Chapter 12: Membrane Structure and Function Flashcards
Lecture 2 and 7
The thickness of most membranes is between —-and —–
- 60 Å (6 nm)
- 100 Å (10 nm)
Membranes are sheetlike structures, only —- molecules thick
two
These lipid bilayers are barriers to the flow of — molecules
polar
Membranes are —- assemblies. The constituent
protein and lipid molecules are held together by many —- interactions, which act cooperatively
- noncovalent
- noncovalent
**hydrophillic head with water
Membrane formation is a consequence of the —- nature of the molecules.
amphipathic
The favored structure for most phospholipids and glycolipids in aqueous media is a —-
lipid bilayer
The hydrophobic effect is the major driving force for (2)
- the formation of lipid bilayers
- the folding of proteins
Furthermore, —- forces between the
hydrocarbon tails favor close packing of the tails. Finally, there are —– between the polar head groups and water molecules
- van der Waals attractive
- electrostatic and hydrogen-bonding attractions
lipid bilayer membranes have a very low permeability for
— and most —-
- ions
- polar molecules
the permeability of small molecules is correlated with their relative —
solubilities in water and nonpolar solvents
Small molecule might traverse a lipid bilayer membrane in the following way: (3)
- first, it sheds the water with which it is associated, called the solvation shell
- it dissolves in the hydrocarbon core of the membrane
- finally, it diffuses through this core to the other side of the membrane, where it is resolvated by water
An ion such as Na+ cannot cross the membrane, because
the replacement of its shell of polar water molecules by nonpolar interactions with the membrane interior is highly unfavorable energetically.
The fatty acid chains in membrane bilayers may be arranged in an ordered, rigid state or in a relatively disordered, fluid state. The transition from the rigid to the fluid state takes place rather abruptly as the temperature is raised above the —-
melting temperature
Long saturated fatty acids interact more strongly because of the increased number of —— than do short ones and thus favor the — state
- van der Waals interactions
- rigid
A cis double bond produces a bend in the hydrocarbon chain. This bend interferes with a highly ordered packing of fatty acid chains, and so melting temp is —
lowered
The bonding formation of cholesterol as its inserted in the membrane:
Cholesterol’s hydroxyl group forms a hydrogen
bond with a carbonyl oxygen atom of a phospholipid head group, whereas its hydrocarbon tail is located in the nonpolar core of the bilayer
lipid rafts (3)
How it forms+ what occurs+ affect
- When cholesterol form specific complexes with saturated fatty acid components of lipids and specific proteins.
- area will be more rigid due to tight packing with saturated fatty chains
- making membranes less fluid but at the same time less subject to phase transitions
Prostaglandin H2 Synthase-1 (4)
Structure+ what it does
- an integral membrane protein
- Held to the membrane by alpha helices coated with hydrophobic side chains
- Part of the protein is embedded in membrane
- Converts arachidonic acid into prostaglandin H2 to promote inflammation
- Arachidonic acid moves from the lipid membrane into the active site of the enzyme via a hydrophobic channel
SImple diffusion
molecules move across a membrane down their concentration gradient
Hard knock model
When a K+ ion enters the S4 binding site, strong electrostatic repulsions simultaneously translocate two ions upward. No water is involved in this mechanism.
Knock on model
In this mechanism, K+, alternate with water molecules and collectively move through the filter when a new K+ enters the filter.
