movement of substances Flashcards
(58 cards)
what are biological membranes
- refers to membrane found in living cells (natural, not artificial - visking tubes)
what are plasma membranes
- membrane surrounding the cytoplasm of the cell (big one)
what are cell membranes
- membrace surrounding any membrane bound organelles found within a cell
what are membranes composed of
- lipids: phospholipid bilayer (two layers)
- proteins: membrane proteins
how is the membrane held together
- hydrophobic interactions
what the plasma membrane does (function)
1) provide shape for a cell
2) forms a physical boundary between cytoplasm and external environment
-> ensures maintenance of constant internal environment within the cell
what the cell membrane does (function)
1) forms compartments within the cell for specific metabolic process
- compartmentalisation of these metabolic processes
1) prevents intermediates of one pathway from interfering with those of another pathway
2) maintains high concentrations of reactants at specific sites
2) cell membranes are selectively permeable:
- control movement, regulates passage of substance in and out of the cell
- serve as an effective barrier to polar/hydrophilic molecules and ions
selectively permeable vs partially permeable
1) able to regulate movement of substances according to the NEED of the cell
- ALL BIOLOGICAL MOLECULES (cell, plasma membrane) are selectively permeable
2) only allows smaller molecules to pass through, excluding larger molecules (according to PARTICLE SIZE)
- visking tubing
how big are membranes, and what are they made of
size: 7-10 nm
components:
1) lipids
- phospholipids
- cholesterol
- triglyceride
2) carbohydrates
3) proteins
hydrophilic vs hydrophobic
1) water loving
- polar
2) water hating
-non polar
phospholipids contain what group
- phosphate group
- bound by 4 oxygen molecules
what does phospholipids contain
- phosphate head
- two hydrocarbon tails (formed by two fatty acid chains - one saturated, one unsaturated)
quality of phospholipid (waterlove/hate - term)
head: hydrophilic - soluble in water
tails: hydrophobic - insoluble in water
term: amphipathic
how are the phospholipids arranged to form a layer (monolayer)
- hydrophobic hydrocarbon tails (made of hydrogen and carbon atoms) project out the water
- hydrophilic phosphate heads lie in the surface of the water
how phospholipids arrange to form a bilayer
- when phospholipid molecules are surrounded on all sides by water, they arrange into a bilayer
- two layers of phospholipids with hydrophilic phosphate groups facing the surrounding aqueous water medium,
- hydrophobic chains facing towards the inside of the bilayer
core of membrane
- hydrophobic hydrocarbon chains of phospholipids form the core of the membrane
- hydrophobic core has low permeability to large molecules and hydrophilic particles including ions and polar molecules
- thus creates a barrier to aqueous solutions
how the PHOSPHOLIPIDS LAYER helps become a good barrier
- the arrangement of the heads maximizes attractive forces within each other, as well as between the head sand the intracellular and extracellular aqueous (watery) environments
- prevents repulsive interactions between hydrophobic tails and intracellular and extracellular aqueous environments
- maximizes attractive forces between hydrophobic tails within each other and the bilayer
freeze-fracture technique for membrane (plasma)
- split along a plane in the middle of the bilayer
- reveals presence of particles (protein)
phospholipid composition
- hydrophilic phosphate group (bound by 4 oxygen molecules) (one double bonded, one negative charged) PO4^3-
- two hydrophobic tails
- one saturated fatty acid, one unsaturated fatty acid
- saturated meaning that the maximum number of hydrogen and carbon atoms attached
how phospholipids (and their components) change by the fluidity
1) more fluid
- high proportion of unsaturated fatty acid chains
- low proportions of saturated chains
shorter fatty acid chains
- high temperature
2) less fluid (more rigid)
- low proportion of unsaturated fatty acids
- high proportion of saturated fatty acid chains
- longer fatty acid chains
- low temp
functionof membrane proteins
helps determine most of membranes functions
integral protein not tested
aka intrinsic protein
- penetrate only partially/all the way through phospholipid
- bound via hydrophobic + hydrophilic bonds
-> hydrophobic: hydrophobic interactions exist due to hydrophobic amino acids and hydrocarbon chains (tails of phospholipid) - mid section of phospholipids bilayer
-> hydrophilic: hydrophilic ends are exposed to aqueous solution on both sides of membrane , thus hydrogen bonds exist between the hydrophilic amino acids and phosphate group of phospholipid molecules (head)
peripheral protein not tested
aka extrinsic protein
- on the surface of phospholipid bilayer
- DOES NOT penetrate deeply into the membrane
- bound to membranes via ionic bonds and hydrogen bonds
- largely hydrophilic
- easily detached using relatively gentle extraction procedures
how integral protein provides and regulates movement of substances into and out of cell and organelles
- not tested -
✔”Spans the membrane” → The protein extends all the way through the phospholipid bilayer, creating a passage.
✔ “Provides a hydrophilic channel” → The inside of the channel is water-friendly, allowing polar molecules and ions to pass through.
✔ “Selective for a particular solute” → Each channel protein is specific to certain molecules (e.g., sodium channels only allow sodium ions to pass).
✔ “Passive transport” → This means that molecules move without requiring energy (ATP). They travel down their concentration gradient (from high to low concentration).
2) Carrier Proteins (Active Transport)
✔ “Hydrolyses ATP as an energy source” → The carrier protein breaks down ATP to release energy.
✔ “Actively pump substances across the membrane” → Unlike passive transport, active transport requires energy to move molecules against their concentration gradient (from low to high concentration).
📌 Example: The sodium-potassium pump actively moves Na⁺ out and K⁺ in, using ATP.
