Cellular Transport Notes

About Cell Membranes

1.All cells have a cell membrane

2.Functions: a.Controls what enters

and exits the cell to maintain an internal balance called homeostasis

b.Provides protection and support for the cell

3.Structure of cell membrane

Lipid Bilayer -2 layers of phospholipidsa. Phosphate head is polar (water

loving)b. Fatty acid tails non-polar (water

fearing)c. Proteins embedded in membraned. Steroids and cholesterol are

embedded within the cell membrane.They provide support and flexibility.

About Cell Membranes (continued)

Phospholipid

Lipid Bilayer

Proteins

Polar heads love water & dissolve.

Non-polar tails hide from water.

Carbohydrate cell markers

Fluid Mosaic Model of the

cell membrane States that the membrane

is in constant motion

• 4. Cell membranes have pores (holes) in ita.Selectively permeable: Allows some

molecules in and keeps other molecules outb.The structure helps it be selective!

About Cell Membranes (continued)

Pores

Cell Membrane

Cholesterol in the Membrane

Outside of cell

Inside of cell (cytoplasm)

Lipid Bilayer

Proteins

Transport Protein Phospholipids

Carbohydratechains

Structure of the Cell Membrane

Go to Section:

Animations of membrane

structure

Cell Transport

• There are three types of cellular transport– Passive Transport– Active Transport– Cytosis

Types of Cellular Transport

• Passive Transport cell doesn’t use energy

1. Diffusion2. Facilitated Diffusion3. Osmosis

• Active Transportcell does use energy

1. Protein Pumps2. Endocytosis3. Exocytosis

high

low

This is gonna

be hard work!!

high

low

Weeee!!!

•Animations of Active Transport & Passive

Transport

Cytosis

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

What determines the rate of diffusion?There 4 factors:

1. The steepness of the concentration gradient. The bigger the difference between the two sides of the membrane the quicker the rate of diffusion.

2. Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster.

3. The surface area. The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment.

4. The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

Passive Transport

• The diffusion of water is called OSMOSIS.

Passive Transport - Osmosis

A good way to remember which way water will move is to remember that the water will ALWAYS move TOWARDS the solutes (salt).

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

• Water moves from high to low concentrations

•Water moves freely through pores.

•Solute (green) to large to move across.

Osmosis animationPassive Transport: 3. Osmosis

Passive Transport

• We have special names for the different types of situations where osmosis occurs in cells.

Passive Transport

• We have special names for the different types of situations where osmosis occurs in cells.

Hypotonic SolutionHypotonic: 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)!

Hypertonic SolutionHypertonic: 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)!

shrinks

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)

What type of solution are these cells in?

A CB

Hypertonic Isotonic Hypotonic

Summary

• Isotonic Solutions are those where the concentration of the solution EQUALS the concentration of the cell.

• Hypertonic Solutions are those where the concentration of the solution is MORE than the concentration of the cell.

• Hypotonic Solutions are those where the concentration of the solution is LESS than the concentration of the cell.

What is the solution?

10% Salt

40% Salt

40% Salt

10% Salt

15% Salt

15% Salt

Hypotonic Hypertonic Isotonic

What is the cell?

10% Salt

40% Salt

40% Salt

10% Salt

15% Salt

15% Salt

Hypertonic Hypotonic Isotonic

Remember!

In osmosis, goes towards the

!

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

High Concentration

Low Concentration

Cell Membrane

Glucosemolecules

Proteinchannel

Passive Transport: 2. Facilitated Diffusion

Transport Protein

Through a

Cellular Transport From a- High

Low

Facilitated Diffusion:• Molecules will randomly move

through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.

Active Transport

• Active transport is when the cell membrane “imports” or “exports” substances that are needed that do not travel by diffusion.

• Usually, this means obtaining substances against the concentration gradient

• Substances go from areas of LOW concentration to areas of HIGH concentration

Active Transport

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!

Active Transport

• Active Transport uses energy called ATP.• Active Transport = ATP

• Accomplished by the proteins embedded within the cell membrane.

Active Transport• The lack of efficient pumps can be classified as

a disease.– Sodium Deficiency can cause muscle spasms, and

Liddie's Syndrome.– Potassium deficiencies can cause an irregular heart

beat, epileptic seizures in infancy, and deafness.•  Examples of active transport include:

– Kidney's removing sodium– Thyroid obtaining iodine– Gills removing salt from water– Plants obtaining minerals through the roots.

Summary

Cytosis: A type of Active Transport

• Large amounts of some substances can be taken in and out of a cell directly by the membrane.

Endocytosis

Exocytosis

Types of Active Transport

• Endocytosis:– Uses energy (ATP)• Cell membrane in-folds around

food particle• Endocytosis of large particles is

called phagocytosis, “cell eating” • Endocytosis of small particles is

called Pinocytosis, “cell drinking”• forms food vacuole & digests food• This is how white blood cells eat

bacteria!

PhagocytosisYour white blood cells can keep you healthy by using PHAGOCYTOSIS

The LYSOSOMES digest the bacteria cell and then spit it out of the cell.

Types of Active Transport

3. Exocytosis: movement of material out of

cytoplasm of the cell using ATP

• membrane surrounding the material fuses with cell membrane (like endocytosis backwards)

• how cells get rid of wastes

Endocytosis & Exocytosis animations

Vesicles and Vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell. Exocytosis is the term applied when transport is out of

the cell.