Ch 8 - Biological Membrane

Question 1

What does the fluid mosaic model account for?

Answer 1

the presence of lipids, proteins, and carbohydrates in a dynamic, semisolid plasma membrane that surrounds cells

Question 2

Where are proteins embedded in the plasma membrane?

Answer 2

phospholipid bilayer

Question 3

How do lipids move within the membrane?

Answer 3

• the membrane is not static

- lipids move freely in the plane of the membrane and can assemble into lipid rafts

Question 4

What are flippases?

Answer 4

specific membrane proteins that maintain the bidirectional transport of lipids between the layers of the phospholipid bilayer in cells

Question 5

How do proteins and carbohydrates move within the membrane?

Answer 5

freely, but are slowed by their relatively large size

Question 6

What is the primary membrane component?

Answer 6

lipids, both by mass and mole fraction

Question 7

What do triacylglycerols and free fatty acids act as and where are they found?

Answer 7

acts as phospholipid precursors and are found in low levels in the membrane

Question 8

What do glycerophospholipids do in membranes?

Answer 8

replace one fatty acid with a phosphate group, which is often linked to other hydrophilic groups

Question 9

How does cholesterol play a role in the fluidity and stability of the plasma membrane?

Answer 9

• moderates membrane fluidity by interfering with the crystal structure of the cell membrane and occupying space between phospholipid molecules at low temperatures, and by restricting excessive movement of phospholipids at high temperatures
• also provides stability by cross linking adjacent phospholipids through interactions at the polar head group and hydrophobic interactions at the nearby fatty acid tail

Question 10

What do waxes do in membranes?

Answer 10

present in very small amounts, if at all; they are most prevalent in plants and function in waterproofing and defense

Question 11

What do proteins located in the membrane do?

Answer 11

act as transporters, cell adhesion molecules, and enzymes

Question 12

What do transmembrane proteins do?

Answer 12

can have one or more hydrophobic domains and are most likely to function as receptors or channels

Question 13

What do embedded proteins do?

Answer 13

are most likely part of a catalytic complex or involved in cellular communication

Question 14

What do membrane-associated proteins do?

Answer 14

may act as recognition molecules or enzymes

Question 15

What can carbohydrates form to function in cell recognition?

Answer 15

a protective glycoprotein coat

Question 16

What do extracellular ligands do?

Answer 16

can bind to membrane receptors, which function as channels or enzymes in second messenger pathways

Question 17

What do cell-cell junctions regulate?

Answer 17

intracellular and intercellular transport

Question 18

What is the difference between gap junctions, tight junctions, and desmosomes/hemidesmosomes?

Answer 18

• gap: allow for the rapid exchange of ions and other small molecules between adjacent cells
• tight: prevent paracellular transport, but do not provide intercellular transport
• des: anchor layers of epithelial tissue together

Question 19

What do concentration gradients help with in membrane transport?

Answer 19

to determine appropriate membrane transport mechanisms in cells

Question 20

What is osmotic pressure (II)?

Answer 20

• a colligative property
• the pressure applied to a pure solvent to prevent osmosis and is used to express the concentration of the solution
• often better conceptualized as a “sucking” pressure in which a solution is drawing water in, proportional to its concentration
  II = iMRT
  M = molarity; R = ideal gas constant; T = absolute temperature (K), i = van’t Hoff factor (the number of particles obtained from the molecule when in solution)

Question 21

Why does passive transport not require energy?

Answer 21

• does not require energy because the molecule is moving down its concentration gradient or from an area with higher concentration to an area with lower concentration

Question 22

Why does simple diffusion not require a transporter?

Answer 22

small, nonpolar molecules passively move from an area of high concentration to an area of low concentration until equilibrium is achieved

• high to low concentration gradient
• no membrane protein required
• no energy required (passive process)
• small, nonpolar (O2, CO2) transported

Question 23

What is osmosis?

Answer 23

describes the diffusion of water across a selectively permeable membrane

• low to high concentration gradient
• no membrane protein required
• no energy required (passive process)
• H2O transported

Question 24

How does facilitated diffusion work?

Answer 24

used transport proteins to move impermeable solutes across the cell membrane

• high to low concentration gradient
• membrane protein required
• no energy required (passive process)
• polar molecules (glucose) or ions transported

Question 25

What does active transport require?

