Chapter 5
Membrane Structure and Function
Read chapter 5 in textbook
Read Lab 1 (Osmosis and Diffusion)
Read appropriate lab and lecture pages in
pages in CliffsAP
Cell Surface SEM
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
 Topics




5.1 Plasma Membrane
Structure and Function
5.2
5.3 Permeability of
the Plasma Membrane
5.4 Modification of
Cell Surfaces
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 All cells have a plasma
membrane
 Functions differently in
different cells
 All have same basic
makeup
 Currently the fluid
mosaic model is thought
to be the best
representation
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Actively functioning part of cell –without it cells die
 Selectively permeable
 Composed of double layer of phospholipid with free floating
proteins imbedded in it (proteins can float laterally)
 Also contains glycolipids, cholesterol and glycoproteins
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Hydrophilic phosphate heads
 Hydrophobic fatty acid tails
 water soluble substances
cannot pass easily ( amino
acids, sugars, proteins, nucleic
acids)
 substances soluble in lipids can
pass more easily (O2, CO 2)
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Fluid Mosaic

Membrane is fluid
because phospholipids
are oil consistency at
body temperature
• Proteins can “float”
around between
phospholipds

Membrane is mosaic
because it has a wide
range of movable
proteins imbedded in it
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Mosaic Quality



Proteins give unique qualities to cells
RBC has over 50 different proteins associated with it
Proteins are of two major types
• Peripheral proteins
• Integral proteins

Proteins can account for 50% of wt of membrane
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Peripheral Proteins




Occur on inside or outside
of membrane
Don’t span the membrane
Often attached to integral
protein
Function:
• Can have structural role
• Sometimes enzymatic
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral proteins



Most span the entire
membrane
Have hydrophilic and
hydrophobic portions
Function as :
•
•
•
•
•
Receptors
Channels or pores
Carriers
Enzymes
Cell recognition
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral Proteins

Channel protein
Mills AP Biology 2012
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral Proteins

Carrier/Transport protein
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral Proteins (usually)

Cell recognition proteins, “fingerprints” of the cell
• These glycoproteins and/or glycolipids are specific for each
species, for individuals within a species and even for different
types of cells within the same individual
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral Proteins

Receptor protein
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Integral Proteins

Enzymatic protein
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Junction Protein
Junction Proteins:
Tight junctions join cells so that a
tissue
can fulfill a function, as when a tissue
pinches off the neural tube during
development. Without this
cooperation between cells, an animal
embryo would have no nervous system.
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.1 Plasma Membrane Structure and Function
 Glycoproteins




Most proteins that abut
the extracellular space
are associated with
branching sugar groups
(glycocalyx)
Branching carbohydrates
Cell surface sticky
Distinct for each cell type
- also mark cells as “self”
Mills AP Biology 2012
Cystic Fibrosis
Problem with a membrane protein
 http://www.ygyh.org/cf/cause.htm

Or (on hard drive) cystic
fibrosis membrane protein
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
Permeability of the Plasma Membrane
 How do substances get
into and out of cells?
Pg 41-43 CliffsAP
 What determines
whether or not a
substance will enter or
exit a cell?
 Outside of cell - interstitial
fluid (intercellular fluid,
extracellular fluid)
 Inside of cell - intracellular
fluid
 Must maintain balance

each has it’s own make up
 Membrane selectively
permeable

if cell looses this property, cell
will die
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
Permeability of the Plasma Membrane
 Selectively (differentially) permeable membrane

Properties due in part to:
• Hydrophilic phosphate heads
• Hydrophobic fatty acid tails




Small, non charged, lipid soluble substances (O2, alcohol)
pass easily
Some small polar molecules (water, carbon dioxide) pass
fairly easily
Large and or charged substances and macromolecules need
help to pass
water soluble substances cannot pass easily ( amino acids,
sugars, proteins, nucleic acids)
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
Permeability of the Plasma Membrane
 Passive processes





 Active processes
Diffusion
Facilitated diffusion
Osmosis(water diffusion)
Filtration
no E needed from cell


Active transport
Bulk transport
• endocytosis
– pinocytosis
– phagocytosis
– receptor mediated endocytosis
» transcytosis
• exocytosis

E needed from cell (ATP)
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Passive Process - Diffusion



down concentration gradient
distributes until equilibrium reached
influenced by:
• distance, temperature, weigh, concentration


small particles, lipid soluble particles – can diffuse across membrane.
O2, CO2, steroids, general anesthetics (lipid soluble), water (small),
alcohol - can diffuse.
http://physioweb.med.uvm.edu/bodyfluids/membrane.htm
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Passive Process - Osmosis (diffusion of water)

water molecules move from area of greater water
concentration to area of lesser water concentration
across a selectively permeable membrane
Mills AP Biology 2012
Mills AP Biology 2012
Osmotic pressure
Isotonic, hypotonic, hypertonic
Mills AP Biology 2012
http://physioweb.med.uvm.edu/bodyfluids/osmosis.htm
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Tonicity

Hypertonic
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Tonicity

Hypotonic
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Tonicity

Isotonic

Osmosis demo site:
• http://physioweb.med.uvm.edu/bodyfluids/osmosis.htm
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Passive Process - Facilitated Diffusion

uses a carrier molecule
• protein channels and protein carriers
• Proteins are specific to the substance they transport

amino acids and sugars too large for pores and aren’t lipid
soluble
Na, K, Cl ions too large, also charged
rate depends on binding rate and concentration
down concentration gradient

glucose carrier activated by insulin



Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
Water molecule
Sodium molecule
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Facilitated Diffusion

