cell boundaries part 2

What happens when we What happens when we reach equilibrium?reach equilibrium?

Particles continue moving across membrane but in Particles continue moving across membrane but in both directions!both directions!***No more changes in concentration***No more changes in concentration

Problems for diffusion…Problems for diffusion…

Things too largeThings too large Charged moleculesCharged molecules

Positive/negativePositive/negative Opposites attract but likes do not…Opposites attract but likes do not… These all present serious problems for These all present serious problems for

things getting across membranes…things getting across membranes…

If things can cross a If things can cross a membrane we call the membrane we call the membrane PERMEABLEmembrane PERMEABLE

If things canNOT cross a If things canNOT cross a membrane we call the membrane we call the membrane IMPERMEABLEmembrane IMPERMEABLE

Biological membranes Biological membranes are…are…

SEMI-PERMEABLESEMI-PERMEABLE Aka…Aka… Selectively permeableSelectively permeable Cell membranes are pickyCell membranes are picky

OsmosisOsmosis Water (H2O) can pass Water (H2O) can pass

easily through most easily through most biological membranesbiological membranes

Def: Def: Diffusion of Water Diffusion of Water

through a semi-through a semi-permeable membranepermeable membrane

How Osmosis works…How Osmosis works… We have water molecules and some We have water molecules and some

other molecules, let’s say sugarother molecules, let’s say sugar If we have more water on one side of the If we have more water on one side of the

membrane (HIGH conc. of H2O), then membrane (HIGH conc. of H2O), then the water will diffuse across…the water will diffuse across…

Membrane will let water thru but not Membrane will let water thru but not sugar sugar

Water can move back and forth (not Water can move back and forth (not sugar)sugar)

Water moves from areas of Water moves from areas of HIGH conc. To areas of LOW HIGH conc. To areas of LOW conc.conc.

Water moves across till equilibrium is reachedWater moves across till equilibrium is reached Isotonic: Isotonic:

when conc. of water = conc. of sugar when conc. of water = conc. of sugar Hypertonic: “above strength”Hypertonic: “above strength”

When we begin with more sugar in waterWhen we begin with more sugar in water More concentrated sugar solution on side AMore concentrated sugar solution on side A

Hypotonic: “below strength”Hypotonic: “below strength” When we end with less sugar When we end with less sugar Dilute sugar solution on side ADilute sugar solution on side A

Osmotic PressureOsmotic Pressure

We will discuss later…We will discuss later… PLEASE read page 186PLEASE read page 186 This is a confusing concept…This is a confusing concept…

How do big molecules How do big molecules diffuse across a membrane diffuse across a membrane so quickly if the membrane so quickly if the membrane is selectively permeable?is selectively permeable?

Facilitated DiffusionFacilitated Diffusion What does facilitate mean?What does facilitate mean? Proteins are the extra helpProteins are the extra help ““escorts” across the membraneescorts” across the membrane We call these protein channels…We call these protein channels…

Allow specific things thruAllow specific things thru

Facilitated Diffusion Facilitated Diffusion (continued)(continued)

FASTFAST SPECIFICSPECIFIC Still diffusion Still diffusion

so we only see so we only see it from high it from high concentration concentration to lowto low

Does NOT Does NOT require energyrequire energy

What about when we want What about when we want to go against the to go against the concentration?concentration?

(From low concentration to (From low concentration to high?)high?)

What do we need???What do we need???

ENERGY!!!!ENERGY!!!!

ACTIVE transportACTIVE transport Process that moves molecules against the Process that moves molecules against the

concentration gradientconcentration gradient Requires ENERGYRequires ENERGY A protein pumps small molecules and ions A protein pumps small molecules and ions

across a cell membrane against the conc. across a cell membrane against the conc. gradientgradient

To pump large molecules and clumps…To pump large molecules and clumps… 2 other processes:2 other processes:

ExocytosisExocytosis EndocytosisEndocytosis The can change shape of membraneThe can change shape of membrane

Types of Active transportTypes of Active transport

Molecular TransportMolecular Transport When small ions and molecules are carried When small ions and molecules are carried

across membraneacross membrane EndocytosisEndocytosis

Endo- means….Endo- means…. -Cyto- means…-Cyto- means… -sis mean….-sis mean….

ExocytosisExocytosis Exo- means….Exo- means…. -Cyto- means…-Cyto- means… -sis mean….-sis mean….

Molecular TransportMolecular Transport

Proteins are used to pump small Proteins are used to pump small molecules and ions across membrane molecules and ions across membrane even against the conc. Gradienteven against the conc. Gradient

The cell devotes a lot of ENERGY to The cell devotes a lot of ENERGY to pumping things across membranepumping things across membrane

Potassium, calcium, and sodium are Potassium, calcium, and sodium are some things that need to pumped acrosssome things that need to pumped across

EndocytosisEndocytosis When cells need to take in large materialWhen cells need to take in large material Process of taking material into the cell by Process of taking material into the cell by

process of infolding, or pockets, of the process of infolding, or pockets, of the cell membranecell membrane

Pocket breaks loose from cell membrane Pocket breaks loose from cell membrane and forms a vacuole inside the celland forms a vacuole inside the cell

Two Types…Two Types… PhagocytosisPhagocytosis PinocytosisPinocytosis

Two types of Two types of endocytosis:endocytosis:

1. Phagocytosis1. Phagocytosis ““cell eating”cell eating” Extensions of cytoplasm surround the particle Extensions of cytoplasm surround the particle

and package it within a food vacuoleand package it within a food vacuole Cell then engulfs the packageCell then engulfs the package AmoebasAmoebas

2. Pinocytosis2. Pinocytosis ““cell drinking”cell drinking” When cell needs to take up liquidWhen cell needs to take up liquid Tiny pockets in cell membrane formTiny pockets in cell membrane form Fill with liquid Fill with liquid Then pinch off to form vacuoles inside of cellThen pinch off to form vacuoles inside of cell

ExocytosisExocytosis Exo- means…Exo- means… Cyto means…Cyto means… Sis means…Sis means… When cell releases large amounts of materialWhen cell releases large amounts of material Excretes stuffExcretes stuff Membrane of vacuole surrounding particle Membrane of vacuole surrounding particle

inside cell fuses with the cell membraneinside cell fuses with the cell membrane The contents in vacuole are then forced out of The contents in vacuole are then forced out of

the cellthe cell We see this in removal of water by contractile We see this in removal of water by contractile

vacuolesvacuoles