Download BUBBLES!!

1
BUBBLES!!
• MUST wear goggles at ALL times!
• NO taking straw out of the dish!
• NO drinking/ inhaling bubble fluid
• THIS IS an EXPERIMENT!!!
• You can have fun, but ALL usual lab safety RULES
APPLY!
2
Questions to think about:
• Can anything pass through the bubble without breaking it?
• Can one bubble divide to become several bubbles?
• Can several bubbles merge to form one- how?
• Can a drop of water pass through a bubble without popping
it?
• Does it look like the surface of the bubble moves? How can
you tell?
3
soapy “membranes”
1. How does a bubble model the fluid nature of a
membrane?
2. Can anything pass through the membrane without
rupturing it? If so what; if no, what did you try?
3. Can one bubble divide to become several bubbles?
4. Can several bubbles merge to become one bubble?
5. Can a drop of water pass through a bubble without
popping the bubble?
6. A bubble is a lipid monolayer – draw a diagram of a
segment of a bubble using this symbol for a lipid
molecule:
4
Bubble Summary!
• A bubble is a lipid monolayer!!
• What is the structure of the
membranes of our cells?
• How does a bubble model the fluid
nature of a cell membrane?
5
L3 Biology
Chapter 4
CELL MEMBRANES
and
TRANSPORT
6
The Cell
7
Learning Objectives
1. Describe the fluid mosaic model of membrane
structure and explain the underlying reasons
for this structure.
2. Outline the roles of phospholipids, cholesterol,
glycolipids, proteins and glycoproteins in
membranes.
3. Outline the roles of the plasma membrane,
and the roles of membranes within cells.
8
Plasma Membrane (aka Cell Membrane)
• All living things are surrounded by a
membrane.
• It controls exchange of materials (like
nutrients, waste) between cells and the
environment.
• Other important functions include:
• communicate to other cells
• respond to hormones.
• To understand FUNCTION in BIOLOGY,
you must first study STRUCTURE!
9
Cell Membranes from Opposing Neurons
(TEM x436,740).
Nerve cell
Cell membrane {
Gap between cells
}
cell membrane
Is 7nm wide
Nerve cell
10
Remember our discussion of
our favorite POLAR Molecule?
• WATER!
• Due to unequal
distribution of electrons
(electronegativity of
Oxygen), one end of
molecule is partially
positive while other end
is partially negative. The
molecule has ‘poles’
• WATER is the solvent
inside and outside every
cell.
Phospholipids are the Primary Building
block of the membrane:
• HYDROPHILIC heads
(water loving)
-Attracted to the water
• called POLAR head
• HYDROPHOBIC tails
(water fearing)
-Not attracted to the water
• called NON-POLAR Tails.
PHOSPHOLIPIDs are AMPHIPATHIC
molecules with both POLAR AND
NONPOLAR regions
• Which
atoms/regions are
Polar?
• Which
atoms/regions are
nonpolar?
13
How does the plasma membrane form?
Why does the
phospholipid have a
Hydrophilic Head?
One end of the
phospholipid has a
phosphate group and
several oxygens atoms
that are not shared
equally. This end of the
molecule has a charge
and is attracted to water.
It is POLAR!
3D model of a
Phospholipid
14
How does the plasma membrane form?
Why does the
phospholipid have
Hydrophobic tails?
Two long chains (tails) at
bottom of each phospholipid
are made up of carbon and
hydrogen. Both these
elements share their
electrons evenly, so there is
no charge (NON POLAR).
This means they are not
attracted to water & water
molecules tend to push
them out of the way as they
are attracted to each other.
These molecules do NOT
dissolve in water.
3D model of a
Phospholipid
15
How does the Plasma Membrane form?
Phospholipid tails
interact AWAY from
the water, and the
heads associate with
the water of the
solution and
cytoplasm
Lipid BILAYER, the
MAIN structure of
the Plasma
Membrane
-The result is 2 layers of
phospholipids with
hydrophobic tails
protected inside the
membrane by the
hydrophilic heads.
16
17
Properties of Cell Membranes
•
Basic structure is Phospholipid Bilayer.
• Phospholipids move laterally within the
membrane.
• Composition of Phospholipid fatty acid
tails can be Saturated (straight) or
Unsaturated (bent) depending on the
organism & environmental conditions (ie
temperature)
Phospholipids move within the membrane:
Lateral movement occurs
107 times per second.
Flip-flopping across the membrane
is rare ( once per month).
