1. Cellular Transport Notes

2. TEM picture of a real cell membrane.
About Cell Membranes
All cells have a cell membrane
Functions:
Controls what enters and exits the cell to maintain an internal balance called homeostasis
Provides protection and structural support for the cell
TEM picture of a real cell membrane.

3. Structure of cell membrane
Lipid Bilayer -2 layers of phospholipids
Phosphate head is polar (water-loving)
Fatty acid tails non-polar (water-fearing)
Only certain substances can pass through the lipid bilayer such as small, nonpolar substances
Ions and most polar substances are repelled by the nonpolar interior
Phospholipid
Lipid Bilayer

4. Fluid Mosaic Model describes the cell membrane because of its flexibility and ‘mosiac’ of different molecules
Polar heads love water & dissolve.
Non-polar tails hide from water.
Carbohydrate cell markers
Membrane movement animation
Proteins

5. Other parts of the plasma membrane
Cholesterol molecules strengthen/stabilize the cell membrane
Carbohydrates attach to membrane proteins in order to provide identification for the cell
Four types of proteins (next slide)

6. Membrane Proteins Cell-surface markers Receptor proteins Enzymes
Proteins attached to cell surfaces that act as identification for a cell
Marked by different chains of carbohydrates (sugar)
Receptor proteins
Recognize and bind to substances outside the cell
Enzymes
Help with important biochemical reactions inside the cell
Transport proteins
Aid in the movement of substances into and out of the cell when they cannot pass through the bilayer

7. About Cell Membranes (continued)
Cell membranes have pores (holes) in it
Selectively permeable: Allows some molecules in and keeps other molecules out
This is good for the cell when environment conditions change rapidly outside the cell
Pores

8. Structure of the Cell Membrane
Outside of cell
Carbohydrate
chains
Proteins
Lipid
Bilayer
Transport
Protein
Phospholipids
Inside of cell
(cytoplasm)
Animations
of membrane structure
Go to Section:

9. How a particular molecule crosses the membrane depends on the molecule’s size, polarity, and concentration inside versus outside the cell
In general:
Small, nonpolar molecules easily pass through the cell membrane
Small, polar molecules are transported via proteins
Large molecules are moved in vesicles

10. Cell Communication
Cells communicate and coordinate activity by sending chemical signals that carry information to other cells
Receptor proteins receive signal molecules and will do an action in response to the signal
It will then bind with a ligand and change shape so that it will not interact with other molecules

11. Two types of receptor proteins
Intracellular receptor
Ex. Many hormones
The receptor-ligand complex will enter the nucleus and interact with DNA to make needed proteins
Membrane receptor
When signals bind to the membrane receptor, it will change shape and trigger a chain of events within the cell

12. Hormones and electrical signals are used for communication between cells that spread far apart.
Receptor proteins are used for communication between cells that are nearby
A receptor protein binds only to the signals that match the specific shape of its binding site
When a receptor protein binds to a signal molecule, the protein changes shape

13. Binding Specificity

14. How do cells respond to signals?
The cell may respond to a signal by:
changing its membrane permeability
activating enzymes
forming a second messenger which acts as a signal molecule within the cell

15. Types of Cellular Transport
Animations of Active Transport & Passive Transport
high
low
Weeee!!!
Passive Transport
cell does NOT use energy
Diffusion
Facilitated Diffusion
Osmosis
Active Transport
cell does use energy
Protein Pumps
Endocytosis
Exocytosis
high
low
This is gonna be hard work!!

16. Passive Transport (HighLow) molecules move randomly
cell uses no energy
Molecules spread out from an area of high concentration to an area of low concentration.
Substances cross the cell membrane DOWN their concentration gradient (the difference in the concentration of a substance from one location to another)
(HighLow)
There are three types

17. Passive Transport: 1. Diffusion
Simple Diffusion Animation
Passive Transport: 1. Diffusion
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.

18. Liquids and gases can both diffuse
Examples of molecules that can diffuse into and out of the plasma membrane:
Small lipids, nonpolar molecules such as carbon dioxide and oxygen
Factors that affect the diffusion of substances
Temperature
Concentration of molecules
Pressure

19. Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer)
Passive Transport: 2. Facilitated Diffusion A B
Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane
Channel proteins (pores) allow ions, sugar, and amino acids to diffuse through the cell membrane
Carrier Proteins are specific – they “select” only certain molecules that fit into their binding site to cross the membrane
Transports larger or charged molecules
Facilitated diffusion (Channel Protein)
Diffusion (Lipid Bilayer)
Carrier Protein

20. Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport From a-
High
High Concentration
Channel Proteins animations
Cell Membrane
Low Concentration
Protein
channel
Low
Carrier Protein
Through a 
Go to Section:

21. Passive Transport: 3. Osmosis
Osmosis animation
Osmosis: diffusion of water through a selectively permeable membrane
Water moves from high to low concentrations
Water is so small and there is so much of it the cell can’t control it’s movement through the channel proteins.
Solute (green) to large to move across.

22. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions
Isotonic Solution
Isotonic: 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)

23. Osmosis Animations for isotonic, hypertonic, and hypotonic solutions
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)!

24. 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)
shrinks
Result: Water moves from inside the cell to the solution; Cell shrinks (Plasmolysis)!

25. Effects of Osmosis
The rigid cell walls of plants and fungi prevent the cells of these organisms from expanding too much
The added water in the central vacuole of a plant cell provides support to the plant
Some unicellular eukaryotes have contractile vacuoles which collect water inside the cell and force the water out

26. B C A What type of solution are these cells in? Hypertonic Isotonic
Hypotonic

27. Active Transport (Low  High) cell uses energy
actively moves molecules to where they are needed
Movement from an area of low concentration to an area of high concentration
Requires energy to move substances against their concentration gradients
(Low  High)
There are three Types

28. Types of Active Transport
Sodium Potassium Pumps (Active Transport using proteins)
Protein Pumps-carrier proteins that require energy to do work
Example: Sodium / Potassium Pumps are important in nerve responses
Three sodiums are needed to transport two potassium ions into the cell
Sodium ions are important to transport glucose into the cell

29. Types of Active Transport
Endocytosis: taking bulky material into a cell
Uses energy
Cell membrane in-folds around food particle
Forms food vacuole & fuses with lysosome to digest food
“cell eating”—phagocytosis
This is how white blood cells eat bacteria!

30. Types of Active Transport
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