Important events in the discovery of the cell and the development of the cell theory…..
1665 – Robert Hooke Observed cells in cork. Coined the term "cells”. Cork Cells
1673- Anton van Leeuwenhoek Created a powerful microscope
1827-33 - Robert Brown -noticed that pollen grains in water jiggled around called “Brownian motion” -discovered the nucleus Nucleus Human Cheek Cell
1838 - Matthias Schleiden A botanist who concluded that all plants are made of cells. Typical Plant Cell
1839 - Theodor Schwann A zoologist who concluded that all animals are made of cells. Nerve Cells
1855 - Rudolph Virchow A physician who did research on cancer cells and concluded “Omnis cellula e cellula”. “All cells are from other pre-existing cells.”
The Cell Theory 1. All living things are composed of one or more cells. 2. Cells are the basic units of structure and function in an organism. 3. Cells come only from existing cells.
Cells are Diverse… both in size, shape, and internal organization.
Why Are Cells So Small? • Transport- Cell volume to surface area ratios favor small size. • Control- Nucleus to cytoplasm consideration. • Metabolic requirements- ……..we’ll come back to this later.
How small can a cell be? Mycoplasmas - bacteria that are 0.1 to 1.0 mm. (1/10 the size of regular bacteria). Note: 1.0 mm = one millionth of a meter
All cells have…… • Plasma (cell) Membrane • Nucleus (eukaryotes only) • Cytoplasm (an area) • Organelles (structures with specialized functions)
Cell Types Prokaryotes- simple cells that do not have internal membranes example = bacteria Eukaryotes- more complex cells that do have internal, membrane-bound structures examples = plants and animals
Timeline Prokaryotic Organisms: First appeared 3.5 BYA include bacteria and cyanobacteria Eukaryotic Organisms: First appeared 2.0 BYA include protists, fungi, plants and animals
Key Differences: Eukaryotes • Have a nucleus and other membrane bounded structures. • Have large ribosomes • DNA is organized into chromosomes • Flagella are made of microtubules and have a 9+2 structure • Cell walls are made of cellulose • Prokaryotes • Lack a nucleus and other membrane bounded structures. • Have small ribosomes • DNA is not organized into chromosomes • Flagella are not made of microtubules and does not have a 9+2 structure • Cell walls are made of peptidoglycan, not cellulose
Examples Prokaryotic Eukaryotic Nucleus