Chapter 1

© 2012 Pearson Education, Inc.

Lectures byKathleen Fitzpatrick

Simon Fraser University

Chapter 1

A Preview of the Cell

Modified by Dr. J. Jordan


The Cell Place

• www.thecellplace.com • Student access codes in front of every

new text.


Introduction

• Cell– Basic unit of life– Cells have the capacity to grow, reproduce,

and specialize– Respond to stimuli and adapt to changes in

the environment– Rapidly changing field of science– Cell biology – cytology, genetics, and

biochemistry


History of Cell

• Story of cell biology started about 300 years ago

• European scientists• Crude microscopes


The Cell Theory: A Brief History

• Robert Hooke (1665) observed compartments in cork, under a microscope, and first named cells (the basic unit of biology)• He focused on empty cell walls of dead plant tissues (cork)

not plant tissues filled with “juices”

• His observations were limited by the low magnification power (30X enlargement) of his microscope.• Magnification – increase in the size of a specimen in

comparison to normal size. Can you see internal structure of the cell at 30X?



History continued

• Antonie van Leeuwenhoek, a few years later, produced better lenses that magnified up to 300X– First to observe living cells – Blood cells, sperm cells, bacteria, and

single-celled organisms in pond water


Early progress in cell biology was slow

• Two factors restricted progress in early cell biology

– Microscopes had limited resolution or resolving power (ability to see fine detail)

– The descriptive nature of cell biology; the focus was on observation, with little emphasis on explanation


Microscopes: essential tools in early cell biology

• By the 1830s, compound microscopes were used (two lenses). What are they?– Increased magnification and resolution– Structures only 1 micrometer in size could be seen

• Can you see individual cells without a microscope?

• Animal cells is 20 micrometers (µm)

• Bacterium about 2 micrometers

• One inch equals about 25,000 micrometers



• Using a compound microscope, Robert Brown (botanist) identified the nucleus, a structure inside plant cells

• Matthias Schleiden concluded that all plant tissues are composed of cells, and Thomas Schwann made the same conclusion for animals cells– They proved that plants and animal cells are

similar structurally.– Name some things that are similar; different?


Figure 1A-1


The cell theory

• In 1839, Schwann postulated the cell theory

– 1. All organisms consist of one or more cells

– 2. The cell is the basic unit of structure for all organisms

• Later, Virchow (1855) added

– 3. All cells arise only from preexisting cells


Properties of Cells

• Wide variety of shapes and sizes of cells– Fungal cells– Bacterial cells– Reproductive cells– Nerve cells


Figure 1-1


Figure 1-1 a-c


Figure 1-1 d,e


Figure 1-1 f


Figure 1-1 g-i


The Cell

• Cell is not only the basic unit of structure for all organisms but also the basic unit of reproduction– Remember movie: Children of Men– We must study cells to understand biology– Cell structure gives us clues to cell function


The Emergence of Modern Cell Biology

• Three historical strands weave together into modern cell biology, each with important contributions to understanding cells

• The cytology strand focuses mainly on cellular structure, and emphasizes optical techniques

• The biochemistry strand focuses on cellular function

• The genetics strand focuses on information flow and heredity


Figure 1-2


The Cytological Strand Deals with Cellular Structure

• Historically, cytology deals primarily with cell structure and observation using optical techniques


The Light Microscope

• The light microscope was the earliest tool of cytologists

• Allowed identification of organelles within cells

• Organelles are membrane-bound structures, such as nuclei, mitochondria, and chloroplasts


Useful tools in early microscopy

• The microtome (mid-1800s) allowed preparation of very thin slices of samples

• A variety of dyes for staining cells began to be used around the same time

• These improved the limit of resolution (how far apart objects must be to appear as distinct)

• The smaller the limit of resolution a microscope has, the greater its resolving power


Visualization of Cells

• The light microscopy so far described is called brightfield microscopy, as white light is passed through a specimen

