Quiz 2 BCMB 311

Two factors that affect membrane fluidity

1)Length of hydrocarbon tails - Range from 14-24 Longer tail = lower fluidity and higher viscosity 2) Number of double bonds (saturated vs unsaturated) More double bonds = higher fluidity and lower viscosity

What are the three major membrane lipid groups?

1)Phospholipids 2) Sterols 3) Glycolipids

Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)? 15 carbons with two double bonds 24 carbons with one double bond 20 carbons with two double bonds 16 carbons with no double bonds

15 carbons with two double bonds (shorter c chain, more double bonds = higher fluidity)

The lateral mobility of plasma membrane proteins can be restricted in several ways

A = Tethering of trans-membrane proteins with internal proteins B = Tethering of trans-membrane proteins to extracellular matrix molecules C= Tethering of trans-membrane proteins to those of other cells D= Diffusion barrier proteins can form a ring around a cell to restrict lateral diffusion

Amphipathic/Amphiphilic

A molecule with a polar (hydrophilic) and nonpolar (hydrophobic) part

Phospholipids and glycolipids are distributed asymmetrically in the lipid bilayer of an animal cell plasma membrane

An example are the ABO blood type antigens.

Detergents such as SDS and Triton X-100 are amphipathic molecules....

Can interface between hydrophobic solutes and the aqueous solvent to allow them to be dissolved in solution

The Lipid Bilayer Is a Flexible Two-dimensional Fluid how does it move?

Constant lateral movement within a leaflet Flip-flop across leaflets is VERY RARE

The melting temperature is a way of quantifying the fluidity of a lipid

Corn oil melting temp = -11C Coconut oil melting temp = 25C Lard melting temp = 30-40C

What is the "fluid mosaic" model of the membrane?

Describes the membrane as a tapestry of several types of molecules (phospholipids, cholesterols, and proteins) that are constantly moving

Membrane proteins can be solubilized by a mild detergent such as Triton X-100

Due to the hydrophobic effect, detergents will naturally form micelle structures in solution • The detergents can interact with the lipids of the bilayer, disrupting it, and with transmembrane proteins, solubilizing them

T/F? Increasing levels of cholesterol in membranes will increase its fluidity and melting temperature

False, does not increase fluidity

T/F? The lipid bilayer is a flexible two-dimensional fluid where phospholipids frequently undergo flip-flip movements across the two leaflets

False, move laterally

---- help to establish and maintain the asymmetric distribution of phospholipids characteristic of animal cell membranes in golgi

Flippases

Fluidity vs. Viscosity of Membranes

Fluid: unsaturated hydrocarbon tails with kinks Viscosity: saturated hydrocarbon tails (close together)

Bacteriorhodopsin is a proton pump in cyanobacteria photosynthesis

It is 250 amino acids long and crosses the lipid bilayer as seven α helices.

In ---- cells, the most important glycerophospholipids are phosphatidylcholines

Mammalian

How does one purify a membrane protein in order to study it?

Membrane Proteins Can Be Solubilized in Detergents

A cell membrane consists of a lipid bilayer in which proteins are embedded also known as

Plasma membrane

Lipid synthesis is largely catalyzed by enzymes at the cytosolic side of the smooth ER. These lipids cannot sustainably be added to just one leaflet; they must be able to get to the inner leaflet as well. What is primarily responsible for this movement between leaflets?

Scramblase

Proteins show different patterns of lateral diffusion within a membrane

Single particle tracking studies can be used to map the diffusion of target proteins within a membrane. • Is it stationary? • Is it affected by a diffusion barrier?

amphipathic phospholipids spontaneously form a bilayer in water. where is that water?

The aqueous environments of the Extracellular and Cytoplasm

How can I spot the difference in the name? (when fat is present)

The beginning of the name is different ex: Triacylglycerols (TAGs) vs Glycerophospholipids

Phospholipid bilayers spontaneously close in on themselves to form sealed compartments (Spheres)

The closed structure is stable because it avoids the exposure of the hydrophobic hydrocarbon tails to water, which would be energetically unfavorable.

