membranes
factors that affect membrane fluidity
1) Shorter tails= less likely to interact --> more fluidity 2) Double bonds present in acyl tails --> unsaturated --> more fluidity 3) presence of cholesterol --> less fluid at high temps, more fluid at low temps
Integral/intrinsic membrane proteins
1-Transmembrane proteins •Region(s) are physically embedded in the hydrophobic portion of the phospholipid bilayer 2-Lipid-anchored proteins •An amino acid of the protein is covalently attached to a lipid
Choline phospholipids
1-phosphatidylcholine no net charge most common lipid in cell membranes 2-sphingomyelin only cell membrane not derived from glycerol
Why are transmembrane proteins able to span the hydrophobic portion of the bilayer? Multiple choice question. Because lipid molecules become covalently attached to these proteins Because these proteins have stretches of nonpolar amino acids Because peripheral polar proteins can complex with these transmembrane proteins Because these proteins are cross-linked with glycolipids
Because these proteins have stretches of nonpolar amino acids
Why are transmembrane proteins able to span the hydrophobic portion of the bilayer? Multiple choice question. Because these proteins are cross-linked with glycolipids Because lipid molecules become covalently attached to these proteins Because these proteins have stretches of nonpolar amino acids Because peripheral polar proteins can complex with these transmembrane proteins
Because these proteins have stretches of nonpolar amino acids
Transmembrane proteins participate in many cellular processes. What are examples of these? Multiple select question. Energy transduction Cell recognition Cell movement Transport Cell signaling
Energy transduction Cell recognition Transport Cell signaling
True or false: The lipid-anchored proteins are loosely associated with membrane proteins. True false question. True False
False; The lipid molecule is covalently attached to an amino acid side chain.
Cell Cortex
Fibrous network attached to the cytosolic surface of the plasma membrane, like a paper-mached balloon
What property of biological membranes describes the ability of individual molecules to move within the membrane? Multiple choice question. Fluidity Mosaic composition Permeability Rigidity
Fluidity
channel transport proteins
Form an open passageway for the direct diffusion of ions or molecules across the membrane through gates that open and close in response to the ion
Which of the following statements is correct about a biological membrane that is fluid? Multiple choice question. The composition of the membrane changes over short periods of time. Individual molecules can move within the membrane. The structure of the membrane is solid and rigid but dissolves readily. Individual molecules remain in static locations.
Individual molecules can move within the membrane.
Which of the following is a valid conclusion of the Frye and Edidin experiment? Multiple choice question. Lateral protein movements within the membrane are temperature-dependent. Transmembrane proteins can flip-flop given an input of energy. Reason: While this is true, the experiment addressed lateral movement within the plane of the membrane, not flip-flopping. Lateral protein movements are affected by pH. Mouse and human transmembrane proteins are not able to mix.
Lateral protein movements within the membrane are temperature-dependent.
Lipid tails are inserted into the hydrophobic portion of the membrane.
Lipid-anchored protein
Integral membrane proteins include which of the following? Multiple select question. Lipid-anchored proteins Noncovalent helix proteins Transmembrane proteins Peripheral membrane proteins
Lipid-anchored proteins Transmembrane proteins
The cell membrane is referred to as a mosaic because it is a mixture of what types of molecules? Multiple select question. Lipids Carbohydrates Proteins Ribosomes
Lipids Carbohydrates Proteins
Why is it more appropriate to describe membranes as semifluid rather than fluid? Multiple select question. Molecules move laterally within the membrane leaflet. Membrane proteins and lipids move freely in three dimensions. Phospholipids spontaneously migrate between leaflets. Phospholipids usually move in two dimensions.
Molecules move laterally within the membrane leaflet. Phospholipids usually move in two dimensions.
Peripheral membrane protein
Noncovalent associations form with phospholipids or other membrane proteins
Peripheral/extrinsic membrane proteins
Noncovalently bound either to integral membrane proteins that project out from the membrane, or to polar head groups of phospholipids
membrane protein receptors
PDGF receptor signals cause the cell to grow and divide
Which of the following regions serve as likely binding sites for peripheral membrane proteins? Multiple select question. Hydrophobic regions of integral membrane proteins Polar head groups of phospholipids Hydrophilic regions of integral membrane proteins Fatty acid tails of phospholipids
Polar head groups of phospholipids Hydrophilic regions of integral membrane proteins
What are the three molecular components of cellular membranes? Multiple select question. Proteins Minerals Phospholipids Nucleic acids Carbohydrates
Proteins Phospholipids Carbohydrates
functions of glycolipids
Receptor binding (for molecules and viruses such as HIV, protection, self Recognition/antiginicity
Why do shorter tails make membranes more fluid? Multiple choice question. Shorter tails interact less with each other. Shorter tails create clumps of lipids. Shorter tails have more nonpolar character. Shorter tails attract each other more strongly.
