Chapter 6 A Tour of the Cell.

Chapter 6 A Tour of the Cell

Overview: The Fundamental Units of Life
All organisms are made of cells Cell structure is correlated to cellular function All cells are related by their descent from earlier cells For the Discovery Video Cells, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cytoskeleton: microtubule, intermediate filament,
Fig. 6-1 Figure 6.1 How do cellular components cooperate to help the cell function? Cytoskeleton: microtubule, intermediate filament,

Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry
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

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

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

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. GFP labelling for detection of the location of the target protein. Confocal : 3D image possible

TEMs are used mainly to study the internal structure of cells
Two basic types of electron microscopes (EMs) are used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The scanning electron microscope (SEM)
Provides for detailed study of the surface of a specimen TECHNIQUE RESULTS 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. (a) Cilia 1 µm 섬모 Figure 6.4 (a)

The transmission electron microscope (TEM)
Provides for detailed study of the internal ultrastructure of cells 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. (b) Longitudinal section of cilium Cross section of cilium 1 µm tracheal cell : 기관지 세포 Figure 6.4 (b)

Ultracentrifuges fractionate cells into their component parts
Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Ultracentrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-5 Figure 6.5 Cell fractionation Homogenization Tissue cells
TECHNIQUE Homogenization Tissue cells Homogenate 1,000 g (1,000 times the force of gravity) 10 min Differential centrifugation Supernatant poured into next tube 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris Figure 6.5 Cell fractionation 150,000 g 3 hr Pellet rich in mitochondria (and chloroplasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes

Protists, fungi, animals, and plants all consist of eukaryotic cells
Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells: Plasma membrane Semifluid substance called cytosol Chromosomes (carry genes) Ribosomes (make proteins) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Prokaryotic cells are characterized by having
No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles Cytoplasm bound by the plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(b) A thin section through the
bacterium Bacillus coagulans (TEM) Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s 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 Flagella: locomotion organelles of some bacteria (a) A typical rod-shaped bacterium 0.5 µm Bacterial chromosome Figure 6.6 A, B

Eukaryotic cells are characterized by having
DNA in a nucleus that is bounded by a membranous nuclear envelope Membrane-bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Carbohydrate side chain
Fig. 6-7 (a) TEM of a plasma membrane Outside of cell Inside of cell 0.1 µm Carbohydrate side chain Hydrophilic region Figure 6.7 The plasma membrane Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane

The surface area to volume ratio of a cell is critical
The logistics of carrying out cellular metabolism sets limits on the size of cells The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2, the volume increases by a factor of n3 Small cells have a greater surface area relative to volume Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Surface area increases while total volume remains constant
Fig. 6-8 Surface area increases while total volume remains constant 5 1 1 Total surface area [Sum of the surface areas (height  width) of all boxes sides  number of boxes] 6 150 750 Total volume [height  width  length  number of boxes] Figure 6.8 Geometric relationships between surface area and volume 1 125 125 Surface-to-volume (S-to-V) ratio [surface area ÷ volume] 6 1.2 6

A Panoramic View of the Eukaryotic Cell
A eukaryotic cell has internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles BioFlix: Tour Of An Animal Cell BioFlix: Tour Of A Plant Cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER
Fig. 6-9a Nuclear envelope ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER Flagellum Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Figure 6.9 Animal and plant cells—animal cell Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome

Rough endoplasmic reticulum
Fig. 6-9b Nuclear envelope Rough endoplasmic reticulum NUCLEUS Nucleolus Chromatin Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments CYTO- SKELETON Microtubules Figure 6.9 Animal and plant cells—plant cell Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell

The nucleus contains most of the DNA in a eukaryotic cell
Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell Ribosomes use the information from the DNA to make proteins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Nucleus: Information Central
The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle (additional DNA where?) The nuclear envelope encloses the nucleus, separating it from the cytoplasm The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Close-up of nuclear envelope
Fig. 6-10 Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope Ribosome 1 µm Figure 6.10 The nucleus and its envelope 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM)

Pores regulate the entry and exit of molecules from the nucleus
The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chromatin condenses to form discrete chromosomes
In the nucleus, DNA and proteins form genetic material called chromatin Chromatin condenses to form discrete chromosomes The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Ribosomes: Protein Factories
Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations: In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) For the Cell Biology Video Staining of Endoplasmic Reticulum, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Endoplasmic reticulum (ER)
Fig. 6-11 Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Figure 6.11 Ribosomes Small subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome

