Copyright © 2009 Pearson Education, Inc.. The World of the Cell Wayne M. Becker Lewis J. Kleinsmith Jeff Hardin Gregory Paul Bertoni Seventh Edition Chapter 1 A Preview of the Cell Copyright © 2009 Pearson Education, Inc..

Overview: The Fundamental Units of Life Cell is the basic unit of life.All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells Cell biology is the science that deals with the form and functions of cells For the Discovery Video Cells, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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The emergence of modern Cell Biology An interweaving of three different branches Cytology, the study of cells,deals with cellular structures use microscopes (300 hundred years ago) Biochemistry led to understanding of cellular functions,by development of various techniques, ultracentrifugation, chromatography, electrophoresis & mass spectrometry to identify and separate cellular components Genetics, deals with the heredity Though usually too small to be seen by the unaided can be complex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Main features of three strands The cytology deals with cellular structures by microscopes, Lm & EM, led to formulation of cell theory All organisms consist of one or more cells The cell is the basic unit of structure(Schwann 1839) All cells arise from preexisting cells(Virchow) Biochemistry covers the chemistry of biological structures and function, it has led to a new field of Proteomics (function and interaction of all proteins present in a cell). Genetics focuses on flow of hereditary information, contributed the knowledge of genes, chromosome theory,sructure of DNA. DNA sequencing has led to a new discipline called bioformatics, that merges computer science & biology to understand sequencing data

THE PROCESS OF SCIENCE Scientists use two main approaches to learn about nature Science Is a way of knowing Seeks natural causes for natural phenomena

Facts and Scientific Method Facts and Scientific Method Science is not a collection of facts but a process of discovering answers to questions about our natural world. Two approaches used Discovery Science In discovery science Scientists describe some aspect of the world and use inductive reasoning to draw general conclusions

Hypothesis-Based Science Hypothesis-Based Science In hypothesis-based science Scientists attempt to explain obser vations by testing hypotheses

With hypothesis-based science, we pose and test hypotheses With hypothesis-based science, we pose and test hypotheses Hypothesis-based science involves Obser vations, questions, hypotheses as tentative statement based on the previous observation or experiment as answers to questions Deductions leading to predictions, and then tests of predictions to see if a hypothesis is falsifiable Hypothesis must be testable, scientist can design a controlled experiment to determine whether the hypothesis will be supported by data or observation When a hypothesis have been tested many times, and by different scientist with the same results, it becomes a THEORY e.g theory of natural selection

A Case Study from Ever yday Life A Case Study from Ever yday Life Deductive reasoning is used in testing hypotheses as follows If a hypothesis is correct, and we test it, then we can expect a par ticular outcome Observations Question Hypothesis # 1: Dead batteries Hypothesis # 2: Burnt-out bulb Prediction: Replacing batteries will fix problem Replacing bulb Test prediction Test falsifies hypothesis Test does not falsify hypothesis Figure 1.8A

Percent of total attacks A Case Study of Hypothesis-Based Science In experiments designed to test hypotheses The use of control groups and experimental groups helps to control variables Percent of total attacks on artificial snakes 100 80 60 40 20 83% 17% 16% 84% Artificial king snakes Artificial brown snakes Coral snakes absent present Figure 1.8B Figure 1.8C Figure 1.8D Figure 1.8E

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Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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The quality of an image depends on Magnification, the ratio of an object’s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in parts of the sample Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Different types of microscopes Can be used to visualize different sized cellular structures Unaided eye 1 m 0.1 nm 10 m 0.1 m 1 cm 1 mm 100 µm 10 µ m 1 µ m 100 nm 10 nm 1 nm Length of some nerve and muscle cells Chicken egg Frog egg Most plant and Animal cells Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Nucleus Most bacteria Mitochondrion Light microscope Electron microscope Figure 6.2 Human height Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 mm = 10–9 m

Units of Measurements Micrometer(um), 1/1ooooo of a meter Micrometer most useful unit for expressing the cells and large organelles. Plant and animal cells are 10-20 ums; in diameter ,bacterial cell much smaller only 1x2 ums can be seen by LM. Nanometer(nm) is one billionth of a meter, it is used to measure organelles fig1A-2 , ribosomes, Membranes, microtubules & microfilaments seen by Em.

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LMs can magnify effectively to about 1,000 times the size of the actual specimen Various techniques enhance contrast and enable cell components to be stained or labeled Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Use different methods for enhancing visualization of cellular structures TECHNIQUE RESULT Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.] (a) Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved). (b) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells. (c) 50 µm Figure 6.3

Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery. Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. 50 µm (d) (e) (f) Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D.

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Electron microscopes (EMs) Focus a beam of electrons through a specimen (TEM) or onto its surface (SEM)

The scanning electron microscope (SEM) Provides for detailed study of the surface of a specimen TECHNIQUE RESULTS Scanning electron micro- scopy (SEM). Micrographs taken with a scanning electron micro- scope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps move inhaled debris upward toward the throat. (a) Cilia 1 µm Figure 6.4 (a)

The transmission electron microscope (TEM) Provides for detailed study of the internal ultrastructure of cells Transmission electron micro- scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections. (b) Longitudinal section of cilium Cross section of cilium 1 µm Figure 6.4 (b)

10 m 1 m 0.1 m 1 cm 1 mm 100 µm 10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm Fig. 6-2 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Unaided eye Chicken egg 1 cm Frog egg 1 mm 100 µm Most plant and animal cells Light microscope 10 µm Nucleus Most bacteria 1 µm Mitochondrion Figure 6.2 The size range of cells Smallest bacteria Electron microscope 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms

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Figure A-26 Comparison of TEM & SEM Electron Micrograph TEM,Rough Endoplasmic reticulum membranes in the cytoplasm of rat pancreas cell. The same structure prepared by SEM, just shows 3D appearance of RER. Figure A-26

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