Section 4 - Membrane Structure and Transport Flashcards
True or false: a cell can exist without a membrane
False: it needs a boundary to distinguish itself
True or false: for proper functioning, the membrane must be immpermeable
False: it must be permeable, although this can be controlled
What is the purpose of the cell membrane?
Maintain the difference between inside and outside, and facilitate transport
What kinds of transport does the cell membrane facilitate?
Transfer of material, information, and energy
What is the structure of the cell membrane?
A think film of lipids and proteins
What holds together the cell membrane?
Noncovalent interactions
True or false: the cell membrane is static
False: it is a very dynamic structure
What do the proteins on the cell membrane do?
Function in signaling, transport, and connection to the cytosol
What is the average thickness of a cell membrane?
~5 nm
What is the cell membrane impermeable to?
Water-soluble molecules
What is the typical structure of a transmembrane protein?
Tend to have a large section on one end of the membrane, and barely poking out on the other side
How much lipid (by mass) composes the cell membrane?
~50%
True or false: all lipids in the cell membrane are amphiphilic
True: they all have hydrophobic regions and hydrophilic regions
What does amphiphilic mean?
A molecule has both hydrophobic regions and hydrophilic regions
What are the majority of the lipids in the cell membrane?
Phospholipids
What is the structure of a phospholipid?
Two hydrocarbon tails and a polar head group are connected via glycerol
What are the majority of the phospholipids (in terms of their tails)?
Have one saturated tail and one unsaturated tail
What does an unsaturated lipid tail look like?
Kinked
What does a saturated lipid tail look like?
Straight
How long is the average carbon chain in a lipid tail?
16-18 carbons long
What happens if a cell membrane has only saturated phospholipids?
It increases packing density, thus decreasing fluidity
What is the significance of having some unsaturated lipid tails in the cell membrane?
Helps reduce packing density, and thus increases fluidity
What is the most common head group on phospholipids?
Choline
What percentage of phospholipids in the cell membrane are phosphatidylcholine?
60-70%