Crystal Structure of the large ribosomal subunit
Harry Noller at the University of California Santa Cruz Venki Ramakrishnan at the University of Cambridge, Thomas Steitz at Yale University

Components of the endomembrane system:
Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected via transfer by vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER: Smooth ER, which lacks ribosomes Rough ER, with ribosomes studding its surface For the Cell Biology Video ER and Mitochondria in Leaf Cells, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER
Fig. 6-12 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 200 nm Smooth ER Rough ER Figure 6.12 Endoplasmic reticulum (ER)

Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates Detoxifies poison Stores calcium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Functions of Rough ER The rough ER
Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) Distributes transport vesicles, proteins surrounded by membranes Is a membrane factory for the cell; adding membrane proteins and phospholipids to its own membrane and other endomembrane system by transport vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Golgi Apparatus: Shipping and Receiving Center
The Golgi apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles For the Cell Biology Video ER to Golgi Traffic, go to Animation and Video Files. For the Cell Biology Video Golgi Complex in 3D, go to Animation and Video Files. For the Cell Biology Video Secretion From the Golgi, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(“receiving” side of Golgi apparatus) 0.1 µm
Fig. 6-13 cis face (“receiving” side of Golgi apparatus) 0.1 µm Cisternae Figure 6.13 The Golgi apparatus trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus

Lysosomes: Digestive Compartments
A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids Animation: Lysosome Formation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) Phagocytosis (b) Autophagy Fig. 6-14 Nucleus 1 µm
Vesicle containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome Digestive enzymes Lysosome Lysosome Plasma membrane Peroxisome Figure 6.14a Lysosomes Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy

Vacuoles: Diverse Maintenance Compartments
A plant cell or fungal cell may have one or several vacuoles Food vacuoles are formed by phagocytosis Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells, hold organic compounds and water Video: Paramecium Vacuole Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Central vacuole Cytosol Nucleus Central vacuole Cell wall Chloroplast
Fig. 6-15 Central vacuole Cytosol Nucleus Central vacuole Figure 6.15 The plant cell vacuole Cell wall Chloroplast 5 µm

The Endomembrane System: A Review
The endomembrane system is a complex and dynamic player in the cell’s compartmental organization Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Nucleus Rough ER Smooth ER Plasma membrane Fig. 6-16-1
Figure 6.16 Review: relationships among organelles of the endomembrane system Plasma membrane

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi
Fig Nucleus Rough ER Smooth ER cis Golgi Figure 6.16 Review: relationships among organelles of the endomembrane system Plasma membrane trans Golgi

Peroxisomes are oxidative organelles
Concept 6.5: Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration, a metabolic process that generates ATP Chloroplasts, found in plants and algae, are the sites of photosynthesis Peroxisomes are oxidative organelles For the Cell Biology Video ER and Mitochondria in Leaf Cells, go to Animation and Video Files. For the Cell Biology Video Mitochondria in 3D, go to Animation and Video Files. For the Cell Biology Video Chloroplast Movement, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Mitochondria and chloroplasts
Are not part of the endomembrane system Have a double membrane Have proteins made by free ribosomes Contain their own DNA Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Mitochondria: Chemical Energy Conversion
Mitochondria are in nearly all eukaryotic cells They have a smooth outer membrane and an inner membrane folded into cristae The inner membrane creates two compartments: intermembrane space and mitochondrial matrix Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix Cristae present a large surface area for enzymes that synthesize ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

in the mitochondrial matrix
Fig. 6-17 Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Figure 6.17 The mitochondrion, site of cellular respiration Matrix 0.1 µm

Chloroplasts: Capture of Light Energy
The chloroplast is a member of a family of organelles called plastids Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis Chloroplasts are found in leaves and other green organs of plants and in algae Chloroplast structure includes: Thylakoids, membranous sacs, stacked to form a granum Stroma, the internal fluid contain chloroplast DNA & ribosome Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Inner and outer membranes
Fig. 6-18 Ribosomes Stroma Inner and outer membranes Granum 1 µm Thylakoid Figure 6.18 The chloroplast, site of photosynthesis

Peroxisomes: Oxidation
Transfer hydrogen from substrates to oxygen producing hydrogen peroxide (H2O2) as a by-product; detoxification break fatty acids down into smaller molecules Glyoxysome in plant seed converts faty acids to sugar Grow larger by incorporating proteins and lipids and increase in number by splitting Chloroplast Peroxisome Mitochondrion 1 µm Figure 6.19

