CELLULAR TRANSPORT

WATCH

• Building a cell membrane

INTRODUCTION

• The plasma membrane is responsible for regulating materials regulating materials that enter and exit the cell.

• The cell must maintain homeostasishomeostasis, the regulation and maintenance of an environment.

• Temperature, chemicals, water concentration, and particle size have an effect on the rate of transport through the membrane.

PLASMA MEMBRANE

FLUID MOSIAC MODEL

PLASMA MEMBRANESelective Permeability or Semipermeable:

– refers to membrane’s ability to ability to allow SOME allow SOME molecules molecules through and others out.

PLASMA MEMBRANEPeripheral proteins – do not go all the way through

Integral proteins – go all the way through

Phospholipids

PLASMA MEMBRANE

• Imbedded Proteins - a variety of proteins attached to the surface and embedded in the membrane.

• Function: Each type of protein has a specific purpose like ion channels, receptor proteins, and proteins that allow cells to connect to each other.

PLASMA MEMBRANE

• Peripheral Proteins - are proteins that adhere only temporarily to the membrane.

• Function: Peripheral proteins allow many molecules to be carried around the cell. Some peripheral membrane proteins carry molecules between other proteins.

PLASMA MEMBRANEREMINDERS

• Selectively permeable: choosy as to what gets in and out of cell. Also semipermeable.

• Phospholipid bilayer: double layer of phospholipids.

• Hydrophilic head: (polar). Water-loving. Carboxyl end of the fatty acid.

• Hydrophobic tail: (nonpolar). Water-fearing. Hydrocarbon chain of the fatty acid.

PHOSPHOLIPID BILAYER

TRANSPORT

• Cell membranes allow nonpolar molecules such as O2 and CO2 slip across.

• Water molecules sometimes pass.

• LargeLarge, polar molecules cross with the help of embedded proteinsembedded proteins.

TRANSPORT

• Molecules or ions move constantly, randomly colliding trying to reach equilibriumequilibrium.

• When dynamic equilibrium is reached, the same amount of molecules will move into and out of the cell.

• The rate depends on size of particle, temperature, composition of solution.

TRANSPORT

• When the concentration in one region is not the same as in an adjoining region, this condition is a concentration gradientconcentration gradient - “THE FORCE”– The steeper the gradient the faster the diffusion.– Increased temperature increases the rate of diffusion.

Ex: sugar dissolved in hot tea.– Increased pressure increases the rate of diffusion.

Molecules have more collisions under high pressure.

EQUILIBRIUM

HOMEOSTASIS

• Homeostasis is the property in which variables are regulated in a system so that internal conditions remain stable and relatively constant.

• Examples include the regulation of temperature and the balance between acidity and alkalinity (pH).

• Homeo (“like”) + stasis (“standing still”)

TO DO

• Do Section A now.

PASSIVE TRANSPORT

• No energyNo energy required to move downdown thethe concentration gradient.

• Movement from high to low high to low concentration.

• TYPES of passive transport:

1) Osmosis

2) Diffusion

3) Facilitated Diffusion

WATCH

• Diffusion and Osmosis

OSMOSIS AND DIFFUSIONSECTION D

In this lab you will observe the diffusion of a substance across selectively permeable (or semipermeable) membrane.

The dialysis tubing is selectively permeable like a cell membrane allowing smaller molecules to pass through easily.

Iodine is an indicator for starch and will turn from reddish brown to dark black in the presence of starch.

PROCEDURE

1. Tie one end of the dialysis tubing in a knot.

2. Add one scoop of cornstarch and water in the dialysis bag. Do NOT fill the bag full.

3. Tie a knot in the other end of the dialysis tubing. Leave some air in the tubing. Wash the tubing off to remove cornstarch from the outside of the bag.

4. In a cup, add water to fill the cup ½ full. Place 5 drops of iodine into the water filled cup.

5. Place the tubing in the cup of water. Let it sit for ten minutes and answer the questions below while you wait.

WHILE WE ARE WAITING

Answer the pre-lab questions (1-4) now.

Pre-lab questions:

1.What is in the tubing? What color is it?

2.What is in the cup? What color is it?

3.What do you predict will happen to the iodine and cornstarch molecules? (Hypothesis)

4.How is the tubing similar to a cell membrane? _________________________________________

Osmosis

OSMOSIS

• movement of H2O from high to low concentration

• Water makes up 70% to 95% of a cell.

