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Cellular Basis of Life

opyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

A Closer Look at Cells The cell Is the lowest level of organization that can perform all activities required for life

Figure 1.5Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

25 m

The Cells Heritable Information Cells contain chromosomes made partly of DNA, the substance of genes Which program the cells production of proteins and transmit information from parents to offspringSperm cell Nuclei containing DNA Fertilized egg with DNA from both parents Embyros cells with copies of inherited DNA

Egg cellFigure 1.6

Offspring with traits inherited from both parents

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Discovery of the Cell Robert Hooke (1665) English scientist, first described and named cells. Observed in a slice a cork and saw that the compartments / tiny boxes or cells were unique to cork.

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Anton van Leeuwenhoek (1674) Dutchman who first saw live cells using grains of sand polished into magnifying glasses. Saw a microbial world in droplets of pond water and also observed blood cells and sperm cells of animals.

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Matthias Schleiden and Theodor Schwann (1839) German biologists, reached a generalization based on many concurring observations reaching a generalization that all living things consists of cells.

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Rudolph Virchow (1858) German doctor, concluded that all cells come from pre-existing cells based on his study on how cells reproduce.

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Cell Theory (Classic) 1. All living things are composed of cells.

2. A cell is the smallest unit with the properties of life. 3. Each new cell arises from division of another, preexisting cell. 4. Each cell passes hereditary material to its offspring.

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

To study cells, biologists use microscopes and the tools of biochemistry

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Light microscopes (LMs) Pass visible light through a specimen Magnify cellular structures with lenses

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Can be used to visualize different sized cellular structures10 m Light microscope Electron microscope 1mHuman height Length of some nerve and muscle cells Chicken egg

0.1 m 1 cm

Frog egg

1 mm 100 m 10 m 1m 100 nm 10 nm

Smallest bacteria VirusesRibosomes Proteins

Electron microscope

Nucleus Most bacteria Mitochondrion

Unaided eye

Different types of microscopes

Most plant and Animal cells

1 nm

LipidsSmall molecules

Figure 6.2

0.1 nm

Atoms

Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 103 m 1 micrometer (m) = 103 mm = 106 m 1 nanometer (nm) = 103 mm = 109 m

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Use different methods for enhancing visualization of cellular structuresTECHNIQUE RESULT

(a) 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.]50 m

(b) Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved).

(c) Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells.

Figure 6.3Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

(d) Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences in density, making the image appear almost 3D. (e) 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.50 m

(f) 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 mCopyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The scanning electron microscope (SEM) Provides for detailed study of the surface of a specimenTECHNIQUE(a) Scanning electron microscopy (SEM). Micrographs taken with a scanning electron microscope 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.

RESULTS1 m

Cilia

Figure 6.4 (a)Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The transmission electron microscope (TEM) Provides for detailed study of the internal ultrastructure of cellsLongitudinal section of cilium (b) Transmission electron microscopy (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. Cross section of cilium1 m

Figure 6.4 (b)Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Eukaryotic cells have internal membranes that compartmentalize their functions Two types of cells make up every organism Prokaryotic Eukaryotic

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Comparing Prokaryotic and Eukaryotic Cells All cells have several basic features in common They are bounded by a plasma membrane They contain a semifluid substance called the cytosol They contain chromosomes They all have ribosomes

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Prokaryotic cells Do not contain a nucleus Have their DNA located in a region called the nucleoid

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cells DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes 0.5 m Flagella: locomotion organelles of some bacteria

Bacterial chromosome (a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

Figure 6.6 A, BCopyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Eukaryotic cells Contain a true nucleus, bounded by a membranous nuclear envelope Are generally quite a bit bigger than prokaryotic cells

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The logistics of carrying out cellular metabolism sets limits on the size of cells

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

A smaller cell Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cellSurface area increases while total volume remains constant

5 1

1Total surface area (height width number of sides number of boxes) Total volume (height width length number of boxes)

6

150

750

1

125

125

Surface-to-volume ratio (surface area volume)

6

12

6

Figure 6.7Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The plasma membrane Functions as a selective barrier Allows sufficient passage of nutrients and wasteOutside of cell Carbohydrate side chain

Hydrophilic region Inside of cell

0.1 mHydrophobic region

Figure 6.8 A, B

(a) TEM of a plasma membrane. The plasma membrane, here in a red blood cell, appears as a pair of dark bands separated by a light band.

Hydrophilic region

Phospholipid

Proteins

(b) Structure of the plasma membrane

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

A Panoramic View of the Eukaryotic Cell Eukaryotic cells Have extensive and elaborately arranged internal membranes, which form organelles

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