Lecture Outline - Chapter 3

3.0. The Cell Theory and Microscopy (Fig. 3A)

1. An adult person is made of approximately 75 trillion (75,000,000,000,000) cells.
2. Antonie van Leeuwenhoek, Robert Hooke, Theodor Schwann, Matthias Schleiden, and Rudolf Virchow all contributed to establishment of the cell theory.
3. Cells are a fundamental unit of life, come in many different shapes and sizes, and each carries on these functions associated with life; outside the cell is the disorganized nonliving environment.
4. The cell theory states:
   • a. Living things are composed of cells (Schleiden and Schwann).
   • b. New cells arise only from preexisting cells (Virchow).
5. Critical Role of Microscopes
   • a. Compound light microscope (Fig. 3A); uses light rays; resolving power = 200 µm; useful magnification = ×1000
   • b. Transmission electron microscope (TEM); uses electrons to view preserved tissue; higher resolving power = 0.5 µm; useful magnification is about 30,000×.
   • c. Scanning electron microscope (SEM); uses electrons scanned over metal-coated specimen; forms three- dimensional image of prepared tissue.

1. Eukaryotic (eu means true; karyon means nucleus) cells have a nucleus.
2. Plasma membrane (Fig. 3.1) separates contents of cell, called the cytoplasm, from surrounding environment; composed of a phospholipid bilayer with protein molecules embedded.
3. Cell wall found only in plants (not animal cells)
   • a. Primary cell wall composed of cellulose; forms several layers of fibrils lying at right angles to one another for strength.
   • b. Secondary cell wall composed of lignin for even greater strength.

1. Nucleus diameter is about 5 µm.
2. Stores genetic information as genes made of DNA.
3. DNA works with RNA to synthesize cell proteins and control cell.
4. Chromatin is thread-like material containing DNA; when cell divides, chromatin condenses into rod-like chromosomes;
5. Nucleoli are specialized parts of chromatin that produce ribosomal RNA (rRNA), which is necessary to form ribosomes in cytoplasm.
6. Nuclear envelope is a double membrane with nuclear pores that permit proteins to pass in and ribosomes to pass out.
7. Granule-like organelles called ribosomes are coded in nucleoli, function in cytoplasm.
8. Ribosomes are small granules composed of two subunits, each containing rRNA and protein.
9. Two subunits are assembled into one ribosome in cytoplasm.
10. Ribosomes are either free or attached to endoplasmic reticulum.
11. Ribosomes are site of protein synthesis.
12. Polyribosomes are functional groups of ribosomes making the same protein.

1. Endoplasmic Reticulum (ER) (Fig. 3.5)
   • a. Smooth ER lacks ribosomes; in some cells produces steroid hormones in testes and adrenal cortex peroxisomes in liver cells attached to smooth ER detoxify drugs.
   • b. Rough ER has ribosomes attached to tubular canals; produces proteins for export out of cell via smooth ER and Golgi apparatus. (Fig. 3.6)
2. Golgi Apparatus (Fig. 3.6)
   • a. Structured as stacks of flattened saccules similar to hollow pancakes; inner face directed toward nucleus and ER, outer face is toward cell membrane.
   • b. Functions to package, store, modify, and distribute molecules produced by ER. Molecules such as hormones are packaged in secretory vesicles and moved to cell membrane for discharge.
3. Vacuoles
   • a. Membrane-enclosed sacs function to storage water, sugars, salts, pigments, etc.
   • b. Small vacuoles are called vesicles.
   • c. Plant cells are supported by a few large central vacuoles filled with watery fluids.
4. Lysosomes
   • a. Formed by Golgi apparatus.
   • b. Contains hydrolytic enzymes to digest macromolecules.
   • c. Function for intracellular digestion when material (large molecules, bacteria) in vesicles is fused with lysosomes or for autodigestion (during development).
   • d. An enzyme is missing in the lysosomal storage disorder called Tay-Sachs disease.

1. Mitochondria (singular is mitochondrion) (Fig. 3.7)
   • a. Found in both plant and animal cells
   • b. Structure is double membrane organelle with inner membrane forming shelves called cristae that project into matrix.
   • c. Function as "powerhouse" of cell; produce ATP for cellular energy via aerobic cellular respiration.
2. Chloroplasts (Fig. 3.8)
   • a. Found only in plant cells and photosynthetic protists
   • b. Structure is double membrane organelle that contains thylakoids (flattened sacs) piled up into stacks (grana) and stroma (fluid-filled space about grana).
   • c. Function to carry on photosynthesis where carbon dioxide, water, and radiant energy is used to produce glucose and oxygen.
   • d. Chlorophyll is a green pigment that absorbs solar energy, is found within grana and makes leaves green.
3. Endosymbiotic hypothesis contends that some early prokaryotes became mitochondria, chloroplasts and flagella found in modern eukaryotic cells. (Fig. 3.9)

1. Functions to help maintain cell's shape, anchor organelles, and allows cell and its organelles to move.
2. Actin filaments (formerly microfilaments) are long, thin fibers composed of actin.
3. Actin filaments allow microvilli to shorten and extend into intestine.
4. They form a constriction ring along with myosin when a cell divides.
5. Microtubules are small cylinders composed of 13 helical rows of tubulin.
6. Assembly of microtubules is under control of a microtubule organizing center called centrosome near nucleus.
7. Microtubules have motor molecules kinesin and dyenin, some of which move vesicles.

1. Centrioles are microtubules arranged in specific patterns. (Fig. 3.11)
2. Centrioles have a ring of nine sets of three microtubules each with none in middle called a 9 + 0 pattern.
3. Found in animal cells, centrioles lying at right angles to one another replicate before cell division.
4. Cilia and longer flagella are hairlike extensions of the cell that have a 9 + 2 pattern of microtubule doublets, which slide along one another. (Fig. 3.12)
5. Cilia provide movement in single-celled paramecia; in respiratory tract of humans, cilia sweep debris trapped in mucus back up into the throat.
6. Flagella cause male sperm cells to move.

1. Prokaryotic cells include bacteria and cyanobacteria
2. Lack most cell organelles and any nuclear envelope.
3. Have a single, circular DNA chromosome located in nucleoid region.
4. The cell wall differs from eukaryotic cell walls.
5. May have a distinct flagella if motile.
6. Prokaryotes are more metabolically varied than any other type of organism.