Answer 25

• low to high concentration gradient
• membrane protein and energy required
  polar molecules and ions are transported
• may be primary or secondary depending on the energy source (secondary active transport can be further classified as symport or antiport)

Question 26

What are endocytosis and exocytosis?

Answer 26

methods of engulfing material into cells or releasing material to the exterior of cells, both via the cell membrane

Question 27

What is the difference between pinocytosis and phagocytosis?

Answer 27

the ingestion of liquid into the cell in vesicles formed from the cell membrane
- phagocytosis is the ingestion of larger, solid molecules

Question 28

How is the membrane potential (Vm) maintained?

Answer 28

by the sodium-potassium pump and leak channels

Question 29

What is the Nernst equation used for?

Answer 29

to calculate the electric potential created by one ion

E = RT/zF x ln[ion]outside/[ion]inside = 61.5/z log[ion]outside/[ion]inside

Question 30

What is the Goldman-Hodgkin-Katz voltage equation used for?

Answer 30

to calculate the resting potential of a membrane at physiological temperature (derived from Nernst)
Vm = 61.5log(pNa x [Na]out + pK+ x [K+] out + pCl- x [Cl-]out)/(pNa x [Na]in+ pK+ x [K+]in+ pCl- x [Cl-]in)

Question 31

What is the difference between the outer and inner mitochondrial membrane?

Answer 31

• the outer mitochondrial membrane is highly permeable to metabolic molecules and small proteins
• the inner mitochondrial membrane surrounds the mitochondrial matrix, where the citric acid cycle produces electrons used in the ETC and where many other enzymes important in cellular respiration are located
• the inner mitochondrial membrane also does not contain cholesterol

Question 32

What are lipid rafts?

Answer 32

aggregates of specific lipids in the membrane that function as attachment points for other biomolecules and play roles in signaling
- cholesterol rich domains

Question 33

List the following membrane components in order from most plentiful to least: carbohydrates, lipids, proteins, nucleic acids

Answer 33

• lipids (including phospholipids, cholesterol, and others) are most plentiful
• proteins (including transmembrane proteins - channels and receptors - membrane-associated proteins, and embedded proteins are next
• carbohydrates (including glycoprotein coat and signaling molecules) are next
• nucleic acids are essentially absent

Question 34

What is the difference between hypotonic, hypertonic, and isotonic movement?

Answer 34

• hypo: if concentration of solutes inside the cell is higher than the surrounding solution; cause a cell to swell as water rushes in, sometimes bursting (lysing)
• hyper: solution that is more concentrated than the cell; water will move out of the cell
• iso: if solutions inside and outside are equimolar (does not prevent movement, but prevents net movement of particles)

Question 35

What is the primary thermodynamic factor responsible for passive transport?

Answer 35

entropy

Question 36

What is the relationship between osmotic pressure and the direction of osmosis through a semipermeable membrane?

Answer 36

• as osmotic pressure increases, more water will tend to flow into the compartment to decrease solute concentration
• osmotic pressure is often considered a “sucking” pressure because water will move toward the compartment with highest osmotic pressure

Question 37

Compare the 2 types of active transport.

Answer 37

• primary active transport uses ATP as an energy source for the movement of molecules against their concentration gradient
• secondary active transport uses an electrochemical gradient to power the transport

Question 38

What is the difference between symport and antiport?

Answer 38

• symport moves both particles in secondary active transport across the membrane in the same direction
• antiport moves particles across the cell membrane in opposite directions

Question 39

What does resting membrane potential depend on?

Answer 39

• the differential distribution of ions across the membrane
• active transport processes
• selective permeability of the phospholipid bilayer

Question 40

What are the functions of the cell membrane?

Answer 40

• a site for cytoskeletal attachment through proteins and lipid rafts
• transport regulation accomplished through channels, transporters, and selective permeability
• phospholipids acts as a reagent for second messenger formation

Question 41

What is the site for protein synthesis?

Answer 41

ribosomes

Question 42

What are the types of sphingolipids?

Answer 42

gangliosides, ceramide, sphingomyelin, and cerebrosides

Question 43

What is the similarity between osmosis and diffusion?

Answer 43

• they rely on electrochemical gradient of only the compound of interest and membrane permeability