1 An Introduction to Molecular and Cellular

BiologyOrigin of Cells

Cells as Experimental ModelsTools of Cell Biology

1 Introduction to Molecular and Cellular Biology

• Why is it important to understand molecular biology of cellular processes?

Medicine

Agriculture

Biotechnology and Biomedical engineering

• Cellular Diversity leads to functional differences between cells.

• Cells contain some basic properties that make them particularly valuable as experimental models.

Energy Metabolism

Genetic material

Plasma Membranes

1 Different Types of Cells

• What is the difference between Prokaryotic cells (bacteria) and eukaryotic cells.

Prokarayotes lack a nuclear envelope, cytoplasmic organelles and cytoskeleton. They are generally smaller/simpler organisms.

Eukaryotes have a nucleus in which the genetic material is separated from the cytoplasm.

1 Origin of Cells

•Life emerged nearly 3.8 million years ago.

•How did the first cell emerge?

•Laboratory experiments have shed some light on how this may have occurred.

Stanley Miller’s discovery of the spontaneous synthesis of organic molecules

Spontaneous polymerization of monomers into complex informational macromolecules

Self replication of nucleic acids

1.2 Nucleic Acids are Capable of Directing their own Replication

Self-replication occurs when DNA and RNA serve as templates for their own synthesis.

Why is this so critical to reproduction and evolution of a species?

1 The First Cell

•The ability of RNA to catalyze chemical reactions was first discovered by Sid Altman and Tom Cech in the 1980s.

RNA can serve as a template and catalyze its own replication – the RNA World.

Interactions between RNA and amino acids gave rise to today’s genetic code.

1.3 Enclosure of self-replicating RNA in a phospholipid membrane

•A cell membrane enclosed the self-replicating RNA to form the first cell.

•Phospholipids are amphipathic molecules that make up all present-day biological membranes.

1 Present-Day Prokaryotes

• Archaebacteria were prevalent in primitive Earth and often live in extreme environments.

• Eubacteria are a large group of organisms (including common forms of bacteria) that live in a wide range of environments, including soil, water, and other organisms (e.g., human pathogens).

• Cyanobacteria, the largest and most complex prokaryote, synthesizes its energy from photosynthesis.

1 Present-Day Prokaryotes

• Escherichia Coli (E. coli) is a typical prokaryotic cell and a common inhabitant of the human intestinal tract.

E. coli is encased by a rigid cell wall that is composed of polysaccharides and peptides.

E. coli’s has a plasma membrane that consists of a phospholipid bilayer and associated proteins.

The DNA of E. coli is a single circular molecule.

There are numerous ribosomes in the cytoplasm of E. coli.

Figure 1.5. Electromicrograph of E.coli.

1 Eukaryotic Cells

• Eukaryotic cells contain a variety of membrane-enclosed organelles within their cytoplasm.

1.7 Evolution of cells

1.8 Scanning Electromicrograph of Saccharomyces cerevisiae.

Yeasts are an example of a multicellular organism that is commonly to study the role of molecules.

1 The Development of Multicellular Organisms

• Cells found in animals are much more diverse than most other organisms.

• Human cells are organized into five main tissue systems: epithelial tissue, connective tissue, blood, nervous tissue, and muscle.

Epithelial cells form sheets that cover the surface of the body and line the internal organs.

Connective tissues include bone, cartilage, and adipose tissue.

Fibroblasts are a cell type that fill the spaces between organs and tissues in the body.

Blood contains red blood cells (erythrocytes) and white blood cells.

1.12 Light micrographs of representative animal cells (Part 1)

These micrographs illustrate the divesisty of cells that exist in the different tissues within the human body.

1.12 Light micrographs of representative animal cells (Part 2)

Fibroblasts

Blood Cells

1 Cells as Experimental Models

• The evolution of present-day cells from a common ancestor has important implications for cell and molecular biology as an experimental science.

• Because of the diversity of present-day cells, many kinds of experiments can be more readily undertaken with one type of cell than with another.

