1. Chapter 6
A Tour of the Cell

2. Overview: The Fundamental Units of Life
All organisms are made of cells (Cell Theory).
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 (heredity / reproduction).
For the Discovery Video Cells, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. 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

4. 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

5. The size range of cells 10 m 1 m 0.1 m 1 cm 1 mm 100 µm 10 µm 1 µm
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
Smallest bacteria
Electron microscope
100 nm
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms

6. LMs (light microscopes) 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

7. Light Microscopy Figure 6.3a-d specimen specimen contrast (Nomarski)
TECHNIQUE
RESULTS
(a) Brightfield unstained
specimen
50 µm
(b) Brightfield stained
specimen
(c) Phase-contrast
(d) Differential-interference-
contrast (Nomarski)
(e )Fluorescence
Figure 6.3a-d
50 µm
(f) Confocal
50 µm

8. 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

9. Electron microscopy Surface Internal structures Cilia
TECHNIQUE
RESULTS
1 µm
Cilia
(a) Scanning electron
microscopy (SEM)
Surface
Longitudinal
section of
cilium
Cross section
of cilium
1 µm
Figure 6.4
(b) Transmission electron
microscopy (TEM)
Internal structures

10. Cell Fractionation
Cell fractionation takes cells apart and separates the major organelles from one another.
Ultracentrifuges fractionate cells and separate their component parts by density.
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

11. Cell fractionation Homogenization
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
1,000 g
(1,000 times the
force of gravity)
10 min
Differential centrifugation : density
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
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloro-
plasts if cells
are from a plant)
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes

12. Differential centrifugation
Cell Fractionation: Part 1
TECHNIQUE
Homogenization
Figure 6.5 Cell fractionation, part 1
Tissue
cells
Homogenate
Differential centrifugation

13. (1,000 times the force of gravity)
Cell Fractionation: Part 2
TECHNIQUE (cont.)
1,000 g
(1,000 times the force of gravity)
10 min
Supernatant poured into next tube
20,000 g
20 min
80,000 g
60 min
Pellet rich in nuclei and cellular debris
150,000 g
3 hr
Pellet rich in mitochondria (and chloro-plasts if cells
are from a plant)
Figure 6.5 Cell fractionation, part 2
Pellet rich in “microsomes” (pieces of plasma
membranes and cells’ internal membranes)
Pellet rich in ribosomes

14. Eukaryotic cells have internal membranes that compartmentalize their functions
Cell = the basic structural and functional unit of all life. (Cell Theory).
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

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

16. No nucleus Prokaryotic cells are characterized by having
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

17. Prokaryotic Cell Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial
chromosome
Cell wall
Capsule
0.5 µm
Flagella
(a)
A typical rod-shaped bacterium
(b)
A thin section through the bacterium Bacillus coagulans (TEM)
Figure 6.6

18. 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

19. The plasma membrane is a selective barrier (semi-permeable) 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

20. Phospholipid Plasma Membrane (a) TEM of a plasma membrane
Outside of cell
Inside of
cell
0.1 µm
Carbohydrate side chain
Hydrophilic
region
Figure 6.7 The
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane

21. 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

22. Surface area increases while total volume remains constant
Geometric relationships
between surface area and volume
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 1
125
125
Surface-to-volume
(S-to-V) ratio
[surface area ÷ volume] 6
1.2 6

23. Eukaryotic cell: animal cell
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

24. Eukaryotic Cell: Plant Cell
Rough endoplasmic reticulum ( Rough ER)
NUCLEUS:
Nuclear Envelope
Smooth endoplasmic reticulum (Smooth ER)
Nucleolus
Ribosomes
Chromatin
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

25. The Nucleus: Information Central : DNA
The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle.
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

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

27. 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

28. 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

29. 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 - ER).
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

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

31. Components of the endomembrane system:
The endomembrane system regulates protein traffic and performs metabolic functions in the cell
Components of the endomembrane system:
Nuclear envelope
Endoplasmic reticulum: ER
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

32. 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

33. Endoplasmic Reticulum Smooth ER ER Rough ER Nuclear envelope ER lumen
Cisternae
Transitional ER
Ribosomes
Transport vesicle
200 nm
Smooth ER
Rough ER
Figure 6.12

