functions of the fluid phospholipid bilayer
- maintains internal/external environment
- prevents passage of water-soluble molecules (eg. ions, sugars, amino acids)
- allows passage of very small uncharged molecules (o2, co2)
- allows passage of lipid-soluble molecules (alcohol, fatty acids, steroids)
which kind of fatty acids increase and decrease fluidity?
- unsaturated fatty acids have kinks, so they prevent the fatty acids from packing tightly together. therefore they increase fluidity
- saturated fatty acids have no kink, so they can pack tightly together. therefore they decrease fluidity
how do temperature and cholesterol affect fluidity of membrane?
- warm temp=membrane becomes more fluid bc phospholipids have more kinetic energy. SO, cholesterol stabilizes phospholipids, which prevents the membrane from getting TOO fluid
- cold temp=membrane becomes more rigid because phospholipids pack together more closely. SO, cholesterol maintains space between phospholipids and prevents tight packing, which maintains fluidity
what are integral proteins
- transmembrane proteins
- have hydrophobic amino acids embedded in the lipid bilayer
- have hydrophilic amino acids that interact with water
peripheral proteins
- only found on one side of the membrane
- have fewer hydrophobic amino acids
what are the 7 types of membrane proteins?
- transport proteins (allow material to cross membrane)
- receptors (receive chemical signal and pass on to nucleus)
- enzymes (increase rate of chemical reactions)
- cell adhesion or anchoring proteins (bind cells together)
- recognition proteins (protrude from surface and identify cells in an immune response)
6+7. glycoproteins and peripheral proteins (allow membrane to interact with ECM and cytoskeleton)
what type of membrane protein has a membrane transport function
transport proteins
what type of membrane protein has a signal transduction function
receptors
what type of membrane protein has a enzymatic activity function
enzymes
what type of membrane protein has a intercellular joining function
cell adhesion or anchoring proteins
what type of membrane protein has a cell-cell recognition function
recognition proteins
what type of membrane protein has a attachment to cytoskeleton and ECM function
glycoproteins and peripheral proteins
define diffusion
net movement of molecules from an area of high concentration to an area of low concentration. no energy is required.
why does diffusion occur?
molecules have KE and are in constant motion, they move randomly collide, which leads to even distribution.
examples of simple diffusion?
- gases like O2 and CO2
- lipid-soluble molecules like drugs, alcohol, steroids
- small uncharged molecules
compare and contrast the functions of the three types of transport proteins and provide an example for each
- carrier proteins
- opens one side at a time, binds to specific ions/molecules and undergoes a conformational change to transport them across the membrane
- passive transport
- ex: GLUT (glucose transporters for facilitated diffusion of glucose) - channel proteins
- form a corridor through the cell membrane that allows SPECIFIC ions to pass through membrane (each channel is structured to accommodate a particular ion based on size and charge)
- passive transport
- ex: ion channels (Na+, K+) - pump proteins
- open one side at a time. specific molecule binds while its open on one side. ATP breaks down into ADP and Pi, the Pi binds to protein, energizing the pump and causing it to undergo conformational change, which allows pump to move molecule against its concentration gradient.
- loss of phosphate reverts protein shape
- active transport
- ex: Na+/K+ pump, proton pump
Describe the molecular movement in diffusion, osmosis, and facilitated diffusion
diffusion: molecules are constantly and randomly moving around due to KE, causing them to collide with each other. this leads to even distribution of molecules. even when they reach equilibrium, the net movement is the same in both directions.
osmosis: water moves from an area of low solute concentration to an area of high solute concentration (high water concentration to low water concentration). the movement of water continues until the concentration of solutes is equal on both sides of the membrane (or until other factors prevent further movement).
facilitated diffusion: the passive movement of larger or charged molecules across the cell membrane through specialized transport proteins. molecules move from an area of high concentration to an area of low concentration, but because these molecules are too large or polar (charged) they need help to pass through (channel proteins or carrier proteins).
what happens to an animal cell and a plant cell placed in an isotonic solution?
animal cell: no change in cell size, normal
plant cell: no change in cell size, flaccid and plant may wilt
what happens to a plant and animal cell placed in a hypertonic solution?
animal cell: cells shrink in size, cell shrivels/crenates
plant cell: membrane pulls away from cell, plasmolysis (lethal)
what happens to an animal and plant cell placed in a hypotonic solution?
animal cell: cell swells and may burst (lysis)
plant cell: swells and presses against cell wall, normal for plant cell
compare passive transport, active transport, co-transport, and bulk transport, including the
direction of transport, size of molecules, and energy requirements
passive:
- down concentration gradient
- typically small, non-polar molecule like O2, CO2 and water. can also move large molecules with facilitated diffusion
- no energy required
active:
- against concentration gradient
- typically larger or charged molecules like K+, Na+, and large nutrients
- requires ATP
co-transport:
- one molecule moves down its concentration gradient while the other moves against it. the molecule moving down its gradient releases energy, this energy is used by the protein to change shape, allowing it to actively transport the other molecule against its concentration gradient.
- typically smaller molecules
- use of stored gradient (indirectly requires ATP)
bulk transport:
- into cell (endocytosis) or out of cell (exocytosis)
- large molecules such as lipids, proteins, or even whole cells
- requires ATP for the formation of vesicles and the movement of materials in or out of the cell.
Explain the processes of exocytosis and endocytosis
exocytosis: vesicles carrying material fuses with membrane to release contents outside of cell
endocytosis: membrane dips in engulfing material, then pinches and fuses to form vesicle surrounding material.
what are the three types of endocytosis?
- phagocytosis “cellular eating”
- membrane reaches out and engulfs other cells/particles in phagocytic vacuole
- used by protists as food gather strategy
- used by host defence cells to get rid of germs - pinocytosis “cellular drinking”
- membrane takes in extracellular fluid and dissolved solutes - receptor mediated endocytosis
- binding of specific molecules to receptors triggers pinching in.
what is a membrane potential?
a membrane potential is a voltage difference across a cell membrane caused by a difference in charges inside vs outside the cell.
