Unit 3: Membranes Flashcards
Where are membranes found?
Around all cells (plasma membrane)
Around some eukaryotic organelles
Membranes are primarily made of
(two types of large biological molecules)
Lipids
&
Proteins
What lipids are found in membranes?
Phospholipids and cholesterol
Two orientations for how proteins can be embedded in membranes
Peripheral (one side) or
Integral (through)
Two faces of a membrane
Cytosolic (or cytoplasmic; toward inside of cell) and
Extracellular (toward environment)
Structure of phospholipid
Phosphate-head, which is polar
Two lipid tails, which are nonpolar
Hydrophilic
meaning
“Water loving”
Hydrophilic substances are
Ionic or polar
Hydrophobic
meaning
“Water fearing”
Hydrophobic substances are
Nonpolar
What would allow a protein to become embedded in a membrane?
Protein with some amino acids with hydrophobic R groups and some with hydrophilic R groups
What part of a phospholipid is hydrophobic
Lipid tails
What part of a phospholipid is hydrophilic
Phosphate head
Phospholipid bilayer
Two layers of phospholipid
- Hydrophobic tails face inward
- Hydrophilic heads face cytosol or extracellular areas
Fluid Mosaic Model
A description of cell membranes
Each phospholipid can move freely laterally
Embedded substances (proteins, etc) can also move laterally
What factors affect membrane fluidity?
Temperature
Type of hydrocarbon (saturated v. unsaturated) tails in phospholipid
Amount of cholesterol
Effect of temperature on membrane fluidity
Higher = more fluid
Lower = less fluid
Effect of lipid type (in phospholipid) on membrane fluidity
Saturated fatty acid tails = fluid at higher temperatures
Unsaturated fatty acid tails = fluid at lower temperatures
Role of cholesterol in cell membranes
Aids in membrane integrity and fluidity
At low temps - prevent solidification of membranes by preventing
What determines the function of a membrane?
The proteins it has in it
Define
Integral protein
Protein that goes all the way through the membrane (often transmembrane proteins)
Define
Peripheral protein
Protein that is embedded only on cytoplasmic OR extracellular side of membrane
List
Functions of membrane proteins
- Transporting materials into/out of cell
- Enzymes
- Cell signaling
- Cell-to-cell recognition
- Joining cells together (connections)
- Attachment to other proteins, such as the cytoskeleton or extracellular matrix
Describe
Proteins that transport materials into / out of cell
Have polar amino acids in the center, forming a channel or carrier to connect cytosol and extracellular environment
