Cell Membranes Flashcards
How do ionic substances, polar molecules and non-polar molecules behave in water?
- Polar and charged things dissolve in water
- Amphipathic things partially dissolve in water (form micelle or bilayer)
- Nonpolar things are excluded by water and do not mix with it
What are phospholipids/bilayers for? What jobs do they do?
1) Isolate cell’s content from outside environment
2) Regulate exchange of substances between inside / outside cell
3) Communicate with other cells
4) Create attachments within / between cells
5) Regulate biochemical reactions
What are proteins for in a cell membrane? What jobs do they do?
1) Integrins — give membrane stronger framework
2) Receptor — trigger cell activity when molecule from outside environment binds to protein
3) Recognition — allow cells to recognize one another
4) Enzymes
5) Attachment — anchor membrane to internal framework and external surface of neighboring cells 6) Transport — move molecules and ions (hydrophilic) across the membrane
What is cholesterol for in a cell membrane? What jobs does it do?
- Decreases/increases the fluidity of the plasma membrane (the colder a cell, the more cholesterol)
- Not just Cold, cholesterol increases in a cell in all temperature extremes (ie: Hot spring, Antartica)
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What are carbohydrates for in a cell membrane? What jobs do they do?
- Allow cellular adhesion to occur (for cells to link together)
- They are the ID tags on lipids and proteins
How/why do phospholipids form a bilayer in water?
- This happens because phospholipids are amphipathic, and their polar heads are attracted to water while the non-polar tails are excluded by water
- The excluded tails are kept separate from the water by the formation of a spherical bilayer with the tails facing each other
- This is important because these forces are the same ones that keep fluid cell membranes intact
What would happen if you put a cell in a hydrophobic environment?
- Amphipathic phospholipids in a membrane would “flip” and their polar heads would cluster together (or towards the cell’s watery interior)
- The hydrophobic tails would mix with the hydrophobic environment
- This would essentially dissolve the cell membrane’s bilayer
What factors affect the fluidity of membranes?
- Temperature
- Lipid tail length
- The degree of unsaturation
- Ratio of cholesterol to phospholipid
How can organisms, like plants, fish and bacteria, which lack the ability to regulate their body temp keep membranes fluid in cold temperatures? (more than one way)
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How can organisms, like plants, fish and bacteria, which lack the ability to regulate their body temp keep membranes together (less fluid) in hotter temperatures? (more than one way)
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Cell membranes are selectively permeable (What does this mean?)
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What types of molecules can move freely across the lipid bilayer? Why can they get across?
- Small
- Nonpolar
What types of molecules cannot easily cross the lipid bilayer? Why can’t they get across easily? How do these molecules cross the cell membrane?
- Large, polar, ionic
Concentration
-The amount of molecules in a given volume
Diffusion
- The tendency of a substance to move down its concentration gradient from where it is more concentrated to less concentrated
- Spread out evenly in available space
- Requires no work
Net diffusion
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