5.1

Question 1

Explain the fluid mosaic model of membrane
structure.

Answer 1

Mosaic of proteins floats in or on the fluid lipid bilayer

Question 2

List the four components of cellular membranes

Answer 2

• phospholipid bilayer
• transmembrane proteins
• interior protein network
• cell surface markers

Question 3

describe the cell surface markers of cellular membranes

Answer 3

 Glycoproteins
• “self recognition” by creating a protein/carb chain shape characteristic of individual
• Ex
o MHC protein recognized by the immune system
 Glycolipids
• Tissue recognition by creating a lipid/carb chain shape characteristic of tissue
• Ex
o A, B, O blood group markers

Question 4

describe the transmembrane proteins of cellular membranes

Answer 4

 Proteins that penetrate through membrane
 Carriers
• Actively/passively transport molecules across membrane by moving specific molecules through the membrane in a series of conformational changes
• Ex
o Glycophorin carrier for sugar transport; Na+/K+ pump
 Channels
• Passively transport molecules across membrane by creating a selective tunnel that acts as a passage through membrane
• Ex
o Na+ & k+ channels in nerve, heart & muscle cells
 Receptors
• Transmit info into cell by signaling molecules that bind to cell-surface portion of the receptor protein
• This alters the portion of receptor protein within the cell, inducing activity
• Ex
o Specific receptors bind peptide hormones and neurotransmitters

Question 5

Understand electron microscopy in the study of cellular membranes

Answer 5

Electron microscopy provides higher magnification and higher resolution with more detail than a light microscope. It can show us the structure of tissues, cells, organelles and macromolecular complexes.

Question 6

List the different components of phospholipids.

Answer 6

1. Glycerol
    3-carbon polyalcohol
2. Phosphate group
    Attached to the glycerol
    Polar and hydrophilic because it has a negative charge
3. 2 fatty acids
    Attached to the glycerol
    Nonpolar and hydrophobic because it has no charge

Question 7

Explain how membranes form spontaneously through the formation of a lipid bilayer.

Answer 7

The hydrophobic fatty acid tails on phospholipids are repelled by water

Question 8

Describe the factors involved in membrane fluidity.

Answer 8

Temperature and lipid composition (made from saturated or unsaturated fats)

Question 9

Illustrate the six different functions of membrane proteins.

Answer 9

1. Transporter
2. Enzyme
3. Cell-surface receptor
4. Cell-surface identity marker
5. Cell-to-cell adhesion
6. Attachment to the cytoskeleton

Question 10

Differentiate between peripheral and integral proteins

Answer 10

Peripheral
- Proteins found on the surface of the plasma membrane that contain anchoring molecules which attach membrane proteins to the surface
Integral
- Aka transmembrane proteins. Span the lipid bilayer. Nonpolar regions are embedded in the interior of the bilayer and polar regions protrude from both sides of the bilayer

Question 11

Describe the properties of transmembrane protein domains

Answer 11

1. Proteins only need ONE to be anchored in the membrane but they often have many
2. Is made of hydrophobic amino acids arranged in alpha helices

Question 12

Understand the formation of membrane pores

Answer 12

1. Extensive nonpolar regions within a transmembrane protein can cause this through the membrane
2. Interior is polar and allows water and small polar molecules to pass through the membrane

Question 13

describe the phospholipid bilayer of cellular membranes

Answer 13

 Flexible matrix for proteins by excluding water-soluble molecules from nonpolar interior of bilayer and cell, barrier to permeability
 Made of phospholipid molecules
 Ex
• Bilayer of cell is permeable to large water-soluble molecules such as glucose

Question 14

describe the interior protein network of cellular membranes

Answer 14

 Peripheral or intracellular membrane proteins
 Spectrins
• Determine shape of cell by forming a supporting scaffold beneath membrane, anchored to both membrane and cytoskeleton
• Ex
o RBC
 Clathrins
• Anchor certain proteins to specific sites, especially on the exterior plasma membrane in receptor-mediated endocytosis by prteins that line coated pits and facilitated binding to specific moleules
• Ex
o Localization of low-density lipoprotein receptor within coated pits