The Cell MembraneWhat do you notice about the picture below?

What parts can you name?

Do you know their functions?

Cell Membrane

8,000 membranes to equal one sheet of paper

Functions of Cell Membrane

1. Control what enters and exits the cell

2. Help cell keep its shape

3. Communicate with other cells

Selectively Permeable? WHY?• The structure of the membrane makes it

determine what substances can enter and not enter!

• Controls traffic in & out of the cell– Selectively permeable - allows some substances

to cross more easily than others.– WHY? Hydrophobic tails vs hydrophilic heads

What has to get in and out of the cell?

• Oxygen CO2

• Glucose Waste

• Amino acid new proteins

• Vitamins

• water

Parts of the Cell Membrane 1. Phospholipids 3. Proteins

2. Cholesterol 4. Carbohydrates

Phospholipids

Fatty acid

Phosphate

1. Fatty acid tails– hydrophobic

2. Phosphate group

3. Glycerol– Hydrophilic

Aaaah, one of those

structure–functionexamples

Why are the phosolipids arrange this way?

• Heads - hydrophilic face outward

• Tails - Hydrophobic face inward

• Water surrounds the cell and is inside the cell. Hydrophilic must face outward.

• Arranged as a bilayer

The Arrangement of the Phosolipids determine how particles pass through

the cell membrane?• If a particle is small and not charged then

it can move straight through the membrane.

• If the particle is large and charged, then it has to move through the cell proteins.

• Aquaporins - protein channel that water moves through.

5 Functions of Proteins 1. Pumps material through the membrane 2. Channels3. Proteins on the inside of cell. Attach to cytoskeleton. Help with structure!!4. Receptors – Carbohydrates are attached to proteins!5. Enzymes!

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

Function of Cholesterol• Strengthen cell membrane – phosolipids

are not bonded so membrane is not strong!

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Fluid Mosaic ModelDescribes the characteristics of the cell

membrane

1. Cell membrane is flexible not rigid. Acts as a fluid. The double bonds between the tails keep them from attaching because of kinks.

2. Cell membrane is constructed for many different parts.

Selective Permeability

• Cell membrane allows some materials in and others not.

• Homeostasis: Cell maintenance of stable internal conditions in a changing environment.

• How a molecules moves across a membrane depends on the size, polarity, and concentration of the molecules.

• Do you Agree that Molecules Must Move Across Membrane?

• VIDEO – molecules moving

• This is called Brownian Movement

Molecules are constantly moving!!• You must understand that molecules are

constantly moving.

• The more energy added the faster they move.

• Move from an area of a higher concentration to an area of lower concentration across the membrane.

3 Ways Particles Move Across Membrane!!

1. Small and non charged particles can just move through the membrane.

2. Small polar molecules move through the protein channels.

3. Large particles move in vesicles or pumps.

Types of Cellular Transport

• Passive Transport

cell doesn’t use energy1. Diffusion

2. Facilitated Diffusion

3. Osmosis

• Active Transport

cell does use energy1. Protein Pumps

2. Endocytosis

3. Exocytosishigh

low

This is gonna

be hard work!!

high

low

Weeee!!!

•Animations of Active Transport & Passive

Transport

Passive Transport

• The energy behind this type of transport is caused by a CONCENTRATION GRADIENT!!!

Concentration Gradient• The difference in the concentration of

molecules in two different regions.

• Can be a room or a cell!!!!

• Equilibrium: molecules will continue to move until equal on both sides.

Transport summarysimplediffusion

facilitateddiffusion

activetransport

ATP

Passive Transport – movement of molecules across cell membrane without energy.1. cell uses no energy 2. molecules move randomly3. Molecules spread out from an area of

high concentration to an area of low concentration.

• (HighLow)• CAN BE THROUGH A

CHANNEL!!!

3 Types of Passive Transport

1. Diffusion

2. Facilitative Diffusion – diffusion with the help of transport proteins

3. Osmosis – diffusion of water through aquaporin.

Passive Transport: 1. Diffusion

1. Diffusion: random movement of particles from an area of high concentration to an area of low concentration.

(High to Low)

• Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out.

http://bio.winona.edu/berg/Free.htm

Simple Diffusion Animation

Diffusion• Move from HIGH to LOW concentration

– “passive transport”– no energy needed– Small and non charged– Straight through membrane

diffusion osmosis

Diffusion through phospholipid bilayer• What molecules can get through directly?

– fats & other lipids– SMALL & NONPOLAR

inside cell

outside cell

lipid

salt

aa H2Osugar

NH3

• What molecules can NOT get through directly?

