Plasma Membrane and Transport of molecules

How do things get in and out of the cell?

I. The Plasma Membrane A. The fluid mosaic model describes the

structure of the plasma membrane. B. In this model the membrane is seen as a

bilayer of phospholipids.

PHOSPHOLIPID BILAYER = CELL MEMBRANE

Structure of the plasma membranePhospholipids with embedded proteins (proteins are for transporting molecules across membrane)

1. Phospholipids2. Proteins

2. Membrane lipids are phospholipids with polar, water-soluble heads and long, nonpolar, insoluble tails.

Polar

Non-Polar

3 Types of Cellular Transport

1. Simple Diffusion

2. Facilitated Diffusion

3. Active Transport

1ST TYPE OF TRANSPORT

I. Simple Diffusion = NO ENERGY REQUIRED

• Brownian motion is the continuous, random motion of molecules.

• Most materials in and around any cell are in H2O solution. Diffusion is the movement of particles from areas of high concentration to areas of low concentration. It is the result of Brownian motion.

Brownian Motion is continuous motion. When materials are evenly distributed in H2O and no further changes in concentration occur, dynamic equilibrium exists.

• Dynamic Equilibrium= random movement continues but there is no change in concentration. (dynamic = change; equilibrium = balance) Dynamic equilibrium is a characteristic of homeostasis in the cell.

Diffusion depends on concentration gradients.• Concentration Gradients = difference in

concentration between two areas (ex: Inside of a cell and outside of a cell).

• Ions and molecules automatically diffuse (move through a membrane) from an area of high concentration to an area of low concentration. This means they move with the gradient.

• Diffusion across a membrane continues until there is no concentration gradient. Dynamic equilibrium then exists because the concentration is the same on both sides of the membrane.

Figure 8.9  The diffusion of solutes across membranes

Selectivity of membrane- only H2O, oxygen, nitrogen, carbon dioxide molecules, and a few other non-polar molecules can diffuse directly across the plasma membrane.• Charged ions of polar molecules CANNOT automatically diffuse across the plasma membrane.

Osmosis- Diffusion of water

Osmosis= a type of simple diffusion!

No net change in concentration in an isotonic solution because the concentration of H2O is the same on either side of the plasma membrane (dynamic equilibrium). However, movement continues (Brownian motion).

Figure 8.10  Osmosis

3 Types of Cellular Transport

1. Simple Diffusion no energy required• Osmosis = diffusion of water– GOAL: reach dynamic equilibrium

2. Facilitated Diffusion

3. Active Transport

Figure 8.11  The water balance of living cells

Plasmolysis VideoHypertonic, Isotonic, Hypotonic?What kind of solution is optimal for plant cells?Animal cells?What happens to a red blood cell in a hypertonic solution?

2ND TYPE OF TRANSPORT

II. Facilitated Diffusion = Facilitated diffusion- transport proteins embedded in the plasma membrane transport ions and molecules (that can’t get thru the membrane on their own) into and out of the cell as needed.PASSIVE = NO ENERGY REQUIREDUses CHANNEL PROTEINS

Figure 8.13  One model for facilitated diffusion

3 Types of Cellular Transport

1. Simple Diffusion no energy required• Osmosis = diffusion of water– GOAL: reach dynamic equilibrium–WITH concentration gradient

2. Facilitated Diffusion no energy required– USES CHANNEL PROTEINS– WITH concentration gradient

3. Active Transport

3rd TYPE OF TRANSPORTIII. Active transport- diffusion goes against the

concentration gradient meaning movement from an area of low concentration to an area of high concentration.

ENERGY REQUIRED! (ATP)GOES AGAINST CONCENTRATION

GRADIENT

TRANSPORT PROTEINS REQUIRED

From low to high

3 Types of Cellular Transport1. Simple Diffusion no energy required

• Osmosis = diffusion of water– GOAL: reach dynamic equilibrium– WITH concentration gradient (High to low conc.)

2. Facilitated Diffusion no energy required– USES channel PROTEINS– WITH concentration gradient (High to low conc.)

3. Active Transport ENERGY (ATP) required!– USES transport PROTEINS– AGAINST concentration gradient (Low to high conc.)

Active vs. Passive Transport

• Active = ATP req.– Against concentration gradient– Transport proteins required– Ex: H+ ion pump

• Passive = No ATP rep.– With concentration gradient– Ex: simple diffusion, osmosis, facilitated

diffusion (req. channel proteins)

Figure 8.15  Review: passive and active transport compared

Transport – 2 Types1. Passive (NO ENERGY REQUIRED):

A. Simple Diffusion (High to Low concentration)A. Osmosis is diffusion of water

B. Facilitated Diffusion (Protein help/ facilitate movement of particles from High to Low concentration)

2. Active (ENERGY REQUIRED ATP)MOVING AGAINST THE CONCENTRATION GRADIENTC. Active Transport

1. Endocytosis2. Exocytosis

Simple vs Facilitated Diffusion• BOTH with concentration gradient• BOTH passive

• FACILITATED = Channel proteins are used

Active vs. Passive Transport

• Active = ATP req.– Against concentration gradient– Transport proteins required– Ex: H+ ion pump

• Passive = No ATP rep.– With concentration gradient– Ex: simple diffusion, osmosis, facilitated

diffusion (req. channel proteins)

Plasmolysis VideoHypertonic, Isotonic, Hypotonic?What kind of solution is optimal for plant cells?Animal cells?What happens to a red blood cell in a hypertonic solution?

Figure 8.11  The water balance of living cells

Transport of large particles 2 Type of ACTIVE TRANSPORT: endo- and

exocytosisEndocytosis- a cell surrounds material and

takes it in from its environment by enclosing it in a newly formed vacuole.

Exocytosis- vacuole containing what the cell needs to dump, merges with the plasma membrane releasing the material outside the cell.

Figure 8.18  The three types of endocytosis in animal cells

V. Diseases Associated with Difficulties in Transport across

membranes.

Diseases resulting from lack of functional channels/pumps

• Motor neuron problems -Na+ channel• Cystic fibrosis - Cl- channel• Bipolar disorder -Na+, K+, ATPase• Heart problems -Na+, K+, ATPase, Na+ channels• Resistance to chemotherapy - peptide transporter, p-

Glycoprotein, (Multi-Drug Resistance)• Color Blindness, H+ gradient as pump (rhodopsin)• Some Food Poisoning - Ca+ channel