2: Membrane Transport Systems

Question 1

3 types of cell surface

Answer 1

a. apical or mucosal surface - face lumen of a tubular tract or external environment

b. basal surface - opposite to the apical side, adjacent to the blood vessels

c. lateral surface - sides facing neighboring cell where specialized structure i.e. junctional complex is found

Question 2

• junctions between cells that makes
  up tissues
• serves as an intercellular communication

Answer 2

intercellular junction

Question 3

3 parts that form the junctional complex

Answer 3

a. tight junction or Zonula occludens
b. desmosomes or Zonula adherens
c. hemi-desmosomes

Question 4

part of the junctional complex that:
- leave no space between cells thus preventing leakage
- tie cells together
- grant strength and stability

Answer 4

tight junction or Zonula occludens

Question 5

part of the junctional complex that:
- consists of intermediate filaments
- hold cells together

Answer 5

desmosomes or Zonula adherens

Question 6

part of the junctional complex:
- attach cells to basal lamina
- focal adhesions

Answer 6

hemi-desmosomes

Question 7

study the junctional complex

Answer 7

see module 2

Question 8

• communication junction or gap in the junctional complex
• channel pores between cells which allow transfer of ions or molecules
• impt to heart, smooth muscles, and epithelial cells

Answer 8

gap junction

Question 9

movement of molecules or atoms through a membrane

Answer 9

membrane transport

Question 10

2 factors influencing membrane transport

Answer 10

size of the molecule
solubility in oil (lipid solubility)

Question 11

particles that can readily pass through the cell membrane

Answer 11

water, urea
O2, N2, CO2
steroid
hormones (estrogen, testosterone)

Question 12

particles that CANNOT readily pass through the cell membrane

Answer 12

ions
polar molecules with no net charge but with electrical imbalances or with molecular mass > 100 daltons:
- sugars
- amino acids
- nucleic acids

Question 13

in summary, CM is permeable to:

Answer 13

gases
small uncharged polar molecules

Question 14

in summary, CM is impermeable to:

Answer 14

ions
large polar molecules

Question 15

2 types of membrane transport

Answer 15

passive transport - down hill, from higher to lower concentration

active transport - up hill, from lower to higher concentration

Question 16

3 types of passive transport

Answer 16

simple diffusion, facilitated diffusion, solvent drag

Question 17

• movement of molecules towards the concentration gradient
• does not require ATP
• no carrier protein

Answer 17

simple diffusion

Question 18

8 factors affecting rate of diffusion

Answer 18

amount or concentration of solute - higher conc. difference, faster diffusion

size of molecules - smaller molecules, faster

velocity of kinetic motion (temperature) - higher temp, faster

number of channels - more channels, faster

viscosity - more viscous, slower

membrane permeability - if permeable, faster

surface area - greater surface area, faster

distance - short distance, faster

Question 19

when will movement of solute will cease

Answer 19

if concentration gradient has been eliminated (state of equilibrium)

Question 20

formula that describes the diffusion of solute in water

Answer 20

Fick’s Law

factors involved:
- flow of solute from region1 to region 2
- diffusion coefficient of solute
- cross-sectional area through which the flow of solute is measured
- solute concentration in region 1
- solute concentration in region 2
- distance between regions 1 & 2

Question 21

• a carrier-mediated transport system
• carrier proteins - move substances towards their chemical or electrical gradients (down hill)
• does not require energy (ATP)
• faster to equilibrate
• shows saturation kinetics
• shows structural specificity for molecules (e.g., L-arabinose > D-arabinose)

Answer 21

facilitated diffusion

Question 22

differences in simple and facilitated diffusion

Answer 22

simple: no carrier proteins, rate depends on concentration differences, e.g., water, O2, N2, alcohol, urea

facilitated diffusion: requires carrier proteins, rate depends on concentration of substance, e.g., sugars and amino acids

Question 23

lipids are not permeable to what?

Answer 23

cations: K+, Na+, Ca2+
anions: Cl-. HCO3-
glucose (hydrophilic)
big molecules (RNA)

Question 24

explain the difference between carrier and channel proteins

Answer 24

carrier proteins: undergo a cycle of conformational changes linked to substrate binding and dissociation on opposite sides of the membrane

channel proteins: membrane-spanning water-filled pores through which substrates passively diffuse

Question 25

3 types of carrier proteins

Answer 25

uniporter symporter or co-transporter antiporter

Question 26

- carrier proteins that transport only 1 substance - e.g., glucose transporters (GLUT)

Answer 26

uniporter (see module for diagram)

Question 27

- carrier proteins that move 2 or more substances across the cell membrane in the same direction - e.g., kidney-Na+/K+/2Cl-______

Answer 27

symporter or co-transporter

Question 28

- carrier protein transport a substance in exchange with another across the membrane - e.g., Na-amino acid pump (SI), 3Na+/Ca2+exchanger (removes Ca from cells)

Answer 28

antiporter (see module for diagram)

Question 29

2 types of channel proteins

Answer 29

ungated channel gated channel

Question 30

- pores in the CM in which ions can permeate - fast transport - e.g., H2O channel protein

Answer 30

ungated channel protein

Question 31

- opening or closing of gate channel protein depends on the presence of:

Answer 31

ion ligand mechanical stimulus light stimulus

Question 32

5 types of gated channels

Answer 32

voltage-gated channel ligand-gated channel ion-gated channel stretch-activated channel light-gated channel

Question 33

- requires electrical potential across the membrane - present in neurons (esp. in nerve axons), fat cells, muscles - e.g., Na (tetrodotoxin in puffer fish and local anesthetics), K, and Ca channels

Answer 33

voltage-gated channel (see module for diagrams please)

Question 34

- _______ (neurotransmitter) binding to extracellular part of the channel to allow passage of ions - present in neurons (esp. dendrites and cell body) - e.g., GABA gated Na channels, acetylcholine-gated Na channel GABA - gamma amino butyric acid

Answer 34

ligand a: ligand-gated channel

Question 35

- ion-selective - present in different cells e.g., liver cells, kidney cells

Answer 35

ion-gated channel (see module)

Question 36

- responds to mechanical forces or pressure - present in skin and ear

Answer 36

stretch-activated channel

Question 37

- present in the retina (rods) - channels for rhodopsin

Answer 37

light-gated channel

Question 38

- requires carrier proteins for up hill transport - requires energy (hydrolysis of ATP) e.g., Na+-K+ pump, Ca pump

Answer 38

active transport

Question 39

normal Ca ion concentration in muscle cells: Ca ion concentration in contracted muscle cells:

Answer 39

10^-7 M 10^-3 M

Question 40

what happens when Ca ion concentrations remain high? what about when Ca ion concentration is low to normal?

Answer 40

high: skeletal muscle remains contracted low: muscle relaxation occurs

Question 41

- solvent flows in one direction (bulk flow) - tends to drag along some molecules of solute

Answer 41

solvent drag

Question 42

2 types of transport processes of macromolecules

Answer 42

exocytosis endocytosis

Question 43

- release of proteins in secretory granules or vesicles - membrane of secretory vesicle becomes part of the cell membrane - e.g., hormones, proteins

Answer 43

exocytosis (see module for diagram)

Question 44

- entry of substances or organisms inside the cell

Answer 44

endocytosis

Question 45

2 types of endocytosis

Answer 45

phagocytosis (cell eating) - bacteria, dead tissues, food particle pinocytosis (cell drinking) - substances in solution