It is composed of three types of molecular structures:
Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers extending throughout the cytoplasm It organizes the cell’s structures and activities, anchoring many organelles It is composed of three types of molecular structures: Microtubules Microfilaments Intermediate filaments For the Cell Biology Video The Cytoskeleton in a Neuron Growth Cone, go to Animation and Video Files For the Cell Biology Video Cytoskeletal Protein Dynamics, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Microtubule Microfilaments 0.25 µm Fig. 6-20
Figure 6.20 The cytoskeleton Microfilaments 0.25 µm

Roles of the Cytoskeleton: Support, Motility, and Regulation
The cytoskeleton helps to support the cell and maintain its shape It interacts with motor proteins to produce motility Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton Recent evidence suggests that the cytoskeleton may help regulate biochemical activities Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Receptor for motor protein
Fig. 6-21 Vesicle ATP Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton (a) Microtubule Vesicles 0.25 µm Figure 6.21 Motor proteins and the cytoskeleton (b)

Components of the Cytoskeleton
Three main types of fibers make up the cytoskeleton: Microtubules are the thickest of the three components of the cytoskeleton Microfilaments, also called actin filaments, are the thinnest components Intermediate filaments are fibers with diameters in a middle range For the Cell Biology Video Actin Network in Crawling Cells, go to Animation and Video Files. For the Cell Biology Video Actin Visualization in Dendrites, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10 µm Column of tubulin dimers Tubulin dimer   25 nm Table 6-1a

Table 6-1b 10 µm Table 6-1b Actin subunit 7 nm

Fibrous subunit (keratins coiled together)
Table 6-1c 5 µm Table 6-1c Keratin proteins Fibrous subunit (keratins coiled together) More permanent than microtubule and microfilament 8–12 nm

Functions of microtubules:
Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long Functions of microtubules: Shaping the cell Guiding movement of organelles Separating chromosomes during cell division For the Cell Biology Video Transport Along Microtubules, go to Animation and Video Files. For the Cell Biology Video Movement of Organelles in Vivo, go to Animation and Video Files. For the Cell Biology Video Movement of Organelles in Vitro, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Centrosomes and Centrioles
In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Longitudinal section of one centriole Microtubules Cross section
Fig. 6-22 Centrosome Microtubule Centrioles 0.25 µm Figure 6.22 Centrosome containing a pair of centrioles Longitudinal section of one centriole Microtubules Cross section of the other centriole

Video: Paramecium Cilia
Cilia and Flagella Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Cilia and flagella differ in their beating patterns Video: Chlamydomonas Video: Paramecium Cilia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Direction of organism’s movement
Fig. 6-23 Direction of swimming (a) Motion of flagella 5 µm Direction of organism’s movement Figure 6.23a A comparison of the beating of flagella and cilia—motion of flagella Power stroke Recovery stroke (b) Motion of cilia 15 µm

Animation: Cilia and Flagella
Cilia and flagella share a common ultrastructure: A core of microtubules sheathed by the plasma membrane A basal body that anchors the cilium or flagellum A motor protein called dynein, which drives the bending movements of a cilium or flagellum Animation: Cilia and Flagella Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cross section of cilium
Fig. 6-24 Outer microtubule doublet Plasma membrane 0.1 µm Dynein proteins Central microtubule Radial spoke Protein cross-linking outer doublets Microtubules (b) Cross section of cilium Plasma membrane Basal body 0.5 µm (a) Longitudinal section of cilium 0.1 µm Figure 6.24 Ultrastructure of a eukaryotic flagellum or motile cilium Triplet (c) Cross section of basal body

How dynein “walking” moves flagella and cilia:
Dynein arms alternately grab, move, and release the outer microtubules Protein cross-links limit sliding Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum For the Cell Biology Video Motion of Isolated Flagellum, go to Animation and Video Files. For the Cell Biology Video Flagellum Movement in Swimming Sperm, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-25 Figure 6.25 How dynein “walking” moves flagella and cilia
Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement ATP Cross-linking proteins inside outer doublets Anchorage in cell Figure 6.25 How dynein “walking” moves flagella and cilia (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion

Microfilaments (Actin Filaments)
Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli of intestinal cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Microfilaments (actin filaments)
Fig. 6-26 Microvillus Plasma membrane Microfilaments (actin filaments) Figure 6.26 A structural role of microfilaments Intermediate filaments 0.25 µm