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

35. 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

36. 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

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

38. 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.
Helps to breakdown and recycle cell material.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

39. A lysosome fuses with the food vacuole and digests the molecules.
Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole.
A lysosome fuses with the food vacuole and digests the molecules.
Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy.
For the Cell Biology Video Phagocytosis in Action, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

40. Lysosomes Lysosome Lysosome 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
Digestion
Food vacuole
Mitochondrion
Digestion
Vesicle
(a) Phagocytosis :engulfs
(b) Autophagy : recycles

41. Vacuoles: Diverse Maintenance Compartments
Food vacuoles are formed by phagocytosis.
Contractile vacuoles, found in many freshwater protists, pump excess water out of cells: osmoregulation.
Central vacuoles, found in many mature plant cells, hold organic compounds and water.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

42. The plant cell vacuole Central vacuole Central vacuole
Tonoplast = central vacuole membrane
Cytosol
Nucleus
Central vacuole
Figure 6.15
Cell wall
Chloroplast
5 µm

43. The Endomembrane System
Nucleus
Rough ER
Smooth ER
cis Golgi
Figure 6.16 Review: relationships among organelles of the endomembrane system
Plasma membrane
trans Golgi

44. Mitochondria and Chloroplasts change energy from one form to another
Mitochondria are the sites of aerobic 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

45. 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

46. 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

47. The mitochondrion = site of cellular respiration
Intermembrane space
Outer membrane
Free ribosomes
in the mitochondrial matrix
Inner membrane
Cristae
Figure 6.17
Matrix
0.1 µm

48. 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: water + carbon dioxide = sugar + oxygen.
Chloroplasts are found in leaves and other green organs of plants and in algae.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

49. Chloroplast structure includes:
Thylakoids, membranous sacs, stacked to form a granum : light dependent reactions.
Stroma, the internal fluid: Calvin Cycle = light independent reactions.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

50. The chloroplast = site of photosynthesis Chloroplast
Ribosomes
Stroma
Inner and outer membranes
Granum
1 µm
Thylakoid
Figure 6.18

51. Peroxisomes: Oxidation
Peroxisomes are specialized metabolic compartments bounded by a single membrane.
Peroxisomes produce hydrogen peroxide and convert it to water.
Oxygen is used to break down different types of molecules.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

52. It is composed of three types of molecular structures:
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

53. The cytoskeleton
Microtubule
Figure 6.20
Microfilaments
0.25 µm

54. 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

55. The cytoskeleton Vesicle Receptor for motor protein
ATP
Receptor for motor protein
Motor protein (ATP powered)
Microtubule
of cytoskeleton
(a)
Microtubule
Vesicles
0.25 µm
Figure 6.21
(b)

56. 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

57. Table 6-1 10 µm 10 µm 10 µm Column of tubulin dimers Keratin proteins
Actin subunit
Fibrous subunit (keratins coiled together)
25 nm
7 nm
8–12 nm  
Tubulin dimer

58. 10 µm
Table 6-1a
Column of tubulin dimers
25 nm  
Tubulin dimer

59. 10 µm
Table 6-1b
Actin subunit
7 nm

60. Fibrous subunit (keratins coiled together)
5 µm
Table 6-1c
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm

61. 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

62. Centrosomes and Centrioles
In many cells, microtubules grow out from a centrosome near the nucleus
The centrosome = “microtubule-organizing center” = MTOC
In animal cells, the centrosome has a pair of centrioles 9x3 Each centriole has nine triplets of microtubules arranged in a ring.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

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

65. Direction of organism’s movement
Comparison
of the
beating of
flagella
and
cilia.
Direction of swimming
(a) Motion of flagella
5 µm
Direction of organism’s movement
Figure 6.23a
Power stroke
Recovery stroke
(b) Motion of cilia
15 µm

66. 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

67. Basal body Ultrastructure of a eukaryotic flagellum or motile cilium
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 9x2
Plasma membrane
Basal body
0.5 µm
(a)
Longitudinal section of cilium
0.1 µm
Figure
Triplet
(c) Cross section of basal body 9x3

68. The motor protein, dynein, moves flagella and cilia by “walking” :
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

69. 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
(b) Effect of cross-linking proteins 1 3 2
(c) Wavelike motion

