1. Learning objectives Understand the basic tenets of the cell theory
Contrast the general features of prokaryotic and eukaryotic cells
Be able to distinguish the organelles and structures typical of eukaryotic plant and animal cells.
Know the functions associated with these organelles and structures.

2. 4.2 Cell Structure
The cell is the smallest unit that shows the properties of life
All cells have a plasma membrane and cytoplasm, and all start out life with DNA

3. Components of All Cells
Plasma membrane
Controls substances passing in and out of the cell
DNA containing region
Nucleus in eukaryotic cells
Nucleoid region in prokaryotic cells
Cytoplasm
A semifluid mixture containing cell components

4. Organelles
Organelles are structures that carry out special metabolic functions inside a cell
Membrane-enclosed organelles compartmentalize tasks such as building, modifying, and storing substances

5. Prokaryotic and Eukaryotic Cells
Cell interior is divided into functional compartments, including a nucleus
Prokaryotic cell
Small, simple cells without a nucleus

6. B A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus.
A A prokaryotic cell.
cytoplasm
DNA
plasma membrane
nucleus
Figure 4.2 Animated Overview of the general organization of a cell.Archaea are similar to bacteria in overall structure; both are generally much smaller than eukaryotic cells. If the two cells depicted here had been drawn to the same scale, the prokaryotic cell would be about this big:
B A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus.
Figure 4-2 p54 6

7. ANIMATED FIGURE: Overview of cells
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8. Preview of Cell Membranes
Lipid bilayer
A double layer of phospholipids organized with their hydrophilic heads outwards and their hydrophobic tails inwards
Many types of proteins embedded or attached to the bilayer carry out membrane functions

9. cell’s exterior plasma membrane cell’s interior
Figure 4.3 Preview of cell membranes. A plasma membrane separates a cell from its external environment. Proteins (in color) embedded in the lipid bilayer (gray) carry out special membrane functions. Chapter 5 returns to membrane structure and function.
plasma membrane
cell’s interior
Figure 4-3 p54

10. The Cell Theory Emerges
Van Leeuwenhoek was the first to describe small organisms seen through a microscope, which he called animalcules and beasties
Hooke was the first to sketch and name cells
Brown was the first to identify a cell nucleus

11. Cell Theory
The cell theory, a foundation of modern biology, states that cells are the fundamental units of life
In 1839, Schleiden and Schwann proposed the basic concepts of the modern cell theory
All organisms consists of one or more cells
A cell is the smallest unit with the properties of life
Each new cell arises from division of a preexisting cell
Each cell passes its hereditary material to its offspring

12. Take-Home Message: How are all cells alike?
All cells start life with a plasma membrane, cytoplasm, and a region of DNA, which, in eukaryotic cells only, is enclosed by a nucleus
The surface-to-volume ratio limits cell size and influences cell shape
Observations of cells led to the cell theory: All organisms consist of one or more cells; the cell is the smallest unit of life; each new cell arises from another cell; and a cell passes hereditary material to its offspring

13. 4.3 How Do We See Cells?
Most cells are 10–20 micrometers in diameter, about fifty times smaller than the unaided human eye can perceive
One micrometer (μm) is one-thousandth of a millimeter, which is one-thousandth of a meter
We use different types of microscopes to study different aspects of organisms, from the smallest to the largest

14. Table 4-1 p56

15. Modern Microscopes Light microscopes Phase-contrast microscopes
Reflected light microscopes
Fluorescence microscopes
Electron microscopes
Transmission electron microscopes
Scanning electron microscopes

16. path of light rays (bottom to top) to eye
prism that directs rays to ocular lens
ocular lens
objective lenses
specimen
stage
Figure 4.5 Animated Examples of microscopes.
a A compound light microscope.
condenser lens
illuminator
light source (in base)
focusing knob
Figure 4-5a p56

17. incoming electron beam
condenser lens
specimen on grid
objective lens
Figure 4.5 Animated Examples of microscopes.
b A transmission electron
microscope (TEM).
projective lens
phosphor screen
Figure 4-5b p56

18. Different Microscopes, Different Characteristics

19. Relative Sizes human eye (no microscope) largest organisms
small animals
frog eggs
100 m
10 m
1 m
10 cm
1 cm
1 mm
100 µm
Figure 4.7 Relative sizes. Below, the diameter of most cells is in the range of 1 to 100 micrometers. Table 4.1 shows conversions among units of length; also see Units of Measure, Appendix VIII.

20. mitochondria, chloroplasts
Relative Sizes
electron microscopes
light microscopes
most eukaryotic cells
viruses
most bacteria
mitochondria, chloroplasts
molecules of life
small molecules
DNA
carbohydrates
proteins
lipids
Figure 4.7 Relative sizes. Below, the diameter of most cells is in the range of 1 to 100 micrometers. Table 4.1 shows conversions among units of length; also see Units of Measure, Appendix VIII.
10 µm
1 µm
100 nm
10 nm
1 nm
0.1 nm

21. Take-Home Message: How do we see cells?
Most cells are visible only with the help of microscopes
Different types of microscopes reveal different aspects of cell structure

22. 4.4 Introducing “Prokaryotes”
Bacteria and archaea are the prokaryotes (“before the nucleus”), the smallest and most metabolically diverse forms of life
Bacteria and archaea are similar in appearance and size, but differ in structure and metabolism

23. General Prokaryote Body Plan
Cell wall surrounds the plasma membrane
Made of peptidoglycan (in bacteria) or proteins (in archaea) and coated with a sticky capsule
Flagellum for motion
Pili help cells move across surfaces
“Sex” pilus aids in sexual reproduction

