Download Cells and Transport-Cell Membrane and Transport

Chapter 7
Membrane Structure/
Function and Cell Transport
Ms. Gaynor
AP Biology
Overview of Cell
Membrane
The plasma (cell) membrane
the boundary that separates
living cell from its nonliving
surroundings
Also called the phospholipid
bilayer
The plasma membrane exhibits selective
permeability. It is semi-permeable
It allows some substances to cross it
more easily than others
Wow…
it’s so
detailed!
Cellular membranes are made
of 2 types of lipids and proteins
LIPID #1:
Phospholipids
most abundant
lipid in membrane
They are
amphipathic
have both hydrophobic
and hydrophilic regions
Phospholipid Bilayer
 Phosphate Groups
in “head” (- charge)
 2 Fatty Acids in
“tail” (hydrocarbon)
Hydrophilic
head
Hydrophobic
tail
Figure 7.2
WATER
NO WATER
WATER
In 1972, scientists
Proposed that membrane proteins are
mixed in and individually inserted into
the phospholipid bilayer
Hey, that
looks like a
sandwich!
Hydrophobic region
of protein
Phospholipid
bilayer
Hydrophobic region of protein
Polar
heads love
water &
dissolve.
Fluid
Mosaic
Model of the
cell membrane
Non-polar
tails “hide”
from water.
Carbohydrate cell
markers
Proteins
Membrane
movement
animation
The Fluidity of Membranes
Phospholipids in the plasma membrane
Can move within the bilayer
Proteins are larger & drift (move) less
Lateral movement
(~107 times per second)
(a) Movement of phospholipids
Figure 7.5 A
Flip-flop
(~ once per month)
Another view…
Temperature decreases  so does fluidity
Hydrocarbon tails in phospholipids
Affects fluidity of the plasma membrane
Need to have some unsaturated fatty acid tails
Fluidity is enhanced
Fluid
Unsaturated hydrocarbon
tails with kinks
(b) Membrane fluidity
Figure 7.5 B
Viscous
Saturated hydroCarbon tails
LIPID #2:
steroid “cholesterol” has different effects on
membrane fluidity at different temperatures
(only in animal cells)
-lower temps  lowers lipid movement  lowers fluidity
- cholesterol in membrane  hinders (stops) solidification
**acts as a temp “buffer”
Cholesterol
(c) Cholesterol within the animal cell membrane
Membrane Proteins and Their Functions
A membrane
Includes different proteins embedded in
the fluid lipid bilayer
Fibers of
extracellular
matrix (ECM)
2 major
types of
membrane
proteins
Glycoprotein
Carbohydrate
GlycolipidEXTRACELLULAR
SIDE OF
MEMBRANE
Microfilaments
of cytoskeleton
Cholesterol
Peripheral
protein
Integral CYTOPLASMIC SIDE
protein OF MEMBRANE
1. Integral proteins
Penetrate the hydrophobic
core of the lipid bilayer
Are often transmembrane Wait…what’s
that
proteins, completely
word for a polar &
spanning the membrane
nonpolar
molecule?
Span of
1+
stretches
of
Nonpolar
amino
acids
Figure 7.8
EXTRACELLULAR
SIDE
a Helix
CYTOPLASMIC
SIDE
2. Peripheral proteins
Are appendages loosely bound to the
surface of the membrane
An overview of six major
functions of membrane proteins
(a)
(b)
(c)
Transport.
Enzymatic
activity.
Signal
transduction.
Enzymes
Signal
Receptor
(d)
(e)
(f)
Cell-cell
recognition.
Intercellular
joining
Attachment to
cytoskeleton &
extracellular
matrix (ECM)
Glycoprotein
ECM
Why have Carbohydrates on
Cell Membrane proteins?
Cell-cell recognition
Is a cell’s ability to distinguish one
type of neighboring cell from
another
It’s their “ID” tag
Membrane carbohydrates
Usually short, branched
carbohydrates
Interact (bind) with the
surface molecules of other
cells
Function as cell “markers”
• Ex: Blood types (A, B, AB, and O)
2 different types membrane carbohydrates
 Glycolipids
Carbohydrates covalently attached to lipids
 Glycoproteins
Carbohydrates covalently attached to
proteins (most abundant)
Review…
Animations
of membrane structure
Chapter 7
Cell Transport
Ms. Gaynor
AP Biology
Membrane structure LEADS
TO selective permeability
A cell must exchange materials
with its surroundings
a process controlled by the
selectively permeable
plasma membrane
Cell Transport
Means moving things INTO and
OUT of the cell
Cells need to take in
Food, gases, water
Get rid of waste products
(excretion)
Give out such useful substances as
hormones and enzymes (secretion).
