1. Anderson Spring 2017 College of the Redwoods
Cell Membranes
Anderson
Spring 2017
College of the Redwoods

2. What did we learn last week?
Eukaryotic cells have endomembrane systems (organelles surrounded by membrane)
Prokaryotic cells have no organelles or nucleus
Membranes are made up of a phospholipid bilayer, with integrated proteins
Organelles have specific structure and function
Let’s review the organelles!

3. How to Cells Communicate?
Extracellular matrix
Space outside of cell that holds cells together to form tissue and allows for communication
Intercellular Junctions
Direct contact of neighboring cells that exist within tissue

4. Intercellular Junctions
Plants - plasmodesmata
Animals
Adhesion – “welds” that allow for stretching
Tight – watertight seal
Gap – channels between cells for transportation

5. Able to flow and change position but still keep basic integrity
Cell Membrane
Phospholipid bilayer – hydrophobic and hydrophilic
Proteins – many roles
Cholesterol – regulates fluidity
Carbohydrates – self recognition
Able to flow and change position but still keep basic integrity

6. Membrane Proteins Integral proteins – embedded in membrane
Peripheral proteins – on exterior or interior surface

7. Cholesterol’s Role
Cholesterol reduces fluidity at moderate temperatures
Keeps membrane from solidifying in low temperatures

8. Glycoproteins (example)
The CD4 receptor (glycoprotein) on white blood cell interacts with HIV – injects genetic material into host cell
HIV has binding sites on outer coat, which mimics those found on human cells – fools human cell

9. Membrane Permeability
Selective permeability – membrane allows some substances to enter and leave, but not others
✔ Hydrophobic substances can pass through membrane easily
✔ Small non-polar molecules can pass through (O2, CO2)
Polar molecules can’t get through hydrophobic region
(except H2O)
Large molecules are too big to pass through

10. Passive Transport Movement of molecules that does NOT require energy
Substances move from HIGH to LOW concentration, across a concentration gradient
Diffusion - Movement of molecules based on concentration

11. Rate of Diffusion Concentration gradient Mass of molecule Temperature
Larger difference in concentration, the faster the diffusion
Slower diffusion when close to equilibrium
Mass of molecule
Larger molecules move slower – harder to move between molecules their diffusing through
Temperature
Higher temperatures increase energy and molecule movement, which increases rate of diffusion
Solvent density
Higher density of solvent, lower diffusion rate

12. Facilitated Transport
Passive transport across concentration gradient
Moves substances that wouldn’t diffuse easily or quickly
Polar molecules
Use integral proteins
Channels
Carriers

13. Membrane limits the diffusion of solutes in the water
Osmosis
Diffusion of WATER (only) across a semipermeable membrane (like a cell membrane)
WATER moves from HIGH to LOW concentration
Membrane limits the diffusion of solutes in the water

14. Relation of osmolarity of extracellular vs intercellular fluid
Tonicity/Osmolarity
Tonicity – amount of solute in solution
Osmolarity – measure of solutes in solution (measure of tonicity)
Relation of osmolarity of extracellular vs intercellular fluid
Hypotonic – extracellular lower solutes vs inside cell
– extracellular higher water concentration
Hypertonic – extracellular higher solutes vs inside cell
– extracellular lower water concentration
Isotonic – equal solutes extracellular and inside cell

15. Tonicity/Osmolarity
Plant cells slightly hypertonic to outside so water is always going in

16. 1. 2. Water: 60% Solute: 40% Water: 30% Solute: 70% Water: 20%
Hypotonic
Hypertonic
Hypertonic
Hypotonic 3. 4.
Water: 90%
Solute: 10%
Water: 90%
Solute: 10%
Water: 55%
Solute: 45%
Water: 60%
Solute: 40%
WATER
WATER
Isotonic
Hypertonic
Isotonic
Hypotonic

17. Active Transport Movement of molecules that requires energy
Substances move from LOW to HIGH concentration, against the concentration gradient
Movement of large molecules
Primary Active Transport – uses ATP
Secondary Active Transport – coupled transport

18. Adenosine Triphosphate

19. Electrochemical Gradient
Most proteins are negatively charged, thus making the inside of a cell electrically negative, extracellular fluid is positive
More sodium ions (Na+) outside than inside
More potassium ions (K+) inside than outside
Na+ will move with concentration and electrical gradient
K+ will move with concentration gradient but against electrical gradient

20. Sodium-Potassium Pump
It’s necessary for Na+ concentrations to stay higher outside and K+ higher inside
Ions have to be actively transported against gradient, which uses energy
Primary active transport – ATP used to move Na+ out and K+ in

21. Glucose Sodium Transporter
Na+ will enter cell with electrochemical gradient
Glucose can be transported into cell with Na+, against concentration gradient
Secondary active transport – no ATP used, uses energy from electrochemical gradient from primary transport

22. Endocytosis
Active transport that moves large particles into cell though vacuole formation (membrane invagination)
Phagocytosis – membrane surrounds particle and pinches off
Pinocytosis – membrane surrounds fluid (solutes) and pinches off
Receptor-mediated – substance binds to receptor on outside

23. Exocytosis Process of expelling material from cell
Vacuole fuses with cell membrane to expel contents

24. Have you been paying attention?!
Socrative Time
Have you been paying attention?!