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

Active & Passive Transport

Transport

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