• Some preparations (fixing, staining, embedding in plastic) may distort tissues

• Various types of microscopy have been developed to allow observation of living cells


Visualizing living cells

• Phase contrast/differential interference contrast microscopy exploit differences in the phase of light passing through a structure. Helps you see living cells clearly

• Fluorescence microscopy detects fluorescent dyes, or labels, to show locations of substances in the cell

• Confocal scanning uses a laser beam to illuminate a single plane of a fluorescently labeled specimen


Figure 1-3


Table 1-1


The Electron Microscope

• The electron microscope, using a beam of electrons rather than light, was a major breakthrough for cell biology

• The limit of resolution of electron microscopes is around 0.1-0.2 nm

• The magnification is much higher than light microscopes up to 100,000X


Electron microscopy

• In transmission electron microscopy (TEM), electrons are transmitted through the specimen

• In scanning electron microscopy (SEM), the surface of a specimen is scanned, by detecting electrons deflected from the outer surface

• Specialized approaches in electron microscopy allow for visualization of specimens in three dimensions, and one allows visualization of individual atoms






Figure 1-4a


Figure 1-4b


Figure 1-4c


Figure 1-4d


Electron Microscopy

• EM is normally used on samples that are fixed (parafilm) and coated with metal (gold).– Most cases of TEM and SEM samples are

dead or will die due to the electron beam– EM has revolutionized our understanding

of cellular structures(ribosomes)


The Biochemical Strand Covers the Chemistry of Biological Structure and Function

• Around the same time cytologists were studying cells microscopically, others began to explore cellular function

• Much of biochemistry dates from the work of Fredrich Wöhler (1828), who showed that a compound made in a living organism could be synthesized in the lab.

• Urea can be synthesized from ammonium cyanate


Developments in early biochemistry

• Louis Pasteur (1860s) showed that living yeast cells could ferment sugar into alcohol. What is this called?

• The Buchners (1897) showed that yeast extracts could do the same

• Led to the discovery of enzymes, biological catalysts. Specifically how do they function?


Early discoveries in biochemistry

• Steps of the pathways of fermentation and others were elucidated in the 1920s and 1930s

• Gustav Embden and Otto Meyerhof described the steps of glycolysis (the Embden-Meyerhof pathway) in the early 1930s

• The Krebs cycle (TCA) was described soon after by Hans Krebs

• Both pathways are important in energy metabolism of cells• Also Fritz Lipmann, showed theat ATP is principle energy

source in cells


Important advances in biochemistry

• Radioactive isotopes - to trace the fate of specific atoms and molecules (led to elucidation of the Calvin cycle, 1950s)

• 3H, 14C, and 32P were first used to trace the metabolic fate of specific atoms and molecules

• Melvin Calvin used 14C-labeled carbon dioxide

• Most common pathway for photosynthetic carbon metabolism. First pathway to use radioactivity


Techniques

• Subcellular fractionation

• Use of Centrifugation to separate/isolate different structures and macromolecules based on size, shape, and density

• Different types of centrifugation (described chp.12)

• Ultracentrifuges - capable of very high speeds (over 100,000 revolutions per minute)– Just as significant as the electron microscope


Ultracentrifuge


Gel electrophoresis


Important advances in biochemistry (continued):

• Chromatography - techniques to separate molecules from a solution based on size, charge, or chemical affinity (pigments in 1107)

• Electrophoresis - uses an electrical field to move proteins, DNA or RNA molecules through a medium based on size/charge

• Mass spectrometry - to determine the size and composition of individual proteins


The Genetic Strand Focuses on Information Flow

• The genetic strand has important roots in the nineteenth century

• Gregor Mendel’s experiments with peas (1866) laid the foundation for understanding the passage of “hereditary factors” from parents to offspring

• The hereditary factors are now known to be genes• His work was not appreciated until 35 years after his

discovery


Chromosomes and the genetic material

• Walther Flemming (1880) saw threadlike bodies in the nucleus called chromosomes

