cell membrane powerpoint diffusion and osmosis revised
TRANSCRIPT
Cell Boundaries
Chapter 6
What are boundaries?
We have borders
surrounding
countries
We have boundaries
on a playing field
Why are borders
important?
What are the borders of a
cell?
Cell membrane
Thin, flexible barrier
Cell wall
Plant, algae, fungi, prokaryotes
Strong supporting layer
Cell Membrane
What does it do for cell?
Controls what goes in and out
Regulates molecules moving from one liquid side of the
cell to the other liquid side of the cell
Protects
Supports
Cell Membrane
Lipid bilayer
What are lipids?
What does bi- mean?
What’s a layer?
A cell membrane is made of two
layers of lipid molecules
Cell membrane
Phospholipids bilayer
Made of a negatively charged
phosphate “head”
PO43-
Attracts water because the phosphate is charged
(-)
Water is a polar , slightly positive ends and
slightly negative ends
Attached to the phosphate
group are 2 fatty acid chains
Hydrophobic= don’t like water
So the inside of the cell
membrane doesn’t let water in
but the outside allows cells to be
dissolved in aqueous
environments
Other things in the
membrane…
Proteins embedded
in lipid bilayer
Carbohydrates
attached to proteins
So many different
molecules in
membrane, we call it
a “mosaic” of
different molecules
Proteins
Proteins help things
get across
membrane
Kinda like a pump
Carbohydrates…
Chemical
identification cards
“ID” card of cell
Helps individual cells
id each other
Cell Walls
Outside cell membrane (does NOT replace membrane!!!)
Plants, algae, fungi, prokaryotes
Have pores to allow things in
Function: SUPPORT and PROTECT
Cell walls made of…
Protein and carbs
Plant cell walls made
up of CELLULOSE
This is a tough
carbohydrate
Wood and paper
A biological membrane
Cells exist in liquid environments
Things need to get in and out of cell
Different ways to do this….
The Cell Membrane
Concentration (conc.)
Solution
Mix of 2 or more substances
Solutes
Substance dissolved in solution
Concentration Molarity (M) is # of Moles of a substance per liter of solution
6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc)
Moles is a unit for measuring EXTREMELY small things
is mass of SOLUTE in a given volume of solution (g/L)
What is the concentration of 12 grams of salt dissolved in 3 liters of water?
12g/3L= 4g/L
Diffusion
Particles constantly move
Collide randomly
Spread out randomly
Diffusion is moving from area of HIGH conc. to
area of LOW conc.
This is what we call the CONCENTRATION
GRADIENT
Equilibrium
When the conc. Of a
system is the same
throughout
(same conc. on both
sides)
What happens when we
reach equilibrium?
Particles continue moving across membrane but in
both directions!
***No more changes in concentration
If things can cross a
membrane we call the
membrane PERMEABLE
If things canNOT cross a
membrane we call the
membrane IMPERMEABLE
Biological membranes
are…
SEMI-PERMEABLE
A.K.A.
Selectively permeable
Cell membranes are picky
What’s this have to do
with cells?
Cell have liquid inside and are found in liquid environment
We have substances (solutes) inside and outside cell
Unequal concentrations means we get DIFFUSION!!!
B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy
What diffuses across the
membrane???
Small, uncharged
(non-polar) molecules
Examples:
Carbon dioxide
Oxygen
Cells are always trying to Maintain Equilibrium by…
3 ways…
PASSIVE Transport 2 types
Requires NO energy
Goes with Conc. Gradient
types:
SIMPLE DIFFUSION- No protein required
Small, uncharged particles
FACILITATED DIFFUSION- CHANNEL or CARRIER proteins
Trans-membrane protein channel
Protein with a specific shape; open-close
mechanism
Ex. Osmosis and ligand-gated channels
ACTIVE Transport 1 type
REQUIRES Energy
Goes Against Conc. Gradient
ACTIVE TRANSPORT
Involves “transporter”
membrane protein and
ENERGY (ATP)
Osmosis
Water (H2O) can pass easily through most
biological membranes
Def:
Diffusion of Water through a semi-permeable
membrane
Small molecules of water can sometimes diffuse
across easily (no protein needed)
AQUAPORIN: What does “aqua” mean???
Protein in cell membrane that allows water through (speeds up
diffusion of water across the membrane)
Type of Facilitated diffusion (more on this later)
How Osmosis works… We have water molecules and some other molecules, let’s
say sugar
If we have more water on one side of the membrane (HIGH
conc. of H2O), then the water will diffuse across…
Membrane will let water thru but not sugar
Water can move back and forth (not sugar)
Water moves from areas of
HIGH conc. To areas of LOW
conc.
Water moves across till equilibrium is reached
Isotonic: when conc. Of both solutions is equal
Hypertonic: “above strength” When we begin with more sugar in water
More concentrated sugar solution on side A
Hypotonic: “below strength” When we end with less sugar
Dilute sugar solution on side A
Osmotic Pressure
Central vacuole fills with water and exerts and
out ward pressure on cell membrane and cell
wall
Cell wall does NOT allow cell to expand past a
certain size
Osmoregulation
Osmoregulation
means by which cells keep the
concentration of cell cytoplasm or blood
at a suitable concentration.
