Download Rev. 1/06 1 LECTURE 3 Cell Structure and Cell Division I. The cell

BIO 120
Field Natural History
1
LECTURE 3
Cell Structure and Cell Division
I.
The cell, the basic unit of life.
A. One of the fundamental principles of biology is that all living things are made up of one or
more similar cells.
1. Three tenets of cell theory:
a. All organisms are composed of one or more cells.
b. The cell is the basic organizational unit of life. (The smallest unit having the
properties of life - Starr)
c. All cells arise from preexisting cells. (The continuity of life arises directly from the
growth and division of single cells -Starr.)
II.
Parts of an Animal Cell.
1. An organelle is to a cell what an organ is to entire organism.
2. Cytoplasm – the watery substance within a cell that contains the organelles and many
dissolved molecules.
3. Ribosomes – The sites of protein synthesis.
4. Endoplasmic reticulum –
a. The rough endoplasmic reticulum is the site of ribosomes. This is where many proteins
are made.
b. Smooth endoplasmic reticulum is the site of synthesis for some hormones. It is also the
site for detoxification (such as in liver cells).
5. Golgi apparatus –Proteins and other molecules made in the cell are packaged here for
export out of the cell.
6. Lysosomes - the recycling center of the cell. These structures contain a mix of powerful
enzymes that are capable of breaking down almost every large molecule in the cell.
a. They also function as digestion chambers for dangerous bacteria and foreign debris.
b. The enzymes are kept safely sequestered by a membrane that surrounds them.
c. The malfunction of lysosomes is the basis for some diseases.
d. Silicosis (a miners disease, when silica dust is inhaled.
e. Asbestosis is s similar disease. Both diseases can be fatal.
f. It is also suspected that Alzheimer’s disease is due to a malfunction of the lysosome.
g. Lysosomes play a role in forming your fingers and removing tadpole tails as frogs
mature.
7. Mitochondrion – kidney bean or sausage shaped organelles that are the powerhouse of the
cell. They are the sites of aerobic cellular respiration.
a. This is where the carbohydrates are oxidized to produce the energy with which the cell
does work.
b. Mitochondria are semiautonomous organelles that grow and reproduce within the cell.
c. They are the only other sites in the cell that contain DNA.
8. The nucleus. The one other major place where DNA is contained in the cell.
a. It has a nuclear membrane -keeps the chemical environment of the nucleus separate.
b. The nucleolus is where the precursors for ribosomes are made.
c. The nucleus contains the chromosomes. Protein helps DNA to coil tightly during cell
division.
Rev. 1/06
BIO 120
Field Natural History
9. Finally, the contents of the cell are all held together by a membrane called the plasma
membrane.
III.
Parts of a Plant Cell. Plant cells differ from animal cells in 4 ways.
1. Rigid cell wall. This protects and supports the cell, and ultimately, the whole plant.
a. The cell wall consists of up to 4 layers of fibrous material (cellulose) each laid down
over the next, the fibers facing a different direction.
2. Large spaces are vacuoles. They may contain any number of substances.
3. Chloroplasts, where photosynthesis takes place.
a. The green pigment, chlorophyll, is responsible for capturing the correct wavelength of
sunlight and assisting in creating sugar from CO2 and H2O.
b. Chloroplasts have their own DNA.
c. It is believed that chloroplasts were at one time photosynthetic bacteria.
4. Cell division that results in two new, identical cells (daughter cells) is called mitosis.
a. Animal and plant cells differ in the process of cytokinesis.
b. In animals, there is a pinching of the cytoplasm and cell membrane, much like tying a
string around the middle of the cell and tightening it.
c. In plants, a cell plate forms.
IV.
Prokaryotes and Eukaryotes.
A. The cells of plants and animals differ in fundamental ways from those of bacteria.
1. Prokaryotic cells or prokaryotes (bacteria).
2. All other plants, animals, fungi and single-celled organisms are comprised of eukaryotic
cells. Sometimes call them eukaryotes.
3. Prokaryotic cells do not have;
a. A nucleus. In fact, their very name means pre –nucleus. (pro – karyotic)
b. Organelles, such as mitochondria, or golgi apparatus or lysosomes.
4. Prokaryotic cells have;
a. DNA, but it is contained in one large loop called a chromosome.
b. The DNA in a prokaryote is held in a less well defined structure called a nucleoid. It
does not have a membrane to separate it from the cytoplasm of the cell.
c. Ribosomes.
d. A rigid cell wall similar to plants.
V.
Endosymbiotic Theory
1. Most biologists believe that eukaryotic cells evolved from prokaryotic cells.
2. It is believed that mitochondria and chloroplasts are the descendents of prokaryotic cells.
a. Both have their own DNA.
b. Their chromosome closely resembles that of a prokaryote.
b. They divide within the cell just like prokaryotic cells (bacteria).
3. The endosymbiotic theory
a. Stage one – An ancestral eukaryotic cell engulfs a prokaryote but fails to digest it. The
second remains alive within the first. Symbiosis, but one cell within the other, so its
called endosymbiosis.
b. Over time, mitochondria become a specialized energy factory (via aerobic respiration).
Energy leaks out into cytoplasm and used by the larger cell.
Rev. 1/06
2
BIO 120
Field Natural History
3
c. In return, the cell provides nutrients from the environment and it moves around and
protects the mitochondria within its cell membrane.
d. The relationship eventually becomes obligate. Mitochondria cannot live alone outside of
the cell.
4. The same process is thought to have occurred with chloroplasts and photosynthesis.
Rev. 1/06