1. Membrane Structure & Function
Chapter 7

2. YOU MUST KNOW Why membranes are selectively permeable
The role of phospholipids, proteins, and carbohydrates in membranes
How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution and be able to predict the effect of different environments on the organism
How electrochemical gradients and proton gradients are formed and function in cells

3. Cell Membrane Structure – Fluid Mosaic Model

4. Phospholipids Modified triglyceride Polar, hydrophilic heads
Non-polar,
hydrophobic tails

5. Embedded Proteins Integral Proteins – span the entire membrane
Used for transport through membrane or as receptors for chemical messengers
Peripheral Proteins – on one side or the other
Often there temporarily
Often associate with integral proteins (gates)
Can move fluidly along the membrane to transport molecules

6. Carbohydrates Cell-to-cell recognition
Immune function (recognize self/non-self)
Important in transfusions and transplants
Cell differentiation

7. Selective Permeability
Small, non-polar molecules (CO2, O2) can cross the phospholipids easily
Ions and polar molecules cannot cross the hydrophobic region so must travel through membrane proteins
Aquaporins – Protein channels for water
Anatomy of a protein channel

8. Passive Transport Requires no energy
Does require a concentration gradient – difference in concentration in 2 adjacent areas
Molecules move constantly, randomly, and away from each other, down or with the concentration gradient

9. Diffusion
Can happen anywhere (through air, water, across a cell membrane)
Small, hydrophobic molecules can cross the phospholipid bilayer by this process
Carbon dioxide, oxygen,
small hydrocarbons
End result is the
elimination of the
concentration
gradient

10. Facilitated Diffusion
Because ions & polar molecules cannot pass through the hydrophobic region of the phospholipid bilayer, they require integral membrane protein channels to pass from high concentration to low concentration
Protein channels – always “open”
Carrier proteins – interaction with molecule that fits causes conformational change which passes them across membrane
***Remember – proteins are specific! So these channels and carriers are specific, too- each one is for a specific substance to pass through

11. Osmosis Diffusion of water across a selectively permeable membrane
A cell has 3 possible water relationships with its surroundings
Remember, we always talk in terms of NET movement of water!

12. Active Transport
Movement of molecules from an area of low concentration to an area of high concentration (against the concentration gradient)
Uses energy (usually in the form of ATP)
Also requires a protein pump
Creates a concentration gradient instead of eliminating it

13. Membrane Potential
The differences in charge between the inside and outside of a cell
A relative voltage created by the concentration of ions inside and outside the cell
Resting potential (normal
conditions) –
the inside of the cell
is negatively charged
in comparison to the
exterior

14. Electrochemical gradients
A combination of forces acting on an ion
Chemical force which is created by the concentration gradient
Voltage gradient created by the membrane potential
Because the inside of the cell is negatively charged, positively charged ions outside the cell are attracted to the inside of the cell

15. Cotransport is the name of a process in which two substances are simultaneously transported across a membrane by one protein, or protein complex which does not have ATPase activity

16. Bulk Transport
Endocytosis
Exocytosis