Permeability and Cell Transport
 Hydrophobic (non polar) molecules
Are lipid soluble (can dissolve)
can pass through membrane easily
Ex: Hydrocarbons, CO2, O2
 Hydrophilic (Polar) molecules
Are NOT lipid soluble (can’t dissolve)
Lipid INsoluble
Do not cross membrane easily
Ex: Na+, Cl- , Glucose/ other sugars
• NOTE: CHARGED molecules need
“help” to cross membrane
Types of Cellular Transport
Weee!
 Passive Transport
cell do NOT use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
high
low
 Active Transport
cell DOESuse energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
This is
going to
be hard!
high
low
Types of Passive
Transport
Diffusion= tendency for a
population of molecules (of ANY
substance) to spread out evenly
into available space
A “net” movement
Ex: Perfume, a fart , tea, food coloring
in water
 http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html
DIFFUSION
In absence of other forces…
Molecules move (diffuse) from area of
HIGH [ ] to an area of lower [ ]
A.k.a. Molecules move DOWN its OWN
concentration gradient
the difference in [ ] of a
substance from one area to
another
No chemical work (ATP energy)
is used diffusion is
spontaneous!
Substances diffuse down their
OWN concentration gradient
Net diffusion
Net diffusion
Net diffusion
Net diffusion
Equilibrium
Equilibrium
Factors Affecting
Diffusion
1. Temperature
 Higher temperature  more
kinetic energy  molecules move
faster (Example: Tea)
2. Pressure
 Higher pressure  molecules
move faster
Introduction to Osmosis
https://www.youtube.com/watch?v=IaZ8Mt
F3C6M
Effects of Osmosis on
Water Balance
Osmosis
The movement of water (water
diffusion) across a
semipermeable membrane
Involves the movement of FREE
water molecules down a water [ ]
gradient
High solute low “free” water [ ]
Low solute  high free water [ ]
or….
Tonicity= the measure of the amount of
dissolved particles in a solution
https://www.youtube.com/watch?v=sdiJtDRJQEc
Osmosis is affected by the concentration
gradient of dissolved substances (solutes)
Osmosis animation
3 Different Types of Solutions
Recall: SOLUTION = a uniform
mixture of 2 or more substances
** compare solutions OUTSIDE cell to inside cell
1. If a solution is isotonic
 [solutes] is the same
outside as inside the cell
 “iso-” means “same”
 There will be NO net
movement of water
ISOTONIC SOLUTION
Result: Water moves equally in both
directions and the cell remains same size!
(Dynamic Equilibrium)
2. If a solution is hypertonic
 [solutes] is greater outside
than inside the cell The cell
will lose water and shrivel or
wilt
 “hyper” means more
 (high [solute])
 Ex: when salinity increases in
lake, fish can die!
HYPERTONIC SOLUTION
Result: Water moves from inside the cell into
the solution: Cell shrinks (Plasmolysis)!
3. If a solution is hypotonic
[solutes] is less outside
than it is inside the cell The
cell will gain water and swell
(and maybe lyse or burst)
“Hypo” is
“hypo” means “less”
LOW!!!
• (low [solute])
Think: Hypo- sounds like
hippo…hippos are big & round; cells
in hypotonic solutions get big & round
Also, think “hypo” is “low” meaning “low”
solutes SURROUNDING cell
HYP0TONIC SOLUTION
Result: Water moves from the solution to
inside the cell): Cell Swells and bursts open
(cytolysis)!
Now…let’s review tonicity using
Gummy Bears!
https://www.youtube.com/watch?v=HqKlL
m2MjkI
•
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
Water Balance of Cells
with Walls
Cell walls
Help maintain water balance
Cell walls are in:
Plants
Prokaryotes
Fungi
Some protists
If a plant cell is turgid
It is in a hypotonic environment
It is very firm
A healthy state in most plants
 If a plant cell is flaccid
It is in an isotonic or hypertonic
environment
Cells are limp
Plasmolysis= when plasma
membrane pulls away from cell wall
in hypertonic solutions ; causes cell
with walls to wilt & can be lethal.
Water balance in cells with walls
H2O
Turgid (normal)
H2O
H2O
Flaccid
H2O
Plasmolyzed
How Organisms Deal
with Osmotic Pressure
•Bacteria and plants have cell walls that prevent
them from over-expanding.