– polar molecules• H2O

– ions• salts, ammonia

– large molecules• starches, proteins

• 2.Osmosis: facilitated diffusion of water through a selectively permeable membrane

• Water moves from high to low concentrations

• AQUAPORIN

•Water moves freely through pores.

•Solute (green) to large to move across.

Osmosis animation

Passive Transport: 2. Osmosis

Effects of Osmosis on Life

• Osmosis- diffusion of water through a selectively permeable membrane

• Water is so small and there is so much of it the cell can’t control it’s movement through the cell membrane.

Aquaporins

• Water moves rapidly into & out of cells– evidence that there were water channels

1991 | 2003

Peter AgreJohn Hopkins

Roderick MacKinnonRockefeller

Concentration of water• Direction of water movement is determined by

the amount of solution in or out of the cell because water is not all that the cell contains.

3 Types of Solutions For a Cell

1. Hypertonic - more solute, less water. More

water inside cell; it leaves

2. Hypotonic - less solute, more water. More

water outside cell; water enters

3. Isotonic - equal solute, equal water

Equal – net movement equal!

Hypotonic Solution

Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water)

Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

• Osmosis Animations for

isotonic, hypertonic, and hypotonic

solutions

Managing water balance• Hypotonic

– a cell in fresh water

• example: Paramecium

• problem: gains water, swells & can burst– water continually enters

Paramecium cell

• solution: contractile vacuole – pumps water out of cell– ATP

– plant cells• turgid

freshwater

ATP

freshwater balanced saltwater

Managing water balance• Cell survival depends on balancing water

uptake & loss

Hypertonic Solution

Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water)

Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

• Osmosis Animations for

isotonic, hypertonic, and hypotonic

solutions

shrinks

Managing water balance• Hypertonic

– a cell in salt water• example: shellfish• problem: lose water & die• solution: take up water or pump

out salt

– plant cells• plasmolysis = wilt

saltwater

Isotonic SolutionIsotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell.

Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

• Osmosis Animations for

isotonic, hypertonic, and hypotonic

solutions

Managing water balance• Isotonic

– animal cell immersed in mild salt solution• example:

blood cells in blood plasma• problem: none

– no net movement of water» flows across membrane equally,

in both directions

– volume of cell is stable

balanced

What type of solution are these cells in?

A CB

Hypertonic Isotonic Hypotonic

How Organisms Deal with Osmotic Pressure

• Paramecium (protist) removing excess water video

•Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure.

•A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.

•Salt water fish pump salt out of their specialized gills so they do not dehydrate.

•Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane a.Transport Proteins are

specific – they “select” only certain molecules to cross the membrane

b.Transports larger or charged molecules

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Passive Transport: Facilitated Diffusion

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

Facilitated Diffusion• Diffusion through protein channels

– channels move specific molecules across cell membrane

– no energy needed

“The Bouncer”“The Bouncer”

open channel = fast transport

facilitated = with help

high

low

High Concentration

Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

Passive Transport: Facilitated Diffusion

Go to Section:

Transport Protein

Through a

Cellular Transport From a-High

Low

• Channel Proteins animations

Active Transport

“The Doorman”“The Doorman”

conformational change

1. Cells may need to move molecules against concentration gradient– shape change transports solute from

one side of membrane to other – protein “pump”– “costs” energy = ATP

ATP

low

high

Active Transport

1. cell uses energy

2. Movement from an area of low concentration to an area of high concentration

•AGAINST THE CONCENTRATION GRADIENT!

•(Low High)

3. Move molecules in vesicles that are too large!

Types of Active Transport

1. Protein Pumps -transport proteins that require energy to do work.

•Example: Sodium / Potassium Pumps are important in nerve responses.

Sodium Potassium Pumps (Active Transport using proteins)

Protein changes shape to move molecules: this requires energy!

Types of Active Transport

• 2. Endocytosis: taking bulky material into a cell in a vesicle.• Uses energy• Cell membrane in-folds

around food particle• “cell eating”• forms food vacuole &

digests food• This is how white blood

cells eat bacteria!

Endocytosis

phagocytosis

pinocytosis

receptor-mediated endocytosis

fuse with lysosome for digestion

non-specificprocess

triggered bymolecular signal

Types of Active Transport

3. Exocytosis: Forces material out of cell in bulk in a vesicle• membrane surrounding the

material fuses with cell membrane

• Cell changes shape – requires energy

• EX: Hormones or wastes released from cell

Endocytosis & Exocytosis animations

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

– through vesicles & vacuoles

1. endocytosis• phagocytosis = “cellular eating”• pinocytosis = “cellular drinking”

2. exocytosis

exocytosis