chap11 Flashcards
Membranes enable cells to create barriers that confine particular molecules to _ They consist of a _.
specific compartments.
_
continuous double layer—a bilayer—of lipid molecules in which proteins are embedded
_
The _ provides the basic structure and barrier function of all cell membranes.
lipid bilayer
Membrane lipid molecules are _, _. This property promotes their _ into _ when placed in _, forming _ that _ if torn.
amphipathic
_
having both hydrophobic and hydrophilic regions
_
spontaneous assembly
_
bilayers
_
water
_
closed compartments
_
reseal
There are three major classes of membrane lipid molecules: _, _, and _.
phospholipids
sterols
glycolipids
Phospholipids: The most common membrane lipids. They have a _ head and two _ tails. This structure allows them to form a _, creating the basic structure of the cell membrane.
hydrophilic
hydrophobic
bilayer
Sterols: Lipids like _ in animal cells. They have a rigid structure that helps _ and make it less permeable to small molecules.
cholesterol
stabilize the membrane
Glycolipids: Lipids with a _ They are mainly found on the _ layer of the membrane and play a role in _
sugar group attached.
outer
cell recognition and protection.
The lipid bilayer is _, and individual lipid molecules are able to _ within their own _; they do not, however, _.
fluid
diffuse
monolayer
_
spontaneously flip from one monolayer to the other
_
The two monolayers of a cell membrane have _, reflecting the different _ of the two faces of the membrane.
different lipid compositions
functions
Cells that live at different temperatures maintain their membrane _ by _.
fluidity
_
modifying the lipid composition of their membranes
_
_ are responsible for most of the functions of cell membranes, including the _
Membrane proteins
_
transport of small, water-soluble molecules across the lipid bilayer.
_
Transmembrane proteins extend across the lipid bilayer, usually as _ but sometimes as a _.
one or more α helices
β sheet rolled into the form of a barrel
Other membrane proteins do not extend across the lipid bilayer but are _, either by _ association with other _, by _, or by association of an _ .
attached to one or the other side of the membrane
_
noncovalent membrane proteins
covalent attachment of lipids
_
exposed amphipathic α helix with a single lipid monolayer
_
Most cell membranes are supported by an _. An especially important example is the meshwork of _ proteins that forms the _ _ the plasma membrane.
attached framework of proteins
fibrous
cell cortex
underneath
Although many membrane proteins can diffuse rapidly in the plane of the membrane, cells have ways of _ proteins to specific membrane domains. They can also immobilize particular membrane proteins by attaching them to _.
confining
intracellular or extracellular macromolecules
Many of the _ and some of the _ exposed on the surface of cells have attached _ chains, which form a _ layer that helps _ and _ the cell surface, while also being involved in _
proteins
lipids
sugar
carbohydrate
protect
lubricate
specific cell-cell recognition.
_ is the most common phospholipid in cell membranes.
Phosphatidylcholine
Phosphatidylcholine is built from five parts:
- the hydrophilic head, which consists of _ linked to a _
- two _ chains, which form the hydrophobic tails
- and a molecule of _, which links the head to the tails.
choline
phosphate group
hydrocarbon
glycerol
Each of the hydrophobic tails is a _—a hydrocarbon chain with a carboxyl (–COOH) group at one end; _ attaches via this carboxyl group. A _ in one of the hydrocarbon chains occurs where there is a _ between two _ atoms.
fatty acid
glycerol
kink
double bond
carbon
Phospholipids and glycolipids are distributed _ in the lipid bilayer of an animal cell plasma membrane
asymmetrically
Phosphatidylcholine (red ) and sphingomyelin (brown) are concentrated in the _ monolayer, whereas phosphatidylserine (light green) and phosphatidylethanolamine (yellow)
are found mainly on the _ side.
In addition to these phospholipids, phosphatidylinositols (dark green head group), a minor constituent of the plasma membrane, are shown in the _ monolayer, where they participate in _
noncytosolic
cytosolic
cytosolic
cell signaling.
Glycolipids are found exclusively in the _ monolayer of the membrane.
noncytosolic
Within the bilayer, cholesterol (green)
is distributed _ monolayers.
almost equally in both
Plasma membrane proteins have a variety of functions. They _ molecules and ions, act as _, _ signals, or _ reactions.
transport
anchors
detect (receptors)
catalyze (enzymes)
