Module 2A - Membrane structure Flashcards
encloses the cell, defines its boundaries, and maintains the essential differences between the cytosol and the extracellular environment.
Plasma membrane
What does the plasma membrane maintains?
- characteristics differences between the contents of each organelle and the cytosol.
Characteristics differences between the contents of each organelle and cytosol
-ion gradients
-protein sensors or receptors
-lipid bilayer
-membrane proteins
- established by the activities of specialized membrane proteins
- can be used to synthesize ATP, to drive the transmembrane movement of selected solutes, or, in nerve and muscle cells, to produce and transmit electrical signals.
ion gradients
- the plasma membrane also contains proteins that act as sensors of external signals, allowing the cell to change its behavior in response to environmental cues
- transfer information—rather than ions or molecules—across the membrane.
proteins sensors or receptors
provides the basic structure for all cell membranes
lipid bilayer
50% of the mass of the most
animal cell membranes
lipids
Lipids are ___% of the mass of most animal cell membranes
50%
lipid molecules are
____
amphiphilic
What is it called when a lipid contains a hydrophobic tail and hydrophilic heads?
Amphiphilic
- are the most abundant membrane lipids
phospholipids
Parts of typical phospholipid molecule
have a polar head group (hydrophilic head) and two hydrophobic hydrocarbon tails
Has phosphate group
Head
composition of hydrophobic tails
two hydrophobic hydrocarbon tails
creates kink in the tail
cis-double bonds (unsaturated)
Major lipids in the cell membranes
-phosphooglycerides
-sphingolipids
-sphingomyelin
-glycolipids
-cholesterol
-main phospholipids
-three-carbon glycerol backbone
-3rd carbon is attached to a phosphate group, which is linked to a head group.
Phosphoglycerides
Examples of phosphoglycerides
-phosphatidylethanolamine
-phosphatidylserine
-phosphatidylcholine
from sphingosine (long acyl acyl chain with an amino group (NH2) and two hydroxyl groups (OH)
Sphingolipids
-most common sphingolipid
-a fatty acid tail is attached to the amino group, and a phosphocholine group is attached to the terminal hydroxyl group.
Sphingomyelin
resemble sphingolipids; sugars
glycolipids
sterol; contains a rigid ring structure, to which attached a single polar hydroxyl group and a short nonpolar hydrocarbon chain
cholesterol
The _____ and _________ nature of the phospholipd molecules cause them to form bilayers spontaneously in aqueous environments.
nature, amphiphilic
spontaneously aggregate to bury their hydrophobic tails in the interior
amphiphilic molecules
soft nanoparticles with a core-shell structure that are formed when amphiphilic molecules or surfactants aggregate in an aqueous solution
spherical micelles
hydrophobic tails sandwiched
bilayers
_____________ in the bilayer creates a free edge with water.
small tear
the lipids tend to rearrange spontaneously to eliminate the free edge.
energetically unfavorable
sealed compartment formed by phospholipid bilayer
energetically favorable
able to refuse freely within the plane of a lipid bilayer
lipid molecules
construct a lipid molecule with a _____________ or small gold particleattached to its polar group and follow the diffusion of molecules
flourescent dye
Lipid bilayer modify a lipid head group to carry a ___________ (=N-O)
spin label
Lipid bilayer contains an unpaired electron whose spin creates a paramagnetic signal that can be detected by ________________ spectrum.
electron spin resonance (ESR)
phospholipid molecules in synthetic bilayers very rarely migrate from the monolayer on one side to that on the other
flip-flop
lipid molecules rapidly exchange places with their neighbors within a monolayer
rapid lateral diffusion
individual lipid molecules rotate very rapidly about their long axis and have ________ hydrocarbon chains
flexible
the lipid component of a biological membrane is a _____________ in which the constituent molecules are free to move laterally
two-dimensional liquid
catalyzes the rapid flip-flop of phospholipids from one monolayer to the other
phospholipid translocators (flippases)
a change from a liquid state to a two-dimensional rigid crystalline state at a characteristic temperature
phase transition
modulates the properties of lipid bilayers
cholesterol
makes lipid bilayer less deformable; decreases the permeability of the bilayer to small water-molecule
decrease mobility of the first few CH2 groups
cholesterol prevents the hydrocarbon chains from ____________ and ____________.
coming together and crystallizing
20-25-carbon-long prenyl chains
archaea
lipid bilayers can be built from molecules with similar features but different ______________.
molecular designs
plasma membranes of most eukaruotic cells are _____________ than those of prokaryotes and archaea.
more varied
there are how many lipid species?
500-2000
specialized membrane microdomains that serve as to organizing centers for assembly of signaling molecules, influence membrane fluidity and trafficking of membrane proteins, and regulate different cellular processes such as neurotransmission and receptor trafficking
lipid rafts
In which specific lipids come together in separate domains
phase segregation
storage of lipids
lipid droplets
specialized for lipid storage
-contain a giant liquid droplet
fat cells or adipocytes
neutral lipids; exclusively hydrophobic molecules and therefore aggregate into 3-dimensional droplets
triacylglycerols and cholesterol esters
contains a large variety of proteins
single monolayer or phospholipids
forms rapidly when cells are exposed to high conc. of fatty acids
Liquid droplets