1. Membrane Structure and Function
Unit D
Chapter 4

2. Main structure of the cell membrane
The cell membrane is made up mostly of fats and proteins
The arrangement of these materials is referred to as a phospholipid bilayer

3. Phospholipid bilayer:

4. Phospholipids Phospholipids are molecules that consist
of a polar (hydrophilic)
phosphate head
and two non-polar
(hydrophobic) tails.

5. Phospholipids Hydrophilic: likes water, polar
Hydrophobic: likes oil (doesn’t like water), non polar

6. Transmembrane Proteins:
All the proteins embedded in the lipid bilayer.
Examples:
Glycoproteins
Channel proteins
Carrier proteins
Receptor proteins
Enzymatic proteins

7. Glycoproteins:

8. Glycoproteins: AKA: recognition proteins
Proteins with carbohydrate (oligosaccharide) molecules attached to the outer surface of animal cell membranes.
Function: cell recognition (like the “finger print” of the cell), they serve as markers on the cell membrane for identifications
So cells can recognize one another
Example: antigens on red blood cells

9. Channel Proteins:
Allows a particular molecule or ion to freely cross the cell membrane through a pore as it enters or exits the cell
Transport of lipid insoluble materials across the membrane
ie: water, ions, amino acids
Always open
Don’t require energy (passive transport)

10. Carrier Protein:
A protein that selectively interacts with a specific molecule or ion so that is can cross the cell membrane to enter or exit the cell.
Glucose enters the cell using carrier proteins
Not always open
Sometimes require energy

11. Carrier Protein:
Certain molecules bind to a proteins triggering a change in shape that transports the molecule across the membrane
Outside cell
Inside cell

12. Receptor Proteins:
A protein that is shaped in such a way that a specific molecule can bind to it.
The binding of the molecule, such as a hormone, that can influence the metabolism of the cell.
“little people” were once believed to be short because they did not produce enough growth hormone
“Little people” are now believed to be short because their cell membrane growth hormone receptors are faulty and cannot interact with the hormone.

13. Receptor Proteins
They bind with external molecules and then activate cellular activity.
Viruses must often attach to receptors before they enter a cell.

14. Enzymatic Proteins:
A protein that catalyzes a specific reaction within the cell.
The active site is usually inside the cell
they allow specific reactions to happen
Figure 4.2 page 62 in text.

15. Glycolipids:

16. Glycolipids:
Carbohydrate (oligosacharide) molecules that are attached to phospholipids on the outer surface of the cell membrane
Functions: they are markers for cell to cell communication, cell to pathogen communication and provide energy
One of the glycolipids found in human red blood cells is involved in the antigens of the ABO blood type.
Some glycoproteins are also involved with the antigens as well.

17. Cholesterol:
lipid (steriod) molecules found in animal cell membranes , mostly in the hydrophilic region.
Function: they lend stability to the lipid bilayer and prevent a drastic decrease in fluidity at low temperatures
Can comprise up to 50% of animal plasma membrane
Hydrophilic OH groups toward surface
Smaller than a phospholipid and less amphipathic (having both polar and non-polar regions of the molecule)

18. Methods of moving molecules across the cell membrane
Molecule movement across a membrane can be separated into two categories:
Passive transport: does not need energy
Active transport: requires energy

19. Comparsion Passive Transport includes:
Simple diffusion (including osmosis)
Facilitated Diffusion
Active Transport includes:
Active Transport
Endocytosis
Phagocytosis
Pinocytosis
Exocytosis

20. Passive Transport Across a Membrane:
Diffusion: the net movement of a substance from a region of higher concentration to a region of lower concentration.
The molecules move down a concentration gradient until they are equally distributed.

21. Diffusion across a membrane:

22. Net flow across a membrane:

23. Diffusion across a membrane:

24. Diffusion:
Only certain molecules can pass through the cell membrane by simple diffusion:
Lipid-soluble molecules (ie. Alcohols)
Oxygen O2
Carbon Dioxide CO2
You need to know the 8 factor that affect cell diffusion (in workbook)

25. Osmosis:
The movement of water across a differentially permeable membrane
Still moves from high concentration to lower concentration
Requires the concentration gradient.
Example: movement of water

26. Important terms
Solvent: a fluid, such as water, that dissolves other molecules (solutes)
Solute: A substance dissolved in a solvent to form a solution.

27. Osmotic pressure:
The measure of the number of collisions water molecules make against the membrane surface.
The greater the difference in concentration of the solute, the greater the number of collisions, the higher the osmotic pressure.

28. Turgor Pressure: AKA Turgidity
The force the cytoplams exerts against the inside of the cell membrane
Large sustained changes in turgidity can affect cell function.

29. Tonicity:
Refers to the strength of a solution in relationship to osmosis
There are three options
Isotonic solutions: cell is stable (no change to cell)
Hypotonic solutions: cells swell
Hypertonic solutions: cells shrivel

31. Hypotonic Solutions
A blood cell (1% salt) is placed in pure water, what will happen to the cell?
Hypo means “less than”
AFTER
BEFORE

32. Hypertonic Solutions
A blood cell (1% salt) is placed in a beaker with a 10% salt solution, what will happen to the cell?
AFTER
BEFORE

33. Comparison of tonicity in animal and plant cells (figure 4.6 in text)
(crenation)

34. Before
After

36. Facilitated Transport:
Direction: molecules move from higher concentration to lower concentration
Requires: carrier protein and a concentration gradient
Examples: sugar (glucose) and amino acids
NO ENERGY REQUIRED

37. Active Transport:
Direction: from low concentration to higher concentration
Requirements: carrier protein and energy
Examples: sugars, amino acids, and ions

40. Endocytosis
Substances too large to pass through the membrane are taken into the cell forming vesicles (ie. food vacuoles)
Direction: towards inside of cell
Requirements: energy and vesicle formation
Phagocytosis: AKA “cell eating”
Ingestion of larger food vacuole (large vesicle)
The food vacuole fuses with a lysosome and digests the contents
Pinocytosis: AKA “cell drinking”
Ingestion of smaller objects or fluids
A smaller vesicle is formed

41. Endocytosis

42. Pinocytosis:

43. Exocytosis:
When vesicles containing wastes and products for secretion fuse with the cell membrane, open its surface, and spill their contents to the other side.
The opposite process of endocytosis
Direction: towards outside of cell
Requirements: Energy and vesicle fusing with cell membrane
Examples: macromolecules, hormones

44. Exocytosis

45. Exocytosis of tear fluid: