Cell Membranes Isolate Cell Contents Whole Allowing Communication With The Environment

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Ch.5 Notes

Cell membranes isolate cell contents whole allowing communication with the environment Functions
Isolate cells contents from external environment, allowing concentration gradients of dissolved substances to be produced across the membrane
Regulate exchange of essential substances between cell and the extracellular fluid, or between membrane enclosed organelles and the surrounding cytoplasm
Allow communication between cells
Create attachments within and between cells
Regulate biochemical reactions

Complex heterogeneous structures, different parts preform different functions, vary from one tissue type to another, change dynamically in response to surroundings

Basic structure:
Proteins floating in double layer of phospholipids
Phospholipids
Isolating functions
Proteins
Selectively exchanging substances and communicating with the environment

Membranes-fluid mosaics in which proteins move within layers of lipids
Fluid mosaic model-each membrane consists of a mosaic of different proteins constantly shifting and flow with a viscous (think and sticky) fluid formed by a double layer of phospholipids

Phospholipid bilayer-fluid portion of membrane
Phospholipid-polar hydrophilic head, pair of fatty acid tails-nonpolar hydrophobic
Double bond, unsaturated
Surrounded by fluids phospholipids arrange themselves in phospholipid bilayer
Hydrogen bonds form between water and the hydrophilic phospholipid heads, causing heads to orient outward toward water on with side of membrane, tails located inside bilayer
Unsaturated fatty acids double bonds produce kinks, more fluid

Cells have different degrees of saturation-preform different functions in diff environments
More fluid at high temp, molecules move faster vice versa
Low temp-rich in unsaturated phospholipids, kinky tails allow the membrane to retain fluidity

Polar and water soluble biological molecules cannot pass through the nonpolar hydrophobic fatty acid tails of bilayer

Animals-bilayer contains cholesterol
Stabilizes bilayer, less fluid at higher temperatures
Less permeable to water soluble substances

Flexible nature of bilayer-important to function, keep sell from breaking and dying

Proteins that form mosaic within membrane
Embedded in or attached surface of bilayer
Carbohydrate groups attached to the portion that is exposed on the outer membrane surface-glycoproteins
Some proteins embedded in bilayer others adhere to bilayer surface
5 categories of proteins
Receptor proteins
Respond to messages sent by other cells
Message molecules bind to RP which Convey message to the interior of the cell
Activated-changes shape, causes response in cell
Trigger sequence of chemical reactions within cell alters cells activities
Allow cells of immune system to recognize and attack foreign invaders
Recognition proteins
Glycoproteins, serve as identification tags
Ex: blood type
Enzymatic proteins
Promote chemical reactions that synthesize or break apart biological molecules
Responsible for synthesizing proteins and carbohydrates of the extracellular matrix
Attachment proteins
Anchor cell membranes
Span plasma membrane-linking cytoskeleton inside cell with extracellular matrix outside, anchoring cell in place within tissue
Help maintain cell shape by linking plasma membrane to the underlying cytoskeleton
Adhere to and move along surfaces
Form connections between adjacent cells
Transport proteins-how stuff gets through the membrane
Regulate movement of hydrophilic molecules through the plasma membrane
Channel proteins
Form channels whose central pores allow water molecules or specific ions to pass through membrane along their concentration gradient
Carrier proteins
Binding sites that can temporarily attach to specific molecules on one side of the membrane
Changes shape, moving molecule across membrane and releasing it on other side
Span the lipid bilayer
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