Download cell transport

Chapter 5
The Working Cell
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5.14 Passive transport is diffusion across a
membrane
• Diffusion is the tendency for particles to spread
out evenly in an available space
– From an area of high concentration to an
area of low concentration
• Passive transport across membranes occurs
when a molecule diffuses down a
concentration gradient
• Small nonpolar molecules such as O2 and CO2
diffuse easily across the phospholipid bilayer
of a membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-14a
Molecules of dye
Membrane
Equilibrium
LE 5-14b
Equilibrium
Animation: Diffusion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5.15 Transport proteins may facilitate diffusion
across membranes
• In facilitated diffusion
– Transport proteins that span the membrane
bilayer help substances diffuse down a
concentration gradient
• To transport the substance, a transport protein
may
– Provide a pore for passage
– Bind the substance, change shape, and
then release the substance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-15
Solute
molecule
Transport
protein
5.16 Osmosis is the diffusion of water across a
membrane
• In osmosis water, molecules diffuse across a
selectively permeable membrane
– From an area of low solute concentration
– To an area of high solute concentration
– Until the solution is equally concentrated on
both sides of the membrane
• The direction of movement is determined by
the difference in total solute concentration
– Not by the nature of the solutes
Animation: Osmosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-16
Lower
concentration
of solute
Higher
concentration
of solute
Equal
concentration
of solute
H2O
Solute
molecule
Selectively
permeable
membrane
Water
molecule
Solute molecule with
cluster of water molecules
Net flow of water
5.17 Water balance between cells and their
surroundings is crucial to organisms
• Osmoregulation is the control of water balance
• Tonicity is the tendency of a cell to lose or gain
water in solution
– Isotonic solution: solute concentration is the
same in the cell and in the solution
• No osmosis occurs
• Animal cell volume remains constant; plant
cell becomes flaccid
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Hypotonic solution: solute concentration is
greater in the cell than in the solution
• Cell gains water through osmosis
• Animal cell lyses; plant cell becomes turgid
– Hypertonic solution: solute concentration is
lower in the cell than in the solution
• Cell loses water through osmosis
• Animal cell shrivels; plant cell plasmolyzes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-17
Isotonic solution
Hypotonic solution
H2O
H2O
H2O
Hypertonic solution
H2O
Animal
cell
(2) Lysed
(1) Normal
H2O
H2O
(3) Shriveled
Plasma
membrane
H2O
H2O
Plant
cell
(4) Flaccid
(5) Turgid
(6) Shriveled
(plasmolyzed)
Video: Plasmolysis
Video: Turgid Elodea
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5.18 Cells expend energy for active transport
• Active transport requires energy to move
solutes against a concentration gradient
– ATP supplies the energy
– Transport proteins move solute molecules
across the membrane
Animation: Active Transport
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-18
Transport
protein
ATP
Solute
Solute binding
P
ADP
Phosphorylation
Protein
changes shape
Transport
P
Phosphate
detaches
P
Protein reversion
5.19 Exocytosis and endocytosis transport large
molecules
• To move large molecules or particles through a
cell membrane
– A vesicle may fuse with the membrane and
expel its contents outside the cell
(exocytosis)
– Membranes may fold inward, enclosing
material from the outside (endocytosis)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5.19 Exocytosis and endocytosis transport large
molecules
• To move large molecules or particles through a
cell membrane
– A vesicle may fuse with the membrane and
expel its contents outside the cell
(exocytosis)
– Membranes may fold inward, enclosing
material from the outside (endocytosis)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-19a
Fluid outside cell
Vesicle
Protein
Cytoplasm
LE 5-19b
Vesicle forming
• Endocytosis can occur in three ways
– Phagocytosis ("cell eating")
– Pinocytosis ("cell drinking")
– Receptor-mediated endocytosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-19c
Pseudopodium of amoeba
Food being ingested
Phagocytosis
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Pinocytosis
Receptor-mediated endocytosis
Animation: Receptor-Mediated Endocytosis
Animation: Exocytosis and Endocytosis Introduction
Animation: Exocytosis
Animation: Pinocytosis
Animation: Phagocytosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
5.20 Faulty membranes can overload the blood
with cholesterol
• Cholesterol is carried in the blood by lowdensity lipoprotein (LDL) particles
• Normally, body cells take up LDLs by receptormediated endocytosis
• Harmful levels of cholesterol can accumulate
in the blood if membranes lack cholesterol
receptors
– People with hypercholesterolemia have
more than twice the normal level of blood
cholesterol
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 5-20
Phospholipid outer layer
LDL particle
Vesicle
Cholesterol
Protein
Plasma
membrane
Receptor
protein
Cytoplasm