1. Cell Structure: A Tour of the Cell
Chapters 6&7
Cell Structure: A Tour of the Cell 1

2. The smallest structural unit of life.
Cell:
A basic unit of living matter separated from its environment by a plasma membrane.
The smallest structural unit of life. 1

3. Cell Theory: Developed in late 1800s.
1. All living organisms are made up of one or more cells.
2. The smallest living organisms are single cells, and cells are the functional units of multicellular organisms.
3. All cells arise from preexisting cells. 1

4. Microscope Features Magnification:
Increase in apparent size of an object.
Ratio of image size to specimen size.
Calculated: Eyepiece (10) x Objective
Example: 40X, 100X, 400X
Resolving power: Measures clarity of image.
Ability to see fine detail.
Ability to distinguish two objects as separate.
Minimum distance between 2 points at which they can be distinguished as separate and distinct. 1

5. Light Microscopes: Earliest microscopes used.
Lenses pass visible light through a specimen.
Magnification: Highest possible from 1000 X to 2000 X.
Resolving power: Up to 0.2 mm (1 mm = 1/1000 mm). 1

6. Types of Microscope
Electron Microscopes: Developed in 1950s. Electron beam passes through specimen.
Magnification: Up to 200,000 X.
Resolving power: Up to 0.2 nm (1nm = 1/1,000,000 mm).
Two types of electron microscopes:
1. Scanning Electron Microscope: Used to study cell or virus surfaces.
2. Transmission Electron Microscope: Used to study internal cell structures. 1

7. Components of All Cells:
1. Plasma membrane: Separates cell contents from outside environment. Made up of phospholipid bilayers and proteins.
2. Cytoplasm: Liquid, jelly-like material inside cell.
3. Ribosomes: Necessary for protein synthesis.

8. Prokaryotic versus Eukaryotic Cells
Feature Prokaryotic Eukaryotic
Organisms Bacteria All others (animals, plants,
fungi, and protozoa)
Nucleus Absent Present
DNA One chromosome Multiple chromosomes
Size Small (1-10 um) Large (10 or more um)
Membrane Absent Present (mitochondria,
Bound golgi, chloroplasts, etc.)
Organelles
Division Rapid process Complex process
(Binary fission) (Mitosis)

9. Relative Sizes of Structures
1 nanometer (10-9 m) water molecule
10 nanomters (10-8 m) small protein
100 nanometers (10-7 m) HIV virus
1 micron (10-6 m) cell vacuole
10 microns (10-5 m) bacterium
100 microns (10-4 m) large plant cell
1 millimeter (10-3 m) single cell embryo

10. Relative Sizes of Procaryotic and Eucaryotic Cells and Viruses

11. Relative Sizes of Cells and Other Objects

12. Prokaryotic Cells Bacteria and blue-green algae.
Small size: Range from micrometers in length. About one tenth of eukaryotic cell.
No nucleus: DNA in cytoplasm or nucleoid region.
Ribosomes are used to make proteins
Cell wall: Hard shell around membrane
Other structures that may be present:
Capsule: Protective, outer sticky layer. May be used for attachment or to evade immune system.
Pili: Hair-like projections (attachment)
Flagellum: Longer whip-like projection (movement)

13. Prokaryotic Cells: Lack a Nucleus and other Membrane Bound Organelles

14. Eukaryotic Cells Include protist, fungi, plant, and animal cells.
Nucleus: Protects and houses DNA
Membrane-bound Organelles: Internal structures with specific functions.
Separate and store compounds
Store energy
Work surfaces
Maintain concentration gradients

15. Membrane-Bound Organelles of Eukaryotic Cells
Nucleus
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
Golgi Apparatus
Lysosomes
Vacuoles
Chloroplasts
Mitochondria

16. Eukaryotic Cells: Typical Animal Cell

17. Eukaryotic Cells: Typical Plant Cell

18. Nucleus Structure Functions Double nuclear membrane (envelope)
Large nuclear pores
DNA (genetic material) is combined with histones and exists in two forms:
Chromatin (Loose, threadlike DNA, most of cell life)
Chromosomes (Tightly packaged DNA. Found only during cell division)
Nucleolus: Dense region where ribosomes are made
Functions
House and protect cell’s genetic information (DNA)
Ribosome synthesis

19. Structure of Cell Nucleus

20. Endoplasmic Reticulum (ER)
“Network within the cell”
Extensive maze of membranes that branches throughout cytoplasm.
ER is continuous with plasma membrane and outer nucleus membrane.
Two types of ER:
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)

21. Rough Endoplasmic Reticulum (RER)
Flat, interconnected, rough membrane sacs
“Rough”: Outer walls are covered with ribosomes.
Ribosomes: Protein making “machines”.
May exist free in cytoplasm or attached to ER.
RER Functions:
Synthesis of cell and organelle membranes.
Synthesis and modification of proteins.
Packaging, and transport of proteins that are secreted from the cell.
Example: Antibodies

22. Rough Endoplasmic Reticulum (RER)

23. Smooth Endoplasmic Reticulum (SER)
Network of interconnected tubular smooth membranes.
“Smooth”: No ribosomes
SER Functions:
Synthesis of phospholipids, fatty acids, and steroids (sex hormones).
Breakdown of toxic compounds (drugs, alcohol, amphetamines, sedatives, antibiotics, etc.).
Helps develop tolerance to drugs and alcohol.
Regulates levels of sugar released from liver into the blood
Calcium storage for cell and muscle contraction.

24. Smooth Endoplasmic Reticulum (SER)

25. Golgi Apparatus
Stacks of flattened membrane sacs that may be distended in certain regions. Sacs are not interconnected.
First described in 1898 by Camillo Golgi (Italy).
Works closely with the ER to secrete proteins.
Golgi Functions:
Receiving side receives proteins in transport vesicles from ER.
Modifies proteins into final shape, sorts, and labels proteins for proper transport.
Shipping side packages and sends proteins to cell membrane for export or to other parts of the cell.
Packages digestive enzymes in lysosomes.

26. The Golgi Apparatus: Receiving, Processing, and Shipping of Proteins

27. Lysosomes
Small vesicles released from Golgi containing at least 40 different digestive enzymes, which can break down carbohydrates, proteins, lipids, and nucleic acids.
Optimal pH for enzymes is about 5
Found mainly in animal cells.
Lysosome Functions:
Molecular garbage dump and recycler of macromolecules (e.g.: proteins).
Destruction of foreign material, bacteria, viruses, and old or damaged cell components.
Digestion of food particles taken in by cell.
After cell dies, lysosomal membrane breaks down, causing rapid self-destruction.

28. Lysosomes: Intracellular Digestion

29. Lysosomes, Aging, and Disease
As we get older, our lysosomes become leaky, releasing enzymes which cause tissue damage and inflammation.
Example: Cartilage damage in arthritis.
Steroids or cortisone-like anti-inflammatory agents stabilize lysosomal membranes, but have other undesirable effects (affect immune function).
Diseases from “mutant” lysosome enzymes are usually fatal:
Pompe’s disease: Defective glycogen breakdown in liver.
Tay-Sachs disease: Defective lipid breakdown in brain. Common genetic disorder among Jewish people.

30. Vacuoles Membrane bound sac. Different sizes, shapes, and functions:
Central vacuole: In plant cells. Store starch, water, pigments, poisons, and wastes. May occupy up to 90% of cell volume.
Contractile vacuole: Regulate water balance, by removing excess water from cell. Found in many aquatic protists.
Food or Digestion Vacuole: Engulf nutrients in many protozoa (protists). Fuse with lysosomes to digest food particles.

31. Central Vacuole in a Plant Cell

32. Interactions Between Membrane Bound Organelles of Eucaryotic Cells

33. Chloroplasts Site of photosynthesis in plants and algae.
CO2 + H2O + Sun Light -----> Sugar + O2
Number may range from 1 to over 100 per cell.
Disc shaped structure with three different membrane systems:
1. Outer membrane: Covers chloroplast surface.
2. Inner membrane: Contains enzymes needed to make glucose during photosynthesis. Encloses stroma (liquid) and thylakoid membranes.
3. Thylakoid membranes: Contain chlorophyll, green pigment that traps solar energy. Organized in stacks called grana.

34. Chloroplasts Trap Solar Energy and Convert it to Chemical Energy

35. Chloroplasts Contain their own DNA, ribosomes, and make some proteins.
Can divide to form daughter chloroplasts.
Type of plastid: Organelle that produces and stores food in plant and algae cells.
Other plastids include:
Leukoplasts: Store starch.
Chromoplasts: Store other pigments that give plants and flowers color.

36. Mitochondria (Sing. Mitochondrion)
Site of cellular respiration:
Food (sugar) + O > CO2 + H2O + ATP
Change chemical energy of molecules into the useable energy of the ATP molecule.
Oval or sausage shaped.
Contain their own DNA, ribosomes, and make some proteins.
Can divide to form daughter mitochondria.
Structure:
Inner and outer membranes.
Intermembrane space
Cristae (inner membrane extensions)
Matrix (inner liquid)

37. Mitochondria Harvest Chemical Energy From Food

38. Origin of Eucaryotic Cells
Endosymbiont Theory: Belief that chloroplasts and mitochondria were at one point independent cells that entered and remained inside a larger cell.
Both organelles contain their own DNA
Have their own ribosomes and make their own proteins.
Replicate independently from cell, by binary fission.
Symbiotic relationship
Larger cell obtains energy or nutrients
Smaller cell is protected by larger cell.

39. Complex network of thread-like and tube-like structures.
The Cytoskeleton
Complex network of thread-like and tube-like structures.
Functions: Movement, structure, and structural support.
Three Cytoskeleton Components:
1. Microfilaments: Smallest cytoskeleton fibers. Important for:
Muscle contraction: Actin & myosin fibers in muscle cells
“Amoeboid motion” of white blood cells

40. Components of the Cytoskeleton are Important for Structure and Movement

41. Three Cytoskeleton Components:
2. Intermediate filaments: Medium sized fibers
Anchor organelles (nucleus) and hold cytoskeleton in place.
Abundant in cells with high mechanical stress.
3. Microtubules: Largest cytoskeleton fibers. Found in:
Centrioles: A pair of structures that help move chromosomes during cell division (mitosis and meiosis).
Found in animal cells, but not plant cells.
Movement of flagella and cilia.

42. Typical Animal Cell

43. Cilia and Flagella Flagella: Large whip-like projections.
Projections used for locomotion or to move substances along cell surface.
Enclosed by plasma membrane and contain cytoplasm.
Consist of 9 pairs of microtubules surrounding two single microtubules (9 + 2 arrangement).
Flagella: Large whip-like projections.
Move in wavelike manner, used for locomotion.
Example: Sperm cell
Cilia: Short hair-like projections.
Example: Human respiratory system uses cilia to remove harmful objects from bronchial tubes and trachea.

44. Structure of Eucaryotic Flagellum

45. Cell Surfaces A. Cell wall: Function: Plasmodesmata:
Much thicker than cell membrane,
(10 to 100 X thicker).
Function:
Provides support and protects cell from lysis.
Plant and algae cell wall: Cellulose
Fungi and bacteria have other polysaccharides.
Not present in animal cells or protozoa.
Plasmodesmata:
Are channels between adjacent plant cells that form a circulatory and communication system between cells.
Sharing of nutrients, water, and chemical messages.

46. Plasmodesmata: Communication Between Adjacent Plant Cells

47. Cell Surfaces B. Extracellular matrix:
Sticky layer of glycoproteins found in animal cells.
Important for attachment, support, protection, and response to environmental stimuli.

48. Junctions Between Animal Cells:
Tight Junctions:
Bind cells tightly, forming a leak-proof sheet.
Example: Between epithelial cells in stomach lining.

49. Anchoring Junctions :
Rivet cells together, but still allow material to pass through spaces between cells.
Ex: desmosomes (add this)

50. Similar to plasmodesmata in plants.
Communicating Junctions (Gap Junctions):
Similar to plasmodesmata in plants.
Allow water and other small molecules to flow between neighboring cells.

51. Different Animal Cell Junctions

52. Important Differences Between Plant and Animal Cells
Plant cells Animal cells
Cell wall None (Extracellular matrix)
Chloroplasts No chloroplasts
Large central vacuole No central vacuole
Flagella rare Flagella more usual
No Lysosomes Lysosomes present
No Centrioles Centrioles present

53. Differences Between Plant and Animal Cells
Plant Cell

54. Typical Plant Cell

55. Summary of Eukaryotic Organelles
Function: Manufacture
Nucleus
Ribosomes
Rough ER
Smooth ER
Golgi Apparatus
Function: Breakdown
Lysosomes
Vacuoles

56. Summary of Eucaryotic Organelles
Function: Energy Processing
Chloroplasts (Plants and algae)
Mitochondria
Function: Support, Movement, Communication
Cytoskeleton (Cilia, flagella, and centrioles)
Cell walls (Plants, fungi, bacteria, and some protists)
Extracellular matrix (Animals)
Cell junctions

57. The Cell Membrane and Cell Transport

58. Separate cell from nonliving environment.
Functions of Cell Membranes
Separate
Separate cell from nonliving environment.
Form most organelles and partition cell into discrete compartments.

59. 2. Regulate
Regulate passage of materials in and out of the cell and organelles.
Membrane is selectively permeable.

60. 3. Receive
Receive information that permits cell to sense and respond to environmental changes.
Hormones
Growth factors
Neurotransmitters

61. 4. Communication
Communicate with other cells and the organism as a whole.
Surface proteins allow cells to recognize each other, adhere, and exchange materials.

62. I. Fluid Mosaic Model of the Membrane
Key Parts:
1. Phospholipid bilayer:
Major component is a phospholipid bilayer.
Hydrophobic tails face inward
Hydrophilic heads face water
2. Mosaic of proteins:
Proteins “float” in the phospholipid bilayer.
3. Cholesterol:
Maintains proper membrane fluidity.
The outer and inner membrane surfaces are different.

63. Membrane
Phospholipids
Form a
Bilayer

64. The Membrane is a Fluid Mosaic of Phospholipids and Proteins
Notice that inner and outer surfaces are different

65. A. Fluid Quality of Plasma Membranes
In a living cell, membrane has same fluidity as salad oil.
Unsaturated hydrocarbon tails INCREASE membrane fluidity
Phospholipids and proteins drift laterally.
Phospholipids move very rapidly
Proteins drift in membrane more slowly
Cholesterol: Alters fluidity of the membrane
Decreases fluidity at warmer temperatures (> 37oC)
Increases fluidity at lower temperatures (< 37oC)

66. B. Membranes Contain Two Types of Proteins

67. 1. Integral membrane proteins:
Inserted into the membrane.
Hydrophobic region is adjacent to hydrocarbon tails.

68. 2. Peripheral membrane proteins:
Attached to either the inner or outer membrane surface.

69. Functions of Membrane Proteins:
1. Transport of materials across membrane
2. Enzymes
3. Receptors of chemical messengers
4. Identification: Cell-cell recognition
5. Attachment:
Membrane to cytoskeleton
Intercellular junctions

70. Membrane Proteins Have Diverse Functions

71. C. Membrane Carbohydrates and Cell-Cell Recognition
Found on outside surface of membrane.
Important for Cell-cell recognition:
Ability of one cell to “recognize” other cells.
Allows immune system to recognize self vs. non-self
Includes:
Glycolipids: Lipids with sugars
Glycoproteins: Proteins with sugars
Major histocompatibility proteins (MHC or transplantation antigens).
Varies greatly among individuals and species.
Organ transplants require matching of cell markers and/or immune suppression.

73. II. The cell plasma membrane is Selectively Permeable
A. Permeability of the Lipid Bilayer
1. Non-polar (Hydrophobic) Molecules
Dissolve into the membrane and cross with ease
The smaller the molecule, the easier it can cross
Examples: O2 , hydrocarbons, steroids
2. Polar (Hydrophilic) Molecules
Small polar uncharged molecules can pass through easily (e.g.: H2O , CO2)
Large polar uncharged molecules pass with difficulty (e.g.: glucose)
3. Ionic (Hydrophilic) Molecules
Charged ions or particles cannot get through
(e.g.: ions such as Na+ , K+ , Cl- )

74. B. Transport Proteins in the membrane: Integral membrane proteins that allow for the transport of specific molecules across the phospholipid bilayer of the plasma membrane.
How do they work?
May provide a “hydrophilic tunnel” (channel)
May bind to molecule and physically move it
Are specific for the atom/molecule transported

75. Active & Passive Transport Mechanisms
Cellular Transport
Active & Passive Transport Mechanisms

76. Passive transport: A. Simple Diffusion:
Movement of molecules across the plasma membrane without using the energy of the cell.
Only involves substances that can cross the bilayer by themselves or with the aid of a protein.
Types:
A. Simple Diffusion:
The net movement of a substance from an area of high concentration to area of low concentration.
Does not require energy from the cell.
Ex: gases move across cell membranes this way.

77. Passive Transport: Diffusion Across a Membrane Does Not Require Energy

78. B. Osmosis: The diffusion of water across a semi-permeable membrane.
Through osmosis, water will move from an area with higher water concentration to an area with lower water concentration.
Solutes can’t move across the semi-permeable membrane.

