cells Flashcards
3 main parts of the cell
- Plasma membrane
- cytoplasm
- nucleus
Plasma membrane structure
phospholipid bilayer
2 types of proteins: integral (transmembrane) and peripheral
Plasma membrane lipids
75% phospholipids
5% glycolipids
20% cholesterol which stiffens the membrane
Plasma membrane proteins
Ion channels –> integral
-have pore for specific ion
carriers/transporters –> integral
-needs substrate binding to function
receptors –> integral
-very specific response to ligands
enzymes –> integral or peripheral
-lower activation energy for chem rxns
linker –> integral or peripheral
- anchors, structures, or links cells
cell identity marker (glycoproteins)
-mark cell as “self” for immune system
Selective permeability
- always permeable to small, nonpolar, uncharged molecules
- transmembrane proteins act as channels or transporters to increase permeability
- macromolecules need vesicular transport
electrochemical gradient
-combination of concentration gradient and electrical gradient
passive vs active transport
passive transport is from high to low concentration and doesn’t require energy
active transport is from low to high concentration and requires energy
Simple diffusion
- passive
- based on random kinetic motion of molecules
- typically small, nonpolar, lipid soluble
- gasses, steroid hormones, fatty acids
Facilitated diffusion
- channel mediated
- leakage channels = always open
- -ligand gated channels = need ligand to open
- voltage gated channels = open in response to transmembrane voltage change - carrier mediated
- solute binds to protein which carries it to the other side of the membrane
- rate is limited by # of carrier proteins
Osmosis
- passive
- water moves from high to low concentration
- pulled by osmotic pressure
osmolarity
solute concentration
tonicity
iso = same hyper = more solutes --> crenation hypo = less solutes --> bursting/ lysing
explain 2 ways water could pass thru membran
osmosis or aquaporins = single-file water channels
what limits rate of diffusion
- molecule size
- steepness of concentration gradient
- temp
- surface area
- diffusion distance
primary active transport
- energy from ATP changes the shape of a transporter proteins (pumps) which pump a substance against its concentration gradient
- sodium potassium pump 3 Na+ out; 2 K+ in
secondary active transport
- get energy from concentration gradient built from primary active transport
- always transport more than 1 thing
- “cotransport proteins”
- e.g. sodium might drag other things along with it as it flows back into the cell
Resting membrane potential
- electrical potential energy from separation of opp. charged molecules
- diff in charge = voltage
- voltage is only at membrane surface
- cells have protein anions, making them negatively charged
- concentration gradient pulls K out of cells, but electrical gradient pulls it in
- voltage is -90mV when K in = K out
- Na+ has some effect and can bring voltage to -70mV, but the membrane is less permeable for it
- Cl has no effect because its concentration and electrical gradient is balanced
- RMP is maintained by Na+K+ATPase
- neuron and muscle cells upset this by opening gated Na and K channnels
Vesicular transport
- Receptor mediated endocytosis
- receptor on outer membrane binds to ligand
- membrane invaginates, bringing ligand in - Phagocytosis
- also uses receptor
- membrane reaches up to surround microbe
- forms pseudopod - Pinocytosis (bulk phase endocytosis)
- no receptor
- randomly invaginates - Exocytosis
- membrane-enclosed vesicles fuse with plasma membrane and expel contents - Transcytosis
- combo of endo- and exocytosis to move something from one end of the cell to the other
Tight junctions
- integral proteins on adjacent cells fuse to form impermeable junction that circles cell
- prevents fluids and most molecules from getting through
- bladder and intestines
Desmosomes
- mechanical, rivet-like couplings formed when linker proteins (cadherins) interlock
- cadherins are anchored to cell through plaques on inside of membrane
- keratin filaments connect plaques intercellularly
- allows give
- cardiac and skin cells
Gap Junction
- Transmembrane proteins (connexons) which form tunnels
- allow cell-to-cell communication
- good for electrical signals to pass quickly b/t cells
- cardiac and smooth muscle cells
mechanical cell-to-cell signalling
- 1000s of sticky cell adhesion molecules (CAMs) which are glycoproteins as part of the glycocalyx
- variety of uses
chemical cell-to-cell signalling (primary)
- interaction between receptors and ligands which cause changes in cellular activity
- same ligand can have dif func.s in dif cells
- activated receptors can become enzymes, gate openers, gate closers
- ligand examples: neurotransmitters or hormones
second messenger chemical signalling
- 1st messenger is ligand
- activates receptor on G protein
- G protein activates effector protein (enzyme)
- effector protein catalyzes a reaction to make the 2nd messenger chemicals (cAMP of Ca+)
- 2nd messenger activates other proteins (kinases)
- -kinases add phosphate to stuff, activating other enzymes
- ligand is usually water soluble, so cant’s get thru membrane
