracellular signaling
Sarcolemma
- in muscle cells
- maintains a membrane potential for contraction to occur
Membrane potential
- Vm
- different in electrical potential across cell membrane
- resting- between -40 and -80 mV and can rise up to +35mV
- maintained through K+, Na+, Cl-
Leak Channels
-ions may passively diffuse through the cell membrane over time so maintaining membrane potential requires energy
Sodium-Potassium Pump
- ion transporter pump
- regulates concentration of intracellular and extracellular sodium and potassium ions
- maintain a low concentration of sodium ions and high concentration of potassium ions intracellularly by pumping 3 Na ions out for every 2 K+ pumped in
- this removes one positive charge from the inside maintaining a negative resting potential
Outer Mitochondrial Membrane
- highly permeable due to many large pores that allow for the passage of ions and small proteins
- completely surrounds the inner mitochondrial membrane with intermembrane space
Inner Mitochondrial Membrane
- much more restricted permeability compared to the outer
- contains infoldings known as cristae that increase the available surface area for integral proteins
- encloses the mitochondrial matrix where TCA produces high energy electron carriers used in ETC
- high level of cardiolipin and does not contain cholesterol
Nernst
E= RT/zF ln [ion]outside/[ion]inside
-where z is charge of ion
What is the primary thermodynamic factor responsible for passive transport
Entropy
What distinguishes the inner mitochondrial memebrane from other biological membranes? what is PH gradient between the cytoplasm and the intermembrane space?
The inner mitochondiral membrane lacks cholesterol, which differenciates it form most other biological membranes. There is no pH gradient between the cytoplasm and the intermembrane space because the outer mitochondrial membrane has such high permeability to biomolecules (the proton motive force of the mitochondria is across the inner membrane, not the outer membrane membrane.