Shorter tails interact less with each other.
Regions inserted into the hydrophobic interior are usually α helices.
Transmembrane protein
An unsaturated lipid contains ______. Multiple choice question. cholesterol double bonds extra protons only single bonds
double bonds
membrane protein anchors
integrins link intracellular actin filaments to extracellular matrix proteins
plasma cell membrane proteins move ______, as proven by the _______.
laterally, mouse-human hybrid cell experiment
In eukaryotic cells, the cytosol and the endomembrane system work together to synthesize mos
lipids
flipase is located
located in ER membrane of euks and plasma membrane of proks
Sphingolipids
long fatty acid chain polar head group backbone=amino alcohol (not glycerol) Third ollecule attached determines if the sphinolipid is h, phos, sugar
Amount of cholesterol found is dependant on
membrane-type and organism dependent -Principle sterol in animal cells -Not present at all in bacteria
Site of calcium triggered membrane fusion
microdomains
Fluid Mosaic
model of a cell membrane as a mobile two-dimensional fluid of mixed composition
Lipids with shorter tails contribute to
more plasma membrane fluidity.
antiporters
move two molecules in opposite directions
Membrane proteins that span both leaflets of the lipid bilayer have transmembrane segments that are composed of ______ amino acids.
nonpolar
Membrane proteins that span both leaflets of the lipid bilayer have transmembrane segments that are composed of ______ amino acids. Multiple choice question. both polar and nonpolar nonpolar polar
nonpolar
The black circle in this figure refers to the region of the plasma membrane that is Multiple choice question. polar and hydrophobic. polar and hydrophilic. nonpolar and hydrophilic. nonpolar and hydrophobic.
nonpolar and hydrophobic.
The transmembrane segments of integral membrane proteins are ______ and interact with the ______ of the phospholipid bilayer. Multiple choice question. polar; hydrophobic tails nonpolar; hydrophobic tails nonpolar; hydrophilic heads polar; hydrophilic heads
nonpolar; hydrophobic tails
The transmembrane segments of integral membrane proteins are ______ and interact with the ______ of the phospholipid bilayer. Multiple choice question. polar; hydrophobic tails nonpolar; hydrophobic tails polar; hydrophilic heads nonpolar; hydrophilic heads
nonpolar; hydrophobic tails
The fatty acid tails of phospholipids are ______ and are found in the ______ of the phospholipid bilayer. Multiple choice question. hydrophobic; exterior polar; exterior nonpolar; interior hydrophilic; interior
nonpolar; interior
The fatty acid tails of phospholipids are ______ and are found in the ______ of the phospholipid bilayer. Multiple choice question. nonpolar; interior polar; exterior hydrophilic; interior hydrophobic; exterior
nonpolar; interior
main component of cell cortex
spectrin
spectrin
-Long thin flexible rod -Intracellular attachment proteins attach spectrin to specific transmembrane proteins which serves to connect spectrin meshwork to the membrane
list internal membranes form organelles
-Nucleus -Lysosomes -Mitochondria -Peroxisomes -Endoplasmic reticulum -Chloroplasts Golgi apparatus
Non-choline phospholipids
-Phosphatidylserine (neg charged) -Phosphatidylethanolamine (neutral) -Phosphatidylinositol (neg charged)
carbohydrate layer is important for
-Protects cell surface from mechanical and chemical damage -cell-cell adhesion and recognition
cholesterol functions
-Regulates membrane fluidity and permeability •Ie: The higher the cholesterol concentration the greater the reduction in proton and sodium permeability -Conductance (myelin sheaths that innervate nerves are high in cholesterol ) -Cell signaling -Intracelluar transport
functions of membrane
-Selective permeable barrier -establish cell boundries -Protection -Allows for compartmentalization -Signal transduction-cell communication like hormones -Binding site for cytoskeleton -Site of enzyme activity -Transport and conductivity -Cell-cell adhesion and attachment -the ability to specifically combine with the final products of the immune response
lipid "raft"
-microdomains -As membranes are moved from one place to another in the cell •Endocytosis and exocytosis -During signal transduction -viral and toxin entry -Cell migration
Proteins bound to membranes
1. Integral membrane proteins 2. Peripheral membrane proteins
Cellular membranes have 4 components
1. phospholipid bilayer 2. transmembrane proteins 3. interior protein network 4. cell surface markers
symporter/cotransporter
2 or more ions or molecules transported in same direction
Which labeled region(s) of the plasma membrane is(are) hydrophilic? Multiple choice question. C only B only A only B and C A and C
A and C
Lipid-anchored protein
A lipid molecule is covalently attached to an amino acid side chain of the membrane protein.