Problems in Plant Cell
Osmotic Pressure
Pressure exerted by osmosis on the
HYPERTONIC side of a semi-permeable
membrane
Think about blowing up a balloon…
Can cause serious problems for cell
Cell is full of sugar, salts, proteins, molecules
Inside of cell is Hypertonic
Osmotic pressure should make fresh water go…?
In or Out?
In
Cell will become inflated/swollen
Too much cell will burst like a balloon
Why don’t all our cells
burst?
What are our cells (animal) contained in? Fresh water?
No…..blood or other fluids, which are ISOTONIC The conc. Of sugars, salts, proteins and molecules in these
fluids is the same as the conc. in the cell
Bacteria and plant cells They DO come in contact with fresh water…what do
they have PROTECTING them?
CELL WALL Prevent cells from expanding even when there’s a lot of
osmotic pressure
But, cell walls are prone to injuries when there is too much osmotic pressure
Which is a RBC in isotonic solution?
RBC in hypertonic solution?
RBC in hypotonic solution?
How do big molecules
diffuse across a membrane
so quickly if the membrane
is selectively permeable?
Problems for diffusion…
Things too large (like Glucose!)
Charged molecules and Polar molecules
Positive/negative
Opposites attract but likes do not…
These all present serious problems for things
getting across membranes…
Facilitated Diffusion
What does facilitate mean?
Proteins are the extra help
“escorts” across the membrane
We call these membrane proteins…
Protein channels
Carrier proteins
LIGAND receptor proteins
Facilitated Diffusion
•takes place through proteins, or assemblies of proteins, embedded in
the plasma membrane
Protein channels
Carrier proteins
LIGAND receptor proteins
Facilitated Diffusion
(continued)
FAST
SPECIFIC
Still diffusion
so we only see
it from high
concentration
to low
Does NOT
require energy
What about when we want to
go against the
concentration?
(From low concentration to
high?)
What do we need???
ENERGY!!!!
ACTIVE transport Process that moves molecules against the concentration gradient
Requires ENERGY
A protein pumps small molecules and ions across a cell membrane against the conc. Gradient
Direct and Indirect Active transport (see animation) Forms of molecular transport proteins are used to pump small molecules
and ions across membrane even against the conc. grad.
Direct: every 3 Na+ ions pumped across for every 2 K+ ions
Indirect: Build up of ions on one side opens up another channel to shuttle in other molecules (Na+/Glucose channel)
Electrochemical gradient membrane potential (cell membrane is negative)
Na+ opens build up on the outside of the cell…draws water out of the cell so it doesn’t swell or burst!
To pump large molecules and clumps…
2 other processes: Exocytosis: exo-means….cyto- means…..-sis means….
Endocytosis: endo-means….cyto- means…..-sis means….
They can change shape of membrane
Build up of Na+ ions on one side of membrane from Na+/K+ pump
Now Na+ will flow thru another channel that allows one glucose in
too!
Pretty convenient!
Endocytosis
When cells need to take in large material
Process of taking material into the cell by
process of infolding, or pockets, of the
cell membrane
Pocket breaks loose from cell membrane
and forms a vacuole or vesicle inside the
cell
Two Types…
Phagocytosis
Pinocytosis
Two types of endocytosis:
1. Phagocytosis “cell eating”
Extensions of cytoplasm surround the particle and package it within a food vesicle
Cell then engulfs the package
Amoebas
2. Pinocytosis “cell drinking”
When cell needs to take up liquid
Tiny pockets in cell membrane form
Fill with liquid or many smaller molecules
Then pinch off to form vesicles inside of cell
Exocytosis
Exo- means…
Cyto means…
Sis means…
When cell releases large amounts of material
Excretes stuff
Membrane of vacuole surrounding particle inside cell fuses with the cell membrane
The contents in vacuole are then forced out of the cell
We see this in removal of water by contractile vacuoles
Cells are always trying to Maintain Equilibrium by…
3 ways…
PASSIVE Transport 2 types
Requires NO energy
Goes with Conc. Gradient
types:
SIMPLE DIFFUSION- No protein required
Small, uncharged particles
FACILITATED DIFFUSION- CHANNEL or CARRIER proteins
Trans-membrane protein channel
Protein with a specific shape; open-close
mechanism
Ex. Osmosis and ligand-gated channels
ACTIVE Transport 1 type
REQUIRES Energy
Goes Against Conc. Gradient
ACTIVE TRANSPORT
Involves “transporter”
membrane protein and
ENERGY (ATP)
MEMBRANE MAMBO!!!
Membrane Mambo 10 minutes to plan
2 teams/Cells
Nucleus for each team
Each member must be assigned a molecular role (must be labeled)
Membrane protein(s)
Molecule A (ex. Glucose)
Molecule B (ex. Na+)
Molecule C (ex. Water)
Remember molecules are ALWAYS moving!!!
MUST act out the following types of membrane transport:
Simple Diffusion
Osmosis
Facilitated diffusion (channel, carrier and ligand)
Active transport (direct and indirect)
Be prepared to determine the concentration on either side of the membrane
Your “Nucleus” must turn in a paper with every ones name and roles
Summary of how each scenario will be acted out