Membranes retain their orientation during transfer between cell compartments...

The membrane lipids on the cytosolic side remain on the cytosolic side throughout vesicular trafficking

We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? What does the abbreviation stand for?

The method is called FRAP. It stands for Fluorescence Recovery After Photobleaching.

Eukaryotic cells are coated with sugars

The polar carbohydrate layer also attracts water, lubricating the cell, which is important for motile cells (white blood cells).

Mild detergents can be used to solubilize and reconstitute functional membrane proteins

This approach allows a membrane to be purified from an organism and reconstituted into a liposome membrane for study.

--- are formed by protein-protein interactions of transmembrane proteins between neighboring cells. They form a continuous band around the cell and act as a lateral diffusion barrier to restrict membrane proteins to distinct membrane domains

Tight junctions

Phospholipids randomly redistributed by

scramblase = a transporter that transfers them from one half of the lipid bilayer to the other

A transmembrane polypeptide chain usually crosses the lipid bilayer as an ---

alpha helix

The Plasma Membrane Is Reinforced by the Underlying

cell cortex

Different membrane lipids have different polar headgroups; some are ---

charged

A ---- chain length reduces the tendency of the hydrocarbon tails to interact with one another and therefore increases the fluidity of the bilayer.

shorter

Newly synthesized phospholipids are added to the --- side of the ER membrane

cytosolic

This means that all cell membranes have distinct "inside" and "outside" faces: the ---- monolayer always faces the cytosol, while the noncytosolic monolayer is exposed to either the cell exterior (lumen)

cytosolic

Which of the following substances is most commonly used to help purify a membrane protein? sucrose high salt solution detergent ethanol

detergent

Fat molecules --- contribute to the structure of the membranes They are entirely hydrophobic

do not

Membrane Assembly Begins in the ---

endoplasmic reticulum

The lateral mobility of plasma membrane proteins cannot be restricted in cells

false (extracellular matrix, adjacent cells, cell cortex)

Although the peptide backbone is --- this is contained in the interior of the helix (transmembrane)

hydrophilic

Pore forming transmembrane proteins typically have a ---- core

hydrophilic

Transmembrane α helices have ---- amino acid side chains which project outward and interact with the lipid tails

hydrophobic

The rate at which a solute crosses membrane depends on

its size and charge

A lipid bilayer is a single membrane containing two

leaflets (layers of lipids)

A transmembrane hydrophilic pore can be formed by

multiple amphipathic α helices

How can I spot the difference in structure? (when fat is present)

number of tails

Certain Phospholipids Are Confined to ---- of the Membrane

one side

Cell membranes are packed with phospholipids, with ---- being the most common (~70%)

phosphatidylcholine

Photobleaching techniques such as FRAP can be used to measure the rate of lateral diffusion of a membrane protein

pic in phone

The recognition of cell-surface carbohydrates on neutrophils allows these immune cells to begin to migrate out of the blood and into infected tissues

pics in phone

The hydrocarbon tail with no double bonds has a full complement of hydrogen atoms and is said to be...

saturated

A cortex made largely of --- gives human red blood cells their characteristic shape

spectrin

Pure phospholipids can form closed ----

spherical liposomes

Melting temperatures are affected by --- length and ---

tail length and unsaturation

Which of the following lipid is the most hydrophobic? triacylglycerol phosphatidylcholine phosphate glycerol

triacylglycerol

lipid bilayers that contain a large proportion of ----- hydrocarbon tails are more fluid than those with lower proportions.

unsaturated

The chain that harbors a double bond does not contain the maximum number of hydrogen atoms that could, so it is

unsaturated with respect to hydrogen.

Porin proteins form --- in the outer membrane of a bacterium (E. Coli)

water-filled channels

simple diffusion (passive transport)

•It is the movement of a substance through a membrane protein from the area of high concentration to an area of low concentration without any interaction with carrier proteins in the membrane •Know that simple diffusion is a passive process that does not require energy •Small lipid-soluble molecules and water are common examples of simple diffusion

↑ % cholesterol =

↑ rigidity = ↑ melting temp