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

TEM picture of a real cell membrane.

3.Structure of cell membrane

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

(hydrophilic or water loving)

b.Fatty acid tails non-polar (hydrophobic or water fearing)

c.Proteins embedded in membrane

About Cell Membranes (continued)

Phospholipid

Lipid Bilayer

Proteins

Membrane movement animation

Polar heads love water & dissolve.

Non-polar tails hide from water.

Carbohydrate cell markers

Fluid Mosaic Model of the

cell membrane

• 4. Cell membranes have pores (holes) in it

a.Selectively permeable: Allows some molecules in and keeps other molecules out

b.The structure helps it be selective!

About Cell Membranes (continued)

Pores

• 5. Size (macro or micro), charge (+ or -) and solubility (lipid-soluble or not) affect a molecule’s ability to cross the cell membrane.

In general, small noncharged, lipid-soluble molecules easily cross the cell membranes

About Cell Membranes (continued)

Pores

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

Types of Cellular Transport

• Passive Transport

cell doesn’t use energy1. Diffusion

2. Facilitated Diffusion

3. OsmosisTonicity

Water Potential

• Active Transport

cell does use energyhigh

low

This is gonna

be hard work!!

high

low

Weeee!!!

•Animations of Active Transport & Passive

Transport

Types of Cellular Transport

• Bulk Transport1. Endocytosis

Phagocystosis

Pinocytosis

Receptor-mediated

2. Exocytosis

Passive Transport• cell uses no energy

• molecules move randomly

• Molecules spread out from an area of high concentration to an area of low concentration.

• (HighLow)• Three types:

3 Types of Passive Transport

1. Diffusion

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

3. Osmosis – diffusion of water

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

Passive Transport: 1. Diffusion

• Occurs in liquid or gas medium

Diffusion of a solute within a solvent is affected by several factors:

Temperature Pressure Density of the solvent Concentration Gradient Solubility of the solute

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

2. Facilitated diffusion: diffusion of specific particles through membrane transport proteins to help them move through the cell membranea. Transport Proteins are specific – they “select” only

certain molecules to cross the membraneb. Transports larger or charged moleculesc. Concentration gradient required – can’t transport from

low to high concentrationd. Energy not needede. Rate of transport reaches a maximum when all

membrane transport proteins are used up (saturated)f. Membrane transport proteins are sensitive to inhibitors

that can cause them not to function

Passive Transport: 2. Facilitated Diffusion

• http://bio.winona.edu/berg/Free.htm

There are 2 types of membrane transport proteins involved:

Channel proteins – contain tunnels/openings that serve as passageways of molecules

Carrier proteins – undergo temporary binding to the molecule it carries resulting in conformational change that moves the molecule through the membrane

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Passive Transport: 2. 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

Go to Section:

Transport Protein

Through a

Cellular Transport From a-High

Low

• Channel Proteins animations

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

•Water moves freely through pores.

•Solute (green) to large to move across.

Osmosis animation

Passive Transport: 3. Osmosis

The water molecules will continue to cross the semi-permeable membrane until an equilibrium is reached, where the two solutions are of equal concentration.

Water is found inside and outside of the cell, separated by a semi-permeable membrane

The presence of different solutes in the water solutions in and out of the cell means concentration of water on both sides is different.

Water Potential – term for movement of water molecules as it undergoes osmosis

- The measure of the difference between the “force” that pushes water molecules and the “force” exerted by the membrane

Passive Transport: 3. Osmosis

Water solution with less solute (more diluted solution because of more water) = higher water potential

Water solution with more solute (more concentrated solution) = lower water potential

Water Potential Gradient - when 2 solutions of different water potentials are separated by a semipermeable membrane, thus allowing osmosis to occur

Osmotic Pressure – “force” that moves water molecules through a semi-permeable membrane

Passive Transport: 3. Osmosis

Passive Transport: 3. Osmosis

Tonicity – strength of a solution in relation to osmosis

3 Types:

IsotonicHypotonicHypertonic

Remember: Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.

If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side.

"ISO" means the same

In this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell, causing it to swell.The cell will gain water and grow larger. As osmosis continues, osmotic pressure builds up inside the cell causing cell lysis.

"HYPO" means less

In plant cells, the vacuoles will fill and the plant becomes stiff and rigid. The pressure exerted by the water molecule is called TURGOR PRESSURE, and the phenomenon TURGIDITY. The turgor pressure in plants will not result in cell lysis as the cell wall keeps the plant from bursting.TURGIDITY is important in maintaining the firm and erect position of a plant.

In this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction.Causes cells to shrink and lose shape because of water loss. In plant cells, the central vacuole loses water and the cells shrink, causing wilting (plasmolysis). In animal cells, the cells also shrink.In both cases, the cell may die.

"HYPER" means more

Active Transport

•cell uses energy (ATP or Adenosine Triphosphate)

•actively moves molecules to where they are needed

•Movement of molecules against concentration gradient (concentration gradient not required)

•Movement from an area of low concentration to an area of high concentration (Low High)

•Transport proteins are highly specific

•Involves carrier proteins (like facilitated diffusion) often called pumps because they use energy to move molecules against a concentration gradient

Example: Sodium -Potassium Pumps are important in nerve responses. They transfer Na and K ions in and out of the nerve and muscle cells.

Sodium Potassium Pumps (Active Transport using proteins)

Protein changes shape to move molecules: this requires energy!

Types of Bulk Transport

1. Endocytosis: taking bulky material that can’t use transport proteins (like macromolecules) into a cell • Uses energy• Cell membrane in-folds

around the macromolecule to be transported

• 3 Types: Phagocytosis Pinocytosis Receptor-mediated

Endocytosis

Types of Bulk Transport

Phagocytosis – “cell eating” - Process by which cells take in large particles by infolding the cell

membrane to form endocytotic vesicles

Ex. WBC capture and kill invading bacteria

Types of Bulk Transport

Pinocytosis – “cell drinking” - Process of taking in fluids into the cell by invagination

of the cell membrane. Any solute or small particles in the fluid will be moved into the cell.

Types of Bulk Transport

Receptor-mediated Endocytosis – “cell drinking” - Compared to pinocytosis, is very specific. The plasma membrane

becomes indented and forms a pit. The pit lined with receptor proteins picks specific molecules from its surroundings. The pit will close and pinch off to form a vesicle which will carry the molecules inside the cytoplasm.

Types of Active Transport

2. Exocytosis: Forces material out of cell in bulk• membrane surrounding the

material fuses with cell membrane

• Cell changes shape – requires energy

• EX: Hormones or wastes released from cell

Endocytosis & Exocytosis animations

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.

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

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

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

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.

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