Chapter 8: Biological Membranes

Question 1

Lipid rafts

Answer 1

Phospholipid bilayer also includes proteins and distinct signaling areas within lipid rafts; collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules; often serve important roles in signaling; both lipid rafts and protein also travel within the plane of the membrane, but more slowly

Question 2

Glycoprotein coat

Answer 2

Carbohydrates associated with membrane-bound proteins; cell walls of plants, bacteria, and fungi contain higher levels of carbohydrates

Question 3

Flippases

Answer 3

Assist in the transition or “flip” between layers

Question 4

Most plentiful to least plentiful membrane components

Answer 4

Lipids > proteins > carbohydrates > nucleic acids

Question 5

What are two essential fatty acids for humans?

Answer 5

Α-linolenic acid and linoleic acid

Question 6

What can phospholipids spontaneously form?

Answer 6

Micelles (small monolayer vesicles) or liposomes (bilayered vesicles)

Question 7

What are glycerophospholipids used for?

Answer 7

Membrane synthesis and can produce a hydrophilic surface layer on lipoproteins such as VLDL (lipid transporter); primary component of cell membranes; serve as secondary messengers in signal transduction; the phosphate group provides an attachment point for water-soluble groups such as choline or inositol

Question 8

Sphingolipids

Answer 8

Do not contain glycerol but contain 2 fatty acid-derived hydrophobic tails and a hydrophilic region

Question 9

What are the classes of sphingolipids?

Answer 9

Ceramide; sphingomyelins; cerebrosides; gangliosides

Question 10

By mass, what percentage of the cell membrane is composed of cholesterol? By mole fraction?

Answer 10

20%; 1/2

Question 11

Waxes

Answer 11

Class of lipids that are extremely hydrophobic and are rarely found in the cell membranes of animals, but are sometimes found in the cell membranes of plants; composed of a long chain fatty acid and a long-chain alcohol which contribute to the high melting point of these substances; role in waterproofing, protection and stability and rigidity (within the nonpolar tail region only)

Question 12

Transmembrane proteins

Answer 12

Pass COMPLETELY through the lipid bilayer; usually transporters, channels, and receptors

Question 13

Embedded proteins

Answer 13

Associated with only the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane

Question 14

Integral proteins

Answer 14

Transmembrane and embedded proteins; associated with the interior of the plasma membrane, which is usually assisted by one or more membrane-associated domains that are partially hydrophobic

Question 15

Peripheral (membrane-associated) proteins

Answer 15

May be bound through electrostatic interactions with the lipid bilayer, especially at lipid rats or to other transmembrane or embedded proteins (like G proteins)

Question 16

Carbohydrate role in cell membrane

Answer 16

Signaling and recognition molecules

Question 17

Membrane receptors

Answer 17

Tend to be transmembrane proteins; mostly protein, can be carbohydrates or lipids too

Question 18

Cell adhesion molecules

Answer 18

Cell-cell junctions; proteins that allow cells to recognize each other and contribute to proper cell differentiation and development

Question 19

Gap junctions

Answer 19

Allow for direct cell-cell communication and are often found in small bunches together; these connexons are formed by the alignment and interaction of pores composed of six molecules of connexin; permit movement of water and some solutes directly between cells (not proteins though)

Question 20

Tight junctions

Answer 20

Prevent solutes from leaking into the space between cells via a paracellular route; found in epithelial cells and function as a physical link between the cells as they form a single layer of tissue; can limit permeability enough to create a transepithelial voltage difference; must form a continuous band around the cell

Question 21

Desmosomes

Answer 21

Bind adjacent cells by anchoring to their cytoskeletons; formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells; primarily found at the interface between two layers of epithelial tissue

Question 22

Hemidesmosomes

Answer 22

Similar function to desmosomes but their main function is to attach epithelial cells to underlying (basement) membrane

Question 23

How does cholesterol provide membrane fluidity? Membrane stability?

