Cell Biology For Bme: Chapter 11 - Membrane Structure

Front 1

How thick is a plasma membrane usually?

Back 1

5 nm or 50 atoms

Front 2

Are cell membranes selective or nonselective?

Back 2

Selective!

Front 3

The plasma membrane is involved in what 3 things involving the cell?

Back 3

1. Cell communication
2. Import and export of molecules
3. Cell growth and motility

Front 4

What is the most common type of phospholipid in most cell membranes?

Back 4

Phosphatidylcholine

Front 5

What is Phosphatidylcholine?

Back 5

Two small choline molecules attached to a phosphate as the hydrophilic head and two long hydrocarbon hydrophobic tails

Front 6

What are Amphipathic molecules?

Back 6

Molecules with both hydrophobic and hydrophilic properties!

Front 7

Why are hydrophobic molecules insoluble in water?

Back 7

Because they are all or almost all of their atoms are uncharged and nonpolar therefore cannot form favorable interactions with water.

Front 8

What are the 5 components of Phosphatidylcholine?

Back 8

1. Choline
2. Phosphate
3. Glycerol
4. One hydrocarbon tail made up of single bonds
5. One hydrocarbon tail made up of single bonds and one double bond

Front 9

What is the profound consequence of the prohibition of free edges regarding lipid bilayers? Why is this important?

Back 9

The only way a finite sheet can avoid having free edges is to bend and seal forming a boundary around a closed space. Important: this is the fundamental creation of a living cell

Front 10

Liposomes are formed when what are added to water?

Back 10

Pure phospholipids are added to water!

Front 11

What 2 properties of hydrocarbon tail affect how tightly they pack in the bilayer?

Back 11

1. length
2. number of double bonds they contain

Front 12

A shorter hydrocarbon chain reduces the tendency of the hydrocarbon tails to interact with one another and therefore increases or decreases the fluidity of the bilayer?

Back 12

INCREASES the fluidity of the bilayer

Front 13

What does it mean for a hydrocarbon to be unsaturated?

Back 13

There is a double (or triple) bond which means there is fewer hydrogens bonded than there would be normally

Front 14

A fatty acid tail with no double bonds has a full complement of hydrogen atoms and is said to be what?

Back 14

Saturated!

Front 15

Lipid bilayers that contain a large proportion of unsaturated hydrocarbon tails are more or less fluid than those with lower proportions?

Back 15

Unsaturated bilayers are MORE fluid than saturated bilayers

Front 16

In animal cells, membrane fluidity is modulated by the inclusion of what sterol?

Back 16

Cholesterol!

Front 17

Does cholesterol in the bilayer loosen or stiffen the layer?

Back 17

It stiffens the bilayer making it more rigid and less permeable.

Front 18

Are cell membranes symmetrical or asymmetrical?

Back 18

Generally asymmetrical!

Front 19

In eukaryotes, where are new phospholipids manufactured?

Back 19

By enzymes bound to the to the ER membrane facing the cytosol.

Front 20

To enable the membrane as a whole to grow evenly, half of the new phospholipid molecules have to be transferred where?

Back 20

To the opposite monolayer

Front 21

The transferring of new phospholipid molecules to the monolayer is catalyzed by what?

Back 21

Flippases!

Front 22

What are Flippases?

Back 22

Enzymes that transfer specific phospholipids selectively so that different types become concentrated in each monolayer.

Front 23

New membrane assembled in the ER is exported to other membranes through a cycle of what?

Back 23

Membrane budding and fusion (think vesicles)

Front 24

What does the preservation of orientation mean?

Back 24

Means that all cell membranes have a distinct inside and outside face that are established at the time of membrane synthesis.

Front 25

Where are glycolipids located?

Back 25

Only in the noncytosolic half of the bilayer.

Front 26

Where do glycolipids acquire their sugar groups?

Back 26

In the Golgi Apparatus!

Front 27

TRUE OR FALSE: Once a glycolipid molecule has been created, it can move freely in the monolayer to the other monolayer.

Back 27

FALSE. It is trapped in the noncytosolic monolayer as there are no flippases that can transfer it.

Front 28

What are inositol phospholipids?

Back 28

Minor components of the plasma membrane but have a role in relaying signals from the cell surface to the intracellular components.

Front 29

In animals, membrane proteins constitute what percentage of the mass of most plasma membranes?

Back 29

50%

Front 30

A cell contains more lipid or protein molecules in the plasma membrane? By what multiple?

Back 30

A cell contains 50 times more lipid molecules than protein molecules.

Front 31

What are 4 types of plasma membrane proteins?

Back 31

1. Transporters
2. Anchors
3. Receptors
4. Enzymes

Front 32

What are 4 ways membrane proteins can associate with the lipid bilayer?

Back 32

1. Transmembrane
2. Monolayer-associated
3. Lipid-linked
4. Protein-Attached

Front 33

TRUE OR FALSE: Transmembrane proteins have hydrophobic and hydrophilic regions.

Back 33

TRUE

Front 34

Proteins that are directly attached to a lipid bilayer (first 3 types of association) can only be removed by what?

Back 34

Detergents!

Front 35

What are the three integral membrane proteins?

Back 35

1. Transmembrane
2. Monolayer-associated
3. Lipid-linked!

Front 36

What is a peripheral membrane protein?

Back 36

Protein-attached membrane protein

Front 37

Hydrogen-bonding is maximized if the polypeptide chain of a protein forms what?

Back 37

Alpha helix

Front 38

What are Detergents?

Back 38

Soapy substance used by biochemists to solubilize membrane proteins.

Front 39

Detergents differ from membrane phospholipids in what way?

Back 39

They only have a single hydrophobic tail

Front 40

Because they have one tail, detergent molecules are shaped like what?

Back 40

Cones

Front 41

In water, detergents aggregate to form what?

Back 41

Micelles

Front 42

What do Detergents do?

Back 42

Detergent disrupts the lipid bilayer and brings the proteins into solution as protein-detergent complexes

Front 43

The standard method for determining protein structure directly is through what?

Back 43

X-Ray Crystallography

Front 44

What is Bacteriorhodopsin?

Back 44

Small protein found in large amounts in the plasma membrane of a certain archaea that lives in salt marshes.

Front 45

What does Bacteriorhodopsin do?

Back 45

Acts as a membrane transport protein that pumps H+ out of the bacterium

Front 46

What is Retinal?

Back 46

Light-absorbing nonprotein molecule that gives Bacteriorhodopsin energy to pump proteins out of the bacterium

Front 47

What is the Cell Cortex?

Back 47

Meshwork of fibrous proteins that is attached to the cytosolic surface of the plasma membrane

Front 48

The shape and mechanical properties of a cell is determined by what?

Back 48

Its cell cortex

Front 49

What is the main component of a red blood cell's cortex?

Back 49

Spectrin

Front 50

What are Membrane Domains?

Back 50

Functionally specialized region in a cell membrane, characterized by the presence of particular proteins.

Front 51

Lateral mobility of the plasma membrane proteins can be restricted in what 3 ways?

Back 51

1. Proteins can be tethered to the cell cortex
2. Proteins can be tethered to extracellular matrix molecules
3. Diffusion barriers

Front 52

Eucaryotic cells are coated with what?

Back 52

Carbohydrates!

Front 53

Oligosaccharides and polysaccharides in the carbohydrate layer do what for the cell? (3 things)

Back 53

1. absorb water
2. give cell slimy surface
3. Allows cells to squeeze through narrow spaces and prevents some cells (blood cells) from sticking to each other