1. Membrane Structure & Function
Chapter 7
By: Kelsie Owens and Akia River

2. What is a Plasma Membrane?
Book definition: The membrane at the boundary of every cell of every cell that acts as a selective barrier, regulating the cell’s chemical composition
Simplified definition: the “traffic controller”, decides what comes in and goes out

3. What makes up a membrane?
Lipids
Proteins
Carbohydrates
(these are the main components)
Most of these lipids are known as phospholipids:
Phospholipids are amphipathic: hydrophilic and hydrophobic

4. Fluid mosaic model
A collage of a variety of proteins embedded in the fluid lipid bilayer

5. 2 major groups of membrane proteins
2. Peripheral Proteins
Not in lipid bilayer
loosely bound to the surface of the membrane or to part of an integral protein
Integral Proteins
penetrate the hydrophobic core of the lipid bilayer, many are known as: transmembrane protein
stretch the membrane
Both help each other to give animal cells a stronger structure

6. Cell-Cell Recognition
A cell’s ability to distinguish one type of neighboring cell from another
Cells recognize each other by binding to surface molecules (short- branched carbohydrates)
Membrane carbohydrates are covalently bonded to lipids, forming Glycolipids
Others are covalently bonded to proteins, forming Glycoproteins

7. Synthesis and Sidedness
Vesicle fuses with the membrane outside layer of vesicle becomes continuous with cytoplasmic (inner) layer.
Molecules that start on the inside face of the ER end up on the outside face of membrane

8. How do membranes control traffic?
They are selectively permeable: very choosy in what comes in and out of the cell
Allows cell membrane to regulate passage of substances

9. Passive Transport DOES NOT USE ENERGY!!!
The “push over” substances can move across the membrane without having to give anything
good for substances like water and oxygen
When they are too close to each other they move around to have more space (diffusion)
This is how cells regulate their water content
Class demonstration!

10. How do cells balance their water without cell walls?
This is an example of osmoregulation: the control of water balance
This is the concept of tonicity: the ability of a solution to cause a cell to gain or lose water
Osmosis works with water that contains dissolved material solutions

11. Hypertonic: if the concentration of a solution is higher inside than outside the membrane, the cell will shrivel
Hypotonic: if the concentration of a solution is less inside than outside the membrane, the cell will swell

12. Isotonic
These solutions are like having a friend, you don’t want the overly crazy, but at the same time you don’t want the extremely depressed sad
You want a happy medium or someone in between, isotonic is that happy medium.
Isotonic: has equal concentration inside and outside the membrane

13. Isotonic
When water attempts to be isotonic it moves across the concentration gradient
Ex: if you take someone’s blood cell (hypertonic) and try to mix it with pure water (hypotonic), because blood is filled with a lot of stuff inside of it compared to outside, water would rush into the cell that it would burst! Therefore, your kidneys would regulate the concentration of blood to keep it isotonic

14. Facilitated Diffusion
In order for water to move across the cell membrane it must cross the phospholipid bilayer, however we know that that phospholipids are amphipathic
Water moves through channel proteins in order to get from one side to another, they are known as….
Ion and gated channel proteins, which open or close in response to a stimulus (can be electrical or chemical)

15. Active Transport USES ENERGY!!!
This happens especially when moving low concentration to high concentration
Requires ATP
ATP is like having $$$, you will ALWAYS need it

16. This Is particularly for the brain and muscle cells
Channel proteins in active transport are the “businessman” vs. channel proteins in passive transport
When a cell requires active transport it has to pay a fee in the form of ATP to transport a protein, called a sodium potassium pump
This Is particularly for the brain and muscle cells
This pumps work against two gradient:
Concentration & electrochemical (the difference of electrical charge on either side of the membrane)
Nerve cells in your brain are typically negative inside and outside is positive

17. Active Transport Steps: Collects 3 positive sodium ions
Protein pump breaks down the molecule of ATP
Enzyme breaks covalent bond of a phosphate
The phosphate releases a burst of energy and changes the shape, allowing it to open it outward
Now the new shape is able to take 2 potassium and pump them inside, resulting in a charged nerve cell
***This process allows the cell to have electrochemical energy, which helps you feel, touch, taste, or even have a thought

18. Membrane Potential
All cells have voltage (electrical potential energy) across their plasma membranes
Transport proteins that generates voltage is called an electrogenic pump
The main electrogenic pump is known as proton pump

19. Vesicular Transport
Cytosis “cell action”, vesicles transports outside of the cell
Ex: In your brain, this is how your nerve cells release neurotransmitters. After neurotransmitters are synthesized and packed into vesicles, their transported until the vesicles meet the membrane , the 2 bilayers rearrange so they fuse and the neurotransmitters are released

20. Endocytosis How material gets inside the cell 3 ways this can happen:
Phagocytosis: “eating” cell action
Pinocytosis: “drinking” cell action
Receptor Mediated

21. Phagocytosis “eating” cell action
A particle outside of a cell outside. Chemical receptors on that cell membrane detect and attach to it, membrane forms a vesicle to eat it

22. Pinocytosis “drinking” cell action
Similar to phagocytosis, instead of surrounding whole particles, surrounds things that have already been dissolved

23. Receptor Mediated Endocytosis
Receptor proteins enables a cell to acquire bulk quantities of substances that have small concentrations
Ex: Cells have specialized cholesterol receptors (ligands), if they don’t work eventually it would cause heart disease.