What is the basic structure of the plasma membrane? Multiple choice question. Arrangement of subunits into a tubule A phospholipid bilayer A phospholipid monolayer A double helix
A phospholipid bilayer
Transmembrane protein
A segment of amino acids is inserted into the phospholipid bilayer.
Glycosphingolipid
A sphingolipid with a head group composed of sugars; cell Adhesion, antigens and Signal transduction
Most transmembrane segments of integral membrane proteins are folded into what type of secondary structure? Multiple choice question. Alpha-helix A bilayer Beta-pleated sheet Globular
Alpha-helix
Most transmembrane segments of integral membrane proteins are folded into what type of secondary structure?
Alpha-helix; Transmembrane segments must have a structure that is favorable in both polar and nonpolar regions.
Why a bilayer?
Amphipathic property of phospholipids Energetically more favorable No edges therefore no "exposed" phospholipid. "self-sealers"
Microdomains
Cholesterol and sphingomyelin enriched area of a membrane
How is a lipid-anchored protein attached to the membrane? Multiple choice question. Via the polar heads of the phospholipids Covalently bound to an amino acid side chain within the protein Non-covalently bound to an amino acid side chain within the protein
Covalently bound to an amino acid side chain within the protein
What separates the internal contents of a cell from the extracellular environment? Multiple choice question. The extracellular matrix The plasma membrane The nucleus The nuclear envelope
The plasma membrane
glycolipid
a lipid with one or more covalently attached carbohydrates (•monosaccharides or polysaccharides) and is the least common component in cell membranes
Match each protein with its proper location with respect to the membrane.
a: transmembrane protein b:peripheral membrane protein c: lipid-anchored membrane protein
membrane protein enzymes
adenylyl cyclase catalyzes the production of intracellular cyclic AMP in response to extracellular signals
A polypeptide chain usually crosses the bilayer as an
alpha helix
example of channel transport proteins
aquaporins (water channel proteins)
bilayer leaflets are {asymetrical/symetrical} with the different amounts of each component
asymetrical
Glycolipids and glycoproteins and proteoglycan equals
carbohydrate layer
Cell Surface Carbohydrates
carbohydrates present on plasma membrane such as -membrane glycoproteins that contain short oligosaccharides extending to the extracellular space -Proteoglycans that have one or more long polysaccharide attached
Two classes of transport proteins based on type of movement
channels and transporters
Peripheral membrane proteins ----- interact with the hydrophobic region of the membrane; rather, they are ------bound to regions of integral membrane proteins that project out from the membrane.
do not, noncovalently
lipid bilayer
flexible double-layered sheet that makes up the cell membrane and forms a barrier between the cell and its surroundings
Phospholipids are amphipathic molecules
hydrophobic (water-fearing) region faces in hydrophillic (water-loving) region faces out
The tails of phospholipids are nonpolar and therefore
hydrophobic.
A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ______ membrane protein. Multiple choice question. locked noncovalent peripheral integral
integral
A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ______ membrane protein. Multiple choice question. noncovalent locked peripheral integral
integral
where are glycolipids found?
outer plasma membrane surface (non-cytoplasmic side) but do not protrude into the cytoplasm
Not covalently bound to membrane
peripheral membrane protein
Proteins that are non-covalently bound to the hydrophilic regions of integral membrane proteins or to the polar head groups of lipids are called
peripheral membrane proteins
The smooth endoplasmic reticulum is where most eukaryotic membrane
phospholipids
three kinds of lipids that are found in the plasma membrane
phospholipids, cholesterol, glycolipid
flippase
protein that facilitates the movement of membrane lipids from one leaflet to the other leaflet of a phospholipid bilayer
The three main types of macromolecules that comprise the plasma membrane are
proteins (polypeptides), lipids (phospolipids), carbohydrates (polysaccharides
Transporters (carrier proteins)
selectively move substances through conformational change -change in shape
Sphingolipids are involved in
signal transduction
cell cortex determines
the shape of the cell and the mechanical properties of the plasma membrane
transport proteins
transmembrane proteins that provide a passageway for the movement of ions and hydrophilic molecules across membranes
uniporter
transporter that carries one specific ion or molecule
Membrane Protein Function
transporters, anchors, receptors, enzymes
Transporter types
uniporter, symporter/cotransporter, antiporter
transporters are primarily used by
uptake of organic molecules, such as nucleotides
phospholipid
•Choline phospholipids •Non-choline phospholipids
cholesterol
•Lipid soluble steroid •amphipathic •Found in both leaflets of the lipid bilayer
membrane protein transporters
•Na+ pump actively pumps Na+ out of cells and K+ in
Cells Can Restrict Movement of Proteins
•Plasma membrane proteins are usually localized to specific areas within the bilayer = membrane domains •Some proteins are linked to extracellular structures or tethered to the cell cortex •Cells can create diffusion barriers which restrict proteins to one area/domain