An Introduction to Molecular and Cellular Biology Origin of Cells Cells as Experimental Models Tools

1
An Introduction to Molecular and Cellular
BiologyOrigin of CellsCells as Experimental
ModelsTools of Cell Biology
2
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

3
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.

4
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 Millers discovery of the spontaneous
  synthesis of organic molecules
• Spontaneous polymerization of monomers into
  complex informational macromolecules
• Self replication of nucleic acids

5
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?

6
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 todays genetic code.

7
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.

8
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.

9
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. colis 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.
10
Eukaryotic Cells

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

11
1.7 Evolution of cells
12
1.8 Scanning Electromicrograph of Saccharomyces
cerevisiae.

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

13
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.

14
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.

15
1.12 Light micrographs of representative animal
cells (Part 2)
Fibroblasts
Blood Cells
16
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

17

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

18
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.
19
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.
20
Drosophila melanogaster

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

21
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.

22
Vertebrates

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

23
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.

24
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.

25
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.
26
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.

27
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.

28
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.

29
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.

30
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.

31
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.

32
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.