• He called the process of cell division mitosis

• Wilhelm Roux (1883) and August Weisman (shortly after) suggested that chromosomes carried the genetic material


The chromosome theory

• Three geneticists formulated the chromosome theory of heredity, proposing that Mendel’s hereditary factors are located on chromosomes

• Morgan, Bridges, and Sturtevant (1920s) were able to connect specific traits to specific chromosomes in the model organism, Drosophila melanogaster (the common fruit fly)


Progress in understanding DNA

• Friedrich Miescher (1869) first isolated DNA, which he called nuclein. What did he use to isolate DNA?

• DNA:

- known to be a component of chromosomes by 1914

- known to be composed of only 4 different nucleotides by the 1930s. Not enough variety???

- proteins, composed of 20 different amino acids, thought more likely to be genetic material


Key experiments (chp.18)

• Experiments with bacteria and viruses in the 1940s began to implicate DNA as the genetic material

• Avery, MacLeod, and McCarty showed that DNA can “transform” a nonpathogenic strain of bacteria into a pathogenic strain.

• Hershey and Chase showed that DNA, not protein, enters a bacterial cell when it is infected and is altered by the virus


DNA is the genetic material

•Beadle and Tatum formulated the one gene-one enzyme concept (each gene is responsible for the production of a single protein). Bread mold

•1953 - Watson and Crick, with assistance from Rosalind Franklin, proposed the double helix model for DNA structure

•1960s - many advances toward understanding DNA replication, RNA production, and the genetic code


Important techniques in genetics

• Ultracentrifugation and electrophoresis, for separating DNA and RNA molecules

• Nucleic acid hybridization, a variety of techniques that use the ability of nucleic acid bases to bind to each other. Why can this occur?

• Recombinant DNA technology, restriction enzymes cut DNA at specific places allowing scientists to create recombinant DNA molecules, with DNA from different sources


Recombinant DNA technology


Important techniques in genetics (continued)

• DNA sequencing, methods for rapidly determining the base sequences of DNA molecules

• It is now possible to sequence entire genomes (entire DNA content of a cell)

• Bioinformatics merges computer science with biology to organize and interpret enormous amounts of sequencing and other data


Bioinformatics

• 25,000 protein-encoding genes• National Center for Biotechnology

Information (NCBI) operated by National Institutes of Health (NIH)– PubMed– NCBI maintains GenBank, database of DNA

and protein sequences– OMIM databases of human genetic disorders


Important techniques in genetics (continued)

• Yeast two-hybrid system allows determination of how proteins interact within a cell

• Nanotechnology, development of tiny tools, sensors and, computer-aided analysis of the results


Yeast two hybrid


“Facts” and the Scientific Method

• In science, “facts” are tenuous and dynamic• The scientific method is used to assess new

information– Scientists formulate a hypothesis (tentative

explanation or model that can be tested)

– Data are collected and interpreted and the model is accepted or rejected

– What are the steps of scientific method?


Research approaches in cell biology

• Research in laboratories may be

– In vitro, using purified chemicals and cellular components. Cell culture workshop

– In vivo, using live cells or organisms (model organisms)

– In silico, using computer analysis of large amounts of data


Cell cultures


Figure 1B-1


Advantages of Model Organisms

• E. Coli– Easy to grow, short generation time, easy

mutagenized for gene function studies. Readily takes up DNA from other organisms (recombinant DNA studies)

• S. Cerevisia

• Drosophila


Advantages of Model Organisms

• C. elegan• Mus Musculus• Arabidopisis


How we explain observations

• Hypothesis - statement consistent with most of the data, may take the form of a model (an explanation that appears to account for the data); must be testable and falsifiable

• Theory - a hypothesis that has been extensively tested by many investigators, using different approaches, widely accepted (cell theory)

• Law - a theory that has been tested and confirmed over a long period of time with virtually no doubt of its validity

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