1. Chapter 7: Cells and Their Environment

2. Cell Membrane 1. Function Selectively (semi-) permeable
a. Some substances can pass through but others cannot
Maintains homeostasis
a. Used to maintain a stable internal environment
b. Cell survives by preventing its interior from mixing w/ a watery environment outside

3. Cell Membrane cont. 2. Structure Composed of 2 organic molecules:
1. Phospholipids
2. Proteins
Arranged in a lipid bilayer

4. Lipid Bilayer

5. Cell Membrane cont. a. Phospholipid Structure “Amphipathic molecule”
Consists of:
1. Head (Polar)
- Hydrophilic attracts H2O
(makes hydrogen bonds)
2. Tail (Non-polar fatty acid chain)
- Hydrophobic repels H2O
(pushes H2O away from middle)

6. Cell Membrane cont.
b. Arrangement of Lipid Bilayer 1. Membrane fluid-like & flexible like a soap bubble 2. Membrane can grow or change * NOTE: Lipid bilayer arrangement is still maintained as new phospholipids will always have heads toward H2O & tails in middle- happens whenever membrane compartments fuse internally

7. Cell Membrane cont. 3. Forms non-polar interior zone (middle layer)
- Polar molecules (glucose, amino acids [AA], ions, cell wastes) can’t pass through b/c repelled by non-polar tails
*** Advantage: Forms good barrier!
- Problem: If cell membranes were made only of lipids, most substances could not pass into/ out of cells
- Solution: Build into lipid bilayer various kinds of passageways composed of proteins (possesses different shapes, sizes, & channels)

8. Kinds of Cell Surface Proteins
Polar molecules floating in non-polar zone
“Like ice cubes in a punch bowl”

9. Kinds of Cell Surface Proteins cont.
1. Channel Proteins - Acts like “passageways” - Special proteins having doughnut-shaped channels - Polar substances (glucose, AA, etc) can enter & pass - Specific channels for certain substances doors w/ locks - Allows for “2-way” travel into/ out of cell (facilitated diffusion)

10. Proteins embedded in cell membrane

11. Kinds of Cell Surface Proteins cont.
2. Receptor Proteins - Acts like “information receivers” - Sends information from outside the cell to inside the cell - Special outer shape only fits specific substances - If substance matches, information sent inside the cell and a response will occur inside the cell - Carries out communication functions between cells chemically a. Many hormones work this way/ ex: insulin b. Nerve impulses between 2 nerve cells/ between nerve cells & muscle cells/ ex: acetylcholine (ACH)

12. Signal molecule binds to receptor protein- leads to message being passed on into the cell

14. Kinds of Cell Surface Proteins cont.
3. Surface Marker Proteins - Acts like “cell identifiers” - Have long external extensions usually made up of CHOs - Both self-markers & tissue markers present - Some markers function in immune response

15. Cell Membrane

16. Solutions
Mixture of solute & solvent 1. Solute substance being dissolved/ ex: sugar, salt, AA, ions 2. Solvent dissolving substance/ ex: usually H2O Equilibrium - Particles evenly distributed in solvent Concentration Gradient - Areas having differences in concentrations - Living cells must have membranes that keep the watery cytoplasm inside the cell different than the watery environment outside the cell

17. Solutions Outside a Cell vs Solutions inside a Cell

18. Solutions Outside a Cell VS Solutions inside a Cell cont.

20. Solutions Outside a Cell VS Solutions inside a Cell cont.

21. Membrane Transport Processes
1. Passive Transport (3 types) - NO ENERGY used!!! - From high conc  low conc a. Diffusion - Random movement of dissolved particles b. Osmosis - Movement of H2O through membrane - When extra H2O accumulates on 1 side, pressure increases osmotic pressure

22. Cont. Passive Transport
c. Facilitated Diffusion (Channel Proteins)
- Substances move through specific channel proteins having pores
(differ in size, shape, & polarity)
- Substances attaches, pore opens/ ex: how glucose enters most cells

23. Membrane Transport Processes cont.
2. Active Transport (5 types) - Cells MUST use energy (ATP) - From low conc  high conc a. Proton Pumps - Results in production of ATP - Process called chemiosmosis occurs in side both chloroplasts & mitochondria

24. Cont. Active Transport
b. Sodium-Potassium Pump - 2 ions moving in opposite directions at the same time - Process will move 3 sodium ions (Na+) out of cell for every 2 potassium ions (K+) that comes into the cell - Occurs in nerve cells (impulse) & small intestine (food absorption)

25. Membrane Transport Processes cont.
c. Coupled Channels (Cotransport)
- 2 ions moving in together in the same direction
- Na+ outside diffuse rapidly inside cell & pulls in other substances/ ex: glucose, AA, ions
-main way sugar and other food molecules
transported into cells

26. Cont. Active Transport d. Endocytosis
- Larger molecules enter as membrane surrounds substance
1. Pinocytosis intake of liquids
2. Phagocytosis intake of solids
- Ex: phagocytes- WBC

27. Cont. Active Transport
e. Exocytosis - Removal of cell waste vacuoles & gland secretions through cell membrane/ ex: hormones & enzymes

28. Cell-Cell Communication
- Needed to coordinate body growth & development
1. Direct Communication
- Physical contact between cells
Ex: tight junctions, gap junctions,
plasmodesmata
  2. Indirect Communication
- No physical contact between cells
Ex: endocrine system chemical (hormones)
nervous system chemicals (neurotransmitters)

29. Cell-Cell Communication cont.
Involves receptor protein channels - Binding of a signal particle to its specific receptor can influence inside of cell in 3 ways: a. Receptor acts as enzyme causing reaction in cytoplasm b. Receptor causes formation of second messenger that works inside cell/ ex: cAMP

30. Cell-Cell Communication cont.
c. Receptor can open gates of specific channels proteins allowing rapid movements of ions through membrane via: Gated Channel Proteins - Have a special area that causes a channel to open/ close when it comes into contact with signals from a cell 1. Chemically Gated Channels - Signal that hits special area neurotransmitter molecule from outside the cell - Causes gates to open & Na+ to move rapidly into the cell/ ex: acetylcholine (ACH) (a neurotransmitter)

31. 2. Voltage Gated Channels - Signal that hits special area electric charge from within cell - Impulse moves along a nerve cell, current cause gates to open & Na+ moves rapidly into nerve cells

32. Factors That Affect the Rate of Diffusion
1. Particle size/ pore size
2. Molecular weight
3. Solubility of H2O
4. Concentration of solvent/ solute
5. Temperature
6. Pressure
7. Organic solvents/ lipid solubility
8. Surface area/ volume