ch. 3 “the cellular level of organization”
TRANSCRIPT
Ch. 3 “The Cellular Level of Organization”
Class 3.5
Cells Cells Rap
http://www.youtube.com/watch?v=-zafJKbMPA8&feature=em-subs_digest-vrecs
Warm-up
1. Microvilli are apt to be found in cells that are specialized for:a. Protectionb. Absorptionc. Insulationd. Contractione. Division
B
2. All of the following are found in the nucleus except:a. Chromatinb. DNA c. Nucleolusd. Chromosomese. Centrioles
E
Warm-up
3. Describe how organelles move within the eukaryotic cell.
Organelles are found within the semi-fluid cytoplasm. The organelles are supported by a supporting network of thin protein fibers called the cytoskeleton. The cytoskeleton supports the organelles, but it can rapidly assemble and disassemble allowing the
organelles to move within the cell.
Warm-up
4. Why is a fishing net a good comparison with the plasma membrane? Why is it a poor comparison?
It’s a good comparison because, like a fishing net, the plasma membrane allows some substances to pass through and prevents other substances from going
through.
However, the plasma membrane does not use size as the primary reason for blocking substances. The plasma membrane is much more complex and uses many
different physical and chemical ways to control the flow of materials.
Review
2. Explain why the ways that the plasma membrane works is called the “fluid mosaic model.”
The different substances in the membrane move around. The movement is similar to
substances floating in water or another fluid, and the positions of the substances form a
mosaic, or pattern.
Review
1. How does the nonpolar middle of the phospholipid bilayer prevent materials from flowing freely inside and outside the cell?
Both the inside and outside of the cell contain watery environments. Water molecules are
polar and are repelled by nonpolar molecules. Therefore, the nonpolar middle of the
phospholipid bilayer repels the polar molecules and separates the material inside and outside of
the cells.
Cell Organelles
http://www.youtube.com/watch?annotation_id=annotation_219283&feature=iv&src_vid=LP7x
Ar2FDFU&v=fKEaTt9heNM
Critical Thinking Question
Sam does not consume alcohol, while his brother Sebastian regularly drinks large quantities of alcohol. If we could examine
the liver cells of each of these brothers, would we see a difference in smooth ER and peroxisomes? Explain.
Since smooth ER inactivates or detoxifies drugs, and peroxisomes also destroy harmful substances such as alcohol, we would
expect to see increased numbers of these organelles in Sebastian's liver cells.
Animation:
Copyright 2010 John Wiley & Sons, Inc. 10
You must be connected to the internet to run this animation.
• Membrane Functions
The Plasma MembraneThe structure of the membrane
– Phospholipids form a lipid bilayer - cholesterol and
glycolipids (sugar-lipids) also contribute.
– Integral proteins - extend into or through the
bilayer.
• Transmembrane proteins (most integral proteins) span
the entire lipid bilayer.
• Peripheral proteins attach to the inner or outer surface
but do not extend through the membrane.
The Plasma Membrane
The Plasma Membrane• Glycoproteins are membrane proteins with a
carbohydrate group attached that protrude into
the extracellular fluid.
• The Glycocalyx is the entire
“sugary coating” surrounding
the membrane (made up of
the carbohydrate portions
of the glycolipids and
glycoproteins).
The Plasma Membrane
The Functions of the membrane
– Some integral proteins are ion channels.
– Transporters - selectively move substances through
the membrane.
– Receptors - for cellular recognition; a ligand is a
molecule that binds with a receptor.
– Enzymes - catalyze chemical reactions
– Others act as cell-identity markers.
The Plasma MembraneExamples of different membrane proteins include
Ion channels
Carriers
Receptors
The Plasma MembraneExamples of different membrane proteins include
Enzymes
Linkers
Cell identity markers
The Plasma Membrane• Because of the distribution of lipids and the
proteins embedded in it, the membrane allows
some substances across but not others; this is
called Selective permeability – Rule of thumb: small, neutrally-charged, lipid-
soluble substances can freely pass. Water is a
special case - it is highly polar,
yet still freely permeable.
courtesy of Dr. Jim Hutchins
Membrane Permeability• For those substances that are needed by the cell
but for which the membrane is impenetrable
(impermeable), transmembrane proteins act as
channels and transporters. – They assist the entrance of certain substances that
either can’t pass at all (glucose) or for which the cell
needs to hasten passage
(ions).
