Principles of Biology

1. Principles of Biology By Frank H. Osborne, Ph. D. Cells

2. THE CELL THEORY • The word theory in science means "explanation." The cell theory is the accepted explanation about cells. It was developed after many observations of living things by biologists.

3. The Cell Theory The Cell Theory (Explanation) • All living things are made of cells. • All cells arise from pre-existing cells Exceptions • Viruses are considered to be non-living. • Mitochondria and chloroplasts can replicate on their own.

4. Basic Types of Cells There are two basic types of cells. The cells that came first are prokaryotic (pro means "before" and karyo means "nucleus"). These cells came before there was a nucleus. The cells with a nucleus are eukaryotic (eu means "true"). So, eukaryotic cells have a "true nucleus" meaning that the cellular nucleus has a membrane around it.

5. Biology of Cells The word cell was used to describe these objects because the first ones seen in cork reminded the observer of the cells in a monastery. Cells are too small to see with the unaided eye so we use microscopes.

6. Biology of Cells Microscopes are used to see cells because they are very small. There are two types of microscopes. • Simple microscope--one lens like a magnifier. • Compound microscope--two lenses working in series to make a magnified image of the specimen.

7. Biology of Cells Simple microscope Compound microscope

8. Biology of Cells Cellular structures include: • Cell membrane--made of two layers of phospholipid and surrounds the cytoplasm. • Nucleus--control center of the cell surrounded by a nuclear membrane. • Cytoplasmic structures--perform various cellular functions: mitochondria, chloroplasts, and others.

9. Biology of Cells When viewed with the light microscope, only the nucleus and cytoplasm are visible. In plant cells chloroplasts are also visible. With the electron microscope, many more fine details are visible. These are referred to as ultrastructure.

10. GENERALIZED CELLS A generalized cell is a drawing that contains all parts of the cell. In reality, there are many cells that lack one or more parts. A red blood cell, for example, contains cytoplasm and a cell membrane but the other parts are missing.

11. Cellular Ultrastructure Diagram of Cellular Ultrastructure

12. Eukaryotic/Prokaryotic Cells Eukaryotic cells are found in all higher organisms. They contain a well-defined nucleus surrounded by a membrane. The prokaryotic organisms, Bacteria and Archaea, do not have a membrane-bounded nucleus.

13. Cell Membrane The cell membrane is a structure that surrounds each cell. • All living cells have a cell membrane • It is the boundary between the cell and its environment. • It has the same function in both plant and animal cells.

14. Proteins of the Cell Membrane Transport proteins assist passage of large molecules or ions into the cell. Integral proteins help maintain the structure of the cell membrane. Some also serve as signal transmitters. Peripheral proteins are associated with the integral proteins. They assist in transmitting messages into the cell.

15. Cell Membrane Structure

16. Cell Membrane Structure In the electron microscope, a single membrane, as illustrated, appears as two parallel lines 80 Angstrom units apart.

17. The "Fluid Mosaic" Model The proteins in the membrane can move around inside the two layers of lipids and even protrude through the surface. This gives the surface of the membrane the appearance of a mosaic. So, the cell membrane is called a "fluid mosaic."

18. The "Fluid Mosaic" Model

19. The Nucleus The nucleus is the central organelle that controls the cell. It is surrounded by a membrane known as the nuclear membrane. It contains chromosomes and a nucleolus.

20. Cellular Ultrastructure The nucleus controls the cell.

21. The Nucleus

22. Parts of the Nucleus • The nuclear membrane surrounds the nucleus. It contains pores and channels that connect to the endoplasmic reticulum, a network of channels that is found in the cytoplasm . • The chromosomes are structures that contain DNA and control the activities of the cell. • The nucleolus is a large, round structure within the cell. It is responsible for the formation of ribosomes.

23. Cellular Ultrastructure The nuclear membrane surrounds the nucleus.

24. Cellular Ultrastructure Chromatin contains the DNA.

25. Cellular Ultrastructure The nucleolus helps form ribosomal parts.

26. The Cytoplasm The cytoplasm is the part of the cell that is found outside the nucleus. It is bounded on the outside by the cell membrane. The cytoplasm contains many different organelles that perform various functions for the cell.

