BIO 360 - Exam 1 - Chapter 5 Cell & Cell Membranes SP 2023 PowerPoint

Question 1

What is “simple” diffusion?

Answer 1

Simplest case: add concentrated solute to solution
* solute moves down its concentration gradient and
redistributes until diffusion equilibrium reached.

Question 2

Why does “simple diffusion” occur?

more movement w/ increased ______ or increased ______.

Answer 2

• molecules in liquid or gas move by random thermal
  motion and bump into each
• more movement w/ increased concentration or increased temperature.
• this is the only energy used for simple diffusion

Question 3

Simple diffusion occurs ______ plasma membranes for some small molecules

Answer 3

across

Question 4

What is “net” flux?

Answer 4

One way flux from higher to lower. Two way flux are equal = no net flux doesn’t mean there isn’t any movement.

Question 5

Diffusion ______ increase with diffusion ______.
* proportional to distance^2 - we need cardiovascular
systems and small cells.

Answer 5

times / distance

Question 6

Net flux of molecule across biological membrane is directly
proportional to:
* ______ ______ across membrane
* ______ ______ of membrane
* ______ of membrane for given molecule

Answer 6

concentration gradient / surface area / permeability

Question 7

Permeability is inversely related to:
* membrane ______
* membrane ______

Answer 7

thickness / resistance

Question 8

What is Fick’s law of diffusion?

Answer 8

F = kpA(Co-Ci)

F = net flux of molecule
A = surface area of membrane
Co = [molecule] outside; Ci = [molecule] inside membrane
kp = permeability constant; inversely related to:
* membrane thickness and
* membrane resistance to diffusion of specific molecule
o proportional to size of molecule
o inversely proportional to lipid-solubility of molecule
o depends upon membrane composition

Question 9

Fick’s law of diffusion - Membrane ______ to diffusion is the inverse of resistance

Answer 9

permeability

Question 10

• Simple diffusion ______ ______ is much slower than
  diffusion through H2O.
• Most polar molecules (e.g. ions) do ______ dissolve or diffuse freely through lipid bilayer.
• Non-polar molecules are soluble in membrane lipids and
  ______ ______ ______.

Answer 10

across membranes / not / diffuse more rapidly

Question 11

How do ions enter cells

• Active:
  (1) D
  (2) I
• Passive:
  (1) F
  (2) I
  (3) A

Answer 11

Figure 5.5 Transport across membranes - Protein mediated

(1) Direct or primary active transport (ATPase)
(2) Indirect and secondary active transport (concentration gradient by ATP).

(1) Facilitated diffusion (concentration gradient),
(2) Ion channel (electrochemical gradient)
(3) Aquaporin channel (osmosis).

Question 12

How does facilitated diffusion work?

Answer 12

Specific substrates transported down concentration gradient
* Concentration gradient is driving force
* does NOT require additional energy (no ATP needed)
* Substrate binds to transporter causing conformational changein transporter leading to release of substrate on the other side of the membrane.

Question 13

What are ion channels?

Answer 13

Integral membrane proteins that form aqueous pore between intra and extracellular fluids. Most are actively “gated” between
open and closed conformations.

Question 14

What causes channels to open or close?

Answer 14

• change in voltage across plasma membrane
• binding of neurotransmitter
• mechanical stretch

Question 15

Ions channels are selective. What does that mean?

Answer 15

Most ion channels allow passage of only certain ions.
* Size and structure of pore determines which ions can
pass.

Channel pore lined with amino acids
* diameter of pore and charge of amino acids determines what can pass.

Question 16

How else does charge on ion affect conductance
of ions into or out of cells?

Answer 16

• Cells have uneven distribution of charge across plasma
  membrane.
• Ions tend to move down electrical as well as chemical
  gradients across membrane Electrochemical gradient.

Question 17

What transport mechanisms are available to import and export polar substances that do not ready cross plasma membranes by simple diffusion and are too large for ion channels (eg. glucose, amino acids)?

Answer 17

Carrier-mediated transport systems
* require transport protein (“carrier” or “transporter”)

Question 18

What are the types of carrier-mediated transport systems?

Answer 18

• facilitated diffusion
  uptake of glucose from interstitial fluid
• active transport:
  primary active transport
  secondary active transport

Question 19

Facilitated diffusion

• Specific substrates transported ______ concentration gradient.
• ______ ______ is driving force
• Does ______ require additional energy (no ATP needed).
  Substrate binds _________________________________________.

Answer 19

down / Concentration gradient / NOT / to transporter causing conformational change.

Question 20

Three types of Carrier-Mediated Transport

Answer 20

(1) Uniport: transport only one kind of substrate.
(2) Symport: move 2+ substrates in the same direction across a membrane.
(3) Antiport: move substrates in the opposite directions.

Question 21

How is the concentration gradient maintained for
glucose?

Answer 21

(1) Facilitated diffusion brings glucose down the concentration gradient using a GLUT transporter.
(2) Diffusion reaches equilibrium with glucose in vs. out of the cell.
(3) Glucose-6-phosphate keeps intracellular glucose levels low so diffusion never reaches equilibrium.

Question 22

How can you tell if a molecule crosses plasma
membrane by simple diffusion vs. facilitated diffusion?

Answer 22

• Transport kinetics differ.
• Rate of flux by simple diffusion dependent upon concentration gradient across membrane.
• Rate of flux by facilitated diffusion limited by # transporters in membrane, [substrate], transporter properties.
• Once transporters are saturated by substrate, flux is limited.

Question 23

GLUTs are … ______ ______ ______ which contain 12 membrane spanning helices …. GLUT proteins transport glucose … according to a model of ______ ______, which predicts that the transporter ________________________ toward either the outside or the inside of the cell.

Binding of glucose to one site provokes a ______ ______ associated with transport, and releases glucose to the other side of the membrane.

Answer 23

integral membrane proteins / alternate conformation / exposes a single substrate binding site / conformational change