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