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Chapter 3b
Transport
Mechanisms
Transport Mechanisms
The next series of slides
describes how various types of
substances move across the
plasma membrane – either into
a cell…or out of a cell.
Transport Mechanisms - Overview
• Passive transport (no ATP needed)
• Diffusion (hi
•
•
[ ] to lo [ ])
Osmosis (hi [ ] to lo [ ])
Filtration (hi P to lo P) ex: kidney
• Carrier-mediated transport (special membrane
proteins needed)
• facilitated transport (hi [ ] to lo [
• Active Transport (ATP needed)
])
• ion pumps (ATP needed)
• Vesicular (“little bubble”) transport
• endocytosis (ex: phagocytosis, pinocytosis)
• exocytosis (ex: secretion of hormones)
The Movement of Water - Osmosis
Osmotic
Flow across
a Cell
Membrane.
(only H2O)
Water crosses
the plasma
membrane thru
special pores
(“aquaporins”)
Figure 3-7
The Cell Membrane
Membrane Transport
• Selective permeability (membrane acts like
a“traffic cop.” Lets certain substances in/out as
needed.)
• What determines permeability of a substance?
•
•
•
•
Molecular size
Electrical charge
Shape of molecule
Lipid solubility (ability to dissolve in the interior of
the phospholipid bilayer.)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Cell Membrane
Filtration
• Hydrostatic (=liquid)
pressure pushes on fluid
(ex. blood)
• Fluid crosses membrane
• Small solutes follow
water. Large solutes (ex:
proteins) stay in blood.
• Ex: filtration starts
urine formation in the
kidney
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Cell Membrane
Carrier-Mediated Transport
• Membrane proteins act as “carriers”
• Facilitated diffusion (no ATP required because
movement is down concentration gradient
(“downhill”)
• Active Transport (ATP required)
• Molecules move against concentration
gradient (“uphill”)
• Ion pumps (e.g., Na-K pump)
• (Note: ATP is the chemical in cells that provides
immediate energy for all cell processes)
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Cell Membrane
Facilitated Diffusion
Figure 3-8
PLAY
Membrane Transport: Facilitated Diffusion
The Cell Membrane
The SodiumPotassium
Exchange Pump
•uses ATP energy
•moves ions from
lower to higher [ ]
Figure 3-9
PLAY
Membrane
Transport:
Active
Transport
The Cell Membrane
Vesicular (“little bubble”) Transport
• Materials enclosed in membranous vesicles
• Transport can be either in or out of cell
• Endocytosis
• Movement into cell
pinocytosis (“cell drinking”)
phagocytosis (“cell eating”)
• Exocytosis (think “exit”)
• Movement out of cell
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Phagocytosis
Cell membrane
of phagocytic
cell
A phagocytic cell comes in contact
with the foreign object and sends
pseudopodia (cytoplasmic
extensions) around it.
Foreign
object
Pseudopodium
(cytoplasmic
extension)
CYTOPLASM
EXTRACELLULAR FLUID
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3-11
2 of 8
Phagocytosis
Cell membrane
of phagocytic
cell
A phagocytic cell comes in contact
with the foreign object and sends
pseudopodia (cytoplasmic
extensions) around it.
The pseudopodia approach one
another and fuse to trap the
material within the vesicle.
Foreign
object
Pseudopodium
(cytoplasmic
extension)
CYTOPLASM
EXTRACELLULAR FLUID
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3-11
3 of 8
Phagocytosis
Cell membrane
of phagocytic
cell
A phagocytic cell comes in contact
with the foreign object and sends
pseudopodia (cytoplasmic
extensions) around it.
The pseudopodia approach one
another and fuse to trap the
material within the vesicle.
The vesicle moves into the
cytoplasm.
Vesicle
Foreign
object
Pseudopodium
(cytoplasmic
extension)
CYTOPLASM
EXTRACELLULAR FLUID
Play Neutrophil Chasing Bacterium
Play Ameba Capturing
Small
Copyright © 2007 Pearson Education, Inc.,
publishing Protozoan
as Benjamin Cummings
Figure 3-11
4 of 8
Secretion (ex. of exocytosis)
Endoplasmic reticulum
EXTRACELLULAR
CYTOSOL FLUID
Lysosomes
Cell
membrane
Secretory
vesicles
Transport
vesicle
Golgi apparatus
(a)
Membrane renewal
vesicles
ex: This is how hormones such as
insulin and glucagon are secreted
from pancreatic beta and alpha islet
cells respectively.
(b) Exocytosis
Vesicle
Incorporation in
cell membrane
Play Endocytosis Animation
Review of Endo- Exocytosis (Animation)
Figure 3-14
Other “Must Know” Organelles
• You must be able to
identify the following
organelles in sketch
from your text
• nucleus, nuclear
envelope, nuclear pore
• mitochondrion (-ia)
• lysosome
• cilia
The “Mighty” Mitochondrion (-ia)
Key Note – “Mighty” Mitochondria
•Mitochondria provide nearly all the
chemical energy (ATP) needed to
keep your cells (and you!) alive.
•Mitochondria consume oxygen and
organic substrates, and they generate
carbon dioxide and ATP.
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings