2. Cells: The Living Units

3. Cell Theory: History
In 1665 Hooke used a microscope to examine thin slices of cork
Tiny boxlike compartments called cellulae
Cell theory postulated by Schwann in 1839

4. Cell Theory All organisms are composed of one or more cells.
Cells are the smallest living units of all living organisms.
Cells arise only by division of a previously existing cell.

5. Definition of Cell
A cell is the smallest unit that is capable of performing life functions.

6. Cell Diversity There is really no “typical” cell.
Cells have different shapes, different sizes, different functions, different life spans

7. Examples of Specialized cells:
Many different types of blood cells
Three different types of muscle cells
Fat Storage cells
Cells that transmit electrical impulses
Cells for reproduction

8. Structure of a Generalized Cell

9. Prokaryotic Eukaryotic
Two Types of Cells
Prokaryotic
Eukaryotic

10. Prokaryotic Do not have structures surrounded by membranes
Few internal structures
One-celled organisms, Bacteria

11. Prokaryotic Cells Simplest organisms
Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall composed of peptidoglycan.
No distinct interior compartments

12. Eukaryotic Cells
Characterized by compartmentalization by an endomembrane system, and the presence of membrane-bound organelles.
Vesicles
Chromosomes - DNA and protein
Cytoskeleton (internal protein scaffolding)

13. Eukaryotic Contain organelles surrounded by membranes
Most living organisms
Plant
Animal

14. Prokaryotic vs. Eukaryotic Cells
Prokaryotic cells
No Nucleus
No Organelles
Cell Wall of peptidoglycan
Binary Fission
1 circular chromosome
Eukaryotic Cells
Nucleus
Organelles
If cell wall, Cellulose or chitin
Mitosis
Linear chromosomes

15. Cell Parts

16. Cell Parts

17. Cell Membrane
Outer membrane of cell that controls movement in and out of the cell
Double layer

18. Cytoplasm Cytoplasm; material between plasma membrane and the nucleus
Cytoplasm ; Gel-like mixture
Cytoplasm ; Surrounded by cell membrane
Cytosol; largely water with dissolved protein, salts, sugars, and other solutes

19. Cytoplasmic Organelles
Membranous
Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus
Nonmembranous
Cytoskeleton, centrioles, and ribosomes

20. Nucleus is the cell's information center
Directs cell activities
Separated from cytoplasm by nuclear membrane(outer and inner)
Pores of the envelope move the molecules between nucleus and cytoplasm

21. Nucleus Contains nucleoli, chromatin
Gene-containing control center of the cell
Dictates the kinds and amounts of proteins to be synthesized

22. Nucleus

23. Nuclear Envelope
Selectively permeable double membrane barrier containing pores
Encloses jellylike nucleoplasm, which contains essential solutes
Pore complex regulates transport of large molecules into and out of the nucleus

24. Nucleoli Dark-staining spherical bodies within the nucleus
Site of ribosome production

25. Nucleolus
Inside nucleus
Contains RNA to build proteins

26. Chromosomes In nucleus Made of DNA
Contain instructions for traits & characteristics
Are visualized during mitosis

27. Mitochondria Double membrane structure with shelflike cristae
Provide most of the cell’s ATP via aerobic cellular respiration
Produces energy through chemical reactions – breaking down fats & carbohydrates

28. Mitochondria
Contain most of enzymes and intermediates involved in processes as the TCA cycle, fat oxidation and ATP generation
Most of intermediates involved in the transport of electrons from oxidizable food molecules to oxygen are located in or on the cristae
Other reaction sequences such as TCA and fat oxidation occur in matrix

29. Mitochondria Contain their own DNA and RNA 70 S Ribosome
Circular chromosomes
Replicate on their own

31. Endosymbiotic Hypothesis
Mitochondria and chloroplasts were once free living prokaryotes that were engulfed by Amoeba-like Eukaryotic cells

32. Same size and shape as bacteria
Double membrane
70 S Ribosomes
Circular chromosomes
Replicate on their own

33. Ribosomes Each cell contains thousands Make proteins
Found on ER & floating throughout the cell
The ribosome consists of ribosomal RNA (rRNA) and some 50 structural proteins
Ribosomes

34. Ribosomes
Unlike other organelles, ribosoms are found in eukaryotic and prokaryotic cells
Are tiny structures and are most numerous of the other structures
Site of protein synthesis
Free ribosomes synthesize soluble proteins
Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

35. Endoplasmic Reticulum
Continuous with the nuclear membrane
Interconnected tubes and parallel membranes enclosing cisternae
Two varieties – rough ER and smooth ER

