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Chapter 7: Cells and Their Environment. Cell Membrane 1. Function Selectively (semi-) permeable a. Some substances can pass through but others cannot.

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Presentation on theme: "Chapter 7: Cells and Their Environment. Cell Membrane 1. Function Selectively (semi-) permeable a. Some substances can pass through but others cannot."— Presentation transcript:

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 H 2 O (makes hydrogen bonds) 2. Tail (Non-polar fatty acid chain) - Hydrophobic  repels H 2 O (pushes H 2 O 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 H 2 O & 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 H 2 O 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.



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 H 2 O through membrane - When extra H 2 O 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 H 2 O 4. Concentration of solvent/ solute 5. Temperature 6. Pressure 7. Organic solvents/ lipid solubility 8. Surface area/ volume

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