Kartlar: Lipid Bilayer and Membrane Proteins | Quizlet

cell membranes act as

selective barriers

plasma membrane

separates cell contents from the surrounding environment; found in bacterial and eukaryotic cells

plasma membrane is involved in

cell communication, import and export of molecules, ell growth and mobility, compartmentation, and energy transduction

lipid bilayer

flexible double-layered sheet that makes up the cell membrane and forms a barrier between the cell and its surroundings

Phospholipids

most abundant in the cell membrane

diglyceride (two fatty acids linked to a glycerol)

head group is X (small, polar molecule; phosphatidyl-)

phospholipids are

amphipathic (polar head and nonpolar body)

types of membrane lipids

phospholipids, glycolipids, cholesterol

liposomes

Membrane-bound droplets that form when lipids are added to water.

triacylglycerol

lipid consisting of three fatty acids linked to one glycerol molecule; also called a fat or triglyceride; storage lipids that are stored in lipid bodies; surrounded by monolayer

small nonpolar molecules

CO2, O2 N2, steroid hormones

Can go through the cell membrane easily,

small uncharged polar molecules

H2O, glycerol, ethanol, permeable

larger uncharged polar molecules

Only a tiny bit can diffuse through (amino acids, glucose, nucleosides)

ions

cannot cross the membrane (H+, Na+, K+, Ca2+, Cl-, Mg2+, HCO3-)

lipid bilayers are

highly fluid (able to move)

lateral diffusion, flexion, and rotation

occur easily

flipping sides within a bilayer is

very rare (non-spontaneous, needs help of enzymes)

factors that affect fluidity

increased temperature = increased fluidity

adding length to the chain = decreases fluidity

increase double bonds in a fatty acid chain = increases fluidity

increase cholesterol = decreases fluidity

Where does membrane assembly begin?

endoplasmic reticulum

what produces and inserts new phospholipids?

biosynthetic enzymes

Scramblase

randomly transfer phospholipids from one monolayer to the other

Flippase

in the golgi; selectively remove specific phospholipids from the noncytosolic monolayer and flip them to the cytosolic side

Where are glycolipids found?

non-cytosolic monolayer of lipid bilayer

where do glycolipids get there sugar group?

in the golgi (non-cytosolic half of the bi-layer)

membrane protein functions

Transporters and channels

Enzymes

anchors

receptors

transmembrane proteins

Integral proteins that span the membrane.

single alpha helix, multiple alpha helices and beta barrel

monolayer associated alpha helix

some membrane proteins are anchored to the cytosolic half of the lipid bilayer by an amphipathic alpha helix

Lipid-linked membrane proteins

protein covalently attached to a lipid

protein-attached membrane proteins

connected to a protein on either the EC or IC side; peripheral; non covalent

hydrophilic pore

can be formed by multiple transmembrane alpha helices

hydropathy plots

help identify possible transmembrane domains from the amino acid sequence

alpha helical transmembrane proteins

have sugars covalently attached to certain amino acid side chains out side the cell

S-S bonds outside cells

reduced SH groups in the cytosolic side

Bacteriorhodopsin

a membrane protein which functions as a light-driven proton pump

beta barrel

created when beta sheets are extensive enough to fold back on themselves; filled with water

porin proteins

proteins that form channels for the transport of small molecules across the outer membrane of gram-negative bacterial cell walls

detergents

amphipathic molecules that tend to form micelles in water (solubilize fats, oils, hydrophobic proteins)

Which detergents completely denature proteins?

Strong ionic detergents (SDS)

which detergents dissolve membranes but dont unfold proteins?

mild ionic detergents (Triton X-100)

what reinforces the plasma membrane?

cell cortex

cell cortex

Mesh of cytoskeletal elements under a plasma membrane; inside the cell

what restricts mobility of membrane proteins?

proteins can be tethered to the cell cortex or diffusion barriers can restrict proteins to a particular domain

FRAP attack

measures the rate of lateral diffusion

Glycoproteins

Membrane carbohydrates that are covalently bonded to proteins.

Proteoglycans

a glycoprotein consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells.

Glycocalyx

carbohydrate coating on cell surface

function of cell surface carbohydrates

- Protect the cells from mechanical damage.

- Cell-cell recognition and adhesion.