37. Rough (ER) External surface studded with ribosomes
Manufactures all secreted proteins
Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

38. Signal Mechanism of Protein Synthesis

39. Catalyzes the following reactions in various organs of the body
Smooth ER
Catalyzes the following reactions in various organs of the body
In the liver – lipid and cholesterol metabolism, breakdown of glycogen and, along with the kidneys, detoxification of drugs
In the testes – synthesis of steroid-based hormones
In the intestinal cells – absorption, synthesis, and transport of fats
In skeletal and cardiac muscle – storage and release of calcium

40. Golgi Bodies Protein 'packaging plant' Move materials within the cell
Move materials out of the cell

41. Golgi Apparatus Stacked and flattened membranous sacs
Functions in modification, concentration, and packaging of proteins
Transport vesicles from the ER fuse with the Golgi
Secretory vesicles leave the Golgi stack and move to designated parts of the cell

42. Enzymes in the Golgi modify the protein products of the ER in stages as they move through the Golgi stack from the cis to the trans face

43. Modification of proteins in the Golgi complex
Glycosylation:
Further steps of glycosylation may occur within the Golgi apparatus (initial glycosylation in the ER)
Depending on the protein enzymes are used for these process
e.g. Glucosyl transferase
galactosyl transferase

45. What is the purpose of glycosylation?
The presence of oligosaccarides tends to make a glycoprotein relatively resistance to protease digestion
e.g. glycocalix which covers the plasma membrane of the absorbtive cells of the small intestine and protects to the intestinal epithelial cells from the digestive enzymes
The oligosaccarides attached to the cell surface proteins (selectins) function in cell-cell adhesion process

46. Sulfation:
Addition of sulfate groups to some proteins
e.g.
proteoglycans ( extracellular matrix glycoproteins)
mucopolysaccarides ( secretory product)

47. Formation of the primary lysosomes
The Golgi complex is responsible for the packing of hydrolytic enzymes as a primary lysosomes
The lysosomal proteins carry a unique marker in the form of mannoz-6-phosphate (M-6-P)groups
M6P is added to lysomal proteins in the lumen of the cis-Golgi network

48. The M-6-P groups are recognized by M6P -receptor proteins in the trans-Golgi network
These receptor binds the lysosomal hydrolase and help package them into specific transport vesicles that eventually fuse with lysosomes.

50. Formation of the acrosome:
Acrosome is a large lysosome and found in sperm
it contains hyaluronidase , acid phosphatase...
During the sperm differantion several small vesicles (primary lysosomes) are formed from Golgi
then they coalesce to form a single large lysosome (acrosome)

51. The Golgi complex is prominent in secretory cell
** in intestine Goblet cells which secrete large amounts of mucus ( mucopolysaccarides)
** in pancreas aciner cells which secrete various digestive enzymes

53. Figure 3.21

54. Lysosome Digestive 'plant' for proteins, fats, and carbohydrates
Digest ingested bacteria
Degrade nonfunctional organelles
Transports undigested material to cell membrane for removal

55. Lysosomes
Spherical membranous bags containing digestive enzymes (hydrolases)
The enzymes are synthesized in ER and transported to the Golji, Where the mannose 6 phosphate tag is added to mark them as lysosomal enzymes
Cell breaks down if lysosome explodes

57. Lysosomal Storage Diseases
They are caused by the accumulation of macromolecules (proteins, polysaccharides, lipids) in the lysosomes
because of a genetic failure to manufacture an enzyme needed for their breakdown.
Neurons of the central nervous system are particularly susceptible to damage.

58. Lysosomal Storage Diseases
Tay-Sachs disease and Gaucher's disease
— both caused by a failure to produce an enzyme needed to break down sphingolipids (fatty acid derivatives found in all cell membranes).
Mucopolysaccharidosis I (MPS-I)
Caused by a failure to synthesize an enzyme (α-L-iduronidase) needed to break down proteoglycans like heparan sulfate.

59. Lysosomal Storage Diseases
I-cell disease ("inclusion-cell disease"), disease
It is caused by a failure to "tag" (by phosphorylation) all the hydrolytic enzymes that are supposed to be transported from the Golgi apparatus to the lysosomes.
Lacking the mannose 6-phosphate (M6P) tag, they are secreted from the cell instead.