Figure 7.8
Fluid
Viscous
Unsaturated hydrocarbon
tails
Saturated hydrocarbon tails
(a) Unsaturated versus saturated hydrocarbon tails
(b) Cholesterol within the animal
cell membrane
Cholesterol
20
Animation of membrane formation
• http://telstar.ote.cmu.edu/biology/MembranePage/index2.
html
21
Why is the Plasma Membrane necessary?
• Provide containment for the cell structures
• Phospholipids are PRIMARY component
that forms the membrane
• Phospholipids protect the cell from
environmental hazards by acting as a
barrier to most water soluble substances
• BUT, Phospholipids are only PART of the
story of the plasma membrane…………
22
Diagram representing the cell membrane
Remember the membrane is 7nm wide
Current Model of the Cell Membrane
Fibers of extracellular matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Cholesterol
Microfilaments
of cytoskeleton
Peripheral
proteins
Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE
24
Fluid mosaic model!!
Cell membranes also contain cholesterol and
proteins within the phospholipid bilayer.
This ‘model’ for the structure of the membrane is
called the: FLUID MOSAIC MODEL
25
Why call it a Fluid Mosaic Model?
FLUID- because phospholipids and
proteins move around freely within the
layer, like it’s a liquid.
MOSAIC- because of the pattern
produced by scattered protein
molecules in the membrane when
viewed from above.
26
Animation of membrane formation
• http://telstar.ote.cmu.edu/biology/MembranePage/index2.
html
27
Remember Cholesterol (Lipids)
28
What is the function of cholesterol?
• Cholesterol regulates the fluidity of the
membrane, gives mechanical stability
and help to prevent ions from passing
through the membrane.
29
Cholesterol between the phospholipid
tails
30
Where are the proteins?
• Integral membrane proteins: Integrated in the
membrane with access to both cytoplasm and
outside cell
• Peripheral membrane proteins: Facing only the
cytoplasm OR outside the cell as part of one side of
the membrane
• Proteins can float or be fixed:
- Like phospholipids, many of them have
hydrophobic and hydrophilic regions
Proteins determine most of the
membrane’s specific functions
31
Individual Proteins serve different functions:
• 1. Proteins act as channels for substances to
move in or out of cell.
• 2. Proteins act Pumps to move molecules
across the membrane.
• 3. Proteins act as membrane enzymes in
chemical reactions.
• 4. Proteins help to stabilize the membrane
32
Some proteins have sugars attached
• These are called Glycoproteins
• What is their function?
• Glycoproteins act as markers for
cell communication, antigens for
other cells to recognise them, or
receptors that hormones & other
proteins can bind.
33
Membrane with protein
• http://telstar.ote.cmu.edu/biology/MembranePage/index2.
html
34
Summary
• Cell membranes have a basic structure
composed of a PHOSPHOLIPID BILAYER.
• Phospholipds have HYDROPHOBIC (non-polar)
tails and HYDROPHILIC (polar) heads.
• The best model of the cell membrane is called
the FLUID MOSAIC MODEL
• The average thickness of the membrane is 7nm.
35
Summary, cont.
• The fatty acid tails of phospholipids can be
SATURATED (straight) or UNSATURATED (bent)
• Phospholipids form the bilayer, act as barrier to
most water soluble substances
• Cholesterol regulates the fluidity of the membrane,
gives mechanical stability and help to prevent ions
from passing through the membrane.
36
Summary, cont.
• Proteins determine specific properties of the
membrane (Key to Cell differentiation!)
• Proteins are integrated or peripheral:
• float or fixed in the membrane
• also have hydrophobic and hydrophilic portions.
• Proteins function in:
• Transport- channels for substances to move in or out
of cell
• Enzymes
• Pumps
• Membrane stabilizers
37
Summary, cont.
• Some proteins have carbohydrates attached
to them to form GLYCOPROTEINS .
• Glycoproteins act as receptor molecules (eg
for hormones and neurotransmitters), as
antigens for cell recognition, as markers for
cell communication.
38
Visualizing structure and function
• http://multimedia.mcb.harvard.edu/anim_innerlife.html
39
Wrap-up!
How is the cell’s membrane
structured (chemically) to
ensure efficiency, survival, &
differentiation?
(Hint-Is it ever the same??)
40
Preview of coming attractions!
• Membrane structure allows for the
movement of substances into and out
of the cell
• Living organisms demonstrate many
adaptations to their membranes
allowing them to survive in their
environments!
41
Movement of selected molecules across
the cell membrane
42
• Moving amoeba
• Contractile vacuole
43
Functions of Cell Membrane Components:
Use the following headings to produce a table summarizing the
functions of the different types of molecules found in the cell
membrane. Use your notes to find the information.
Component
1.
Phospholipids
2.
Cholesterol
3.
Proteins
4.
Glycoproteins
Structure
Functions