4-1 Introduction to

the Cell

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 SchleidenA botanist who concluded that all plants are made of cells.

Typical Plant Cell

1839 - Theodor SchwannA 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 m. (1/10 the size of regular

bacteria).

Note: 1.0 m = 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 membranesexample = bacteria

Eukaryotes- more complex cells that do have internal, membrane-bound structuresexamples = 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: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

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

Prokaryotic Eukaryotic

Nucleus

Examples

Prokaryotic

Eukaryotic