AP Biology2005-2006

Cell Membrane and the Movement across it!

AP Biology2005-2006

Cell (plasma) membrane Cells need an inside & an outside…

separate cell from its environment cell membrane is the boundary

INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUTwasteammoniasaltsCO2

H2O products

cell needs materials in & products or waste out

IN

OUT

Can it be an impenetrable boundary? NO!

AP Biology

Lipids of cell membrane Membrane is made of phospholipids

phospholipid bilayer

phosphate

lipid

hydrophilic

hydrophobic

inside cell

outside cell

Phospholipid bilayer

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

AP Biology

Phospholipid bilayer What molecules can get through directly?

inside cell

outside cell

fats & other lipidscan slip directly through the phospholipid cell membrane, but…

what about other stuff?

lipid

salt

aa H2Osugar

NH3

AP Biology2005-2006

A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

AP Biology2005-2006

Membrane Proteins Proteins determine most of membrane’s

specific functions cell membrane & organelle membranes each

have unique collections of proteins

Membrane proteins: peripheral proteins = loosely

bound to surface of membrane integral proteins = penetrate into

lipid bilayer, often completely spanning the membrane =

transmembrane proteins

Many Functions of Membrane Proteins

Outside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

AP Biology

The many functions of proteins…. Channel proteins – wide open passage Ion channels – gated Aquaporins – water only, kidney and

plant root only Carrier proteins – change shape Transport proteins – require ATP Recognition proteins - glycoproteins Adhesion proteins – anchors Receptor proteins - hormones

Membrane carbohydrates Play a key role in cell-cell recognition

ability of a cell to distinguish one cell from another antigens

important in organ & tissue development

basis for rejection of foreign cells by immune system

AP Biology

Cholesterol Provides stability in animal cells “temperature buffer” quality for membrane Replaced with sterols in plant cells

Membrane fat composition varies Fat composition affects flexibility

membrane must be fluid & flexible about as fluid as thick salad oil

% unsaturated fatty acids in phospholipids keep membrane less viscous cold-adapted organisms, like winter wheat

increase % in autumn

cholesterol in membrane

AP Biology

Getting through cell membrane Passive transport

No energy needed Movement down concentration gradient

Active transport Movement against concentration gradient

low high requires ATP

AP Biology

Diffusion 2nd Law of Thermodynamics

- Universe tends towards disorder

Diffusion movement from high low concentration

AP Biology2005-2006

Simple diffusion across membrane

inside cell

outside cell

Which way will lipid move?

low

high

lipid

lipid

lipid

lipid

lipid

lipid lipid

lipidlipid

lipid

lipid

lipid

lipid

lipid

AP Biology

Diffusion of 2 solutes Each substance diffuses down its own

concentration gradient, independent of concentration gradients of other substances

AP Biology2005-2006

Facilitated diffusion Move from HIGH to LOW concentration

through a protein channel passive transport no energy needed facilitated = with help

AP Biology2005-2006

Gated channels Proteins that open only in presence of stimulus

(signal) stimulus usually different from transported

molecule ex: ion-gated channels ex: voltage-gated channels

AP Biology

Active transport Cells may need molecules to move

against concentration situation need to pump against concentration protein pump requires energy

ATP

Na+/K+ pump in nerve cell membranes

AP Biology2005-2006

Transport summary

AP Biology2005-2006

How about large molecules? Moving large molecules into & out of cell

requires ATP(energy)! through vesicles & vacuoles endocytosis

phagocytosis = “cellular eating” pinocytosis = “cellular drinking” receptor-mediated

endocytosis exocytosis

exocytosis

AP Biology2005-2006

Endocytosis

phagocytosis

pinocytosis

receptor-mediated endocytosis

fuse with lysosome for digestion

non-specificprocess

triggered byligand signal

AP Biology2005-2006

The Special Case of Water

Movement of water across the cell membrane

AP Biology2005-2006

Osmosis is diffusion of water Diffusion of water from

high concentration of water to low concentration of water across a

semi-permeable membrane

AP Biology2005-2006

Concentration of water Direction of osmosis is determined by

comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water

hypotonic hypertonic

water

net movement of water

AP Biology2005-2006

Managing water balance Cell survival depends on balancing

water uptake & loss

freshwater balanced saltwater

AP Biology

Hypotonicity animal cell in hypotonic

solution will gain water, swell & possibly burst (cytolysis)

Paramecium vs. pond water Paramecium is hypertonic H2O continually enters cell

contractile vacuole - pumps H2O out of cell = ATP

plant cell Turgid (turgor pressure) Cell wall

AP Biology2005-2006

Hypertonicity animal cell in hypertonic

solution will loose water, shrivel & probably die

salt water organisms are hypotonic compared to their environment

they have to take up water & pump out salt

plant cells plasmolysis = wilt

AP Biology2005-2006

Cell (compared to beaker) hypertonic or hypotonic

Beaker (compared to cell) hypertonic or hypotonic

Which way does the water flow? in or out of cell

.05 M .03 M

Osmosis…

AP Biology

Water Potential Water moves from a place of greater water

potential to a place of lesser water potential (net).

