Transcript Chap 5 – Transport Across Membranes

Figure 5.1
CYTOPLASM
Enzymatic
activity
Fibers of
extracellular
matrix (ECM)
Phospholipid
Cholesterol
Cell-cell
recognition
Receptor
Signaling
molecule
Transport
Attachment to the cytoskeleton
and extracellular matrix (ECM)
Signal
transduction
ATP
Intercellular
junctions
Glycoprotein
Microfilaments
of cytoskeleton
CYTOPLASM
Passive transport
 Passive transport = diffusion across cell
membrane
– No energy required!!
– No transport protein required!!!
 Moves WITH concentration gradient
 Examples:
– Urea, CO2, O2, Water, small hydrophobic
Animation: Diffusion
Animation: Membrane Selectivity
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Figure 5.3A
Molecules of dye
Membrane
Pores
Net diffusion
Net diffusion
Equilibrium
Figure 5.3B
Net diffusion
Net diffusion
Equilibrium
Net diffusion
Net diffusion
Equilibrium
Osmosis =
diffusion of
water
across a
membrane
Lower
Higher
concentration concentration
of solute
of solute
Equal
concentrations
of solute
H2O
Solute
molecule
Selectively
permeable
membrane
Water
molecule
Solute molecule
with cluster of
water molecules
Osmosis
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Figure 5.5
Hypotonic solution
H2O
Isotonic solution
H2O
H2O
Hypertonic solution
Crenation
H2O
Animal
cell
Normal
Lysed
Plasma
membrane
H2O
H2O
Shriveled
H2O
Plant
cell
Turgid
(normal)
Flaccid
Turgor pressure = pressure of cell membrane
and vacuole against plant cell wall
Shriveled
(plasmolyzed)
plasmolysis
Osmoregulation = Water Balance
 Osmoreguatation = all organisms must regulate
internal water concentrations
– Remove excess water:
– Contractile vacuoles - protists
– Freshwater organisms – kidneys, gills
– Prevent water loss:
– Guard cells in plants (close stomates in leaves to prevent
water loss)
– Kidneys; our skin
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Video: Chlamydomonas
Video: Plasmolysis
Video: Paramecium Vacuole
Video: Turgid Elodea
Facilitated Diffusion = Passive diffusion of solute
using a transport protein
Solute
molecule
Transport
protein
Only moves solutes with concentration gradient!
Examples: ion channels, aquaporin, GLUT1 (glucose) transporter
5.7 SCIENTIFIC DISCOVERY: Research on
another membrane protein led to the discovery
of aquaporins
 Dr. Peter Agre received the 2003 Nobel Prize in
chemistry for his discovery of aquaporins.
 His research on the Rh protein used in blood
typing led to this discovery.
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Figure 5.7
Active Transport (using transport protein)
 In active transport, a cell
– must expend energy to
– move a solute against its concentration gradient.
 Primary active transport = ATP used as direct energy source
– Ex: Na-K-ATP Pump
 Secondary active transport = ATP used indirectly
– H+ Pump; Na-Glucose Cotransporter
 The following figures show the four main stages of
active transport.
Animation: Active Transport
© 2012 Pearson Education, Inc.
Figure 5.8_s4
Transport
protein
Solute
1
Solute binding
2
P
ATP
ADP
Phosphate
attaching
P
Protein
changes shape.
3
Transport
Phosphate P
detaches.
4
Protein
reversion
Na-K-ATP Pump
3 Na+ OUTSIDE CELL
Net effect:
High [Na+] built up outside cell
High [K+] built up inside cell
ATP
hydrolysis
2 K+ INSIDE CELL
Na-Glucose Cotransporter
Found in small intestine
3 Na+
OUTSIDE
CELL
Uses potential energy of [Na+]
to drive glucose INTO cell,
against glucose [ ] gradient.
ATP
hydrolysis
2 K+
INSIDE
CELL
Na+ is
allowed to
come
back INTO
cell,
following
its [ ]
Glucose
pumped INTO
cell
H+ Pumps
 Use energy of moving electrons to transport H+
against [ ] gradient
H+ can be pushed AGAINST [ ]
gradient to one side of a membrane
or the other
High energy electrons
ELECTRON SLIDE
Low energy electrons
5.9 Exocytosis and endocytosis transport large
molecules across membranes
 There are three kinds of endocytosis.
1. Phagocytosis = cell eating (cell takes in solids by vesicle)
2. Pinocytosis = cell drinking (cell takes in fluids by vesicle).
3. Receptor-mediated endocytosis receptors on surface
bind molecule and bring in inside cell thru a vesicle.
Animation: Exocytosis and Endocytosis Introduction
Animation: Exocytosis
Animation: Pinocytosis
Animation: Phagocytosis
Animation: Receptor-Mediated Endocytosis
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Figure 5.9
Phagocytosis
EXTRACELLULAR
FLUID
Pseudopodium
CYTOPLASM
Food
being
ingested
“Food” or
other particle
Food
vacuole
Pinocytosis
Plasma
membrane
Vesicle
Plasma membrane
Receptor-mediated endocytosis
Coat protein
Receptor
Coated
vesicle
Coated
pit
Specific
molecule
Coated
pit
Material bound
to receptor proteins