Chapter 5 Cell Structure

1. Chapter 5 Cell Structure

2. Warning!! • Much of this chapter is covered in Biology I so the pacing will be rapid. • Focus on what is new to you while you review what is already familiar.

3. “Faith is a fine invention when gentlemen can see, but microscopes are prudent in an emergency.”Emily Dickinson

4. 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.

6. Light Microscope - LM • Uses visible light to illuminate the object. • Relatively inexpensive type of microscope. • Can examine live or dead objects.

7. Light Microscope Occular Lens Objective Lens Stage with specimen Light Source

8. Resolution • Ability to detect two discrete points as separate from each other. • As Magnification increases, resolution decreases. • LM working limits are 100 - 1000X.

9. Limitations - LM • Miss many cell structures that are beyond the magnification of the light microscope. • Need other ways to make the observations.

10. Light Microscope Variations • Fluorescence: uses dyes to make parts of cells “glow”. • Phase-contrast: enhances contrasts in density. • Confocal: uses lasers and special optics to focus only narrow slides of cells.

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

13. TEM SEM

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

15. Disadvantages • Need a Vacuum. • Specimen must stop the electrons. • High cost of equipment. • Specimen preparation.

16. Transmission Electron Microscope - TEM • Sends electrons through thinly sliced and stained specimens. • Gives high magnification of interior views. Many cells structures are now visible.

17. TEM Limitations • Specimen dead. • Specimen preparation uses extreme chemicals so artifacts are always a concern.

18. Scanning Electron Microscope - SEM • Excellent views of surfaces. • Produces 3-D views. • Live specimens possible.

19. Other Tools for Cytology • Cell Fractionation • Chromatography • Electrophoresis

20. Cell Fractionation • Disrupt cells. • Separate parts by centrifugation at different speeds. • Result - pure samples of cell structures for study.

21. Cell Fractionation

22. Chromatography • Technique for separating mixtures of chemicals. • Separates chemicals by size or degree of attraction to the materials in the medium. • Ex - paper, gas, column, thin-layer

23. Electrophoresis • Separates mixtures of chemicals by their movement in an electrical field. • Used for proteins and DNA.

24. History of Cells • Robert Hooke - Observed cells in cork. • Coined the term "cells” in 1665.

25. History of Cells • 1833 - Robert Brown, discovered the nucleus. • 1838 - M.J. Schleiden, all plants are made of cells. • 1839 - T. Schwann, all animals are made of cells. • 1840 - J.E. Purkinje, coined the term “protoplasm”.

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

27. R. Virchow • “Omnis cellula e cellula” • All cells are from other cells.

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

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

30. Prokaryotic Eukaryotic Nucleus

31. Eukaryotic Prokaryotic

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

34. Basic Cell Organization • Membrane • Nucleus • Cytoplasm • Organelles

35. AnimalCell

36. Plant Cell

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

38. 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

39. Organelle • Term means "small organ” Formed body in a cell with a specialized function. • Important in organizational structure of cells.

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

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

42. Nucleus • Most conspicuous organelle. • usually spherical, but can be lobed or irregular in shape.

43. Structure • Nuclear membrane • Nuclear pores • Nucleolus • Chromatin

45. Nuclear Membrane • Double membrane separated by a 20-40 nm space. • Inner membrane supported by a protein matrix which gives the shape to the nucleus.

46. Nuclear Pores • Regular “holes” through both membranes. • 100 nm in diameter. • Protein complex gives shape. • Allows materials in/out of nucleus.

47. Nucleolus • Dark staining area in the nucleus. • 0 - 4 per nucleus. • Storage area for ribosomes.

48. Chromatin • Chrom: colored • - tin: threads • DNA and Protein in a “loose” format. Will form the cell’s chromosomes.

49. Nucleus - Function • Control center for the cell. • Contains the genetic instructions.

50. Ribosomes • Structure: 2 subunits made of protein and rRNA. No membrane. • Function: protein synthesis.