Exam 1: Ch 4 Notes Flashcards
if you change size you change
surface area to volume ratio
strength to weight ratio
organisms of different sizes face the same challenge and have different solutions due to the laws of physics
pond skater vs hovercraft on water
diffusion only works for some sizes
high surface area to volume ratio
3 big environmental factors
temperature
oxygen
access to water
temperature environment example
tropical fish (22-29°C) vs polar fish (-1.9°C)
0°C is freezing and ice crystals expand and puncture cells
ice fish developed antifreeze proteins in cells that wrap around ice crystals to prevent growth
disadvantage: ice crystals don’t thaw above freezing
6°C paradigm
cool tropical fish to 6°C and they die
heat ice fish to 6°C and they die too
5 thermoregulation adaptions
insulation
circulatory
cooling by evaporative heat loss
adjust metabolic heat production
change behavior
oxygen environment example
if you live at altitude you have less O2 than at sea level
evolutionary adaptions of other animals vs. humans
geese vs. humans
tibet vs. peru
water environment example (presence vs. absence)
osmotic challenge
desert beetle has ridges that allow water to condense and drip toward mouth
to have viable life you must have…
controlled chemical reactions
for controlled chemical reactions you must have…
a controlled environment… in cells this is the phospholipid bilayer (10-20nm)
membrane regulates influx and efflux
what forces are at play in cell membranes
permeability
concentration gradients
electrical charge
diffusion
active pumping
what level of permeability do cell membranes exhibit
semi-permeable
prevents large molecules (proteins), charged molecules or ions, and hydrophilic substances from crossing
water, oxygen, and fat soluble molecules can cross
what does the fluid mosaic membrane model tell us
membranes are dynamic and complex
the properties of the membrane depend on…
the properties of the lipids
saturated: no db so better packing
unsaturated: db kinks less packing
cholesterol stiffens and strengthens the membrane
what enables self repair between fatty acid tails in membranes
van der waals forces
these forces also allow geckos to climb smooth surfaces
integral proteins
proteins in the membrane must have hydrophobic aas in the membrane and polar aas outside the membrane
mostly alpha helices
diffusion
random movement from areas of high concentration to areas of low concentration until equilibrium is reached
movement in both directions does not stop at equilibrium, the net movement is just 0
what affects speed of diffusion
temperature (speed)
size of the concentration gradient (speed)
membrane properties
properties of the crossing molecule
membrane permeability
rate at which a substance passively crosses the membrane at a set temp etc.
greater permeability = greater flux across membrane
permeability constant equation
Pm = (Dm)(K) / x
Dm = diffusion constant
K = partition coefficient
x = thickness of the membrane
partition coefficient
indication of ability to dissolve in membrane
how can the permeability of a membrane change?
cell opens ion or aquaporin channels
diffusion doesn’t factor in…
charge
active pumping
as cell membrane thickens, diffusion is affected how
takes more time
osmosis
movement of water across membrane from areas of highest water purity to lower water purity (water + dissolved substances)
at equilibrium net movement of water is 0 b/c hydrostatic pressure balances osmotic pressure
osmotic pressure
pi = RTC
R = gas constant
T = temp
C = solute concentration
osmolarity
theoretical comparison
iso is equal amounts of 1mM NaCl
hypo (lower osmotic pressure, fewer solutes, more pure H2O)
hyper (higher osmotic pressure, more solutes, less pure H2O)
moves from hypo to hyper
tonicity
cell based comparison
tonicity example
sea urchin egg
isotonic to seawater
isoosmotic in NaCl
isoosmotic CaCl2, but hypotonic in CaCl2 b/c cell more permeable to Ca2+ (water moves in to swell cell)
Na diffusion permeability example
cell membrane slightly permeable to Na, which has a higher [ ] outside the cell
movement of Na is into cell (high to low)
consequences: higher osmotic pressure, H2O swells
solution: pump Na out of cell using ATP
prove presence of Na pump
metabolic inhibitor lowers ATP
pump slows and cells burst b/c buildup of Na inside cell causes H2O to follow
how do plant cells and bacterial cells withstand high pressure buildup?
cell wall
mechanism of secondary active transport
uses concentration gradient or electrical gradient to move other molecules against their gradients
why does rate of channels, pumps, carriers taper off?
at high [substrate] all channels, pumps, carriers are saturated
carriers saturate faster
nystatin
an antibiotic that forms channels in a membrane
H2O, urea, and Cl- allowed through, but not cations
if using a patch, no need to puncture membrane
inject aquaporin RNA into frog oocyte
expresses channels for H2O
water moves into oocyte, which has a concentrated cytoplasm
carrier proteins exhibit…
selectivity
coupled carriers
symporters and antiporters
use [ ] gradient of one to power movement of the other
cystic fibrosis and Cl- channel mutation
normally CF channel lets Cl- out of cell (slippery normal mucous)
in mutation the Cl- doesn’t move out (sticky mucous)
Na/K ATPase
pump that uses ATP to create a [ ] gradient of low Na in cell and high K in cell
3 Na out, 2 K in
creates net negative resting potential inside cell
Na/K ATPase steps
bind 3 Na+ form cytosol
phosphorylation by ATP changes conformation
Na+ released in extracellular fluid, 2 K+ binds
dephosphorylation changes conformation
2 K+ released in cytosol
alanine/Na symporter
alanine moves against concentration gradient, Na moves down concentration gradient
depends on Na/K ATPase to maintain Na gradient
if excess Na inside cell, symporter moves alanine out
antiporter example
Na in, Ca out
active transport summary
ATP required to move substances against [ ] gradient
highly selective
some pumps perform electrical work
selectively inhibit pumps (ouabain inhibits Na/K ATPase)
epithelial sheets
polarity of cells and location of pumps, channels, and transporters regulates movement
different membranes/regions of the cell can have different ______
selectivity
ex. voltage gated Na channel lets Na and Li through
Na/K ATPase lets Na through but not Li
how is selectivity achieved?
size, shape, charge
energy of dehydration
interaction of channel charges with ions
endocytosis
protein clathrin coats membrane, ligand binds, invagination vesicle fuses with other cellular membrane component, clathrin recycled
recycles membrane added from exocytosis
exocytosis
out of cell
ex. neurotransmitter release
gap junction stucture
1/2 of structure made by cell 1, other half by cell 2
6 proteins –> 1 connexon + 1 connexon = gap junction
gap junction purpose
direct electrical coupling between cells for ions, ATP, small molecules, 2nd messengers
gap junction test
inject dye of varying size and see if it diffuses through the cells
tight junctions
seal gap between cells to form an impermeable, intact sheet
things cant move inbetween individual cells, so must move through the cell bodies
allows cells to regulate what moves through
intermediate junctions
allow more rapid flow b/c moving through cell takes times
can move on [ ] gradient
