This document summarizes the history and components of the plasma membrane model. It describes early models such as the phospholipid bilayer model proposed by Gorter and Grendel in 1925. The Sandwich Model of Danielli and Davson in 1935 proposed proteins were also part of the membrane. In 1972, Singer and Nicolson proposed the Fluid Mosaic Model, which is depicted accurately in electron micrographs as having a phospholipid bilayer with integral proteins. The document then discusses the key components and functions of the plasma membrane, including transport mechanisms like diffusion, facilitated diffusion, and active transport.

2.  1665: Robert Hooke
 1895: Charles Overton - composed of lipids
 1900-1920’s: must be a phospholipid
 1925: E. Gorter and G. Grendel - phospholipid bilayer
 1935: J.R. Danielli and H. Davson – proteins also part,
proposed the Sandwich Model
 1950’s: J.D. Robertson – proposed the Unit Membrane
Model
 1972: S.J. Singer and G.L. Nicolson – proposed Fluid
Mosaic Model

3.  Gorter + Grendel
Red Blood Cells analyzed
Enough for Phospholipid bilayer
Polar heads face out and
Nonpolar tails face in
Does not explain why some
nonlipids are permeable

4. Sandwich Model
(Danielli + Davson)
2 layers of globular proteins with phospholipid
inside to make a layer and then join 2 layers
together to make a channel for molecules to
pass
Unit Membrane Model
(Robertson)
Outer layer of protein with phospholipid bilayer
inside, believed all cells same composition,
does not explain how some molecules pass
through or the use of proteins with nonpolar
parts, used transmission electron microscopy
Fluid Mosaic Model
(Singer + Nicolson)
Phospholipid bilayer with proteins partially or
fully imbedded, electron micrographs of freeze-
fractured membrane

5. 1) Rapidly freeze specimen
2) Use special knife to cut membrane in half
3) Apply a carbon + platinum coating to the surface
4) Use scanning electron microscope to see the surface
According to the electron micrograph which membrane model is correct?
Why?
Fluid-Mosaic Model

6.  Fluid – the plasma membrane is the consistency of olive oil at body
temperature, due to unsaturated phospholipids. (cells differ in the
amount of unsaturated to saturated fatty acid tails)
 Most of the lipids and some proteins drift laterally on either side.
Phospholipids do not switch from one layer to the next.
 Cholesterol affects fluidity: at body temperature it lessens fluidity by
restraining the movement of phospholipids, at colder temperatures it
adds fluidity by not allowing phospholipids to pack close together.
 Mosaic – membrane proteins form a collage that differs on either
side of the membrane and from cell to cell (greater than 50 types of
proteins), proteins span the membrane with hydrophilic portions
facing out and hydrophobic portions facing in. Provides the functions
of the membrane

8.  Phospholipid bilayer
 Phospholipid
 Hydrophilic head
 Hydrophobic tails
 Cholesterol
 Proteins
 Transmembrane/
Intrinsic/Integral
 Peripheral/Extrinsic
 Cytoskeletal filaments
 Carbohydrate chain
 Glycoproteins
 Glycolipids

9. 1) Transport Proteins
2) Receptor Proteins
3) Enzymatic Proteins
4) Cell Recognition Proteins
5) Attachment Proteins
6) Intercellular Junction
Proteins

10. Channel Proteins –
channel for lipid
insoluble molecules
and ions to pass freely
through
Carrier Proteins – bind
to a substance and
carry it across
membrane, change
shape in process

11. – Bind to chemical
messengers (Ex.
hormones) which sends
a message into the cell
causing cellular
reaction

12. – Carry out enzymatic
reactions right at the
membrane when a
substrate binds to the
active site

13. – Glycoproteins (and
glycolipids) on
extracellular surface
serve as ID tags (which
species, type of cell,
individual).
Carbohydrates are
short branched chains
of less than 15 sugars

14. - Attach to cytoskeleton (to
maintain cell shape and
stabilize proteins) and/or the
extracellular matrix (integrins
connect to both).
- Extracellular Matrix – protein
fibers and carbohydrates
secreted by cells and fills the
spaces between cells and
supports cells in a tissue.
- Extracellular matrix can
influence activity inside the cell
and coordinate the behavior of
all the cells in a tissue.

