Terms in this set (17)
Plasma Membrane Function
Plasma membranes enclose all living cells
Internal membranes have same structure
functions determined by lipids, proteins, and carbohydrates present in membranes (structure function)
PM-Boundary that separates the cell from the non-living surroundings
Selectively permeable-constant exchange between cell and environment - this ability todiscriminate is fundamental to life
a fluid mosaic
PM consists of many components that are constantly in motion
Most abundant component are phospholipids
Phosphate-containing hydrophilic head and a hydrophobic fatty acid tail
Amphipathic! Means phospholipid has both hydrophobic and hydrophilic regions
Membranes are fluid
Phospholipids are held in place by many many weak hydrophobic & van der Waals interactions
Can move laterally in plane of membrane
Rarely flip-flop from one layer to other
The type of fatty acid tail affects fluidity
The cell membrane must maintain the correct consistency and not be too stiff or too fluid
Unsaturated fat more fluid.
If too stiff, won't have flexibility for psuedopod to extend out.
Cholesterol also affectsfluidity! (animals)
Amphipathic molecule: rings are hydrophobic and -OH is hydrophilic
Adding more cholesterol adds more space.
Different effects on membrane fluidity at different temperatures
At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
At cool temperatures, it maintains fluidity by preventing tight packing. Increase unsaturated fat or cholesterol.
Organisms acclimate to low or high temperatures
Changes in ambient temperature cause fluctuations in the fluidity of cell membranes (just like grease!)
Organisms can change the biochemistry of cell membranes by increasing the number of membrane proteins, amount of unsaturated fatty acids, or amount of cholesterol
more fluid in cold temperatures
less fluid in warm temperatures
membrane has many different proteins embedded in lipid bilayer
Proteins in lipid bilayer determine specific functions of a membrane
—Proteins in each membrane vary, thus structure/composition of membrane varies and thus membrane function varies
—Many different types of proteins allows membrane carry out many different functions simultaneously
—two sides of membrane (extracellular vs. intracellular can have different proteins in them and do different functions!)
Three ways you can get proteins associated with membrane: integral proteins
Penetrate hydrophobic core of lipid bilayer, often completely spanning the membrane
Also called transmembrane proteins
Coiled into alpha helices
Hydrophobic regions of amino acids in contact with hydrophobic core of bilayer
Hydrophilic regions of amino acids toward center of helix which created a hydrophilic area across the membrane
Can make pores
Cylinder of b sheets in the protein secondary structure called a b-barrel
Interior is polar and allows water and small polar molecules to pass through the membrane
Three ways you can get proteins associated with membrane: Peripheral proteins
Not embedded in lipid bilayer at all
Attached loosely to membrane surface through integral proteins
Three ways you can get proteins associated with membrane:Lipid linked proteins
Anchoring molecules are modified lipids with
1. nonpolar regions that insert into internal portion of lipid bilayer
2. chemical bonding domains that link directly to proteins.
Different proteins, different functions!
Transport proteins facilitate the movement of materials into and out of the cell
Some proteins are mainly structural
anchor the plasma membrane to the cytoskeleton and the extracellular matrix (ECM)
Many are enzymes and catalyze chemical reactions
A suite of membrane-bound enzymes facilitates cellular respiration
Membrane proteins facilitate cell-to-cell interactions
help cells communicate
glycoproteins are carbohydrate-protein complexes that can be used to identify cells
Membrane proteins also move!
-move more slowly but do drift in phospholipid sea
Which of the following organisms use cholesterol as the primary membrane sterol?
Which of these is an example of an amphipathic molecule?
Correct This answer choice is correct because these proteins must have both hydrophobic regions to cross the membrane and hydrophilic regions on the extracellular and/or intracellular faces of the membrane.
Complete the following sentence: Integral membrane proteins must be...
Which of the following will be able to cross the phospholipid bilayer of a cell membrane without a protein transporter?
Transporting materials into the cell
binding to other cells
receiving signals from the environment
acting as enzymes in chemical reactions
None of the answers are correct; they all identify functions of membrane proteins.
Which of these is NOT a function of membrane proteins?
What is the role of carbohydrates in the cell membrane?
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