1. What’s wrong with this picture?
Cell Membranes
What’s wrong with this picture?

2. The Plasma Membrane
Lay the phospholipid bilayer with the cytoskeleton facing toward you. We will call this the inside of the cell.

3. Membranes
Cells separate “inside and outside” with lipid barriers called membranes.
Organelle membranes separate too.
Limits passage of polar substances.
Protein channels allow specific passage.
BILL: What is the difference between polar and charged?
In journal: What is the difference between polar and charged?

4. What passes freely? Small, uncharged polar molecules
Small nonpolar molecules like N2
Model simple diffusion

5. Cell Walls Are outside the membrane Structural
Plant cell walls are made of cellulose
Prokaryotes and fungi also have cell walls.
Discuss plasmodesmata. Relate to the onion osmosis.

6. Phospholipid Bilayer This represents a phospholipid-
The tails are fatty acid, the head, phosphorylated alcohol
These form a sheet two molecules thick.
Polar head-Hydrophilic-label
Nonpolar tail-Hydrophobic-label
At your table, combine your macromolecule pieces to model the membrane. Review.

7. Why the embedded cholesterol?
What might a membrane in an arctic dweller look like?
Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids. But the presence of cholesterol in a phospholipid membrane interferes with close packing of fatty acid tails in the crystal state, and thus inhibits transition to the crystalline state. Phospholipid membranes with a high concentration of cholesterol have a fluidity intermediate between the liquid crystal and crystal states.
Increase or decrease fluidity depending on temperature.(Decreases fluidity when warm, increases fluidity when cold…keeps membranes fluid at very cold temperatures) *

8. Membrane Proteins Function in
Transport-
Enzyme
Surface receptors
ID Markers
Cell-cell connection
Attachment

9. Embedded Proteins
Can be hydrophilic with charges and polar side groups or…
Hydrophobic, with nonpolar
Place your proteins in the membrane.
Place your proteins in the membrane.

10. Anchoring in the membrane
A hydrophobic core
What could keep proteins in the membrane? *

11. Transmembrane Proteins
Carriers- change shape
Active and passive transport
Sodium potassium pump
Channels-
are tunnels through the hydrophobic core
Receptors
Transmit information from the outside of the cell
Hormone receptors, neurotransmitters.

12. What needs a channel?
Hydrophilic substance like large polar molecules and ions
Label the membrane hydrophobic and hydrophilic. Make a hydrophilic.
/hydrophobic protein. Discuss evolution and conserved elements.

13. Have you seen shape changes before?
Carrier proteins
Have you seen shape changes before?
Holds ion or molecule
Changes shape
To move something across the membrane
Green ball is one K+ in a potassium pump
Campbelll p 125 8th edition.

14. What might the positively charged region do?
Aquaporins
Channel Protein
Each aquaporin allows 3 billion water molecules per second to pass into the cell single file.
Fig 3. Passage of water molecules through the aquaporin AQP1. Because of the positive charge at the center of the channel, positively charged ions such as H3O+, are deflected. This prevents proton leakage through the channel.
What might the positively charged region do? *

15. Receptor Proteins
Example:
G protein linked receptor
neurotransmitter

16. Cell Surface Markers
Glycoproteins- a carbohydrate combined with a protein. Add a carbohydrate chain to a protein embedded in the membrane. Add and label
Important in the self recognition.
Recognized by the immune system.
Glycolipid- a carbohydrate combined with a lipid . Add a carbohydrate to a lipid. Add and label.
Important in tissue recognition.
Example is blood group marker.

17. Cell surface markers Glycocalyx- “Sugar coating”
You Me
Glycoproteins- “self” recognition
The protein/carbohydrate chain shape is different person to person. For example, the major histocompatibility complex proteins are recognized by the immune system.
Glycolipids-tissue recognition
The lipid/carbohydrate chain
shape is specific for a certain
tissue. For example blood group
markers.

18. Transport Modes Through the cell membrane
Passive - Down the concentration gradient-primary role in importing resources and exporting waste
Diffusion
Facilitated Diffusion- membrane proteins help charged and polar molecules pass.
Osmosis
Active- Against the concentration gradient. Energy requiring. Requires membrane proteins.
Endocytosis/Exocytosis
Na+/K+ Pump
Proton Pump

19. Diffusion Often by Ion Channels Direction of movement determined by
Relative concentration
Voltage
Each channel is specific for one or a few ions
Nervous system

20. Facilitated Diffusion
Carrier Proteins
Specific also
Bind/release
Moves things down the concentration gradient
Passive transport
Can become saturated

21. Active Transport Uses Energy Moves things against the gradient
Na/K Pump
Coupled Transport
Gradients created by one process can power another

22. Sodium Potassium Pump
Cytoplasmic Na+ binds (high affinity in this shape).
Na+ binding stimulates phosphorylation by ATP
Phosphorylation causes shape change, lower Na+ affinity, now high K+ affinity.
The K+ binding causes phosphate to be released
Phosphate release causes shape to return. Now low K+ affinity,
Work the pump with model pieces.

23. Endocytosis and Exocytosis
Exocytosis-internal vesicles fuse with the plasma membrane to release large macromolecules out of the cell.
Endocytosis-cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane.
Endocytosis Activity

24. Bulk Transport Endocytosis Phagocytosis-particulate Pinocytosis-liquid
Receptor-Mediated endocytosis
Clathrin coated pits bind to specific molecules.

25. Bulk Transport Exocytosis Neurotransmitter discharge Hormone secretion
Digestion enzymes
Explain the diagram.

26. Eukaryotic cells are compartmentalized By Membranes
These special areas let things happen by…
Minimizing competing interactions
Increasing surface area where reactions can occur
Compartmentalizing metabolic processes and enzymatic reactions.
Examples: Endoplasmic Reticulum, mitochondria, chloroplast, Golgi, nuclear envelope
Archaea and Bacteria generally lack internal membranes and organelles.

27. Protein Pieces