80. Higher osmotic pressure than cell due to:
Is the ability of a solution to take up water through osmosis.
Example: The cytoplasm of a cell has a certain osmotic pressure caused by the solutes it contains.
There are three different types of solution when compared to the interior (cytoplasm) of a cell:
Hypertonic solution:
Higher osmotic pressure than cell due to:
Higher solute concentration than cell or
Lower water concentration than cell.
2. Hypotonic solution:
Lower osmotic pressure than cell due to:
Lower solute concentration than cell or
Higher water concentration than cell.

81. 3. Isotonic solution:
Same osmotic pressure as the cell.
Equal concentration of solute(s) and water as the cell.

82. V. Cells depend on proper water balance
Animal Cells:
Do best in isotonic solutions.
Examples:
0.9% NaCl (Saline)
5% Glucose
If solution is not isotonic, cell will be affected:
Hypertonic solution: Cell undergoes crenation. Cell “shrivels” or shrinks.
Example: 5% NaCl or 10% glucose
Hypotonic solution: Cell undergoes lysis. Cell swells and eventually bursts.
Example: Pure water.
Called:“D5-normal saline”

83. V. Cells depend on proper water balance
Plant Cells: Do best in hypotonic solutions, because the cell wall protects from excessive uptake of water.
Hypertonic solution: Cell undergoes plasmolysis. Cell membrane shrivels inside cell wall.
Isotonic solution: Cell becomes flaccid or wilts.
Hypotonic solution: Turgor. Increased firmness of cells due to osmotic pressure.
This is the reason why supermarkets spray fruits and vegetables with pure water, making them look firm and fresh.

85. VI. Facilitated Diffusion (F.D.):
Some substances cannot cross the membrane by themselves due to their size or charge.
Membrane proteins facilitate the transport of solutes down their concentration gradient.
No cell energy is required.
Transport Proteins
Are specific : Only transport very specific molecules (due to the shape of the binding site)
Examples of molecules moved by F.D.:
Glucose
Specific ions (Na+, K+, Cl- )
Video link

86. Facilitated Diffusion Uses a Membrane Transport Protein

87. 1.) The Na+-K+ ATPase pump:
Active Transport:
Proteins use energy from ATP to actively “pump” solutes across the membrane
Solutes are moved against a concentration gradient.
Energy is required.
Example:
1.) The Na+-K+ ATPase pump:
Energy of ATP hydrolysis is used to move Na+ out of the cell and K+ into the cell

89. Active Transport 2.) Bulk Transport
Large substances are moved in or out of the cell using vesicles.
2 types:
1.) Endocytosis
2.) Exocytosis

90. Not a specific process, all solutes in droplets are taken in.
Endocytosis:
Moving materials into cell with vesicles.
Requires use of cell energy.
3 Types of Endocytosis:
Pinocytosis
(“Cell drinking”):
Small droplets of liquid are taken into the cell through tiny vesicles.
Not a specific process, all solutes in droplets are taken in.

91. 2. Phagocytosis
(“Cell eating”):
Large solid particles are taken in by cell.
Example:
Amoebas take in food particles by surrounding them with cytoplasmic extensions called pseudopods.
Particles are surrounded by a vacuole.
Vacuole later fuses with the lysosome and contents are digested.

92. 3. Receptor mediated endocytosis:
Highly specific.
Materials moved into cell must bind to specific receptors first.
Example: Low density lipoproteins (LDL):
Main form of cholesterol in blood.
Globule of cholesterol surrounded by a single layer of phospholipids with embedded proteins.
Liver cell receptors bind to LDL proteins and remove LDLs from blood through receptor mediated endocytosis.
Familial hypercholesterolemia:
Genetic disorder in which gene for the LDL receptor is mutated.
Disorder found in 1 in 500 human babies worldwide.
Results in unusually high levels of blood cholesterol.

93. Endocytosis Uses Vesicles to Move Substances into the Cell

94. Blood Cholesterol is Taken Up by Liver Cells through Receptor Mediated Endocytosis

95. Exocytosis:
Used to export materials out of cell.
Materials in vesicles fuse with cell membrane and are released to outside.
Tear glands export salty solution.
Pancreas uses exocytosis to secrete insulin.

96. Endo/Exo.Receptor-mediated Video Link
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Endo/Exo.Receptor-mediated Video Link