•In plants the pressure exerted on the cell wall is
called tugor pressure.
•A protist like paramecium has contractile vacuoles
that collect water flowing in and pump it out to
prevent them from bursting.
•Salt water fish pump salt out of their specialized
gills so they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
Types of Passive
Transport
#1 Passive Transport
DOES NOT require chemical energy
(ATP)
Moves DOWN (WITH) [ ] gradient
Kinetic energy drives movement
#2 Active Transport
DOES require chemical energy (ATP)
Moves AGAINST its [ ] gradient

2 Types of PASSIVE TRANSPORT
1. SIMPLE DIFFUSION
**INCLUDES DIFFUSION
Uses NO membrane proteins
GOES DOWN
CONCENTRATION
GRADIENT (no ATP
needed)
 Molecules move HIGH [ ]low [ ]
Uncharged & lipid-soluble
molecules also pass freely
through bilayer.
solutes move down a
concentration gradient
• Examples: CO2, O2…H2O
WAIT!!!
Isn’t
water
polar?
Aquaporins
 water is polar but very small
It can pass easily through
membrane
uses aquaporins
EXTRACELLULAR
FLUID
AQUAPORIN
Channel protein
Water
CYTOPLASM
Oh…now
I get it!
2 Types of PASSIVE TRANSPORT
2. FACILITATED DIFFUSION
needs a little “help”
Uses help of channel or carrier
proteins
GOES DOWN CONCENTRATION
GRADIENT (no ATP needed)
Moves POLAR molecules  can
NOT easily pass through
HYDROPHOBIC region of membrane.
Example: ions, smaller polar molecules (ex:
sugar)
 Channel/carrier proteins specific
receptor site for substances they
Channel proteins
-Provide “tunnels”
• Channel Proteins animations
EXTRACELLULAR
FLUID
Channel protein
Solute
CYTOPLASM
(a)
A channel protein (purple) has a channel through which
water molecules or a specific solute can pass.
Carrier proteins
-Undergo a subtle change in shape
“carry” solute across the membrane
Carrier protein
Solute
2 Types of Passive Transport
Active transport
Uses energy to move solutes
against their [ ] gradients across the
cell membrane
Energy required  usually ATP
Carrier proteins are used…NEVER
channel proteins
Ex: sodium-potassium pump
Passive vs. Active
Transport
Figure 7.17
1. PROTEIN PUMPS
•Protein Pumps transport proteins
that require energy
to do work
•Examples:
•Na+/K+ Pumps
are important in
nerve responses
•Antiports and
Symports
(Cotransport)
•H+ (proton) pump
Sodium Potassium
Pumps (Active
Transport using
proteins)
Protein changes
conformational shape
to move molecules:
this requires energy!
REVIEW OF ACTIVE TRANSPORT…
ANIMATIONS
•http://www.wisconline.com/objects/ViewObject.aspx?ID=a
p11203
Cotransport, Proton Pumps and
Sodium/Potassium Pumps…
ANIMATIONS
http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter6/animations.html#
2. Bulk transport across
the plasma membrane
Occurs by exocytosis and
endocytosis
BOTH MOVE “BIG”
AMOUNTS OF STUFF in OR
out OF THE CELL
Exocytosis
In exocytosis
Transport vesicles move to
the plasma membrane, fuse
with it, and release their
contents
“exo-” means “exit”
Ex: hormone excretion; nerve cells and
transmitters; removal of wastes
ER
1
ROUGH ER
Glycolipid
2
GOLGI
APPARATUS
Vesicle
3
4
Secreted
protein
Membrane glycolipid
Endocytosis
In endocytosis
Cell takes in macromolecules
by forming new vesicles from
the plasma membrane
“endo-” means “enter”
2 types of Endocytosis
1. Phagocytosis
 “cell eating”
 Cell engulfs SOLIDS
into vesicle &
“digests” it
2. Pinocytosis
“pineapple juice)
(think
 “cell drinking”
 Cell engulfs LIQUIDS
into vesicle &
“digests” it
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/
animation__phagocytosis.html
Endocytosis and Exocytosis
Animations
http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter6/animations.html#
REVIEW ANIMATIONS
http://www.hippocampus.org/Biology
Click on “Membranes and Transport”
Listen to animation #3 (7 minutes long)
http://www.northland.cc.mn.us/biology/Biol
ogy1111/animations/passive3.swf
Excellent Review all Passive
(simple/facilitated diffusion) and Active
Transport 
No verbal explanation…you have to read the
tutorial!