Cells: The Working Units of Life

1. Cells: The Working Units of Life

2. 5 Cells: The Working Units of Life • 5.1 What Features Make Cells the Fundamental Units of Life? • 5.2 What Features Characterize Prokaryotic Cells? • 5.3 What Features Characterize Eukaryotic Cells? • 5.4 What Are the Roles of Extracellular Structures? • 5.5 How Did Eukaryotic Cells Originate?

3. 5 Cells: The Working Units of Life Cells are the fundamental units of life. Stem cells are able to differentiate into any type of cell in the body and are being investigated for treating a host of human diseases. Opening Question: What is the status of stem cell treatment for heart disease?

4. 5.1 What Features Make Cells the Fundamental Units of Life? • Cell theory was the first unifying theory of biology: • Cells are the fundamental units of life. • All organisms are composed of cells. • All cells come from preexisting cells.

5. 5.1 What Features Make Cells the Fundamental Units of Life? • Implications of the cell theory: • Functions of all cells are similar. • Life is continuous. • Origin of life was the origin of cells.

6. 5.1 What Features Make Cells the Fundamental Units of Life? • Cells are small (mostly). • Exceptions: Bird eggs, some algae, and bacteria.

7. Figure 5.1 The Scale of Life (Part 1)

8. Figure 5.1 The Scale of Life (Part 2)

9. Figure 5.1 The Scale of Life (Part 1)

10. 5.1 What Features Make Cells the Fundamental Units of Life? • Cells are small because a high surface area-to-volume ratio is essential. • Volume determines the amount of chemical activity in the cell per unit time. Larger cells have more chemical activity. • Cell surface area limits the amount of resources and waste products that can cross the cell boundary per unit time.

11. Figure 5.2 Why Cells Are Small

12. 5.1 What Features Make Cells the Fundamental Units of Life? • Most cells are < 200 μm in size. To see them, we use microscopes: • Magnification: increases apparent size. • Resolution: clarity of magnified object—minimum distance two objects can be apart and still be seen as two objects.

13. 5.1 What Features Make Cells the Fundamental Units of Life? • Two basic types of microscopes: • Light microscopes: use glass lenses and light. Resolution = 0.2 μm • Electron microscopes: electromagnets focus an electron beam. Resolution = 0.2 nm

14. Figure 5.3 Looking at Cells (Part 1)

15. Figure 5.3 Looking at Cells (Part 2)

16. Figure 5.3 Looking at Cells (Part 3)

17. 5.1 What Features Make Cells the Fundamental Units of Life? • Pathology is a branch of medicine that uses microscopy to analyze cells and diagnose diseases. • Many methods are used, including phase-contrast microscopy, staining the cells with general or selective dyes, and electron microscopy.

18. In-Text Art, Ch. 5, p. 79

19. 5.1 What Features Make Cells the Fundamental Units of Life? • The plasma membrane is the outer surface of every cell and has more or less the same structure in all cells. • It is made of a phospholipid bilayer with embedded proteins and other molecules.

20. 5.1 What Features Make Cells the Fundamental Units of Life? • The plasma membrane: • is a selectively permeable barrier • allows cells to maintain a constant internal environment • is important in communication and receiving signals • often has proteins for binding and adhering to adjacent cells

21. 5.1 What Features Make Cells the Fundamental Units of Life? • Two types of cells: Prokaryotic and eukaryotic. • Bacteria and Archaea are prokaryotes. They have no membrane-enclosed internal compartments. • The first cells were probably prokaryotic.

22. In-Text Art, Ch. 5, p. 81

23. 5.1 What Features Make Cells the Fundamental Units of Life? • Eukarya are eukaryotes—cells with membrane-enclosed compartments called organelles. • The DNA is in a compartment called the nucleus. Specific chemical reactions occur in other organelles. • This “division of labor” was important in the evolution of complex organisms.

24. 5.2 What Features Characterize Prokaryotic Cells? • Prokaryotic cells are very small. • Individuals are single cells but often form chains or clusters. • Prokaryotes are very successful; and there is a huge diversity of species in the Bacteria and Archaea domains.

25. 5.2 What Features Characterize Prokaryotic Cells? • Characteristics of prokaryotic cells: • Enclosed by a plasma membrane. • DNA is contained in a region called the nucleoid. • Cytoplasm consists of cytosol (liquid component) plus filaments and particles.