Transport Processes• Passive processes involve substances moving
across the cell membranes without the input of
any energy - they are said to move “with” or
“down” their concentration gradient ([gradient] ,
where [ ] indicates “concentration”).
• Active processes involve the use of energy,
primarily from the breakdown of ATP, to move a
substance against its [gradient].
Transport Processes• Passive processes
– Diffusion of solutes
– Diffusion of water (called osmosis)
– Facilitated diffusion (requires a specific channel or a
carrier molecule, but no energy is used)
• Active processes – Various types of transporters are used, and energy is
required.
Passive Transport Processes• Diffusion is the passive spread of particles through random
motion, from areas of high concentration to areas of low
concentration.
– It is affected by the amount of
substance and the steepness of
the concentration gradient.
– Temperature
– Surface area
– Diffusion distance
Passive Transport Processes• Channel-Mediated Facilitated Diffusion
• Carrier-Mediated Facilitated Diffusion
Passive Transport Processes• An example of Channel-Mediated Facilitated Diffusion
is the passage of potassium ions through a gated K+
Channel
• An example of Carrier-Mediated Facilitated Diffusion is
the passage of glucose across the cell membrane.
Passive Transport Processes
• Osmosis is the net movement of water through a
selectively permeable membrane from an area of high
water concentration to one of lower water concentration.
• Water can pass through plasma membrane in 2 ways:
– through lipid bilayer by simple diffusion
– through aquaporins (integral membrane proteins)
Passive Transport Processes
In the third tube, the force generated by the movement of
water from the left to the right side is called osmotic
pressure.
Passive Transport ProcessesIn the body, tonicity refers to the concentration of salt
solutions in the blood and elsewhere. Since semipermeable
membranes separate these fluid compartments, osmosis of
water is free to occur between
any fluid space and another.
The effect of changing tonicity
is demonstrated in this graphic,
as water moves in and out
of red blood cells.
Active Transport ProcessesSolutes can also be actively transported across a plasma
membrane against their concentration gradient ([low] to
[high]) by using energy (usually in the form of ATP).
The sodium-potassium pump is found in all cells.
Secondary Active Transport Mechanisms
• Antiporters carry two substances across the membrane in opposite directions.
• Symporters carry two substances across the membrane in the same direction.
Transport in Vesicles
Vesicle - a small spherical sac formed by budding off from a
membrane
Endocytosis - materials move into a cell in a vesicle formed from the
plasma membrane
three types: receptor-mediated endocytosis
phagocytosis
bulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane, releasing their
contents into the extracellular fluid
Transcytosis - a combination of endocytosis and exocytosis
Receptor-Mediated
Endocytosis
Phagocytosis
Bulk-phase Endocytosis
Copyright 2010 John Wiley & Sons, Inc. 33
Animation:
You must be connected to the internet to run this animation.
• Transport Across the Plasma Membrane
Transport of Large Particles
http://youtube.com/watch?v=4gLtk8Yc1Zc
http://youtube.com/watch?v=HndmASfmI8Y
http://youtube.com/watch?v=U9pvm_4-bHg
Tonicity on Cells
Tonicity
RBCs
Cell Communication
http://learn.genetics.utah.edu/content/begin/cells/cellcom/
Class Work
Complete WS QC 62
http://www.classzone.com/cz/books/bio_07/chapter_home.htm?cin=3
Review
1. Endocytosis and exocytosis
2. Diffusion, osmosis, and facilitated diffusion
3. When a cell is in dynamic equilibrium with its environment, there is continuous movement across the plasma membrane with no overall change in concentration.
Class Work
3. When the concentration of the solutes outside the cell is the same as the concentration of solutes inside the cell, the cell solution is isotonic relative to its environment.
4. After 24 h, the egg will appear shriveled.
The salt water solution is hypertonic to the egg’s interior environment.
Class Work
4. The net movement of water by osmosis is out of the cell because the concentration of the solute (salt) is higher outside the cell than inside the cell.
5. Diffusion, the random movement of a substance down its concentration gradient, uses no energy.
Active transport, the movement of particles against their concentration graident, requires energy.
Interactive Review
Getting through a cell membrane
http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit2/bio_ch
03_0093_ab_cellmem.html
Class Work
Start working on the WSs
“Cell Physiology” 32-33
HW
Complete the WSs on
“Cell Physiology” 32-33