CellsBIO 224

Introduction to Cell and Molecular Biology

Cells Overview• Cells are the basic structural and functional

units of life• All share similarities in function and structure• Cells are found as one of two basic types– Prokaryotic– Eukaryotic

• Cells have a variety of sizes and shapes• Cells may exist as part of an organism or be an

organism individually

Properties of Life

• Growth• Reproduction • Evolution• Energy conversion• Complex organization• Homeostasis• Response to stimuli

Basic Cellular Architecture

• All cells are enclosed within a membrane• All cells contain a combination of substances

in a water based fluid typically referred to as cytoplasm , where many metabolic activities take place

• All cells contain DNA as their genetic material• Overall similarities allow cells to be used as

experimental models

Prokaryotes

• Single-celled organisms• Include all bacterial cells • Most are spherical, rod-shaped, or spiral• Smallest cells , with diameter from 1 to 10 µm• Have no internal cytoskeleton or organelles• DNA is not enclosed in a nuclear membrane• Divided into Domains of Archaea and

Eubacteria

Archaea

• Newer taxonomic grouping• Older group of organisms• Can live in extreme conditions that were

common in primitive Earth• Some may have flat or square shapes• Share biochemical similarities with both

Eubacteria and Eukarya

Eubacteria

• Domain that contains common present-day bacteria

• Found in a wide range of environments, including in or on other organisms

• Cyanobacteria are the most common and complex

• E. coli is widely used as an example of a typical prokaryotic cell

E. coli Cell Architecture

• Rod shaped cell, about 1µm by 2µm• Contained within a plasma membrane bilayer

of phospholipids• Surrounded by a rigid and porous cell wall

made of polysaccharides and peptides• DNA is a single circular molecule found within

a nucleoid region• Cytoplasm contains around 30,000 ribosomes

Eukaryotes

• Organisms may be single-celled or multicellular• Cells may become highly specialized • Shapes and sizes of cells vary greatly• Cells are larger and more complex than those

of prokaryotes with internal cytoskeleton and membrane-enclosed organelles

• DNA is enclosed in a nuclear envelope• Cells are highly compartmentalized internally• Found in Domain Eukarya

Eukaryotic Cell Architecture

• Contained within a phospholipid bilayer plasma membrane

• Some may be surrounded by a cell wall• Cytoplasm contains many membrane-bound

organelles with various functions• Some may contain cytoplasmic inclusions• The cytoskeleton provides structural framework

and organization for the cell

Studying Cells

• Most cells are too small to be seen with the naked eye

• Cell study relies heavily on microscopes• Cells were discovered as a result of microscopic

development• Robert Hooke observed cork with simple light

microscopes in the 1660s and introduced the word “cell”

1.21 The cellular structure of cork

Studying Cells

• In the 1670s Antony van Leeuwenhoek observed many cell types

• Matthias Schleiden (botanist) and Theodor Schwann (zoologist) observed cells under microscopes in the early 1800s– Their conclusions were similar for both plants and

animals– All organisms are composed of cells

Studying Cells

• Rudolf Virchow made observations with microscopes in the mid-1800s

• He rejected the idea of spontaneous generation and proposed that all living things come from cells

• Combinations of ideas of Hooke, Virchow, Leeuwenhoek, Schleiden, and Schwann were combined to propose the cell theory

The Cell Theory

• Cells are the basic units of life– They are the smallest bodies capable of carrying

out life processes• All living things are composed of cells– Living things may be made of multiple cells, or

may be found as single-celled organisms• All cells arise from pre-existing cells– Experiments by Redi, Spallanzani, and Pasteur

discredited the idea of spontaneous generation of organisms

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