As the concentration of a solute increases in a solution, the water potential will decrease accordingly. Which has the greater water potential:

.2M or .8M? Which has the greater water potential:

20% or 80% water?

AP Biology

intracellular waste

Animal systems evolved to support multicellular life

O2

CHO

CHO

aa

aa

CH

CO2

NH3aa

O2

CH

O2

aa

CO2

CO2

CO2

CO2

CO2

CO2 CO2

CO2

CO2

CO2

NH3

NH3 NH3

NH3

NH3

NH3

NH3NH3

O2

aa

CH

aa

CHO

O2

Diffusion too slow!

single cell

but whatif the

cells areclustered?

for nutrients in & waste out

extracellular waste

AP Biology

Overcoming limitations of diffusion Evolution of exchange systems for

distributing nutrients circulatory system

removing wastes excretory system

gas exchange respiratory system

systems to support multicellular organisms

systems to support multicellular organisms

aa

CO2

CO2

CO2

CO2

CO2

CO2 CO2

CO2

CO2

CO2

NH3

NH3 NH3

NH3

NH3

NH3

NH3NH3

O2

aa

CH

aa

CHO

O2

AP Biology

When is Diffusion Needed? Respiratory and Circulatory systems

Oxygen/CO2 transport into and out of bloodstream Skins, gills, alveoli, capillaries

Excretory systems Movement of wastes into or out of blood

Skin, nephridia, nephrons, gills

Q: What do these systems have in common for diffusion to occur? Large surface area

AP Biology

Gas exchange in many forms…

one-celled amphibians echinoderms

insects fish mammals

endotherm vs. ectothermsize

cilia

water vs. land ••

AP Biology

Counter current exchange system Water carrying gas flows in one direction,

blood flows in opposite direction

just keepswimming….

AP Biology

Blood & water flow in opposite directions maintains diffusion gradient over whole length

of gill capillary

maximizing O2 transfer from water to blood

water

blood

How counter current exchange worksfront back

blood

100%15%

5%90%

70% 40%

60% 30%

100%

5%

50%

50%

70%

30%

watercounter-current

concurrent

AP Biology

Gas Exchange on Land Advantages of terrestrial life

air has many advantages over water higher concentration of O2

O2 & CO2 diffuse much faster through air respiratory surfaces exposed to air do not have to

be ventilated as thoroughly as gills air is much lighter than water & therefore

much easier to pump expend less energy moving air in & out

Disadvantages keeping large respiratory surface moist

causes high water loss reduce water loss by keeping lungs internal

AP Biology

Intracellular Waste What waste products

are made inside of cells? what do we digest our food into…

carbohydrates = CHO lipids = CHO proteins = CHON nucleic acids = CHOPN

CO2 + H2O

NH2 =

ammonia

CO2 + H2O CO2 + H2O

CO2 + H2O + N

CO2 + H2O + P + N

|

| ||H

HN C–OH

O

R

H–C–

Animalspoison themselves

from the insideby digesting

proteins!

cellular digestion…cellular waste

AP Biology

Nitrogen waste Aquatic organisms

can afford to lose water ammonia

most toxic

Terrestrial need to conserve

water urea

less toxic

Terrestrial egglayers

need to conserve water need to protect

embryo in egg uric acid

least toxic

AP Biology

Land animals Nitrogen waste disposal on land

need to conserve water must process ammonia so less toxic

urea = larger molecule = less soluble = less toxic 2NH2 + CO2 = urea produced in liver

kidney filter solutes out of blood reabsorb H2O (+ any useful solutes) excrete waste

urine = urea, salts, excess sugar & H2O urine is very concentrated concentrated NH3 would be too toxic

OC

HNH

HNH

Ureacosts energyto synthesize,

but it’s worth it!

mammals

AP Biology

Animal Osmoregulation (blood solute levels)

Kidneys – generate urine by filtering wastes from blood Nephrons – basic unit of kidney

Water will move towards urine or blood as it becomes hypertonic via AQUAPORINS

Anti-Diuretic Hormone increases water movement back to blood….why?

Blood pressure is highly regulated by the kidney because without pressure, there is no filtration = toxic blood = death!!!

AP Biology

Osmotic control in nephron How is all this re-absorption achieved?

tight osmotic control to reduce the energy cost of excretion

use diffusion instead of active transportwherever possible

the value of acounter current exchange system

AP Biology

Osmoregulation

Why do all land animals have to conserve water?

always lose water (breathing & waste) may lose life while searching for water

Water balance vs. Habitat freshwater

hypotonic to body fluids water flow into cells & salt loss

saltwater hypertonic to body fluids water loss from cells

land dry environment need to conserve water may also need to conserve salt

hypotonic

hypertonic