Answer 23

Interfering with the crystal structure of the cell membrane and occupying space between phospholipid molecules; cross-linking adjacent phospholipids through interactions of the polar head group and the hydrophobic interactions at the nearby fatty acid tails

Question 24

Passive transport

Answer 24

Do not require energy (negative delta G); includes diffusion, facilitated diffusion, and osmosis; generally increase in rate as temperature increases; primary thermodynamic motivator in passive transport is an increase in entropy

Question 25

Active transport

Answer 25

Nonspontaneous and require energy (positive delta G); may or may not be affected by temperature depending on the enthalpy

Question 26

Osmotic pressure

Answer 26

Colligative property; physical property of solution that is dependent on the concentration of dissolved particles but not on the chemical identity of those dissolved particles; water will move towards the compartment with the highest osmotic pressure; opposed by hydrostatic pressure

Question 27

Van’t Hoff factor

Answer 27

The number of particles obtained from the molecule when in solution

Question 28

Carriers

Answer 28

Only open to one side of the cell membrane at any given point; for a brief time, the carrier is in the occluded state in which the carrier is not open to either side of the phospholipid bilayer

Question 29

Channels

Answer 29

May have an open or closed conformation; open conformation - channels are exposed to both sides of the cell membrane like a tunnel for particles to diffuse through

Question 30

Primary active transport

Answer 30

Uses ATP or another energy molecule to directly transport molecules across a membrane

Question 31

Secondary active transport

Answer 31

Coupled transport; also uses energy to transport molecules across the membrane but without direct coupling to ATP hydrolysis; uses energy released from one particle going down its electrochemical gradient

Question 32

What molecules are transported via simple diffusion?

Answer 32

Small, non-polar (O2, CO2)

Question 33

What molecules are transported via facilitated diffusion?

Answer 33

Polar molecules (glucose) or ions (Na+, Cl-)

Question 34

What molecules are transported via active transport?

Answer 34

Polar molecules or ions (Na+, Cl-, K+)

Question 35

Endocytosis

Answer 35

Occurs when the cell membrane invaginates and engulfs material to bring it into the cells

Question 36

Pinocytosis

Answer 36

Endocytosis of fluids and dissolved particles

Question 37

Phagocytosis

Answer 37

Ingestion of large solids such as bacteria

Question 38

What initiates endocytosis?

Answer 38

Substrate binding to specific receptors embedded within the plasma membrane

Question 39

Exocytosis

Answer 39

Occurs when secretory vesicles fuse with the membrane, releasing material from inside the cell to the extracellular environment; important in the NS and intercellular signaling

Question 40

Membrane potential

Answer 40

The difference in electrical potential across cell membranes; the impermeability of the cell membrane to ions and the selectivity of ion channels both lead to an electrochemical gradient between the exterior and interior of the cell

Question 41

What is the resting potential for most cells?

Answer 41

-40 to -80 mV, although the membrane potential can rise as high as +35 mV during depolarization

Question 42

Faraday constant

Answer 42

96 485 C/mol e-

Question 43

Leak channels

Answer 43

Ions passively diffuse through the cell membrane over time; cell membranes are more permeable to K+ than Na+ at rest because there are more K+ leak channels

Question 44

Sodium-potassium pump

Answer 44

Maintains the membrane potential; pumps 3 Na+ out for every 2 K+ ions in

Question 45

Nernst equation

Answer 45

``` E = RT/zf*ln [ion out]/[ion inside] E = 61.5/z log [ion out]/ [ion inside] ```

Question 46

Goldman-Hodgkin-Katz voltage equation

Answer 46

Vm = 61.5 log [P ion * [ion] outside/ Pion * [ion] inside]

Question 47

Outer mitochondrial membrane

Answer 47

Highly permeable due to many large pores that allow for the passage of ions and small proteins; completely surrounds the inner mitochondrial membrane with the presence of a small intermembrane space in between the two layers

Question 48

Inner mitochondrial membrane

Answer 48

Much more restricted permeability compared to the outer mitochondrial membrane; contains numerous infoldings known as cristae which increase the surface area available for the integral proteins associated with the membrane; encloses the mitochondrial matrix where the CAC occurs; contains a very high level of cardiolipin and does not contain cholesterol