Notes

There are two main types or categories of cells: prokaryotic cells and eukaryotic cells. Both of these types of cells have several things in common. All cells are surrounded by a plasma membrane, which is made of a double layer (a bilayer) of phospholipids. Within this membrane, is the cytoplasm which is composed of the fluid and organelles of the cell.

In this lab you will look at the eukaryotic cells of plants and animals. Eukaryotic cells are distinguished from the more primitive prokaryotic cells by the presence of 1) cytoplasmic membranous organelles, 2) a nuclear membrane (i.e. a true nucleus), and 3) chromosomal proteins. In this lab we will focus primarily on organelles, their functions within the cell and how they differ between plant and animal cells.

Think of the cell as a microscopic city. Like a real city it requires many services to keep it clean and running smoothly. Think of some of the services a real city needs: traffic control, waste disposal, and authority figure just to name a few. Like our imagined city a cell needs the same services. Organelles are the “workers” that provide these services. The following is a list describing the various functions of some common organelles.

The NUCLEUS (“mayor of city hall”)
Branching off from and continuous with the outer membrane of the nuclear envelope is a double walled space which zigzags through the cytoplasm. This is the endoplasmic reticulum (ER for short) and its central space or lumen is a continuation of the lumen between the membranes of the nuclear envelope. There are two kinds of ER: smooth ER and rough ER. Typically ER closer to the nucleus is rough and that farther away is smooth. Smooth ER is a transition area where chemicals like proteins the cell has manufactured are stored in the lumen for transportation elsewhere in the cell. Pieces of the smooth ER called vesicles pinch off from the smooth ER and travel other places in the cell to transfer their contents. Rough ER gets its name because it has other organelles called ribosomes attached, which give it a rough appearance when viewed by an electron microscope. Rough ER and its associated ribosomes are involved in protein synthesis, with the new polypeptide being threaded into the lumen of the ER as it is formed.

Ribosomes are special organelles that are directly involved in protein synthesis. They are made of RNA (ribonucleic acid) and protein and are manufactured in the nucleus (from a DNA template), then go out into the cytoplasm to function. Ribosomes of prokaryotes and eukaryotes are chemically different enough that some of our antibiotics such as tetracycline, streptomycin, and the new Zithromax® (azithromycin), can interfere with bacterial ribosomes’ ability to do protein synthesis without also interfering with our ribosomes.

Vacuoles and vesicles are similar in that both are storage organelles. Generally, vacuoles are larger than vesicles. Plant cells generally have one large central vacuole that takes up most of the space within the cell and is used for storage of all sorts of molecules. Paramecium have a special type called a contractile vacuole that serves to excrete water from the cell, sort of like our kidneys excrete water from our bodies. Vesicles are small enough and mobile enough that they are often used to move chemicals to other locations in the cell where they might be needed.

One of the places to which vesicles travel is the Golgi apparatus or Golgi bodies. These look like stacks of water-balloon-pancakes. They are sort of like the shipping and receiving department of the cell. Materials are received as vesicles unite with the Golgi apparatus, and sent elsewhere as other vesicles pinch off. Materials are temporarily stored in the Golgi bodies, and some further chemical reactions do take place there.


Bacteria (Kingdom Monera) are prokaryotes. They do have DNA, but it is not organized into a true nucleus with a nuclear envelope around it. Also, they lack many other internal organelles such as mitochondria and chloroplasts.
http://biology.clc.uc.edu/courses/bio104/cells.htm
Organisms in the other four kingdoms are eukaryotes. Their DNA is organized into a true nucleus surrounded by a nuclear envelope which consists of two bilayer membranes. The nucleus of eukaryotic cells contains the genetic material which chemically directs all of the cell’s activities. Usually this is in the form of long strands of chromatin made of DNA and affiliated proteins. When a cell is getting ready to divide, the chromatin coils and condenses into individual, distinguishable chromosomes. Because the nuclear envelope consists of two bilayer membranes, there is a space between these two membranes called a lumen CITATION:
"Cells and Organelles." Cells and Organelles. J. Stein Carter, n.d. Web. 23 Sept. 2014. <http://biology.clc.uc.edu/courses/bio104/cells.htm>.