26. 5.2 What Features Characterize Prokaryotic Cells? • Cytosol: water with dissolved ions, small molecules, and soluble macromolecules. • Ribosomes: RNA and protein complexes;sites of protein synthesis.

27. Figure 5.4 A Prokaryotic Cell

28. 5.2 What Features Characterize Prokaryotic Cells? • Most prokaryotes have a rigid cell wall outside the plasma membrane. • Bacterial cell walls contain peptidoglycan. • Some bacteria have an additional outer membrane. • Some bacteria have a slimy capsule of polysaccharides.

29. 5.2 What Features Characterize Prokaryotic Cells? • Photosynthetic bacteria have an internal membrane system that contains molecules necessary for photosynthesis. • Others have internal membrane folds that are attached to the plasma membrane; they may function in cell division or in energy-releasing reactions.

30. 5.2 What Features Characterize Prokaryotic Cells? • Some prokaryotes swim by means of flagella, made of the protein flagellin. • Some bacteria have pili—hairlike structures projecting from the surface. They help bacteria adhere to other cells. • Fimbriae are shorter than pili; they help cells adhere to surfaces such as animal cells.

31. Figure 5.5 Prokaryotic Flagella

32. Figure 5.5 Prokaryotic Flagella (Part 1)

33. 5.2 What Features Characterize Prokaryotic Cells? • Cytoskeleton: system of protein filaments that maintain cell shape and play roles in cell division.

34. 5.3 What Features Characterize Eukaryotic Cells? • Eukaryotic cells are up to ten times larger than prokaryotes. • Eukaryotic cells have membrane-enclosed compartments called organelles. • Each organelle has a specific role in cell functioning.

35. 5.3 What Features Characterize Eukaryotic Cells? • Compartmentalization allowed eukaryotic cells to specialize and form the tissues and organs of multicellular organisms.

36. 5.3 What Features Characterize Eukaryotic Cells? • To determine the functions of organelles, they were first studied using light microscopy and then electron microscopy. • Cell fractionation separates organelles by size or density for study by chemical methods.

37. Figure 5.6 Cell Fractionation (Part 1)

38. Figure 5.6 Cell Fractionation (Part 2)

39. Figure 5.7 Eukaryotic Cells (Part 1)

40. Figure 5.7 Eukaryotic Cells (Part 2)

41. Figure 5.7 Eukaryotic Cells (Part 3)

42. Figure 5.7 Eukaryotic Cells (Part 4)

43. 5.3 What Features Characterize Eukaryotic Cells? • Ribosomes: sites of protein synthesis. • Occur in both prokaryotic and eukaryotic cells and have similar structure. • Ribosomes consist of ribosomal RNA (rRNA) and more than 50 different protein molecules.

44. 5.3 What Features Characterize Eukaryotic Cells? • In eukaryotes, ribosomes are free in the cytoplasm, attached to the endoplasmic reticulum, or inside mitochondria and chloroplasts. • In prokaryotic cells, ribosomes float freely in the cytoplasm.

45. 5.3 What Features Characterize Eukaryotic Cells? • The nucleus is usually the largest organelle. • Contains the DNA • Site of DNA replication • Site where gene transcription is turned on or off • Assembly of ribosomes begins in a region called the nucleolus

46. 5.3 What Features Characterize Eukaryotic Cells? • The nucleus is surrounded by the nuclear envelope. Many pores control the movement of molecules across the envelope. • In-text art, p. 9

47. 5.3 What Features Characterize Eukaryotic Cells? • In the nucleus, DNA combines with proteins to form chromatin in long, thin threads called chromosomes. • Before cell division, chromatin condenses, and individual chromosomes are visible in the light microscope.

48. Figure 5.8 The Nucleus, Chromatin, and Chromosomes

49. 5.3 What Features Characterize Eukaryotic Cells? • The chromatin is attached to a protein meshwork (the nuclear lamina), which maintains the shape of the nucleus. • The outer membrane of the nuclear envelope folds outward into the cytoplasm and is continuous with the endoplasmic reticulum.

50. 5.3 What Features Characterize Eukaryotic Cells? • The endomembrane system includes the plasma membrane, nuclear envelope, endoplasmic reticulum, Golgi apparatus, and lysosomes. • Tiny, membrane-surrounded vesicles shuttle substances between the various components.