Cell Membranes III

Question 1

What determines what crosses the selectively permeable cell membrane?

Answer 1

Depends on the properties of the cell membrane (lipid and protein composition) and the size and lipid solubility of the substance

Question 2

What are the active transport?

Answer 2

Vesicular transport (exocytosis, endocytosis, phagocytosis), direct or primary active transport, indirect or secondary active transport

Question 3

What are the passive transports?

Answer 3

Facilitated diffusion/ion channel, aquaporin channel (osmosis), simple diffusion

Question 4

What are protein-mediated transports?

Answer 4

Primary and secondary active transport, facilitated diffusion/ion channel, aquaporin channel

Question 5

What is diffusion?

Answer 5

Movement of molecules from area of higher concentration to an area of lower concentration

Question 6

Properties of diffusion?

Answer 6

1. Uses kinetic energy of molecular movement and no outside energy source
2. Diffused from higher concentration to lower
3. Continues until concentration come to equilibrium, molecular movement continues after equilibrium
4. Diffusion is faster along higher concentration gradient, shorter distances, higher temperatures, smaller molecules
5. Can take place over open system or across a partition that separates two systems

Question 7

What is Fick’s law of diffusion?

Answer 7

Rate of diffusion = surface area x concentration gradient x membrane permeability

Question 8

Simple diffusion for what lipophilic molecules?

Answer 8

O2, CO2, NH3, lipids, steroids

Question 9

Rate of simple diffusion is faster if:

Answer 9

• membrane surface area larger
• membrane is thinner
• concentration gradient is larger
• membrane is more permeable to the molecule

Question 10

Membrane permeability to molecule depends on:

Answer 10

• molecules lipid solubility
• molecules size
• lipid composition of the membrane

Question 11

What are channel proteins?

Answer 11

• made of membrane spanning protein subunits that create a cluster of cylinders with a pore through the center
• channels from water filled pore that links ICF to ECF and allows substances to move between
• 2 classifications: open “leak” channels and gated channels
  -facilitated diffusion (>10 million ions per second)

Question 12

What are gated channels?

Answer 12

-chemically gated (ligand)
-voltage gated
-mechanically gated
-all need stimulus to open

Question 13

How is selectivity of channel proteins determined?

Answer 13

• size of pore
• charge of the amino acids lining the pore (opposites attract)

Question 14

What are carrier proteins?

Answer 14

• large, complex
• change conformation to move molecules
• never form open channel between the ICF and ECF
• slow (1000 to 1,000,000 per/sec)
• moves small organic molecules

Question 15

How are carrier proteins classified?

Answer 15

• uniport carriers: transport only one kind of substance
• symport carriers (cotransporters): move two or more substrates in same direction
• antiport carriers (exchangers): move substrates in opposite directions

Question 16

What is facilitated diffusion?

Answer 16

• uses channels or carrier proteins
• move down concentration gradient or electrochemical gradient
• no energy
• stops when equilibrium reached

Question 17

What is active transport?

Answer 17

• moves molecules against their concentration gradients: from low to high
• requires energy
• support state of disequilibrium
• uses carrier proteins
• two types: primary and secondary

Question 18

What is primary active transport?

Answer 18

• energy to move molecule comes directly from hydrolyzing ATP (ATPase)
• most important: Na+/K+ ATPase (3 Na+ out, 2 K+ in)

Question 19

What is secondary active transport?

Answer 19

• uses potential energy stored in concentration gradient of one molecule to push another molecule against concentration gradient
• need Na+ concentration gradient to move second molecule against
• molecule 1 moves down which causes molecule 2 to move against
• can move symport or antiport

Question 20

What is specificity?

Answer 20

Refers to the ability of a transporter to move one molecule or a closely related group of molecule

Question 21

What is competition?

Answer 21

A carrier may move several members of a related group of substances but these substances compete with one another
-carrier may have a preference for one family member

Question 22

What is saturation?

Answer 22

Rate of transport depends on concentration and number of transporters
Transport normally increases with increasing concentration until transport maximum is reached (all of the transporters are in use)

Question 23

What is vesicular transport?

Answer 23

Macromolecules that cannot fit through a carrier or channel
-phagocytosis, endocytosis, exocytosis

Question 24

What is phagocytosis?

Answer 24

Creates vesicles using cytoskeleton
- requires ATP to move cytoskeleton and for intracellular transport of the vesicle (active transport)

Question 25

What is endocytosis?

Answer 25

• membrane indents, vesicles smaller, requires ATP
• non-selective: pinocytosis
• selective: receptor mediated transport
• caveolae or clathrin coated pits used
• protein hormones, growth factors, antibodies, plasma proteins

Question 26

What is exocytosis?

Answer 26

-vesicles filled with large lipophobic molecules such as proteins synthesized in cell or wastes left by lysosomes at pushed out
-can occur continuously or initiated by signal
-requires ATP, can be regulated by calcium