27. Cellular Ultrastructure The cytoplasmic membrane surrounds the cell.

28. Mitochondria Mitochondria are the structures that produce energy for the cell. They contain an internal membrane that is folded to form cristae. Each single crista is an individual fold of this membrane where cellular respiration occurs.

29. Mitochondria

30. Cellular Ultrastructure Mitochondria provide energy for the cell.

31. Endoplasmic Reticulum The endoplasmic reticulum (ER) is a series of channels in the cytoplasm. It provides rapid movement of materials within the cell.

32. Endoplasmic Reticulum Rough ER has ribosomes attached to it. Its appearance in the electron microscope is that of sandpaper, hence "rough." Smooth ER does not have ribosomes attached to its membranes. It forms part of the internal membrane system of the cell.

33. Cellular Ultrastructure Endoplasmic reticulum is for communications.

34. Cellular Ultrastructure It has ribosomes for protein synthesis.

35. Ribosomes • Ribosomes are the places where proteins are made. Each ribosome has a small subunit and a large subunit. • When a protein is being synthesized, you find ribosomes attached to a piece of messenger RNA. This structure is sometimes called a polysome.

36. Golgi Bodies Golgi bodies serve as packaging organelles for materials to be exported outside of the cell. They start out as flat membranes that fill up as the material enters them. They become spherical and migrate toward the outside.

37. Cellular Ultrastructure The Golgi apparatus is for external secretions.

38. Lysosomes • Lysosomes are structures that are membrane-bounded and contain digestive enzymes. • Lysosomes digest large particles that are brought into the cell. • The process of digestion is the reverse of dehydration synthesis.

39. Vacuoles • Vacuoles are areas in the cytoplasm that have a membrane surrounding them. • They are filled with cytoplasmic liquids or storage materials of various kinds.

40. The Cytoskeleton • The cell has a network of flexible fibers within the cytoplasm. This network of fibers is called the cytoskeleton. • The fibers are made of polymers of proteins known as microtubules. These fibers have elastic properties that provide flexibility to the cell. They act as little muscles inside the cell.

41. Plant Cell Structures • A generalized plant cell is shown below. The cell wall and plastids are found only in plants. Cell wall Chloroplast

42. Cell Wall • The cell wall is made of cellulose. • It is considered non-living. • Cellulose fibers form primary (thin) and secondary (thick) walls. Different types of plant cells have different thicknesses of cell wall. • The cell membrane is pushed up against the inside of the cell wall by turgor pressure so it cannot be seen.

43. Cell Wall Layers The middle lamella is produced when the plant cell divides. Each cell produces a thin primary wall on its side of the middle lamella. All plant cells generally have a primary wall. The secondary wall is much thicker. Not all plant cells produce secondary walls.

44. Plastids Plastids are structures found only in plant cells. There are three kinds which are chloroplasts, chromoplasts and leukoplasts. Diagram of chloroplast structure. Stroma

45. Chloroplast Structure Grana Stroma

46. Chloroplasts • Chloroplasts are plant organelles that make food by the process of photosynthesis. • Photosynthesis is the synthesis of organic materials from inorganic raw materials. • Using light energy the chloroplast converts carbon dioxide and water to glucose. • The chloroplast contains layers of membranes called grana that contain chlorophyll. Chlorophyll traps the light energy from the Sun.

47. Chromoplasts Chromoplasts are plastids that are colored but do not perform photosynthesis. Most contain carotenoid pigments that are related to carotene. These pigments are various shades of orange or yellow. The pigments can be separated from leaves by means of a technique known as chromatography.

48. Leukoplasts "Leuko" means lacking color or without color. Leukoplasts are plastids that do not have any color. They are used for storage of materials. An example is the starch grain which is found within the cells of potatoes.

49. Cilia and Flagella Cilia and flagella are organelles of locomotion. They contain contractile proteins. The proteins allow cilia and flagella to move. Flagella are much larger than cilia. Cilia are more numerous on a cell than flagella. A cell will have either cilia or flagella but not both. The contractile proteins of cilia and flagella form a characteristic arrangement. They come in pairs.

50. Cilia and Flagella There are nine pairs around the outside with two fibers in the middle. This structural configuration is known as the 9+2 arrangement.