• The cell has no control over osmosis. Water will flow into and out of the cell until equilibrium is reached.

OSMOSIS

PASSIVE TRANSPORT

• Osmosis

DIFFUSION• Movement of particles from a high to a low

concentration. • Example: drop of food coloring in water -

Diffusion will continue until the molecules of food coloring are evenly distributed.

DIFFUSION

DIFFUSION• One of the major mechanisms of molecular

transport in cells.• Oxygen and Carbon Dioxide diffuse readily

through the cell membrane.• Living cells maintain a balance by

regulating what enters and leaves the cell.• Without this ability, cells cannot maintain

homeostasis and will die.

GAS EXCHANGE IN THE LUNGS

PASSIVE TRANSPORT

• Diffusion

glucose transportersolute (glucose)

high

low

Figure 5.10Figure 5.10Page 88Page 88

Stepped Art

Passive Transport

OSMOSIS AND DIFFUSION LAB

Do the Post-Lab questions

•What is in the tubing? What color is it?

•What is in the cup? What color is it?

•Which molecule(s) diffused across the membrane?

•Explain the movement of the molecule(s).

•Is this active or passive transport? How did you know?

FACILITATED DIFFUSION

• Use of transport molecules to diffuse particles.

• When carrier proteins are used to transport substances such as amino acids & sugars across the membrane down the concentration gradient.

• Substances are moving from high to low concentration, no energy is expended, so this is passive transport.

FACILITATED DIFFUSION

Different ways it can happen:•Carrier proteins: transport large molecules across the membrane, very specific. Ex: Glucose.•Bind, carry, and release. Protein molecule changes shape and shields molecule from the interior of the lipid bilayer.

FACILITATED DIFFUSION

GATED CHANNELS• Ions & most polar molecules cannot diffuse across the

membrane because they cannot pass through the nonpolar interior of the lipid bilayer.

• Substances can cross when aided by Carrier proteins.• Transport proteins called channels provide polar passageways

though which ions & polar molecules can move across the membrane.

• Ions are moving down the concentration gradient, so no energy is expelled, making this process a form of passive transport. Ion charge also has an affect on movement.

• Ions such as Na+, K+, Ca+2, & Cl- pass through ion channels, a doughnut-shaped transport protein with a polar pore.

ION CHANNEL

PASSIVE TRANSPORT

ACTIVE TRANSPORT

• EnergyEnergy is required to move against the against the concentration gradient.

• Movement from low to high low to high concentration. • Moving molecules against the concentration gradient

requires the use of energy (ATP).• TYPES of Active Transport:

1. Membrane transport proteins

2. Endocytosis

3. Exocytosis

MEMBRANE TRANSPORT PROTEINS

SODIUM-POTASSIUM PUMPTransports three Na+ ions out of the cell, and two K+ ions into the cell against the concentration gradient.

•Pump prevents Na+ from accumulating in the cell, which would be toxic. If not controlled, this would cause water to enter the cell by osmosis and cause the cells to burst.

•The Na+-K+ pump creates an electrical gradient that is important to many physiological processes in animals, such as nerve conduction & muscle contraction.

SODIUM-POTASSIUM PUMP

BULK TRANSPORT

Requires energy, so active transport.2. 2. EndocytosisEndocytosis: materials are engulfed by enclosing the cell membrane around a substance forming a pouch or a vesicle and being brought inside the cell. Two types:

- Pinocytosis: movement of liquids with solutes or small particles.

- Phagocytosis: Movement of large particles, solids, or whole cells.3. Excocytosis3. Excocytosis: Materials inside cell are excreted out of the cell. The vacuole, or vesicle, fuses with the cell membrane, dumping contents into the external environment.

ENDOCYTOSIS

EXOCYTOSIS

Endocytosis andEndocytosis and Exocytosis Exocytosis

plasma membrane

cytoplasm

cytoplasm

Exocytosis

Endocytosis

ACTIVE TRANSPORT

Active Transport

ATP

ADP

Pi

higher calcium concentration

lower calcium concentration

Figure 5.11Figure 5.11Page 89Page 89

Stepped Art

Active Transport

TO DO

• Do Sections B and C now.