CELL STRUCTURE AND FUNCTION
I. Today, scientists know that all living organisms are composed of cells.
A. Cells are defined as the smallest living, functional units in living organisms.
B. Cells come in a variety of sizes and shapes; however, most cells are extremely
small and can only be seen with the aid of a microscope.
C. CytologyD. Unicellular vs. Multicellular
II. HISTORICAL STUDIES ON CELLS
A. Galileo-17th century astronomer.
B. Antone von LeeuwenhoekC. Robert HookeD. Robert BrownE. Theodor Schwann and Matthias Schleiden-independently developed The Cell Theory.
1. Key Points in The Cell Theory
III. WHY ARE CELLS SO SMALL?
A. Small cell size allows for:
IV. 2 MAJOR TYPES OF CELLS
A. Prokaryotic Cells-
B. Eukaryotic Cells-
V. PROKARYOTIC CELLS-are extremely simple cells.
A. Bacteria-unicellular organisms.
1. They essentially live everywhere.
2. They are so small that they can only be seen with special microscopes.
3. Some bacteria are helpful; others, however, can be deadly.
4. Bacteria occur in one of three possible shapes:
a) Spirillum-refers to bacteria that have a spiraled shape.
b) Cocci-refers to bacteria that are rounded.
c) Bacillus-refers to rod-shaped bacteria.
5. Parts of a Typical Prokaryotic (Bacterial Cells)
a. The Cell Wallb. The Plasma (Cell) Membrane-
c. The Nucleoid-
d. Cytoplasm-
e. RibosomesVI. EUKARYOTIC CELLS
A. Major Components of a Eukaryotic Cells
1. Cell Walls-only found in plant cells. This is an outer, protective layer around the plant
cell. What are cell walls composed of?
2. Plasma (Cell) Membranes-found in all eukaryotic cells.
a. In plant cells, these are located under the cell wall. In animal cells, these are
serve as the outer covering around the cell.
b. What are these composed of?
c. Plasma Membranes are described as being semipermeable. What does this
mean?
3. Cytoplasm
4. Organelles-structures that carry out specific functions for cells. These are like “little
organs.”
B. The Major Cellular Organelles
1. The Nucleus-largest and most distinct organelle. It makes up 5-10% of the total
volume of the cell. It is typically round in shape.
a. What is the function of the nucleus?
b. The nucleus stores a cell’s supply of DNA.
1) Chromatin-a compound composed of DNA and proteins. In dividing
cells, chromatin condenses to form chromosomes.
2) The Nuclear Envelope-a double-layered membrane that surrounds and
protects the nucleus.
a) Nuclear Pores-
2. The Nucleolus-an organelle located in the center of the nucleus.
a. This structure has a role in RNA production and protein synthesis.
3. The Endoplasmic Reticulum (E.R.)-a series of continuous membranes within a cell.
a. 2 Types of E. R.
1) Rough Endoplasmic Reticulum-is covered with ribosomes.
a) What are ribosomes involved in?
2) Smooth Endoplasmic Reticulum-lacks ribosomes.
a) This structure is involved in lipid synthesis.
4. The Golgi Complex-a set of flat discs in eukaryotic cells.
a. This structure functions by packaging and removing wastes from the cell.
b. This Golgi complex packages materials into vesicles that are pushed out of the
cell.
c. Secretory or glandular cells often contain numerous golgi bodies.
d. Cisternae1) Why are these important?
5. Lysosomes-membrane-bound organelles that contain digestive enzymes that help to
breakdown carbohydrates, lipids and proteins.
a. Internally, these are very acidic.
b. In old cells, these may rupture which releases digestive enzymes into the cytoplasm
of the cell. Why is this important?
6. Peroxisomes-contain enzymes that breakdown molecules to produce hydrogen peroxide.
a. Furthermore, the peroxisomes contain catalase which breaks down hydrogen
peroxide into water and oxygen.
7. Mitochondria-slipper-shaped organelles found in all cells.
a. These are involved in the conversion of glucose into ATP (through a process
known as Aerobic Cellular Respiration).
b. These require an input of oxygen to function properly, thus they are referred to as
being aerobic.
c. Most cells contain numerous mitochondria.
d. Structure of Mitochondria
1) Double-layered membrane
2) Cristae-
8. Plastids-serve as storage areas in cells. These are most commonly found in plant cells.
a. These are always surrounded by a membrane.
b. Types of Plastids:
1) Chloroplasts-green structures found only in plant cells.
a) What are these involved in?
b) Why are these green in color?
2) Chromoplasts-contain pigments that give plants a red, orange and
yellow color.
3) Amyloplasts (Leucoplasts)-store starch for plants. These are most
common in the roots of plants-including potatoes, turnips, wheat and
rice.
9. Vacuoles-storage compartments in cells. Again, these are most common in plant cells.
a. Waste vacuoles, nutrient vacuoles.
b. Contractile vacuoles-remove excess water from some cells. These are most
common in unicellular animals (such as the Amoeba, Paramecium).
10. The Cytoskeleton-a series of protein fibers found in all eukaryotic cells. These fibers
provide support and structure to the cell.
a. The Cytoskeleton contains two types of fibers:
1) Microtubules
2) Actin filaments
11. Organelles involved in movement:
a. Flagella
b. Ciliac. Internally, flagella and cilia have the same structure. They have what is known
as a 9 + 2 Arrangement of the Microtubules.
C. Differences Between Plant and Animal Cells:
VII. CELL JUNCTIONSA. These allow for communication between cells.
B. Types of Cell Junctions Include:
1. Plasmodesmata
2. Gap Junctions
VIII. ENDOSYMBIOTIC THEORY OF EUKARYOTIC CELL DEVELOPMENT
A. Fossils indicate that the first cells appeared on Earth about 3.7 billion years ago. These
cells were prokaryotic cells in nature. The first eukaryotic cells observed in the fossils
dates back about 1.6 billion years ago.
B. Biologists have shown that mitochondria and chloroplasts have a small amount of DNA.
1. This DNA is circular-as in most ancient and modern prokaryotic cells.
2. Furthermore, the DNA in mitochondria and chloroplasts is very similar from one
cell type to another.
C. The Endosymbiotic Theory states that mitochondria and chloroplasts were once living
prokaryotic cells that became incorporated into larger living cells. Over time, the small
prokaryotic cells evolved specific functions in the larger cell.
1. According to this theory, the mitochondria and chloroplasts have evolved a life
living and functioning in eukaryotic cells.