Microfilaments that function in cellular motility contain the protein myosin in addition to actin
In muscle cells, thousands of actin filaments are arranged parallel to one another Thicker filaments composed of myosin interdigitate with the thinner actin fibers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-27 Figure 6.27 Microfilaments and motility Muscle cell
Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Nonmoving cortical cytoplasm (gel) Figure 6.27 Microfilaments and motility Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall (c) Cytoplasmic streaming in plant cells

Muscle cell Actin filament Myosin filament Myosin arm
Fig, 6-27a Muscle cell Actin filament Myosin filament Myosin arm Figure 6.27a Microfilaments and motility (a) Myosin motors in muscle cell contraction

Cortex (outer cytoplasm): gel with actin network
Fig. 6-27bc Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Nonmoving cortical cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Figure 6.27b,c Microfilaments and motility Vacuole Parallel actin filaments Cell wall (c) Cytoplasmic streaming in plant cells

Localized contraction brought about by actin and myosin also drives amoeboid movement
Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Video: Cytoplasmic Streaming
Cytoplasmic streaming is a circular flow of cytoplasm within cells This streaming speeds distribution of materials within the cell In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming Video: Cytoplasmic Streaming Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Intermediate Filaments
Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules They support cell shape and fix organelles in place Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes For the Cell Biology Video Interphase Microtubule Dynamics, go to Animation and Video Files. For the Cell Biology Video Microtubule Sliding in Flagellum Movement, go to Animation and Video Files. For the Cell Biology Video Microtubule Dynamics, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

These extracellular structures include:
Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions For the Cell Biology Video Ciliary Motion, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Prokaryotes, fungi, and some protists also have cell walls
Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plant cell walls may have multiple layers:
Primary cell wall: relatively thin and flexible Middle lamella: thin layer between primary walls of adjacent cells (pectin) Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells For the Cell Biology Video E-cadherin Expression, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Secondary cell wall Primary cell wall Middle lamella Central vacuole
Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Figure 6.28 Plant cell walls Plant cell walls Plasmodesmata

The Extracellular Matrix (ECM) of Animal Cells
Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins For the Cell Biology Video Cartoon Model of a Collagen Triple Helix, go to Animation and Video Files. For the Cell Biology Video Staining of the Extracellular Matrix, go to Animation and Video Files. For the Cell Biology Video Fibronectin Fibrils, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Collagen is about half of the total protein in human body
Fig. 6-30 Collagen is about half of the total protein in human body Collagen Proteoglycan complex Polysaccharide molecule EXTRACELLULAR FLUID Carbo- hydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Figure 6.30 Extracellular matrix (ECM) of an animal cell, part 1 Micro- filaments CYTOPLASM Integrins are the linker between microfilaments in cytoskeleton and ECM in extracellular fluid And transmit signals between the ECM and the cytoskeleton and result in changes in cell behavior

Functions of the ECM: Support Adhesion Movement Regulation of genes :
information of ECM reaches the nucleus by a combination of mechanical and chemical signaling pathways. Changes in the cytoskeleton may in turn trigger chemical signaling pathways inside the cell, leading to change in proteins and functions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Intercellular Junctions
Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact There are several types of intercellular junctions Plasmodesmata Tight junctions Desmosomes Gap junctions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Plasmodesmata in Plant Cells
Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata
Fig. 6-31 Cell walls Interior of cell Interior of cell Figure 6.31 Plasmodesmata between plant cells 0.5 µm Plasmodesmata Plasma membranes

Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells
At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid. Continuous sealing in an intestine Desmosomes (anchoring junctions) fasten cells together into strong sheets; anchor intermediate filament in cytoplasm and attach muscle cells to each other in a muscle. “muscle tears” involve the rupture of desmosomes. Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells, just like plasmodesmata in plants. Necessary for communication between cells in heart, muscle and in animal embryos. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 6-32 Tight junction Tight junctions prevent fluid from moving
across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Desmosome Gap junctions 1 µm Figure 6.32 Intercellular junctions in animal tissues Extracellular matrix Space between cells Gap junction Plasma membranes of adjacent cells 0.1 µm

Animation: Tight Junctions
Fig. 6-32a Tight junctions prevent fluid from moving across a layer of cells Tight junction Intermediate filaments Animation: Tight Junctions Desmosome Animation: Desmosomes Gap junctions Animation: Gap Junctions Figure 6.32 Intercellular junctions in animal tissues—tight junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells

The Cell: A Living Unit Greater Than the Sum of Its Parts
Cells rely on the integration of structures and organelles in order to function For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

TAXOL Paclitaxel은 Taxus brevifolia Nutt. (Taxaceae)(미국 주목나무-Western Yew)의 주피(bark)에서 추출한 diterpenoid taxane 유도체로 천연 taxane ring을 가진 alkaloid이다. (1) 이 taxane ring과 ester side chain이 cytotoxicity 작용을 가지는 것으로 알려졌다.(1) Paclitaxel은 수용성이 극히 낮아 제제화하기 위해 polyoxyethylated castor oil과 absolute ethanol의 혼합물인 Cremorphor® EL이라는 용제를 사용하고 있다. (3) 따라서 임상적으로 이러한 용제가 과량 투여되므로 심장독성과 과민반응이 발생하는 것으로 보고되고 있다. Taxol 와 a-, b- tubulin complex 구조 Mechanism of Action Paclitaxel은 1992년12월에 난치성 난소암의 치료제로 FDA의 승인을 받은 항암제로 세포 내 microtubule의 assembly를 증진시키고 disassembly를 저해함으로써 항암효과를 나타내는 독특한 약물이다.(2) Microtubule이란 세포질(cytoplasm)에 있는 가는 tube 같은 구조로써 세포의 골격 형성과 motility를 유지하며 유사분열 중기에서 방추사의 형성과 분열시 이동에 관여한다.(2) Microtubule은 tubulin dimer라는 고유의 subunit로 이루어졌고 이 tubulin이 assembly되어 microtubule을 형성한다. .(2) 형성된 microtubule은 유사분열시 기능수행을 위해서는 disassembly 되어야 한다. .(2) Paclitaxel은 암세포의 microtubule의 assembly를 증진 시키고 일단 형성된 microtubule을 안정화시켜 polymerization 상태로 남아있게 한다.(2) Fuchs과 Johnson의 초기 발견에 의하면, microtubule의 disassembly를 저해하여 유사분열에 필요한 방추사의 형성을 억제하므로 세포 주기상 암 세포가 G2기와 M기에 머무르게 되어 cytotoxic effect를 가진다. 이는 vincristine, vinblastine, colchicines, podophyllotoxin, maytansine과 같은 항암제와 같은 작용이나,(1) paclitaxel은 다른 항암제와 달리 microtubule을 stabilize시키고, depolymerization을 억제시킨다.(2) 또한 이 G2기와 M기 는 방사선에 매우 민감한 주기이므로 radiation therapy와 병용할 시 cytotoxicity가 증가하게 된다. (6)

Fig. 6-UN1a Cell Component Structure Function Concept 6.3 Nucleus
Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is continuous with the endoplasmic reticulum (ER). Houses chromosomes, made of chromatin (DNA, the genetic material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit os materials. The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes (ER) Ribosome Two subunits made of ribosomal RNA and proteins; can be free in cytosol or bound to ER Protein synthesis

Fig. 6-UN1b Cell Component Structure Function Concept 6.4
Endoplasmic reticulum Extensive network of membrane-bound tubules and sacs; membrane separates lumen from cytosol; continuous with the nuclear envelope. Smooth ER: synthesis of lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons The endomembrane system regulates protein traffic and performs metabolic functions in the cell (Nuclear envelope) Rough ER: Aids in sythesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Golgi apparatus Stacks of flattened membranous sacs; has polarity (cis and trans faces) Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many polysaccharides; sorting of Golgi products, which are then released in vesicles. Breakdown of ingested substances cell macromolecules, and damaged organelles for recycling Lysosome Membranous sac of hydrolytic enzymes (in animal cells) Vacuole Large membrane-bounded vesicle in plants Digestion, storage, waste disposal, water balance, cell growth, and protection

Fig. 6-UN1c Cell Component Structure Function Concept 6.5
Mitochondrion Bounded by double membrane; inner membrane has infoldings (cristae) Cellular respiration Mitochondria and chloroplasts change energy from one form to another Chloroplast Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Photosynthesis Peroxisome Specialized metabolic compartment bounded by a single membrane Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H2O2) as a by-product, which is converted to water by other enzymes in the peroxisome

Chapter 6 A Tour of the Cell.

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