Lecture 5 Outline: Cell Structure

Cells make up all organisms.

1. 3 features common to all cells: a plasma membrane, a nucleoid or nucleus and cytoplasm.

2. The plasma membrane surrounds the cell

3. The nucleus or nucleoid contains the genetic material.

4. The cytoplasm comprises the rest of the cell’s interior.

5. Eukaryotic cells also contain membrane-bound organelles

The cell theory

Modern principles of cell theory

1. All organisms composed of one or more cells

2. Cell is smallest living organizational unit

3. Cells arise only from division of other cells

Cells are small.

1. surface area to volume ration: As surface area increases, volume increases more

2. Large cells have special adaptations to compensate for their size.

Prokayotic cells:

1. Bacteria : the simplest cellular organisms.

2. Surrounded by membrane.

3. Strong rigid cell wall

4. No internal compartments.

Eukaryotic cells

1. More complex than prokaryotes: compartmentalized

2. Possess internal membrane-bound organelles.

The nucleus:

1. Largest organelle in most cells, readily visible

2. The repository of all genetic information.

3. The nuclear envelope is made up of two membranes.

4. The nucleus contains the cell’s DNA contained in packages called chromosomes.

Mitochondria

1. The cell’s energy source.

2. Tubular or sausage-shaped organelles bounded by double membrane.

3. Occur in all eukaryotes.

4. Mitochondria have their own DNA

Chloroplasts

1. Occur photosynthetic organisms

2. Contain chlorophyll, which give plants green color.

Endosymbiosis or the endosymbiont theory

1. Eukaryotes have radically different cell structure and possess organelles that resemble bacteria.

2. Some scientists have proposed that there has been a joining (symbiosis) of different species of prokaryotes to create cell organelles.

3. Specifically: mitochondria resemble bacteria and chloroplasts are like photosynthetic bacteria.

4. One species of prokaryote was engulfed by and lived inside another species of prokaryote. This was the beginning of eukaryotic cells.

There is evidence supporting theory

1. Mitochondria and chloroplasts surrounded by double membrane

2. Mitochondria and bacteria have similar size

3. Mitochondrial ribosomes resemble bacterial ribosomes

4. Mitochondria and chloroplast DNA is circular like that found in bacteria

5. Mitochondria divide by simple fission