Cellular Transport

I. Introduction to Cell Transport • All living cells need to be able to:– Take in oxygen and nutrients– Get rid of wastes

• Cell transport= moving materials in and out of a cell

• The cell membrane separates the inside of the cell from the outside.– It allows some things to enter and blocks other

things

A. Cell Membrane Structure

Phospholipid Bilayer- double layer of phospholipids enclosing the cell

1. Each phospholipid is made of a glycerol bonded to 2 fatty acids and a phosphate group.• Phosphate group is polar (hydrophilic)• Fatty acids are non-polar (hydrophobic)

2. Bilayer:• Exterior and interior surface: polar heads• Internal part: non-polar tails

Phospholipid Bilayer

B. Membrane Proteins• Proteins embedded in or thru the lipid bilayer.

1. Integral proteins- are embedded in the lipid bilayer.

2. Peripheral proteins- are loosely held on the surface.

B. Membrane Proteins

• Membrane proteins can be used to transport materials thru the membrane, serve as chemical signals or receptors of chemical signals.

• Membranes also can contain cholesterol (animal cells) and glycoproteins containing carbohydrates.

C. Fluid Mosaic Model

• Describes the cell membrane as a fluid rather than a solid.– Phospholipids and some proteins are able to move

laterally within each other.– This creates a mosaic that is able to change its

shape and form.

• http://www.youtube.com/watch?v=Qqsf_UJcfBc

D. Selective Permeability

• Due to its structure, polarity, and proteins, the cell membrane regulates what can pass in or out of the cell.– this maintains a stable internal environment

(homeostasis) – Factors that determine a substances’ ability to pass

thru the membrane:• Size• Shape• Polarity• Charge • Chemical make-up

II. Movement Through the Membrane

A. Solution Lingo

• Solution= combination of solute and solvent

– Solute= Substance being dissolved– Solvent= thing substance is dissolved in

• Universal solvent= water

*Solute dissolves in the solvent

• Concentration Gradient= A difference in concentrations within a system

B. Particle Movement

• Brownian motion- constant random motion of all particles.

C. Passive Transport

Movement across the membrane requiring no additional energy from the cell.

• Types:– Diffusion– Facilitated Diffusion– Osmosis

1. DiffusionNet movement of particles from areas of high

concentration to low concentration.– Particles will have NET movement towards low

concentration until concentration is equal throughout the system (Dynamic Equilibrium)

– Particles will continue to move, but there will be no NET movement.

Diffusion Animation

2. Facilitated Diffusion

• Diffusion of particles thru the cell membrane w/ the assistance of membrane proteins.i. Carrier proteins• Integral proteins that change shape to move large

molecules thru the lipid bilayer.

Facilitated diffusion of Glucose

ii. Ion channels– integral proteins that provide a tube for dissolved

ions to pass thru the lipid bilayer.• Ex. Na+ ion channel

Important!

• ***movement thru the proteins involves kinetic E, but no cellular E because the particles are moving with the concentration gradient.

3. Osmosis

The diffusion of water across a membrane.– particles dissolved in water are solutes; water is the universal

solvent.– water will have a net movement (opposite of solute

movement)

Types of solutions:i. Hypertonic solution- aqueous solution with a higher

concentration of solute than the cell.• particles will move into the cell• water will rush out of the cell

– Causes plasmolysis (wilting) in plant cells.

ii. Hypotonic Solution

Solution with a lower concentration of solute than the cell.– particles will move out of the cell– water will move into the cell causing it to swell• causes Turgor Pressure in plant cells• Can cause cytolysis (bursting) of animal cells

iii. Isotonic solution

Equal concentration of solute in the solution and the cell.– net movement of water and solute is equal– cell is in dynamic equilibrium w/ the solution

Osmosis in plant cells

Osmosis of red blood cells

Osmotic pressure

Which way will the water move?

How Cells Deal with Osmosis

• How do cells like paramecium that live in water, not blow up?– Contractile vacuoles – organelles that remove

water from the cell.

D. Active Transport

• Movement of substances against the concentration gradient. (low to high)– Requires the use of cellular E.– Necessary to maintain homeostasis in non-

isotonic environments

Carrier Proteins (pumps)

• Integral proteins that force particles against the concentration gradient– ATP (E) is used to change the shape of the protein.

– ex. Na+/K+ ion pump• Uses ATP to keep a high concentration of Na+ outside the cell and

K+ inside the cell. • Keeps an unbalanced charge on opposite sides of the membrane

allowing for the transmission of electrical signals.

http://www.youtube.com/watch?v=P-imDC1txWw

Na+/K+ ion pump

Endocytosis

• Process by which cells ingest large particles or large amounts of solution.– membrane pinches off around material creating a

vacuole which often joins w/ lysosomes to digest the material.

– Types• Pinocytosis- ingesting large amounts of fluid or solutes.• Phagocytosis- ingesting large particles or whole cells.

– ex. White blood cells, Ameoba

Exocytosis

Release of large particles from the cell– excretory vesicles carrying proteins, wastes or

other large particles fuse w/ the cell membrane releasing the material extra-cellularly.

• http://www.youtube.com/watch?v=DuDmvlbpjHQ

Endocytosis and Exocytosis

Endocytosis vs. Exocytosis

• Which is endocytosis? Exocytosis?

Questions

Write out the questions and answer in complete sentences.• How is selective permeability related to

passive and active transport?

• Describe two differences between active and passive transport.