..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology movies\Facilitated Diffusion.dir
Mills AP Biology 2012
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.2 Passive Transport Across a Membrane
 Passive Process - Filtration

molecules forced through membrane by blood pressure
• this is how tissue fluid formed
• blood pressure too high ---> tissue edema
• urine formed in kidneys

down a pressure gradient
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
 Active processes
 Passive processes





diffusion
facilitated diffusion
osmosis (water
diffusion)
filtration
no E needed from cell


active transport
bulk transport
• endocytosis
– pinocytosis
– phagocytosis
– receptor mediated
endocytosis
• exocytosis

E needed from cell (ATP)
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 Active Process - Active Transport

moves particles up concentration gradient
• from low concentration to high
• involves carrier proteins - pumps

often coupled reactions ( Na - K pump)
very important for homeostasis

useful for amino acids, sugars and ions

Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
NORMAL CONDITIONS
More K inside cell than outside
More Na outside cell than inside
Na - K Pump
Pumps ions up
concentration gradients.
2 K into cell for every
3 Na out of cell.
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
Active Transport Animation ..\..\Biology\Biology Clipart Movies
Animations Sounds\Biology movies\active transport animation.mov
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
Active Process - Bulk Transport
 Endocytosis




 Exocytosis
moves particles into cell
requires energy
particles too large for
diffusion or active
transport
three types:
• pincytosis
• phagocytosis
• receptor mediated
endocytosis



moves particles out of cell
requires energy
nerve cells use to secrete
neurotransmitter
 Transcytosis


requires energy
ferries particles across cell
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 Active Process - Endocytosis - Pinocytosis



liquid droplets, “cell drinking”
small (0.1um) vesicles
most cells use, esp. cells that function in
absorption
Mills AP Biology 2012

“Different stages of the pinocytosis, an
endocytic process, in an endothelial
cell. The vessel lumen is to the right;
the underlying connective tissue is to
the left. Notice the thin gray (electrondense) line of the basal lamina
immediately along the left border of the
cell. 1 = Vesicle open to the outside of
cell, facing the extracellular matrix; 2 =
Vesicle partially enclosed by cell
membrane; 3 = Vesicle limited by
membrane and wholly within cytoplasm
of cell. The elongate nucleus lies in the
center of the cell.”

http://www.meddean.luc.edu/lumen/M
edEd/Histo/frames/h_frame2.html
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 Active Process Endocytosis Phagocytosis




“cell “eating”
vesicles larger
WBC’s, macrophages
combine with
lysosome, get
digested
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
Phagocytosis animation ..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology movies\phagocytosis animation and tutorial.swf
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 ActiveProcess - Endocytosis - Receptor mediated
endocytosis



moves specific particles (ligands)
receptor proteins on cell membrane
insulin, cholesterol taken into cells this way
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 Active Process Exocytosis



Moves particles out
of cell
vesicles form within
cell
proteins can be
secreted this way
Mills AP Biology 2012
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.3 Active Transport Across a Membrane
 Active Process Transcytosis


Ferries particles
from one side of cell
to other
important in HIV
transmission
Mills AP Biology 2012
Passage of Molecules into and out of Cells
Uses
energy
Name
Direction
Requirement
Examples
Passive Processes
Active Processes
No
Diffusion
Osmosis
Toward lower
concentration
Concentration
gradient
Lipid soluble
molecules,
water, gasses
No
Facilitated
diffusion
Toward lower
concentration
Concentration
gradient and
carrier
Some sugars and
amino acids
Yes
Active
Transport
Toward greater Carrier
concentration
Other sugars,
amino acids and
ions
Yes
Exocytosis
Toward outside
Vesicle
Macromolecules
Yes
Endocytosis
Toward inside
Vacuole
Cells and
subcellular
material
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Many cells have modifications that are
exterior to the plasma membrane


Plants, bacteria, algae and fungi have cell walls
Animals have extracellular matrix
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Extracellular Matrix
of Animal Cells



Meshwork of insoluable
glycoproteins and
proteoglycans
Fills spaces between
cells, supports cells
Influences cell
development,
migration, shape and
function
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Desmosomes (Adhesion junctions)



“spot welds”, scattered like rivets
binds cells together and reduces tension
Found in skin, heart muscle, neck of uterus,stomach,
bladder
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Tight junctions




protein molecules in adjacent cells fuse together
Impermeable, zipperlike junction
digestive tract epithelium, nephrons
capillaries of brain
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Gap junctions



allow chemical substances to pass from one cell to
another, adjacent channel proteins join
Found in electrically excitable tissue - heart muscle,
smooth muscle
important in embryonic cells prior to circulatory system
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
Mills AP Biology 2012
Chapter 5 Membrane Structure and Function
5.4 Modifications of Cell Surfaces
 Plant Cell Walls




Freely permeable, variable in
thickness
All plants have a primary cell
wall composed cellulose, pectin
and noncellulose polysaccharides
Some plants (esp woody) have a
secondary cell wall composed of
lignin and cellulose
Plasmodesmata (only in plants)
• Narrow, membrane lined
channels that connect cells
cytoplasm
Mills AP Biology 2012
Read Connecting the
Concepts on pg 101
THE END
Mills AP Biology 2012