1. Overview: The Fundamental Units 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
For the Discovery Video Cells, go to Animation and Video Files.

2. 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
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
100 nm
Smallest bacteria
Electron microscope
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms

3. Figure 6.3a-d Light microscopy
(c) Phase-contrast
(e) Fluorescence
Figure 6.3a-d Light microscopy
50 µm
(f) Confocal

4. 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

5. SCANNING ELECTRON MICROSCOPE

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

9. 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

10. Differential centrifugation
TECHNIQUE
Homogenization
Figure 6.5 Cell fractionation, part 1
Tissue
cells
Homogenate
Differential centrifugation

11. 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

12. 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

13. 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

14. Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells:
Plasma membrane
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)

15. 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

16. Carbohydrate side chain
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

17. 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 (What up wit da?)
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

18. Surface area increases while total volume remains constant5 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

22. ENDOPLASMIC RETICULUM (ER) Nucleolus NUCLEUS Rough ER Smooth ER
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

23. Rough endoplasmic reticulum
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

24. The Nucleus: Information Central
The nucleus contains most of the cell’s genes
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

25. Close-up of nuclear envelope
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)

26. 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

27. 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.

29. 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

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

31. 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.

32. 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)

33. Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates
Detoxifies poison
Stores calcium

34. 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.

35. (“receiving” side of Golgi apparatus) 0.1 µm
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

36. 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

39. Video: Paramecium Vacuole
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

40. 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

41. 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.

42. Mitochondria and chloroplasts
Are not part of the endomembrane system
Have a double membrane
Have proteins made by free ribosomes
Contain their own DNA

43. 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

44. 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

47. 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

48. Chloroplast structure includes:
Thylakoids, membranous sacs, stacked to form a granum
Stroma, the internal joo-joo

49. 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

50. 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

51. 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.

52. 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)

53. 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.

54. 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

55. 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.

56. 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

57. Longitudinal section of one centriole Microtubules Cross section
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

59. 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

60. Direction of organism’s movement
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

61. 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

62. Cross-linking proteins inside outer doublets
ATP
Cross-linking proteins inside outer doublets
Anchorage in cell
(b) Effect of cross-linking proteins 1 3
Figure 6.25b, c How dynein “walking” moves flagella and cilia 2
(c) Wavelike motion

63. Muscle cell Actin filament Myosin filament Myosin arm
Figure 6.27a Microfilaments and motility
(a) Myosin motors in muscle cell contraction

64. 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.

65. 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.

66. 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

67. 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.

68. Secondary cell wall Primary cell wall Middle lamella Central vacuole
Cytosol
Plasma membrane
Figure 6.28 Plant cell walls
Plant cell walls
Plasmodesmata

69. Functions of the ECM:
Support
Adhesion
Movement
Regulation

70. 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

71. 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

72. Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells
At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
Desmosomes (anchoring junctions) fasten cells together into strong sheets
Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells
Animation: Tight Junctions
Animation: Desmosomes
Animation: Gap Junctions

73. Figure 6.32 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 Intercellular junctions in animal tissues
Extracellular
matrix
Space
between
cells
Gap junction
Plasma membranes
of adjacent cells
0.1 µm

74. 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

75. 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

76. 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