cell boundaries part 2
DESCRIPTION
part 2 of cell boundary notesTRANSCRIPT
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