1. Cell Structure
Chapter 4

2. Cell Theory Cells were discovered in 1665 by Robert Hooke.
Early studies of cells were conducted by
Mathias Schleiden (1838) - plant cells
Theodor Schwann (1839) - animal cells
Schleiden and Schwann proposed the Cell Theory.

3. Cell Theory Cell Theory
1. All organisms are composed of cells.
2. Cells are the smallest living things.
3. Cells arise only from pre-existing cells.
All cells today represent a continuous line of descent from the first living cells.

4. Cell Theory Cell size is limited.
As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell.
Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area

5. Cell Theory

6. Cell Theory Microscopes are required to visualize cells.
Light microscopes can resolve structures that are 200nm apart.
Electron microscopes can resolve structures that are 0.2nm apart.

7. Fig. 4.2

8. Cell Theory All cells have certain structures in common:
1. Genetic Material – in a nucleoid or nucleus
2. Cytoplasm – a semifluid matrix
3. Plasma Membrane – a phospholipid bilayer

9. Nonpolar Hydrocarbon Tail
Phospholipids
Chapter 3: Phospholipids are Amphiphilic molecules
Polar Head Group
Nonpolar Hydrocarbon Tail
101

10. Page 63

11. Two Cell Types Prokaryotic Cells Eukaryotic Cells
Recall Three Domains (Ch. 1)
Defined by cell type
Eukarya
Plantae
Fungi
Animlia
Protista
Bacteria
Archaea
Eukaryotic
Prokaryotic 11

12. 1. Prokaryotic Cells Prokaryotic Cells
Origin: ‘pro’-before; ‘karyote’ - nut
Lack a membrane-bound nucleus.
genetic material is present in the nucleoid
Two types of prokaryotes:
Archaea
Bacteria

13. 1. Prokaryotic Cells Prokaryotic Cell Characteristics:
Simplest organisms - simple internal organization
Very small (1 to 10 microns across)
Genetic material in the nucleoid
No membrane-bound organelles
Capsules
Cytoplasm

14. 1. Prokaryotic Cells Prokaryotic and Eukaryotic Characteristics:
DNA, RNA
Ribosomes
Plasma membrane
Cell walls (bacteria, archaea)
Flagella
Pilli

15. 1. Prokaryotic Cell Structure

16. Prokaryotic Cell Structure
Prokaryotic cell walls
Surround and protect cell and maintain cell shape
Composed of polysaccharides (sugar coated)
Bacterial cell walls composed of peptidoglycan
Archaean cell walls lack peptidoglycan.

17. Recall Ch. 3 Polysaccharides
b. Function
1. Structural Molecules
Cellulose - plant cell walls
Chitin – Fungi cell walls
Peptidoglycan - Bacterial cell walls 22

18. Prokaryotic Cell Structure
Bacterial cell walls composed of peptidoglycan
Two Types of Bacterial Cell Walls
Gram Positive
Gram Negative
Gram Positive/Gram Negative type is determined by cell cell wall structure and the Gram Stain Reaction
Gram Positive Bacteria Stain Purple
Gram Negative Bacteria Stain Pink

19. Gram + vs. Gram - Gram + Bacteria stain Purple
Gram – Bacteria stain Pink
Courtesy: Dr. O’Steen

20. Prokaryotic Cell Structure
Flagella (singular, flagellum)
Whip-like proteins attached to cell wall used for locomotion
Present in some prokaryotic cells
one to several flagella on a single cell
Rotary motion of flagellum propels the cell through fluid environment
Flagella powered by protein motors
uses energy of a proton gradient

21. Flagella Structure

22. 2. Eukaryotic Cells Eukaryotic Cells
Origin: ‘eu’ - true, good; ‘karyote’ - nut
Possess a membrane-bound nucleus.
genetic material is highly organized within double-layer nuclear envelope
DNA never leaves the nuclear envelope
Types of eukaryotes divided into 4 kingdoms:
1. Plantae Fungi
3. Animalia 4. Protista

23. 2. Eukaryotic Cells Eukaryotic Cell Characteristics:
More complex organisms
highly organized structure (compartmentalization) known as endomembrane system
Typically larger than prokaryote ( microns)
Genetic material in the membrane-bound nucleus
Many membrane-bound organelles
Cytoplasm
Cytoskeleton

