Table of Contents

1. Cell Size
2. Cell Compartments
3. Cell Organelles
4. Mitosis
5. Protein Characteristics
6. Essential Nutrients
7. Adenosine TriPhosphate
8. Mechanisms for Substance Movement In and Out of a Cell

I. Cell Size

Cell Size

II. Cell Compartments

Human Cell

A. Nucleus

– contains the chromosomes; often in center

B. Cytoplasm

1. Remainder of the cell;
   
   

   Cytoplasm and Cytosol

   • all the fluid inside the cell
   • extracellular fluid is located in very small space between outer cell membranes
   • cell obtains dissolved nutrients from extracellular fluid and wastes pass from the intracellular fluid across the cell membrane into the extracellular fluid
2. Internal cell membranes further compartmentalizes the cell
3. Tubules and matrix skeletal materials provide rigidity and movement

   Cytoskeletal Filaments

III. Cell Organelles

• Plamsa Membrane
• Nucleus
• Nucleolus
• Ribosome
• Endoplamsic Reticulum
• Golgi Apparatus
• Mitochondria
• Lysosomes
• Peroxisomes

Cell organelles are sub-units of the cell that cannot function if removed from the cell; perform specific functions

A. Plasma Membrane

1. Function

Membrane

It is the outer boundary of the cell and is responsible for regulating whether substances enter or leave the cell; semi-permeable; barrier for material to move into and out of the cell

2. Structure

1. bounded sheet of fat - lipid bilayer

   Phospholipid	Fluid Mosaic

2. integral associated proteins

3. Location

1. proteins extending through membrane
   1. stabilize the membrane & physically link cells together
   2. other proteins link protein filaments to the inner surface of the cell membrane
   3. channels and gates
2. proteins on outer surface of membrane
   1. receptor proteins or "sensitive" spots interact with chemical messengers when present at the outer membrane surface
   2. enzymes
   3. associated with carbohydrates, serve as recognization molecule
3. proteins on inner surface of membrane - enzymes

4. Junctions between cells

1. overview – constructed of protein; necessary to link cells together to form tissues. A blood cell is an example of a cell that is not linked to another blood cell, but rather it remains as an independent cell suspended in a fluid [plasma]. Most cells are closely associated with like cells to form tissues; e.g., muscle tissue, fat tissue, epithelial tissue, and nerve tissue.
2. proteins that serve to bind cells to each other include integrins, desmosomes, tight junctions, and gap junctions

   Desmosome	Gap Junction

   1. integrins are cell membrane proteins of the type that either extend all the way through the cell membrane [from the outer surface of the cell to the inner surface of the cell membrane] or of the type that are associated with the outer region of the cell membrane – present in all cells that associate to form tissues.
   
   
   2. desmosomes hold adjacent cells firmly together in areas that are subject to considerable stretching, such as in the skin. Cells with desmosomes may have movement of substances between the cells.
   
   
   3. tight junctions form connections between cells that is much more firm than simple desmosomes. Tight junctions restrict the movement of most organic substances, but there is ionic and water movement between adjacent cells. An example of tight junctions is the epithelial cell layer of the small intestine. Nutrients must be transported to the interior of one of these cells to pass from the intestinal lumen to the extracellular space. The nutrients cannot diffuse between the epithelial cells of the intestinal lining. From the extracellular space, the nutrients move to the blood stream; or in the case of large fatty acids, to the lymph vessels.
   
   
   4. junctions that consist of protein channels linking the interiors of two cells are called gap junctions. Small molecules and ions may pass between the cells; however, larger molecules such as proteins cannot. Gap junctions are extremely important in the transmission of electrical activity between some of the muscle cells.
   
   

back to Cell Organelles

B. Nucleus

Genetic Information	Genetic Code	Deletion Mutation	Transfection

1. general function

2. components

back to Cell Organelles

C. Nucleolus

Nucleolus	Gene Transcription	Splicesomes

back to Cell Organelles

D. Ribosome

Base Pairing	Protein Synthesis	Ribosomes	Protein Splitting

Transcription	Protein Assembly 1	Protein Assembly 2

– platforms that provide a surface location for the assembly of amino acids into proteins. Ribosomes are constructed of protein and ribosomal ribonucleic acid (r-RNA) and are attached to endoplasmic reticulum [an internal cell membrane]. When ribosomes are attached to endoplasmic reticulum, the endoplasmic reticulum is called rough or granular endoplasmic reticulum. Also present are proteins that serve as enzymes that allow the linkage of amino acids to form a polymer of amino acids [protein]

back to Cell Organelles

E. Endoplasmic Reticulum

Endoplasmic Reticulum

1. rough (granular) endoplasmic reticulum

2. smooth endoplasmic reticulum

back to Cell Organelles

F. Golgi Apparatus

Golgi Apparatus

back to Cell Organelles

G. Mitochondria

Mitochondria

Mitochondria are rod-shaped organelles with a double outer membrane. The mitochondria contain a special set of enzymes that enable the creation of large amounts of an energy storage molecule called adenosine triphosphate (ATP). Oxygen is required to be present for the enzyme systems to function in the mitochondria.

back to Cell Organelles

H. Lysosomes

Lysosomes are small vesicles containing acid and digestive enzymes that breakdown bacteria, debris from dead cells, and non-functioning organelles from the same cell.

back to Cell Organelles

I. Peroxisomes

Peroxisomes are similar to lysosomes except they contain enzymes.These enzymes are primarily hydrogen peroxide, which is toxic to the cell. Within the cell, there is a variety of filaments including those necessary for cell division and those necessary for movement of the cell.

back to Cell Organelles

IV. Mitosis

Mitosis is the process which produces cell "clones". It is multiplication through division; one cell divides into two identical clone cells and has increased the total cell population. Using the poweres of multiplication; 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, ... it does not take long to produce millions and billions of cells. We call the uncontrolled proliferation of cells in this manner "cancer". Normally, we have a myriad of controls which limit and specify cell growth and division.

Cell Cycle

The "Cell Cycle" is the set of events that a cell typically transverses during its life. After a cell separates from it sibling daughter cell it enters a stage known as G1. (Which is the first growth or gap period.) Some cells tend to hang at this point forever, e.g., liver, nerve, and muscle cells. However, given proper stimuli, they will move on to the next stage.

The second stage is the "S" stage where the synthsis of DNA occurs. Once a cell passes from G1 to S stage, it will divide.

Replication

Subsequently the cell proceeds through a second "Growth" stage where it performs the rest of the tasks required in preparation for the actual division, Mitosis.

Mitosis can generally be divided into four phases, Prophase, Metaphase, Anaphase, and Telophase.

During prophase, the chromosomes condense and the nuclear membrane dissappears.

During metaphase, the chromsomes align along a center axis of the cell and the astrocytes align on either side of the equator.

During anaphase, the chromosomes are pulled apart and one set is segregated to each half of the cell.

During telephase, the cell is pinched into two around the equator, the nuclear membrane reforms, the chromosomes disperse, and we are left with two daughter cells.

Mitosis

The majority of cells are 10 to 20 mm, but the range of cell size is from 2 mm to 120 mm. However, a nerve cell may be a meter in length. It is necessary to use a microscope to view the typical cell. Approximately 64,000 cells lined up would occupy one inch.

V. Protein Characteristics

VI. Essential Nutrients

The essental nutrients comprise of the mineral elements, nine of the 20 amino acids, and 2 of the fatty acids.

VII. Adenosine Triphosphate

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VIII. Mechanisms for Substance Movement In and Out of Cell

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Copyright © 2000 by M. J. Malachowski, Ph.D.

This page last updated: 1/27/01