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)
A cortex made largely of _ gives human red blood cells their characteristic shape.
spectrin
Red blood cells lack a _ and _
nucleus
other intracellular organelles.
In the cortex of a red blood cell, _ are linked end-to-end to form longer _. The _, together with a smaller number of _ molecules, are linked together into a _. This network is attached to the plasma membrane by the _
spectrin dimers
tetramers
spectrin tetramers
actin
mesh
_
binding of at least two types of attachment proteins
_
The _ is a mat of extracellular matrix that supports all epithelial sheets
basal lamina
Eukaryotic cells are coated with _.
sugars
This carbohydrate-rich layer is made
- of the _ side chains attached to membrane _ and _, and
- of the _ chains on membrane _.
oligosaccharide
glycolipids
glycoproteins
polysaccharide
proteoglycans
Note that all the carbohydrate is on the _ surface of the plasma membrane.
external (noncytosolic)
The recognition of cell- surface _ on neutrophils allows these immune cells to begin to _
carbohydrates
migrate
out of the blood and into infected tissues.
Specialized transmembrane proteins (called _) are made by the _ cells lining the blood vessel in response to chemical signals emanating from a site of infection. These proteins recognize _ carried by _ and _ on the surface of neutrophils circulating in the blood. The neutrophils consequently stick to the endothelial
cells that line the blood vessel wall. This association is not very strong, but it leads
to another, much stronger protein-protein interaction (not shown) that helps the neutrophil _ between the endothelial cells, so it can migrate out of the bloodstream and into the tissue at the site of infection
lectins
endothelial
particular sugar groups
glycolipids
glycoproteins
slip