60. Proxysomes
The enzymes and other proteins destined for peroxisomes are synthesized in the cytosol.
Each contains a peroxisomal targeting signal (PTS) that binds to a receptor molecule that takes the protein into the peroxisome and then returns for another load

61. Proxysomes Peroxisomes are about the size of lysosomes (0.5–1.5 µm)
like them are bound by a single membrane.
They also resemble lysosomes in being filled with enzymes.
However, peroxisomes bud off from the endoplasmic reticulum, not the Golgi apparatus (that is the source of lysosomes)

62. Proxysomes Breakdown (by oxidation) of excess fatty acids
Breakdown of hydrogen peroxide (H2O2), a potentially dangerous product of fatty-acid oxidation It is catalyzed by the enzyme catalase.
Participates in the synthesis of cholesterol.
One of the enzymes involved, HMG-CoA reductase, is the target of the popular cholesterol-lowering "statins".
Participates in the synthesis of bile acids.
Participates in the synthesis of the lipids used to make myelin.
Breakdown of excess purines (AMP, GMP) to uric acid.

63. Proxysomes Are Found in plant and animal cells
Their function is differ in different cells
They have common property of generating and degrading of H2O2 (Catalase)
Regulation of oxygen tension in the cell

64. Proxysomes Breakdown (by oxidation) of excess fatty acids
Breakdown of hydrogen peroxide (H2O2), a potentially dangerous product of fatty-acid oxidation It is catalyzed by the enzyme catalase.
Participates in the synthesis of cholesterol.
One of the enzymes involved, HMG-CoA reductase, is the target of the popular cholesterol-lowering "statins".
Participates in the synthesis of bile acids.
Participates in the synthesis of the lipids used to make myelin.
Breakdown of excess purines (AMP, GMP) to uric acid.

65. Proxysomes Oxidative breakdown of the fatty acids
Fatty acids with more than 12 atom carbons are oxidized rapidly
Detoxification of other harmful compounds (methanol, ethanol, formate, formaldhyde)

66. Cytoskeleton The “skeleton” of the cell
Series of rods running through the cytosol
Maintain the shape
Has an important role in movement
Has an important role in division
About 80% of proteins are not freely but are associated with skeleton

67. Cytoskeleton Consists of a network of : Microtubules – hollow tubes
Microfilaments – thin, solid strands of actin
Intermediate filaments – coiled strands of protein

68. Cytoskeleton

69. Microtubules
The wall consists of protofilaments, usually 13 arranged side by side around a hollow center
Each protofilament is a polymer of tubulin
Tubulin is a dimeric protein consisting of two subunits

70. Microtubules Are found in : Axoneme of flagella and cilia
Axoneme of sperm tail
Spindle fibers that separate chromosomes
Are very flexible in living cells

71. Microtubules In addition to motility have roles in :
Organization the cytoplasm
Shape of the cell
Spatial disposition of the organelles
Distribution of the microfilaments and intermediate

72. Microfilaments Are the thinnest
Are best known for their role in contraction
They can form connections with the plasma membrane and thereby influence locomotion and cytoplasmic streaming
Maintenance the shape

73. Intermediatefilaments
Intermediate filaments are major components of the nuclear and cytoplasmic cytoskeletons.
Are the most stable and least soluble of cytoskeleton framework
Are the scaffold that support the entire cytoskeletal framework

74. Intermediate filaments:
are between actin filaments and microtubules in diameter
form robust networks
Intermediate filaments are polymers of protein subunits.

75. Intermediatefilaments
Have a tension bearing role in some cells
Intermediate filaments are essential to maintain correct tissue structure and function
In contrast to microtubles and microfilaments , If are differ in composition from tissue to tissue

76. Intermediate filament proteins:
are heterogeneous
re encoded by a large and complex gene superfamily
Over 50 human diseases are associated with intermediate filament mutations.

77. Most of the intermediate filament proteins in mammals are keratins.
Desmin is an essential muscle protein.
Vimentin is often expressed in solitary cells.
Lamins are intranuclear, forming the lamina that lines the nuclear envelope.

78. The eye lens contains two highly unusual intermediate filament proteins, CP49 and filensin.

79. Motor Molecules Protein complexes that function in motility
Powered by ATP
Attach to receptors on organelles

80. Motor Molecules
Figure 3.25a

81. Motor Molecules

82. Centrioles
Small barrel-shaped organelles located in the centrosome near the nucleus
Organize mitotic spindle during mitosis
Form the bases of cilia and flagella

83. Centrioles

84. Cilia
Whiplike, motile cellular extensions on exposed surfaces of certain cells
Move substances in one direction across cell surfaces

85. Cilia

86. Cilia