15. – Bind cells together
Tight junctions
Gap junctions

16.  Tight Junctions
 Desmosomes
 Gap Junctions

17.  Transmembrane Proteins of opposite cells attach in a
tight zipper-like fashion
 No leakage
 Ex. Intestine, Kidneys, Epithelium of skin

18.  Cytoplasmic plaques of two cells bind with the aid of
intermediate filaments of keratin
 Allows for stretching
 Ex. Stomach, Bladder, Heart

19.  Channel proteins of opposite cells join
together providing channels for ions, sugars,
amino acids, and other small molecules to
pass.
 Allows communication between cells.
 Ex. Heart muscle, animal embryos

20. • Materials must move
in and out of the cell
through the plasma
membrane.
• Some materials move
between the
phospholipids.
• Some materials move
through the proteins.

21. • Molecules move across the plasma membrane
by:

22. 1) Diffusion
2) Facilitated Diffusion
3) Osmosis
ATP energy isATP energy is notnot
needed to move theneeded to move the
molecules through.molecules through.

23. • Molecules can move directly through
the phospholipids of the plasma
membrane
This is called …

24. •Diffusion is the net
movement of molecules
from a high concentration
to a low concentration
until equally distributed.
•Diffusion rate is related
to temperature, pressure,
state of matter, size of
concentration gradient,
and surface area of
membrane.
http://www.biologycorner.com/resources/diffusion-animated.gif

25. •Gases (oxygen, carbon
dioxide)
•Water molecules (rate
slow due to polarity)
•Lipids (steroid hormones)
•Lipid soluble molecules
(hydrocarbons, alcohols,
some vitamins)
•Small noncharged
molecules (NH3)

26. • Cell respiration
• Alveoli of lungs
• Capillaries
• Red Blood Cells
• Medications: time-
release capsules

27. • Molecules can move through
the plasma membrane with the
aid of transport proteins
This is called …

28. • Facilitated diffusion is
the net movement of
molecules from a high
concentration to a
low concentration
with the aid of
channel or carrier
proteins.

29. • Ions
(Na+
, K+
, Cl-
)
• Sugars (Glucose)
• Amino Acids
• Small water soluble
molecules
• Water (faster rate)

30. • Channel and Carrier proteins are specific:
• Channel Proteins allow ions, small solutes, and water to
pass
• Carrier Proteins move glucose and amino acids
• Facilitated diffusion is rate limited, by the number of
proteins channels/carriers present in the membrane.

31. • Cells obtain food for
cell respiration
• Neurons communicate
• Small intestine cells
transport food to
bloodstream
• Muscle cells contract

32. • Water Molecules can move directly
through the phospholipids of the
plasma membrane
This is called …

33. • Osmosis is the diffusion of water through a
semipermeable membrane. Water molecules bound
to solutes cannot pass due to size, only unbound
molecules. Free water molecules collide, bump into
the membrane, and pass through.

34. • What will happen in the
U-tube if water freely
moves through the
membrane but glucose
can not pass?
• Water moves from side with
high concentration of water
to side with lower
concentration of water.
Movement stops when
osmotic pressure equals
hydrostatic pressure.

35. • Cells remove water
produced by cell
respiration.
• Large intestine cells
transport water to
bloodstream
• Kidney cells form
urine

36.  Tonicity refers to the total solute
concentration of the solution outside the
cell.
 What are the three types of tonicity?
1) Isotonic
2) Hypotonic
3) Hypertonic

37.  Solutions that have the same concentration of
solutes as the suspended cell.
 What will happen to a cell placed in an Isotonic
solution?
 The cell will have no net movement of water and
will stay the same size.
 Ex. Blood plasma has high concentration of
albumin molecules to make it isotonic to tissues.

