Cell membrane powerpoint diffusion and osmosis revised

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