24. 2. Eukaryotic Cells Eukaryotic and Prokaryotic Characteristics:
DNA, RNA
Ribosomes
Plasma membrane
Cytoplasm
Cell walls (plantae, fungi, protista, not present in animal cells)
Flagella

25. Eukaryotic Cells

26. Eukaryotic Cells

27. Eukaryotic Cells Nucleus
Largest most definitive organelle in the cytoplasm
Surrounded by a nuclear envelope composed of 2 phospholipid bilayers
Stores the genetic material of the cell as long separate chains of DNA known as chromosomes
Cell DNA is organized with proteins to form chromatin

28. Eukaryotic Cells Nucleus
Cell DNA is organized with proteins to form chromatin
Chromosomes are tightly packed (condensed) with proteins inside the nucleus into nucleosomes
DNA is wound around histone proteins to resembles beads on a string

29. Fig. 4.9

30. Eukaryotic Cells Nucleolus (plural, nucleoli)
Dark staining zone within the nucleus
Composed of RNA
Synthesis of ribosomal RNA (rRNA) occurs here
rRNA is involved in the translation of DNA into protein

31. Eukaryotic Cells Nuclear Envelope
Composed of an inner and outer phospholipid bilayer
the outer layer is continuous with the membrane of the endoplasmic reticulum - an organelle for protein synthesis
Nuclear pores provide passage for proteins and rRNA into and out of the nucleus
DNA never leaves the nucleus

32. Eukaryotic Cells

33. Eukaryotic Cells Ribosomes Present in prokaryotic and eukaryotic cells
Composed of ribosomal RNA and proteins
Found in the cytoplasm and attached to internal membranes of the endoplasmic reticulum
Important protein function in protein synthesis in the cell
Translate the DNA code into RNA

34. Eukaryotic Cells Ribosomes
Composed of 2 subunits of ribosomal RNA (rRNA) and protein
The two subunits associate to form complete Ribosomes
Other types of RNA assist with protein synthesis:
mRNA
tRNA

35. Fig. 4.10

36. Endomembrane System Endomembrane system
A series of membranes throughout the eukaryotic cytoplasm
Divides cell into compartments where different cellular functions occur:
1. Endoplasmic Reticulum
2. Golgi Apparatus
3. Lysosomes

37. Endomembrane System 1. Endoplasmic Reticulum (ER)
Membranes that create a network of channels throughout the cytoplasm
Membrane continuous with the outer membrane of the nuclear envelope
Location for protein synthesis
Two Sections of the ER
Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum

38. Endomembrane System 1. Rough Endoplasmic Reticulum (RER)
System of cytoplasmic membranes that create a network of channels throughout the cytoplasm
Ribosomes are attached to the outside of the RER membrane giving it a rough appearance under the microscope
Synthesis of proteins to be secreted out of the cell, or packaged and sent to lysosomes or plasma membrane
Proteins are synthesized into the RER channels (cisternal space)

39. Endomembrane System 2. Smooth Endoplasmic Reticulum (SER)
Relatively few associated ribosomes
Functions:
- Synthesis of membrane lipids
- Calcium storage
- Detoxification of foreign substances

40. Endomembrane System

41. Endomembrane System Golgi Apparatus
Flattened stacks of interconnected membranes folds (cisternae) known individually as Golgi bodies
Located peripheral to the nucleus and ER
Function in packaging and distribution of materials to different parts of the cell
Synthesis of cell wall components

42. Fig. 4.12

43. Cis face of
Golgi faces
and receives
products from
the ER
Trans face of
Golgi releases
secretory
vesicles

44. Endomembrane System Lysosomes
Membrane bound vesicles containing digestive enzymes to break down macromolecules
Packaged and secreted by Golgi apparatus
Function to destroy cells or foreign matter that the cell has engulfed by phagocytosis

46. Endomembrane System Microbodies
Membrane bound vesicles that do not originate from the endomembrane system
Contain enzymes:
Glyoxysomes in plants contain enzymes for converting fats to carbohydrates
Peroxisomes contain oxidative enzymes such as H2O2 and catalase

