Download Cell Membrane2013

Main Function: Isolate the cell’s contents
from the external environment and regulate
what moves in and out of the cell.
1972 Singer and Nicolson
developed the fluid mosaic model
“Fluid portion”- phospholipid bilayer
“Mosaic portion”- membrane proteins
Fluid Mosaic Model
Structure of the Plasma membrane
A. Phosopholipid bilayer- isolates the cell
interior from the external environment.
Structure: 2 layers of phospholipids
hydrophilic heads form the outer
borders of the bilayer and the
hydrophobic “tails” form the inner
portion of the bilayer.
Phospholipids make up Cell Membranes
B. Membrane Proteins -responsible for
moving substances across the membrane and
communicating with other cells
•Transport Proteins
–Form Channels or act as Carriers
Ex. Glucose enters our RBCs through a
transport protein that acts as a carrier.
Glucose
Outside Cell
Inside Cell
B. Membrane Proteins
•Receptor Proteins
when a specific molecule binds to them
it triggers a specific cellular response
Ex. secretion of hormones and initiation
of cell division
Pancreas
Pancreas cells
secreting hormones
•Recognition Proteins (many are glycoproteins)
serve as cell ID tags or cell surface
attachment sites
Ex. our WBCs recognize certain bacteria
as invaders from the other cells of our
body that belong there
•Recognition Proteins
Ex. WBCs recognize invaders
Fluid Mosaic Model
C. Cholesterol
makes the bilayer stonger, more flexible,
and less permeable to water-soluble
substances such as ions and simple
sugars.
Fluid Mosaic Model
Does the Plasma Membrane allow
most dissolved substances to pass
through? No!
The plasma membrane is selectively
permeable.
Only certain substances are allowed to
pass through the membrane freely
Ex. Water, gases (CO2,and O2), and
some small dissolved substances
Glucose
Plasma Membrane
Glucose
Water
Glucose
How are substances brought across
the membrane?
A. Passive Transport -does not require ATP
Ex.
•Simple Diffusion
•Osmosis
•Facilitated Diffusion
1. Simple diffusion is the movement of
molecules from an area of high concentration
to an area of low concentration
Requirements for simple diffusion
Concentration gradient - difference in
concentration of a substance b/w 2 areas
Brownian motion - random motion of
molecules
What factors might affect the rate of
diffusion?
• Temperature
• Concentration gradient
• Size of molecules
What is Osmosis and how is it different
than simple diffusion?
2. Osmosis is the movement of water
molecules from an area of high concentration
to an area of low concentration through a
selectively permeable membrane
Osmosis is affected by temperature and a
change in the concentration gradient
also.
Parts of a solution
Solute- dissolved substances
Solvent- a liquid in which another
substance may be dissolved
Ex. Sugar water
(Hummingbird food)
* Solute = sugar
* Solvent = water
Cellular Environment
Isotonic –equal concentrations of solute outside and
inside the cell (Result: Dynamic equilibrium permeable molecules move in and out of the cell but
result in no net change)
50%
Sugar
Plasma
membrane
50%
Sugar
Cellular Environment
Hypertonic –a higher concentration of solute
outside the cell than inside the cell
Result:
water moves out of the cell; cell shrinks or shrivels
50%
Sugar
50%
Water
100%
water
Plasma
membrane
Cellular Environment
Marine fish must deal with saltwater environment
Cartilaginous fish reabsorb urea
Bony fish excrete salt
Cellular Environment
Hypotonic –a lower concentration of solute outside
the cell than inside the cell
Result: water moves into the cell; cell expands
Some cases cell may burst (cell lysis)
100%
Water
Plasma
membrane
50%
sugar
Cellular Environment
Response of plant cell
Hypotonic Environment
Hypertonic Environment
Plants vs. Animal Cells
• Animal cells are better in an isotonic
environment.
• Plant cells in fleshy parts of plants are better in
a hypotonic environment. These cells need the
influx of water to remain turgid to support nonwoody parts of the plant.
How are substances brought across
the membrane?
A. Passive Transport -does not require ATP
•Simple Diffusion
•Osmosis
•Facilitated Diffusion
B. Active Transport- requires ATP
•Ion Pumps
C. Endocytosis - requires a vesicle
•Phagocytosis
•Pinocytosis
•Receptor-mediated Endocytosis
D. Exocytosis - requires a vesicle
A. Passive Transport -does not require ATP
Ex.
•Simple Diffusion
•Osmosis
•Facilitated Diffusion- molecules move
through the membrane with the aid of a
transport protein from high to low
concentration.
Ex. Glucose enters our RBCs through a
transport protein that acts as a carrier.
Facilitated Diffusion –Carrier Protein
B. Active Transport: Ion Pumps
Specialized carrier proteins require energy (ATP) to
move specific particles and molecules against their
concentration gradient.
Active transport sets up a
concentration/electrical
gradient
Na+
Na+
Na+ Na+
Na+
Na+ Na+
Na+ rushes back into the
cell causing an electrical
impulse.
Na+
Na+
Na+
Na+
Na+
-Na+
Na+
-Na+
-Na+
Na+
C. Endocytosis- requires a vesicle (3types)
•Pinocytosis- “cell drinking” the cell
engulfs liquid by formation of a vesicle.
•Phagocytosis- “cell eating” the cell
engulfs large particles (including whole
microorganisms) by surrounding the
particle with extensions of the cytoplasm
(pseudopodia).
Video
Ex. Amoeba
and WBCs
engulf large
particles.
•Receptor-mediated endocytosis- the cell
takes up specific substances that bind to
a receptor protein in the membrane.
Video
Ex. Cells take
up LDL
complexes to
obtain
cholesterol for
the membrane
D. Exocytosis
Involved in the elimination of waste or
the secretion of a substance.
So, how does a cell take in nutrients and
eliminates wastes?
membrane or surface
Through its plasma
_________________________
Why are cells so small?
Maybe we could answer this question
better with an analogy.
Which canned drink
would get colder faster?
40 0z.
10 0z.
A cell takes in nutrients and eliminates
wastes through its surface like a canned
drink exchanges heat with the
environment.
A cell needs to have more surface area than
volume (high SA/V ratio) in order to obtain
nutrients and eliminate waste efficiently
with the environment.
Specialized cell surfaces
How are our cells held together to form tissues?
- Desmosomes
Specialized cell surfaces
How is it that our intestines or bladder doesn’t leak?
- Tight junctions
Specialized cell surfaces
How do adjacent cells communicate with one another?
- Gap junctions and Plasmodesmata (plants)