E.coli

Yeast (S. cervisiae)

Caenorhabditis elegans (C. elegans)

Drosophila melangaster

Arabidopsis thaliana

Xenopus laevis

Zebrafish

Mouse and Human cells

•The number of Genes in an organism is indicative of its simplicity and use as an experimental model.

1 E. Coli is a Very Useful Experimental Model System

•E. coli is the most thoroughly studied species of bacteria.

•E. coli has been especially useful to molecular biologists:

Its relative simplicity – contains a single chromosome.

Ease of propagation in the laboratory – rapid growth.

Figure 1.13. E.Coli on agar medium.

1 Yeasts are used study Structure and Function of Eukaryotes

• The yeast genome is 3x larger than E.coli.

• It is far more manageable than the genomes of more complex eukaryotes to study eukaryotic cellular processes such as DNA replication and transcription.

• Yeasts can be readily grown in the laboratory and can be studied by many of the same molecular genetic approaches that have proved so successful with E. coli.

Fig. 1.14. Electromicrograph of

S.cervisiae.

1 Drosophila melanogaster

•The fruit fly, Drosophila melanogaster, can be easily maintained and bred in the laboratory.

1 Vertebrates

•Vertebrates, the most complex animals, include humans and other mammals.

•Cultured human and other mammalian cells can be isolated and grown in culture where they can be manipulated under controlled laboratory conditions.

•Muscle and nerve cells possess specialized properties that make them important models for studies of particular aspects of cell biology.

1 Vertebrates

• Xenopus laevis and Zebrafish are used to study to early vertebrate development.

Xenopus – it’s eggs develop outside the mother and all stages of development from egg to tadpole can be readily studied in the laboratory.

Zebrafish – it is easy to maintain in the laboratory, and they reproduce rapidly.

1.20 The mouse as a model for human development

Very often Mice are used as a model for human disease.They are useful to study the genetic analysis or to study

gene function.

1 Microscopes are a Necessary tool of Cell Biology

• The light microscope remains a basic tool of cell biologists and can to magnify objects up to about a thousand times.

1 Light Microscopy

•Bright-field microscopy, in which light passes directly through the cell, is routinely used to study various aspects of cell structure because of its simplicity.

Fig. 1.23. Brightfield micrograph of a stained section of benign kidney tumor.

1 Light Microscopy

•Phase-contrast microscopy and differential interference-contrast microscopy use optical systems that convert variations in density or thickness between different parts of the cell to differences in contrast that can be seen in the final image.

1 Flourescence Microscopy

• Fluorescence microscopy is a widely used and very sensitive method for studying the intracellular distribution of molecules.

The green fluorescent protein (GFP) of jellyfish is used to visualize proteins within living cells.

Fluorescence recovery after photobleaching (FRAP) is used to study the movements of GFP-labeled proteins.

1.27 Fluorescence micrograph

A microtubule associated protein fused to GFP (green flourescent protein) was introduced into mouse neurons in cell culture. The nuclei of the cells is stained blue.

Allows for the determination of cellular localization.

1 Electron Microscopy

• The electron microscope was developed jointly by Albert Claude, Keith Porter, and George Palade in the 1940s and 1950s.

• The electron microscope can achieve much greater resolution than that obtained with the light microscope.

1.38 Subcellular fractionation

Differential centrifugation separates and isolates eukaryotic cell organelles on the basis of their size and density for use in biochemical studies.

The force of an ultracentrifuge causes cell components to move toward the bottom of the centrifuge tube and form a pellet at a rate that depends on their size and density.

1 Growth of Animal Cells in Culture

• In vitro cell culture systems enable scientists to:

study cell growth and differentiation

perform genetic manipulations to understand gene structure and function.

•Culture media contains:

Serum

Salts

Glucose

Various amino acids and vitamins that the cells do not make for themselves.

1 Growth of Animal Cells in Culture

•Primary cultures are the original cultures established from a tissue.

•Permanent (or immortal) cell lines are embryonic stem cells or tumor cells that proliferate indefinitely in culture.