2: Membrane Transport Systems Flashcards
3 types of cell surface
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
- junctions between cells that makes
up tissues - serves as an intercellular communication
intercellular junction
3 parts that form the junctional complex
a. tight junction or Zonula occludens
b. desmosomes or Zonula adherens
c. hemi-desmosomes
part of the junctional complex that:
- leave no space between cells thus preventing leakage
- tie cells together
- grant strength and stability
tight junction or Zonula occludens
part of the junctional complex that:
- consists of intermediate filaments
- hold cells together
desmosomes or Zonula adherens
part of the junctional complex:
- attach cells to basal lamina
- focal adhesions
hemi-desmosomes
study the junctional complex
see module 2
- 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
gap junction
movement of molecules or atoms through a membrane
membrane transport
2 factors influencing membrane transport
size of the molecule
solubility in oil (lipid solubility)
particles that can readily pass through the cell membrane
water, urea
O2, N2, CO2
steroid
hormones (estrogen, testosterone)
particles that CANNOT readily pass through the cell membrane
ions
polar molecules with no net charge but with electrical imbalances or with molecular mass > 100 daltons:
- sugars
- amino acids
- nucleic acids
in summary, CM is permeable to:
gases
small uncharged polar molecules
in summary, CM is impermeable to:
ions
large polar molecules
2 types of membrane transport
passive transport - down hill, from higher to lower concentration
active transport - up hill, from lower to higher concentration
3 types of passive transport
simple diffusion, facilitated diffusion, solvent drag
- movement of molecules towards the concentration gradient
- does not require ATP
- no carrier protein
simple diffusion
8 factors affecting rate of diffusion
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
when will movement of solute will cease
if concentration gradient has been eliminated (state of equilibrium)
formula that describes the diffusion of solute in water
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
- 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)
facilitated diffusion
differences in simple and facilitated diffusion
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
lipids are not permeable to what?
cations: K+, Na+, Ca2+
anions: Cl-. HCO3-
glucose (hydrophilic)
big molecules (RNA)
explain the difference between carrier and channel proteins
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
3 types of carrier proteins
uniporter
symporter or co-transporter
antiporter
- carrier proteins that transport only 1 substance
- e.g., glucose transporters (GLUT)
uniporter
(see module for diagram)
- carrier proteins that move 2 or more substances
across the cell membrane in the same direction - e.g., kidney-Na+/K+/2Cl-______
symporter or co-transporter
- 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)
antiporter
(see module for diagram)
2 types of channel proteins
ungated channel
gated channel
- pores in the CM in which ions can permeate
- fast transport
- e.g., H2O channel protein
ungated channel protein
- opening or closing of gate channel protein depends
on the presence of:
ion
ligand
mechanical stimulus
light stimulus
5 types of gated channels
voltage-gated channel
ligand-gated channel
ion-gated channel
stretch-activated channel
light-gated channel
- 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
voltage-gated channel
(see module for diagrams please)
- _______ (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
ligand
a: ligand-gated channel
- ion-selective
- present in different cells
e.g., liver cells, kidney cells
ion-gated channel
(see module)
- responds to mechanical forces or pressure
- present in skin and ear
stretch-activated channel
- present in the retina (rods)
- channels for rhodopsin
light-gated channel
- requires carrier proteins for up hill transport
- requires energy (hydrolysis of ATP)
e.g., Na+-K+ pump, Ca pump
active transport
normal Ca ion concentration in muscle cells:
Ca ion concentration in contracted muscle cells:
10^-7 M
10^-3 M
what happens when Ca ion concentrations remain high?
what about when Ca ion concentration is low to normal?
high: skeletal muscle remains contracted
low: muscle relaxation occurs
- solvent flows in one direction (bulk flow)
- tends to drag along some molecules of solute
solvent drag
2 types of transport processes of macromolecules
exocytosis
endocytosis
- release of proteins in secretory granules or vesicles
- membrane of secretory vesicle becomes part
of the cell membrane - e.g., hormones, proteins
exocytosis
(see module for diagram)
- entry of substances or organisms inside the cell
endocytosis
2 types of endocytosis
phagocytosis (cell eating) - bacteria, dead tissues, food particle
pinocytosis (cell drinking) - substances in solution