38.  Solutions that have a lower solute concentration
than the suspended cell.
 What will happen to a cell placed in a Hypotonic
solution?
 The cell will gain water and swell.
 If the cell bursts, then we call this lysis. (Red
blood cells = hemolysis)
 In plant cells with rigid cell walls, this creates
turgor pressure.

39.  Solutions that have a higher solute concentration
than a suspended cell.
 What will happen to a cell placed in a Hypertonic
solution?
 The cell will lose water and shrink. (Red blood
cells = crenation)
 In plant cells, the central vacuole will shrink and
the plasma membrane will pull away from the cell
wall causing the cytoplasm to shrink called
plasmolysis.

40. • Diffusion – O2 moves in and CO2 moves out during
cell respiration
• Facilitated Diffusion – glucose and amino acids
enter cell for cell respiration
• Osmosis – cell removal or addition of water

41.  What will happen to a red blood cell in a hypertonic
solution?
 What will happen to a red blood cell in an isotonic
solution?
 What will happen to a red blood cell in a hypotonic
solution?

42. 1) Active Transport
1) Primary
2) Secondary (no ATP)
2) Bulk Transport
1) Exocytosis
2) Endocytosis
1) Phagocytosis
2) Pinocytosis
3) Receptor-Mediated
endocytosis ATP energy isATP energy is
requiredrequired to move theto move the
molecules through.molecules through.

43.  Molecules move from areas of low concentration to
areas of high concentration with the aid of ATP
energy.
 Requires protein carriers called Pumps.

44.  Bring in essential molecules: ions,
amino acids, glucose, nucleotides
 Rid cell of unwanted molecules (Ex.
sodium from urine in kidneys)
 Maintain internal conditions different
from the environment
 Regulate the volume of cells by
controlling osmotic potential
 Control cellular pH
 Re-establish concentration
gradients to run facilitated diffusion.
(Ex. Sodium-Potassium pump and
Proton pumps)

45.  3 Sodium ions move out of
the cell and then 2
Potassium ions move into
the cell.
 Driven by the splitting of
ATP to provide energy and
conformational change to
proteins by adding and then
taking away a phosphate
group.
 Used to establish an
electrochemical gradient
across neuron cell
membranes. http://www.biologie.uni-hamburg.de/b-online/library/biology107/bi107vc/fa99/terry/images/ATPpumA.gif

46.  Counter Transport – the transport
of two substances at the same
time in opposite directions,
without ATP. Protein carriers are
called Antiports.
 Co-transport – the transport of
two substances at the same time in
the same direction, without ATP.
Protein carriers are called
Symports.
 Gated Channels – receptors
combined with channel proteins.
When a chemical messenger binds
to a receptor, a gate opens to
allow ions to flow through the
channel.

47.  Movement of large
molecules bound in
vesicles out of the cell
with the aid of ATP
energy. Vesicle fuses
with the plasma
membrane to eject
macromolecules.
 Ex. Proteins,
polysaccharides,
polynucleotides, whole
cells, hormones, mucus,
neurotransmitters, waste

48.  Movement of large molecules into the cell by
engulfing them in vesicles, using ATP energy.
 Three types of Endocytosis:
 Phagocytosis
 Pinocytosis
 Receptor-mediated endocytosis

49.  “Cellular Eating” – engulfing large molecules, whole
cells, bacteria
 Ex. Macrophages ingesting bacteria or worn out red
blood cells.
 Ex. Unicellular organisms engulfing food particles.

50.  “Cellular Drinking” – engulfing liquids and small
molecules dissolved in liquids; unspecific what enters.
 Ex. Intestinal cells, Kidney cells, Plant root cells

51.  Movement of very specific
molecules into the cell with the
use of vesicles coated with the
protein clathrin.
 Coated pits are specific
locations coated with clathrin
and receptors. When specific
molecules (ligands) bind to the
receptors, then this stimulates
the molecules to be engulfed
into a coated vesicle.
 Ex. Uptake of cholesterol (LDL)
by animal cells

52.  What is phagocytosis?
 What is pinocytosis?
 What is receptor-mediated
endocytosis?