Cells and Organelles
January 21, 2004

Readings: Text Chapter 4, p 50-65, 70-72, Ch 19 p. 300-301. GREAT figures in the text!
CD-Rom (optional): Chapter 4 - great animations.
Highly recommended: Take the quiz - you can keep answering the questions until you get them right...a stress-freeway to check your knowledge!!

Don't Forget: Warm Up 1 due is due Wednesday, January 21nd at 9:30, AND Good For 1 is due Friday, January 23rd by noon. Don't wait till the last minute to submit!

I . The cell is the basic unit of life:

As we have already discussed....The discovery of the cell was made possible by the invention of the microscope (1600s) As microscopes improved, scientists observed that all living organisms were made up of cells, leading eventually to the development of the Cell Theory

What defines a cell? A cell

1. Is the lowest level of structure capable of performing all 5 activities of life
2. Is bounded by a plasma membrane "envelope"
3. Contains cytoplasm, DNA, enzymes, organelles

II. How big are cells?

Our eyes can see things as small as ~0.1 mm. There are a few cells that can be seen without the aid of a microscope, but, a general rule is that most eukaryotic cells are ~ 0.05 mm (50 microns) to 0.005 mm (5 microns) long, bacterial cells are much smaller (~ 3 microns or less). Viruses are even smaller (nano-meters!)

Check out How Big are They?

III. What do cells do?

Cells perform all of the 5 activities of life! They also eat, swim, reproduce, beat, protect your body, kill other cells, infect your body, etc...

IV. What types of cells are there? Prokaryotic vs. Eukaryotic.

1. Features of Prokaryotic ("pre-nucleus") cells: Few internal parts: bacteria and blue-green algae (Kingdoms Archaebacteria and Eubacteria)

1. Very small (typically less that 5 microns)
2. Lack internal compartments and organelles
3. Lack a nucleus - DNA is not separated from the cytoplasm
4. One circular chromosome
5. Tough external walls

2. Features of Eukaryotic ('true-nucleus") cells: (Kingdoms: protists, plants, fungi and animals) Numerous internal structures. See p 57 for details and labels to all structures.

1. Subdivided by internal membranes into different compartments
2. DNA is enclosed by a membrane-bound nucleus
3. DNA organized into chromosomes
4. Cytoplasm surrounds the nucleus and organelles
5. Plant cells, yeast cells, and protists have a tough cell wall, animal cells do not.

A typical animal cell
A typical plant cell

V. Cellular Compartments and Organelles: What is inside (and surrounds the outside) of cells?

1. Plasma Membrane: All cells are surrounded by a plasma membrane! The plasma membrane is a phospholipid bilayer studded with proteins. Lipids have a hydrophilic head and a hydrophobic tails that, in water, spontaneously form into a bilayer.

• Function of the lipids: Keeps the inside in and outside out! Materials enter and exit the membrane through diffusion, osmosis, or membrane transport proteins or recognition proteins.
• This picture (left) just shows the lipids, but that's only part of the story...A cutaway view of the plasma membrane illustrating the Fluid-mosaic model of plasma membrane structure is shown on the right:

2. Cytoplasm semifluid "soup" of proteins, enzymes, dissolved salts, sugars. All the organelles and the nucleus float in the cytoplasm...

3. Nucleus contains chromatin: a combination of DNA (genes) and associated proteins, floating in a liquid nucleoplasm, surrounded by nuclear envelope (another lipid bilayer). The nucleolus is an area where synthesis of ribosomal genes rRNA) takes place

4. The EndoMembrane (or CytoMembrane) System (see figure above):

• A. Ribosomes small structures in the cytoplasm made of RNA and protein that assemble protein chains. Can be "free" in the cytoplasm or bound to the ER
• B. Rough Endoplasmic Reticulum (rough ER) sorts and modifies protein chains delivered by bound ribosomes
• C. Smooth Endoplasmic Reticulum (smooth ER) lacks ribosomes. Site of lipid (membrane) synthesis
• D. Golgi Body connects with the smooth ER, completes lipid synthesis and sorts proteins to their correct destination in small vesicles
• E. Vesicles transport proteins and lipids to the cell surface; bring proteins and lipids into cell from the cell surface, digest compounds (in lysosomes)
• F. Lysosomes: intracellular digestion - contain a potent brew of digestive enzymes
• G. Peroxisomes: break down fatty acids, amino acids, and alcohol

5. Mitochondria: A double membrane-bound organelle that makes ATP for cellular energy (not just one lipid bilayer, but TWO). Contains its own genome!

6. Chloroplast: (Plants only) A double membrane-bound organelle that makes sugar from sunlight and CO2 during photosynthesis (not just one lipid bilayer, but TWO). Contains its own genome!

7. Cytoskeleton (microtubles and microfilaments) provide cell shape, internal "skeleton" and cell movement.

8. Centioles made of microtubules, may assist in cell division.

9. Cell Wall (Plant, Protists, and Fungi): A tough, rigid (but somewhat elastic) structure made up of cellulose (plants) chitin (fungi) a variety of proteins (protists).

VI. Way cool cells: The "typical" cell is usually shown as a ball, or a box, but REAL cells come in all kinds of shapes and sizes! However, inside each of these cells is all the same components as the typical cells above (exception: mature blood cells - which live for only a short time - lose their nucleus because they are essentially finished with any new protein synthesis, but the cells below have generally all of the components above.)

Human Nerve cell	Human Red Blood Cells
Human sperm cell	Pseudomonas, a bacteium associated with lung infections [Image]

Striated skeletal muscle cell [Image]	Endothelial cell, stained for cytoskeletal Actin [Image]
Closterium, a single-celled protist [Image]	Human white blood cell attacking bacteria [Image ]
Human nerve cells [Image]	Human Heart Cells [Image]
Anabaena, a photosynthetic bacteria [Image]	Diatoms, 1-celled protists with glass shells (Starr)

For a look at some more "way cool" cells, check out the Cells Alive webpage.

Next: A closer look at all the building blocks of the cell...lipids, proteins, carbohydrates, etc...