Chapter 11

Question 1

Describe the evolution of the plasma membrane model from the beginning to a lipid bilayer (3 models)

Answer 1

Permeable to nonpolar molecules → Made of lipids

Pure phospholipids in vitro form monolayers → Monolayer of lipids

Measurements of lipid number vs surface area → Bilayer of lipids

Question 2

Describe the evolution of the plasma membrane model from a lipid bilayer to the current model (2 models)

Answer 2

Properties cannot be explained by only lipids → Lipid bilayer coated in proteins

Current Model → Cell membranes are a fluid bilayer of lipids with a mosaic of associated proteins

Question 3

Describe FRAP

Answer 3

Fluorescent Recovery After Photobleaching

Attach dye to component of interest → destroy fluorescence with laser → look at % and rate of recovery

Question 4

Describe the movements of lipids in membranes

Answer 4

Lipids can diffuse laterally, or flex and rotate in place

Can flip-flop with the aid of flippases

Question 5

Describe lipid synthesis (made by X, goes to X, ends at X)

Answer 5

New lipids are made with enzymes on the outer/cytosolic side of the ER membrane

Scramblases in Golgi place lipids on the correct side and in the correct composition (ex: glycolipids are only found on extracellular side)

Question 6

Describe how lipid asymmetry is maintained from creation to insertion in membranes

Answer 6

Membrane asymmetry (two sided) continues to Golgi to vesicles to plasma membrane

Side facing the cytosol will remain facing the cytosol

Question 7

Name the most common phospholipid and describe its structure

Answer 7

Phosphatidylcholine

Hydrophobic head → choline linked to a phosphate group
Two fatty acid tails → one saturated, on with a double bond in the middle
Glycerol → links head to tail

Question 8

Name and describe the three lipid components of the plasma membrane

Answer 8

Phospholipids: hydrophilic head (made of a polar group, a phosphate, and a glyceroal) and two fatty acid tails

Glycolipid: hydrophilic head with two fatty acid tails, one or more sugars in polar region in head

Steroid: Multiple ring structure with hydrophobic head

Question 9

Define Tm

Answer 9

TM is the temperature above which the membrane is fluid and functional (want to be low)

Question 10

What are the two main factors that affect membrane fluidity and what are their effects?

Answer 10

It depends on saturation levels and the length of phospholipid tails

More double bonds → Lower TM
Fewer double bonds → Higher TM

Longer → Higher TM
Shorter → Lower TM

Question 11

What is the role of cholesterol in the plasma membrane?

Answer 11

Cholesterol (and other sterols) stiffens membranes

Very rigid, decreases fluidity above TM and increases fluidity below TM (buffer)

Also makes membrane less permeable

Question 12

Define cell cortex

Answer 12

Meshwork of fibrous proteins that stabilizes the plasma membrane and is attached to the underside of the membrane

Question 13

Name the four ways proteins can associate with the plasma membrane

Answer 13

transmembrane, monolayer, lipid-linked, protein-attached

Question 14

Describe a general transmembrane protein

Answer 14

one or more alpha helices that pass through the plasma membrane
(may also be beta sheets → rare)

Question 15

Describe a general monolayer protein

Answer 15

rarer, amphipathic

Question 16

Describe a lipid-linked protein

Answer 16

covalently attached to a lipid inserted in the membrane, lipid can be attached to C or N terminus and proteins can be on either side

Question 17

Describe a protein attached protein

Answer 17

also called peripheral membrane proteins, protein-protein interaction with noncovalent bonds, most loosely attached

Question 18

Describe alpha helices and beta sheets in the plasma membrane

Answer 18

Have hydrophobic and hydrophilic regions to pass through membrane or form channels

Question 19

What are four ways proteins can be anchored?

Answer 19

Attached to actin cytoskeleton

Attached to extracellular matrix (ex: collagen)

Forming cell-cell interactions

Tight junctions between cells

Question 20

Describe the experiment that proves some proteins are nonmotile

Answer 20

Studies using protein molecules tagged with antibody-coated gold nanoparticles have shown that proteins display a range of movement from random diffusion to complete immobility.

Question 21

Describe the structure and role of detergents in protein study

Answer 21

Mild detergents with hydrophobic tails and hydrophilic tails can be used to separate out membrane proteins when followed with purification with antibodies

Can be used to study proteins in isolation when also followed with removal of detergent and addition of phospholipids

Question 22

Describe the four main functions of proteins in the plasma membrane

Answer 22

Transporters/channels

Anchors

Receptors

Enzymes

Question 23

Define lectin. Give an example of its role in the cell.

Answer 23

A protein that binds to a particular oligosaccharide chain

Cells lining blood vessels bind to neutrophil sugars on white blood cells to allow them to migrate to the infected tissue

Question 24

Describe the use of x-ray crystallography in determining protein structure

Answer 24

Can be done, super hard because of hydrophobic regions

Question 25

Describe the use of hydropathy analysis in determining protein structure

Answer 25

Find delta G of transforming amino acid from hydrophobic → hydrophilic environment Hydrophobic amino acids have positive values Hydrophobic stretches of 20+ amino acids are likely transmembrane alpha helices

Question 26

Define glycoprotein and proteoglycan

Answer 26

Some proteins also have short chains of sugars, and are called glycoproteins, or have long polysaccharide chains, and are called proteoglycans

Question 27

Define glycocalyx

Answer 27

a protective layer of sugar residues, including the polysaccharides to protein or lipid molecules, on the outer surface of a cell

Question 28

Describe the role and location of sugars in the plasma membrane

Answer 28

All of the sugars on the outside of the cell membrane help form the glycocalyx. Some also are involved in cell-cell recognition and adhesion.

Question 29

What are the two main roles of the glycocalyx?

Answer 29

It protects the cell from mechanical damage by giving it a slimy surface, helping it squeeze through narrow spaces and also prevents blood cells from sticking to one another or to the walls of blood vessels.

Question 30

Describe the use of lectin in sugar study

Answer 30

Staining with particular lectin-fluorescent dyes can selectively show sugars