Life is Cellular Chapter 7.1

Discovery of The Cell Made possible by the invention of the microscope.

First observed and named by Robert Hooke in 1665

Living cells were first discovered by ◦ Anton van Leeuwenhoek ◦ Observed microscopic organisms in pond water

The Cell Theory All living things are made up of one or more cells Cells are the basic units of structure and function in an organism New cells only come from the reproduction of existing cells

Scientists Involved Matthias Schleiden - (botanist) concluded all plants are made of cells Theodor Schwann - concluded all animals are made of cells Rudolph Virchow - (physician) cells only come from other cells

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Diversity of Cells Cells differ in size, shape, and function

Shared characteristics of all cells: ◦Cell membrane – Outer boundary/covering ◦Cytoplasm – Internal space, gel-like

Types of Cells 2 categories Based on presence or absence of a nucleus ◦ Prokaryotes- Do not contain a nucleus ◦ Eukaryotes – Do contain a nucleus, which contains the cell’s genetic material (DNA)

Prokaryotes (Prokaryotic Cells) Mainly Bacteria ◦No Nucleus ◦No membrane bound organelles ◦Very small (1-10 μm) ◦Circular DNA

Flagella & Pilli Some prokaryotic cells feature one or more flagella. These are long helical tubes extending out of the cell wall, which rotate to provide locomotion. Flagella are powered by protein motors and can propel bacteria at a rate of more than 50 lengths per second. Many bacteria also feature pili. These are hollow protein structures used during bacterial conjugation – the transfer of genetic material from one bacterium to another.

Eukaryotes (Eukaryotic Cells) Most other cells (plants, animals, etc) Contains a nucleus Contains Organelles Small ( μm) Linear DNA

Microscopes

Compound Microscope A typical light microscope allows light to pass through a specimen and uses two lenses to form an image.

The objective lens enlarges the image of the specimen. The ocular lens magnifies the image further

Most living cells are nearly transparent, so chemical stains are used to solve this problem.

Another technique is to use fluorescent dyes that can be attached to specific molecules and can be made visible using a special fluorescence microscope.

Electron Microscope Instead of using light, electron microscopes use beams of electrons that are focused by magnetic fields. Some electron microscopes can be used to study cellular structures that are 1 billionth of a meter in size. The two major types of electron microscopes are transmission (TEM) and scanning (SEM).

Transmission electron microscopes make it possible to explore cell structures and large protein molecules. ◦Cells and tissue must be cut into ultrathin slices to be examined.

In scanning electron microscopes, a beam of electrons is scanned over the surface of a specimen. ◦They produce three-dimensional images of a specimen’s surface.

Because electrons can be scattered by air, samples must be placed in a vacuum to be studied. ◦Electron microscopy can only be used to examine nonliving cells and tissues.