Chapter 12 (Exam 2) Flashcards
(42 cards)
What are biological membranes?
Complex lipid-based structures that form pliable sheets and are composed of a variety of lipids and proteins.
What is the purpose of a cell membrane?
Separates the cell from its surrounding.
What do eukaryotic cells have?
Various internal membranes that divide the internal space into compartments (ex. organelles).
What classes of lipids are found in membranes?
Phospholipids, glycolipids, steroids.
Does maintaining the lipid bilayer require energy?
No because it happens spontaneously.
What does the membrane bilayer consist of?
2 leaflets (layers) of lipid monolayers; the thickness of most membranes is 6 - 10 nm.
When does the membrane bilayer form?
When lipids with polar head groups and more than one lipid tail are in aqueous solution.
What do hydrophilic head groups interact with?
Water on both sides of the bilayer.
How are hydrophobic fatty acid tails set up inside the membrane bilayer?
Packed inside.
What is the structure of individual units in the membrane bilayer?
Cylindrical (cross section of head equals that of side chain).
What is the nucleus surrounded by?
A double membrane, or 2 lipid bilayers, with occasional pores. Only one of the lipid bilayers is expanded.
Are lipid bilayers highly impermeable to ions and most polar molecules?
Yes.
What is the function of a molecule’s hydrophobicity?
The ability of small molecules to cross a membrane.
Why is indole more soluble than tryptophan in membranes?
Because it is uncharged.
Why can ions not cross membranes?
Because of the energy cost of shedding their associated water molecules.
Can oxygen and CO2 pass the membrane?
Yes, because they are uncharged and small.
Can steroid hormones pass through the membrane?
Yes, because they are pretty hydrophobic and nonpolar, so they can pass through the membrane easily without receptors.
What is membrane fluidity determined by?
Mainly by the fatty acid composition.
What do more fluid membranes require?
Shorter and more unsaturated fatty acids.
- Melting temperature decreases as double bonds are added.
- Melting temperature increases with length of saturated fatty acids.
What do cells need at higher and lower temperatures?
Higher temperatures: cells need more long, saturated fatty acids.
Lower temperatures: cells need more unsaturated fatty acids.
Can organisms adjust the membrane composition?
Yes.
What is cholesterol?
The key modulator of membrane fluidity in animals.
Works as a buffer of membrane fluidity.
Amphipathic molecule.
What does cholesterol disrupt?
The tight packing of fatty acid chains.
What is the most abundant steroid in the body?
Cholesterol.