70. Microfilaments (Actin Filaments)
Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of protein 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

71. 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

72. Microfilaments and motility Figure 6.27 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
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
Cell wall
(c) Cytoplasmic streaming in plant cells

73. Sarcomere – muscle cell unit of contraction
Actin filament
Myosin filament
Myosin arm
Figure 6.27a Microfilaments and motility
(a) Myosin motors in muscle cell contraction

74. 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

75. 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

76. 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

77. 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

78. Intercellular junctions
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

79. 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

80. Plant cell walls may have multiple layers:
Primary cell wall: relatively thin and flexible
Middle lamella: thin layer between primary walls of adjacent cells
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

81. Plant cell walls Secondary cell wall
Primary cell wall outermost of the cell walls
Middle lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Figure 6.28
Plant cell walls
Plasmodesmata

82. 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

83. Extracellular matrix (ECM) of an animal cell
Collagen
Proteoglycan
complex
Polysaccharide
molecule
EXTRACELLULAR FLUID
Carbo-
hydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Figure 6.30
Micro-
filaments
CYTOPLASM

84. ECM of Animal cell Proteoglycan complex Collagen EXTRACELLULAR FLUID
Fibronectin
Integrins
Plasma membrane
Figure 6.30 Extracellular matrix (ECM) of an animal cell, part 1
Micro-filaments
CYTOPLASM

85. Functions of the ECM: Support Adhesion Movement Regulation
Identification “ID” cell-to-cell recognition
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

86. 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 = channels / plant cells
*Gap junctions = channels / animal cells
Tight junctions – waterproof
Desmosomes - anchors
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

87. 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

88. Plasmodesmata between plant cells
Cell walls
Interior of cell
Interior of cell
Figure 6.31
0.5 µm
Plasmodesmata
Plasma membranes

89. Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells
At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid… waterproof.
desmosomes (anchoring junctions) fasten cells together into strong sheets.
gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

90. Intercellular junctions
in animal tissues
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
Extracellular
matrix
Space
between
cells
Gap junction
Plasma membranes
of adjacent cells
0.1 µm

91. 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

92. The emergence of cellular functions –> Macrophages’s ability to engulf and destroy bacteria
Figure 6.33

93. Cell Structures & Functions 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 of
materials.
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
(ER)
Ribosome
Two subunits made of ribo-
somal RNA and proteins; can be
free in cytosol or bound to ER
Protein synthesis
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 carbohy-
drates, Ca2+ storage, detoxifica-tion of drugs and poisons
The endomembrane system
regulates protein traffic and
performs metabolic functions
in the cell
(Nuclear
envelope)
Rough ER: Aids in synthesis 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, carbo-
hydrates on proteins, and phos-
pholipids; synthesis of many
polysaccharides; sorting of Golgi
products, which are then
released in vesicles.
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Breakdown of ingested substances,
cell macromolecules, and damaged
organelles for recycling
Vacuole
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Concept 6.5
Mitochondrion
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Cellular respiration
Mitochondria and chloro-
plasts 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

94. The eukaryotic cell’s Genetic Instructions are housed in
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 ribo-
somal RNA and proteins; can be
free in cytosol or bound to ER
Protein synthesis

95. The endomembrane system regulates protein traffic and
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 carbohy-
drates, Ca2+ storage, detoxifica-
tion 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, carbo-
hydrates on proteins, and phos-
pholipids; synthesis of many
polysaccharides; sorting of
Golgi products, which are then
released in vesicles.
Breakdown of ingested sub-
stances 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

96. Mitochondria and chloroplasts change energy from
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

97. You should now be able to:
Distinguish between the following pairs of terms: magnification and resolution; prokaryotic and eukaryotic cell; free and bound ribosomes; smooth and rough ER.
Describe the structure and function of the components of the endomembrane system.
Briefly explain the role of mitochondria, chloroplasts, and peroxisomes.
Describe the functions of the cytoskeleton.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

98. Describe the structure of a plant cell wall.
Compare the structure and functions of microtubules, microfilaments, and intermediate filaments.
Explain how the ultrastructure of cilia and flagella relate to their functions.
Describe the structure of a plant cell wall.
Describe the structure and roles of the extracellular matrix in animal cells.
Describe four different intercellular junctions.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings