1. the fundamental unit of life
A TOUR OF THE CELL
the fundamental unit of life

2. Microscopes - windows to the world of the cell
The discovery and early study of cells progressed with the invention and improvement of microscopes in the 17th century.
Robert Hooke
Anton van Leeuwenhoek
Microscopes are a major tool in cytology, the study of cell structures
Cytology coupled with biochemistry, the study of molecules and chemical processes in metabolism, developed modern cell biology.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

3. From Monk’s Room to Unit of Life
Robert Hooke thought what he was looking at resembled the rooms monk’s occupied…..
Cells

4. The Instruments

5. Compound Light Microscope
Uses visible light
Has at least 2 sets of lenses
Can achieve maximum 2000X magnification
Resolution of objects as small as 0.2 m

6. Light Microscopy
In a light microscope visible light passes through the specimen and then through glass lenses.
The lenses refract light such that the image is magnified into the eye or a video screen.

7. Brightfield Illumination
Usual operations
Specimens must be stained for viewing
Best magnification and resolution with the oil immersion objective
Oil has same refractive index as glass

8. Light Microscopes
Microscopes vary in magnification and resolving power.
Magnification is the ratio of an object’s image to its real size.
Resolving power is a measure of image clarity.
It is the minimum distance two points can be separated and still viewed as two separate points.
Resolution is limited by the shortest wavelength of the source, in this case light.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. Resolution of Light Microscopes
The minimum resolution of a light microscope is about 2 microns, the size of a small bacterium
Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen.
At higher magnifications, the image blurs.
Fig. 7.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

10. Electron Microscopy
Beam of electrons has shorter  so gives better resolution than visible light
Electromagnetic lenses rather than glass
Done in a vacuum
Can resolve to 0.5nm and magnify up to 100,000 times.
Specimen must be dry….dead

11. Electron micrographs

12. Cell Fractionation
The goal of cell fractionation is to separate the major organelles of the cells so that their individual functions can be studied.

13. The Procedure
Fractionation begins with homogenization, gently disrupting the cell
Then, the homogenate is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the supernatant.
As the process is repeated at higher speeds and longer durations, smaller and smaller organelles can be collected in subsequent pellets
ultracentrifuge
can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times gravity (1,000,000 g).

14. Why Look at the Parts rather than the Whole
Cell fractionation prepares quantities of specific cell components.
enables the functions of these organelles to be isolated, especially by the reactions or processes catalyzed by their proteins.
For example, one cellular fraction is enriched in enzymes that function in cellular respiration.
Electron microscopy reveals that this fraction is rich in the organelles called mitochondria.
Cytology and biochemistry complement each other in connecting cellular structure and function.

15. Fluorescent stain of cell
Cell Structure and Function
Fluorescent stain of cell

16. Early Discoveries
Mid 1600s - Robert Hooke observed and described cells in cork
Late 1600s - Antony van Leeuwenhoek observed sperm, microorganisms
1820s - Robert Brown observed and named nucleus in plant cells

17. Cell Theory Schleiden and Schwann Virchow
Every organism is composed of one or more cells
Cell is smallest unit having properties of life
Virchow
All exisiting cells arise from pre-existing cells.

18. Cell Smallest unit of life
Can survive on its own or has potential to do so
Is highly organized for metabolism
Senses and responds to environment
Has potential to reproduce

19. Measuring

20. Cells Vary in Size

21. Why Are Cells So Small? Surface-to-volume ratio
The bigger a cell is, the less surface area there is per unit volume
Above a certain size, material cannot be moved in or out of cell fast enough

22. Size is Limited

23. Smaller objects have a greater ratio of surface area to volume.
Metabolic requirements also set an upper limit to the size of a single cell.
As a cell increases in size its volume increases faster than its surface area.
Smaller objects have a greater ratio of surface area to volume.
Fig. 7.5

24. Structure of Cells Two or Three types of cells Archeo - cell type
There is much evidence that this is a third cell type
Prokaryotic
Eukaryotic
All cells have:
Plasma membrane
Region where DNA is stored
Cytoplasm
ribosomes

25. Archeo-cell type and Prokaryotes
No nucleus
Nucleoid area where DNA resides
No membrane bound organelles.
70s ribosomes
Cell walls contain petidoglycan Prokaryotic Organisms
Eubacteria
Cyanobacteria
Archeo-cell type
Pseudomurein rather than peptidoglycan
Organisms belong to the Archeobacter

26. A prokaryotic cell

27. E. coli

28. Eukaryotic Cells Have a nucleus and other organelles
Eukaryotic organisms
Protistans
Fungi
Plants
Animals

29. Overview of a plant cell

30. Overview of an animal cell

31. The nucleus contains a eukaryotic cell’s genetic library
contains most of the genes in a eukaryotic cell.
Some genes are located in mitochondria and chloroplasts.
The nucleus averages about 5 microns in diameter.
The nucleus is separated from the cytoplasm by a double membrane.
These are separated by nm.
Where the double membranes are fused, a pore allows large macromolecules and particles to pass through.

32. Nucleolus
In the nucleus is a region of densely stained fibers and granules adjoining chromatin, the nucleolus.
ribosomal RNA (rRNA) is synthesized
assembled with proteins from the cytoplasm to form ribosomal subunits.
The subunits pass from the nuclear pores to the cytoplasm where they combine to form ribosomes.

33. The nucleus and its envelope

34. Functions of Nucleus
Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm
Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells

35. The nucleus and its envelope

36. Cytomembrane System
Group of related organelles in which lipids are assembled and new polypeptide chains are modified
Products are sorted and shipped to various destinations
Components of the cytomembrane system
Endoplasmic reticulum
Golgi apparatus
vesicles

37. Endoplasmic Reticulum
In animal cells, continuous with nuclear membrane
Extends throughout cytoplasm
Two regions - rough and smooth

38. Rough ER Arranged into flattened sacs
Ribosomes on surface give it a rough appearance
Some polypeptide chains enter rough ER and are modified
Cells that specialize in secreting proteins have lots of rough ER

39. Smooth ER A series of interconnected tubules No ribosomes on surface
Lipids assembled inside tubules
Smooth ER of liver inactivates wastes, drugs
Sarcoplasmic reticulum of muscle is a specialized form

40. Endoplasmic reticulum (ER)

41. Golgi Bodies
Put finishing touches on proteins and lipids that arrive from ER
Package finished material for shipment to final destinations
Material arrives and leaves in vesicles

42. The Golgi apparatus

43. Vesicles Membranous sacs that move through the cytoplasm Lysosomes
Peroxisomes

44. Lysosomes

45. Review: relationships among organelles of the endomembrane system

46. The mitochondrion, site of cellular respiration

47. Specialized Plant Organelles
Plastids
Central Vacuole

48. The chloroplast, site of photosynthesis

49. Other Plastids Chromoplasts Amyloplasts No chlorophyll
Abundance of carotenoids
Color fruits and flowers red-to-yellow
Amyloplasts
No pigments
Store starch

50. The plant cell vacuole 

51. Organelles with no Membranes
Ribosomes
Function in protein synthesis
Cytoskeleton
Function in maintenance of cell shape and positioning of organelles
Centrioles (animals only)
Function during cell division

52. Figure Ribosomes

53. Ribosomes build a cell’s proteins
Ribosomes contain rRNA and protein.
A ribosome is composed of two subunits that combine to carry out protein synthesis.
Fig. 7.10
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

54. Cytoskeleton Present in all eukaryotic cells
Basis for cell shape and internal organization
Allows organelle movement within cells and, in some cases, cell motility

55. Cytoskeletal Elements
intermediate
filament
microtubule
microfilament

56. Microtubules Largest elements Composed of the protein tubulin
Arise from microtubule organizing centers (MTOCs)
Polar and dynamic
Involved in shape, motility, cell division

57. Microfilaments Thinnest cytoskeletal elements
Composed of the protein actin
Polar and dynamic
Take part in movement, formation and maintenance of cell shape

58. Intermediate Filaments
Present only in animal cells of certain tissues
Most stable cytoskeletal elements
Six known groups
Different cell types usually have 1-2 different kinds

59. Cell-to-Cell Junctions
Plants
Plasmodesmata
Animals
Tight junctions
Adhering junctions
Gap junctions
plasmodesma

60. Animal Cell Junctions
tight
junctions
gap
junction
adhering
junction