47. Fig. 4.15

48. Endomembrane System Vacuoles ‘Blank spaces’
Membrane-bound structures with a variety of functions depending on the cell type
There are different types of vacuoles:
- Central Vacuole in plant cells
- Contractile Vacuole of some protists
- Storage Vacuoles

49. Fig. 4.16

50. Mitochondria Mitochondria ‘Power house of the cell”
Present in all types of eukaryotic cells
Contain oxidative metabolism enzymes for the chemical reactions of cellular respiration
the transferring of energy within macromolecules to ATP

51. Mitochondria Structure
Surrounded by 2 membranes:
Smooth outer membrane
Folded inner membrane with layers (cristae)
intermembrane space is located between the two membranes
matrix within the inner membrane
Similar in structure and function to chloroplasts of photosynthesis
Contain their own DNA (Mitochondrial DNA)
Produce some essential proteins
Mitochondria undergo their own division

52. Mitochondria

53. Chloroplasts
Organelles present in cells of plants and some other eukaryotes (Kingdom Protista)
Contain chlorophyll for photosynthesis
Surrounded by 2 membranes
Inner membrane forms sacs known as thylakoids
Stacks of thylakoids are known as Grana
Mitochondria, chloroplasts and similar DNA containing organelles known collectively as plastids

54. Chloroplasts

55. Mitochondria & Chloroplasts
Endosymbiosis
Proposal that eukaryotic organelles evolved through a symbiotic relationship
One prokaryotic cell engulfed a second prokaryotic cell and a symbiotic relationship developed
Mitochondria and chloroplasts are thought to have evolved this way

56. Mitochondria & Chloroplasts
Evidence supports this endosymbiosis theory:
Mitochondria and chloroplasts:
have 2 membranes
possess DNA and ribosomes
are about the size of a prokaryotic cell
divide by process of simple fission similar to bacteria

57. Mitochondria & Chloroplasts

58. Cytoskeleton Cytoskeleton
Network of protein fibers found in all eukaryotic cells
Supports the shape of the cell
Keeps organelles in fixed locations
Helps move materials within the cell

59. Cytoskeleton Three Fiber Types of Cytoskeleton:
Actin Filaments – responsible for cellular contractions, crawling, “pinching”
Composed of actin protein subunits
Microtubules – provide organization to the cell and move materials within the cell
Composed of tubulin protein subunits
Intermediate Filaments – provide structural stability
Composed of vimentin protein subunits

60. Cytoskeleton

61. Fig. 4.20a

62. Cytoskeleton Centrosomes
Organelles that organize microtubule function within the cell
Cell division
Composed of two perpendicular centrioles
bundles of microtubules organized in 9 triplets

63. Fig. 4.21

64. Cell Movement Cell movement takes different forms:
Crawling is accomplished via actin filaments and the protein myosin
Molecular motor proteins such as kinesin and dyein use ATP energy to move organelles in the cytoplasm along microtubule tracks
Flagella undulate to move a cell
Cilia can be arranged in rows on the surface of a eukaryotic cell to propel a cell forward

65. Fig. 4.22

66. Cell Movement
The cilia and flagella of eukaryotic cells have a similar structure:
9-2 structure: 9 pairs of microtubules surrounded by a 2 central microtubules
dynein protein motors slide the microtubules across each other causing them to undulate
Flagella attached to cell body at basal body
Cilia are usually more numerous than flagella on a cell

67. Cell Movement

68. Fig. 4.24b

69. Fig. 4.24a

70. Extracellular Structures
Cell Walls:
plants
fungi
some protists
Extracellular Matrix
surrounding animal cells

71. Extracellular Structures
Cell Walls
Present surrounding the cells of plants, fungi, and some protists
Composed of carbohydrates
Type of carbohydrate present in the cell wall vary depending on the cell type:
plant and protist cell walls composed of cellulose
fungal cell walls composed of chitin

72. Fig. 4.25

73. Extracellular Structures
Extracellular matrix (ECM)
Surrounds animal cells
animal cells lack cell walls
Composed of glycoproteins and fibrous proteins such as collagen and elastin
provide a protective layer over the cell
Connected to plasma membrane via fibronectins
Connected to the cytoplasm via integrin proteins present in the plasma membrane

74. Extracellular Structures