24. General Prokaryote Body Plan
Ribosomes
Organelles upon which polypeptides are assembled
Nucleoid
An irregularly shaped region of cytoplasm containing a single, circular DNA molecule
Plasmids
Small circles of DNA carry a few genes that can provide advantages, such as resistance to antibiotics

25. General Prokaryote Body Plan7
flagellum 1
cytoplasm,
with ribosomes
plasma membrane 3 5
capsule 6
pilus
Figure 4.8 Animated Generalized body plan of a “prokaryote” (a bacterium or archaeon).
DNA in nucleoid
cell wall 2 4

26. Bacteria
Figure 4.9 A sampling of bacteria (this page) and archaea (facing page).

27. Biofilms Although prokaryotes are all single-celled, few live alone
Single-celled organisms sharing a secreted layer of polysaccharides and glycoproteins
May include bacteria, algae, fungi, protists, and archaeans

28. Dental Plaque: A Biofilm
Figure 4.10 Oral bacteria in dental plaque, a biofilm. Three species of bacteria (tan, green) and a yeast (red) stick to one another and to teeth via a gluelike mass of shared, secreted polysaccharides (pink). Other secretions of these organisms cause cavities and periodontal disease.

29. Take-Home Message: How are bacteria and archaea alike?
Bacteria and archaea do not have a nucleus. Most kinds have a cell wall around their plasma membrane; the permeable wall reinforces and imparts shape to the cell body
The structure of bacteria and archaea is relatively simple, but as a group these organisms are the most diverse forms of life; they inhabit nearly all regions of the biosphere
Some metabolic processes occur at the plasma membrane of bacteria and archaea; they are similar to complex processes that occur at certain internal membranes of eukaryotic cells

30. 4.5 Introducing Eukaryotic Cells
All protists, fungi, plants, and animals are eukaryotes
Eukaryotic (“true nucleus”) cells carry out much of their metabolism inside membrane-enclosed organelles
Organelle
A structure that carries out a specialized function within a cell

31. Importance of Organelles
Membranes around eukaryotic organelles control the types and amounts of substances that enter and exit them
Such control maintains a special internal environment that allows the organelle to carry out its particular function
Some metabolic pathways take place in a series of different organelles

32. Components of Eukaryotic Cells

33. Components of Eukaryotic Cells

34. Cell Wall Central Vacuole
Chloroplast
nuclear envelope
Cytoskeleton
nucleolus
Nucleus
DNA in nucleoplasm
microtubules microfilaments intermediate filaments
(not shown)
Ribosomes
Rough ER
Mitochondrion
Plasmodesma
Smooth ER
Figure 4.12 Animated Organelles and structures typical of (a) plant cells and (b) animal cells.
A Typical plant cell components.
Golgi Body
Plasma Membrane
Lysosome-Like Vesicle
Figure 4-12a p61 34

35. Modifies proteins made by ribosomes attached to it Rough ER
Makes lipids, breaks down carbohydrates and fats, inactivates toxins
Smooth ER
Finishes, sorts, ships lipids, enzymes, and proteins
Golgi Body
Digests, recycles materials
Lysosome
Stepped Art
p64

36. Prepare to be amazed….

37. Take-Home Message: What do eukaryotic cells have in common?
All eukaryotic cells start life with a nucleus and other membrane-enclosed organelles

38. 4.6 The Nucleus All of a eukaryotic cell’s DNA is in its nucleus
The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm
The nuclear envelope controls when DNA is accessed

39. Table 4-2 p60

40. nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER
Figure 4.13 Animated The cell nucleus. TEM at right, nucleus of a mouse pancreas cell. ER
Figure 4-13a p62

41. nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER
Figure 4.13 Animated The cell nucleus. TEM at right, nucleus of a mouse pancreas cell. ER
Figure 4-13b p62

42. The Nuclear Envelope Nuclear envelope
Two lipid bilayers pressed together as a single membrane surrounding the nucleus
Outer bilayer is continuous with the ER
Nuclear pores allow certain substances to pass through the membrane

43. Structure of the Nuclear Envelope

44. B Each nuclear pore is an organized cluster of membrane proteins that selectively allows certain substances to cross it on their way into and out of the nucleus.
nuclear pore
Figure 4.14 Animated Structure of the nuclear envelope.
A The outer surface of this nuclear envelope was split apart to reveal the pores that span the two lipid bilayers.
Figure 4-14ab p63

45. nuclear envelope (two lipid bilayers)
nuclear pore
nuclear envelope (two lipid bilayers)
Figure 4.14 Animated Structure of the nuclear envelope.
cytoplasm
Figure 4-14b p63

46. The Nucleoplasm and Nucleolus
Viscous fluid inside the nuclear envelope, similar to cytoplasm
Nucleolus
A dense region in the nucleus where subunits of ribosomes are assembled from proteins and RNA

47. Chromosomes Chromatin
All DNA and its associated proteins in the nucleus
Chromosome
A single DNA molecule with its attached proteins
During cell division, chromosomes condense and become visible in micrographs
Human body cells have 46 chromosomes

48. A Condensed Chromosome

49. Take-Home Message: What is the function of the cell nucleus?
A nucleus protects and controls access to a eukaryotic cell’s DNA
The nuclear envelope is a double lipid bilayer. Proteins embedded in it control the passage of molecules between the nucleus and the cytoplasm