1. Chapter 6 A Tour of the Cell

2. Warning!!
Much of this chapter is covered in Biology I and is considered pre-requisite knowledge.
Focus on what is new to you while you review what is already familiar.

3. Cell Biology or Cytology
Cyto = cell ology = study of
Should use observations from several types of microscopes to make a total picture of how a cell is put together.

5. Electron Microscopes Use beams of electrons instead of light.
Invented in 1939, but not used much until after WWII.

6. TEM
SEM

7. Advantages Much higher magnifications.
Magnifications of 50,000X or higher are possible.
Can get down to atomic level in some cases.

8. Other Tools for Cytology
Cell Fractionation – break the cell apart and separate out the pieces.
Chromatography – separates mixtures based on their solubility.
Electrophoresis – separates mixtures of protein or DNA using gels and electricity.

9. History of Cells Robert Hooke - Observed cells in cork.
Coined the term "cells” in 1665.
Robert Brown, discovered the nucleus.
M.J. Schleiden, all plants are made of cells.
T. Schwann, all animals are made of cells.

10. Cell Theory All living matter is composed of one or more cells.
The cell is the structural and functional unit of life.
All cells come from cells.

11. Types of Cells
Prokaryotic - lack a nucleus and other membrane bounded structures.
Eukaryotic - have a nucleus and other membrane bounded structures.

12. Both Have:
Membrane
Cytosol
Ribosomes (but the size is different)

13. Prokaryotic Eukaryotic
Nucleus

14. Why Are Cells So Small?
Cell volume to surface area ratios favor small size.
Nucleus to cytoplasm consideration (control).
Metabolic requirements.
Speed of diffusion.

16. Basic Cell Organization
Membrane
Nucleus
Cytoplasm
Organelles

17. Animal Cell

18. Plant Cell

19. Membrane Separates the cell from the environment.
Boundary layer for regulating the movement of materials in/out of a cell.

20. Cytoplasm or Cytosol
Cell substance between the cell membrane and the nucleus.
The “fluid” part of a cell. Exists in two forms:
gel - thick
sol - fluid

21. Organelle
Term means "small organ” Formed body (or compartment) in a cell with a specialized function.
Important in organizational structure of cells.

22. Organelles - function
Way to form compartments in cells to separate chemical reactions.
Keeps various enzymes separated in space.

23. You must be able to: Identify the major organelles
Give their structure
Give their function

24. Nucleus Most conspicuous organelle.
Usually spherical, but can be lobed or irregular in shape.
Structure – double membrane, contains nuclear pores.
Function – information center

26. Ribosomes Structure: 2 subunits made of protein and rRNA. No membrane.
Function: protein synthesis.
Note – eukaryotes and prokaryotes BOTH have ribosomes, but they are different in size.

28. Endomembrane System
Membranes that are related through direct physical continuity or by the transfer of membrane segments called vesicles.

29. Endomembrane System

30. Endoplasmic Reticulum
Often referred to as ER.
Makes up to 1/2 of the total membrane in cells.
Often continuous with the nuclear membrane.

32. Structure of ER Folded sheets or tubes of membranes.
Very “fluid” in structure with the membranes constantly changing size and shape.

33. Types of ER – structure & function
Smooth ER: no ribosomes.
Used for lipid synthesis, carbohydrate storage, detoxification of poisons.
Rough ER: with ribosomes.
Makes secretory proteins.

34. Golgi Apparatus or Dictyosomes
Structure: parallel array of flattened cisternae. (looks like a stack of Pita bread)
3 to 20 per cell.
Likely an outgrowth of the ER system.

36. Function of Golgi Bodies
Processing - modification of ER products.
Distribution - packaging of ER products for transport into vesicles.

37. Lysosome
Single membrane.
Made from the Golgi apparatus.

38. Function Breakdown and degradation of cellular materials.
Contains enzymes for fats, proteins, polysaccharides, and nucleic acids.
Over 40 types known.

40. Vacuoles
Structure - single membrane, usually larger than the Golgi vesicles.
Function - depends on the organism.

41. Plants
Large single vacuole when mature making up to 90% of the cell's volume.
Tonoplast - the name for the vacuole membrane.

43. Function – Plant Vacuole
Water regulation.
Storage of ions.
Used to enlarge cells and create turgor pressure.
Enzymes (various types).
Storage of hydrophilic pigments (e.g. red and blues in flower petals).
Store toxins.

44. Microbodies Structure: single membrane.
Often have a granular or crystalline core of enzymes.

45. Function Specialized enzymes for specific reactions.
Peroxisomes: use up hydrogen peroxide.
Glyoxysomes: lipid digestion.

46. Mitochondria
Structure: 2 membranes. The inner membrane has more surface area than the outer membrane.
Matrix: inner space.
Intermembrane space: area between the membranes.

48. Inner Membrane Folded into cristae.
Amount of folding depends on the level of cell activity.
Contains many enzymes.
ATP generated here.

49. Function Cell Respiration - the release of energy from food.
Major location of ATP generation.
“Powerhouse” of the cell Comment – be careful NOT to overuse this phrase.

50. Mitochondria Have ribosomes (small size). Have their own DNA.
Can reproduce themselves.
Likely were independent cells at one time. (Endosymbiotic Theory)

51. Chloroplasts Structure - two outer membranes.
Complex internal membrane.
Fluid-like stroma is around the internal membranes.

53. Inner or Thylakoid Membranes
Arranged into flattened sacs called thylakoids.
Some regions stacked into layers called grana.
Contain the green pigment chlorophyll.
Function - photosynthesis

54. Chloroplasts Contain ribosomes (small size). Contain DNA.
Can reproduce themselves.
Often contain starch.
Likely were independent cells at one time (cyano-bacteria) (Endosymbiotic Theory)

55. Cytoskeleton Network of rods and filaments in the cytoplasm. Function:
Cell structure and shape.
Cell movement.
Cell division - helps build cell walls and move the chromosomes apart.

56. Cytoskeleton Components
Microtubules
Microfilaments
Intermediate Filaments

58. Microtubules
Structure - small hollow tubes made of repeating units of a protein dimer.
Size - 25 nm diameter with a 15 nm lumen. Can be 200 nm to 25 mm in length.

59. Microtubules Regulate cell shape.
Coordinate direction of cellulose fibers in cell wall formation.
Tracks for motor molecules.
Internal cellular movement.
Make up centioles, basal bodies and spindle fibers.
Form cilia and flagella.

60. Cilia vs. Flagella Cilia - short, but numerous.
Flagella - long, but few.
Function - to move cells or to sweep materials past a cell.

61. Cilia and Flagella
Structure arrangement of microtubules, covered by the cell membrane.
Dynein - motor protein that connects the tubules.

63. Centrioles Usually one pair per cell, located close to the nucleus.
Found in animal cells.
9 sets of triplet microtubules.
Help in cell division.

64. Microfilaments 5 to 7 nm in diameter.
Structure - two intertwined strands of actin protein.

65. Microfilaments are stained green.

66. Functions Muscle contraction. Cytoplasmic streaming. Pseudopodia.
Cleavage furrow formation.
Maintenance and changes in cell shape.

67. Intermediate Filaments
Fibrous proteins that are super coiled into thicker cables and filaments nm in diameter.
Made from several different types of protein.

68. Functions
Maintenance of cell shape.
Hold organelles in place.

69. Cell Wall Nonliving jacket that surrounds some cells. Found in: Plants
Prokaryotes
Fungi
Some Protists

70. Plant Cell Walls All plant cells have a Primary Cell Wall.
Some cells will develop a Secondary Cell Wall.

71. Primary Wall Thin and flexible.
Cellulose fibers placed at right angles to expansion.
Placement of fibers guided by microtubules.

72. Secondary Wall Thick and rigid.
Added between the cell membrane and the primary cell wall in laminated layers.
May cover only part of the cell; giving spirals.
Makes up "wood”.

74. Cell Walls
May be made of other types of polysaccharides and/or silica.
Function as the cell's exoskeleton for support and protection.

75. Extracellular Matrix - ECM
Fuzzy coat on animal cells.
Helps glue cells together.
Made of glycoproteins and collagen.
Evidence suggests ECM is involved with cell behavior and cell communication.

77. Intercellular Junctions
Plants-Plasmodesmata

78. Plasmodesmata Channels between cells through adjacent cell walls.
Allows communication between cells.
Also allows viruses to travel rapidly between cells.

79. Intercellular Juctions
Animals:
Tight junctions
Desmosomes
Gap junctions

81. Tight Junctions Very tight fusion of the membranes of adjacent cells.
Seals off areas between the cells.
Prevents movement of materials around cells.

83. Desmosomes Bundles of filaments which anchor junctions between cells.
Does not close off the area between adjacent cells.
Coordination of movement between groups of cells.

85. Gap Junctions Open channels between cells, similar to plasmodesmata.
Allows “communication” between cells.

87. Chapter Summary
Why is Life cellular and what are the factors that affect cell size?
Be able to identify cellular parts, their structure, and their functions.
Differences between prokaryotic and eukaryotic; plant and animal cells.

88. Cell Animation Link
You may need to replay this several times to catch all of the parts.