Chapter 4

1. 0 Chapter 4 A Tour of the Cell

2. The Art of Looking at Cells Early scientists who observed cells made detailed sketches of what they saw Art is important to biology because biologists use art to illuminate their findings.

3. These early sketches revealed an important relationship Between art and biology, the most visual of the sciences

4. INTRODUCTION TO THE CELL Eyepiece Ocularlens 4.1 Microscopes provide windows to the world of the cell The light microscope (LM) enables us to see the overall shape and structure of a cell Light Microscopes use light and glass lenses to magnify an image Objective lens Specimen Condenserlens Lightsource Figure 4.1A

5. Light microscopes magnify cells, living and preserved, up to 1,000 times Resolving power is the  ability of an optical instrument to show two close objects as separate. LM 1,000 Figure 4.1B

6. The electron microscope allows greater magnification and reveals cellular details, but the specimens must be dead. A scanning electron microscope is used to study cell surfaces, whereas a transmission electron microscope is used to study internal cell structures. TEM 2,800  SEM 2,000 Figure 4.1D Figure 4.1C

7. Different types of light microscopes Use different techniques to enhance contrast and selectively highlight cellular components 1,000 220 Figure 4.1F Figure 4.1E

8. CellTheory • All living organisms are composed of one or more cells. • Cells are the basic units of structure & function in an organism. • Cells come only from the reproduction of existing cells.

9. 10 m Human height 1 m Length of somenerve andmuscle cells 100 mm(10 cm) Unaided eye Chicken egg 10 mm(1 cm) Frog egg 1 mm 4.2 Most cells are microscopic Cells vary in size and shape 100 m Light microscope Most plant andanimal cells 10 m Nucleus Most bacteria Mitochondrion 1 m Mycoplasmas(smallest bacteria) 100 nm Electron microscope Viruses Ribosome 10 nm Proteins Lipids 1 nm Small molecules Figure 4.2A Atoms 0.1 nm

10. The microscopic size of most cells ensures a sufficient surface area Across which nutrients and wastes can move to service the cell volume

11. 10 m 30 m A small cell has a greater ratio of surface area to volume than a large cell of the same shape As cell size increases, the volume increases faster than the surface area. 30 m 10 m Surface areaof one large cube 5,400 m2 Total surface areaof 27 small cubes 16,200 m2 Figure 4.2B

12. Prokaryotic cell Nucleoidregion Colorized TEM 15,000  4.3 Prokaryotic cells are structurally simpler than eukaryotic cells There are two kinds of cells Prokaryotic and eukaryotic Nucleus Eukaryotic cell Organelles Figure 4.3A

13. Prokaryoticflagella Prokaryotic cells are small, relatively simple cells that do not have a membrane-bound nucleus or membrane-bound organelles. Capsule and pilli used for attaching to surfaces. Nucleoid-contains the cell’s DNA. Ribosomes Capsule Cell wall Plasmamembrane Nucleoid region (DNA) Pili Figure 4.3B

14. 4.4 Eukaryotic cells are partitioned into functional compartments All other forms of life are composed of more complex eukaryotic cell distinguished by the presence of a true nucleus

15. Membranes form the boundaries of many eukaryotic cells compartmentalizing the interior of the cell and facilitating a variety of metabolic activities Cytoplasm-fluid-filled region between the nucleus and the plasma membrane; includes organelles. Cytosol-the part of the cytoplasm that does not contain the membrane-bound organelles.

16. Smooth endoplasmicreticulum Nucleus Roughendoplasmicreticulum Flagellum Not in mostplant cells A typical animal cell Contains a variety of membranous organelles Lysosome Ribosomes Centriole Golgiapparatus Peroxisome Microtubule Plasma membrane Intermediatefilament Cytoskeleton Mitochondrion Microfilament Figure 4.4A

17. Roughendoplasmicreticulum Nucleus Ribosomes Smoothendoplasmicreticulum Golgiapparatus A typical plant cell has some structures that an animal cell lacks Such as chloroplasts and a rigid cell wall Microtubule Centralvacuole Intermediatefilament Cytoskeleton Not inanimalcells Microfilament Chloroplast Cell wall Mitochondrion Peroxisome Plasma membrane Figure 4.4B

18. Internal membranes: • Greatly increase a cell's total membrane area.   • Provide additional area where many metabolic processes occur.   • Form membranous compartments called organelles.   • Contain proteins essential for metabolic processes.  

19. ORGANELLES OF THE ENDOMEMBRANE SYSTEM 4.5 The nucleus is the cell’s genetic control center The largest organelle is usually the nucleus which is separated from the cytoplasm by the nuclear envelope

20. Nucleus Chromatin Two membranesof nuclearenvelope Nucleolus The nucleus is the cellular control center containing the cell’s DNA, which directs cellular activities The function of the nucleolus is to help manufacture ribosomes. Long fibers of DNA and protein are called chromatin. Pore Roughendoplasmicreticulum Figure 4.5 Ribosomes

21. 4.6 Overview: Many cell organelles are connected through the endomembrane system The endomembrane system is a collection of membranous organelles that manufactures and distributes cell products Endoplasmic Reticulum-acts as an intracellular highway

22. Smooth ER Rough ER 4.7 Smooth endoplasmic reticulum has a variety of functions Smooth endoplasmic reticulum Synthesizes lipids Processes toxins and drugs in liver cells Stores and releases calcium ions in muscle cells Nuclearenvelope Ribosomes Rough ER Smooth ER TEM 45,000 Figure 4.7

23. 4.8 Rough endoplasmic reticulum makes membrane and proteins The rough ER manufactures membranes and proteins to be secreted by the cell. The rough and smooth ER work together. Ex. Rough ER produces hair & Smooth ER produces oils to coat the hair.

24. Transport vesiclebuds off 4 Ribosome Ribosomes on the surface of the rough ER Produce proteins that are secreted, inserted into membranes, or transported in vesicles to other organelles Secretory(glyco-) proteininside trans-port vesicle 3 Sugar chain 1 2 Glycoprotein Polypeptide Rough ER Figure 4.8

25. 4.9 The Golgi apparatus finishes, sorts, and ships cell products Stacks of membranous sacs receive and modify ER products Then ship them to other organelles or the cell surface Golgi apparatus “Receiving” side ofGolgi apparatus Golgiapparatus Transportvesiclefrom ER TEM 130,000 New vesicleforming Transportvesicle fromthe Golgi “Shipping” sideof Golgi apparatus Figure 4.9

26. The Golgi apparatus : • stores, modifies, and packages proteins.   • works closely with the endoplasmic reticulum.   • serves as a molecular warehouse and finishing factory.   • modifies chemicals received from the endoplasmic reticulum.   • sorts molecules according to their destination. • increases in size when a cell increases its protein production.  

27. Rough ER 1 Transport vesicle(containing inactivehydrolytic enzymes) 4.10 Lysosomes are digestive compartments within a cell Lysosomes are sacs of enzymes That function in digestion within a cell Golgiapparatus Plasmamembrane Lysosomeengulfingdamagedorganelle 2 Engulfmentof particle “Food” Lysosomes 3 5 4 Foodvacuole Digestion Figure 4.10A

28. Lysosome Lysosomes in white blood cells Destroy bacteria that have been ingested Nucleus TEM 8,500 Figure 4.10B

29. Lysosome containingtwo damaged organelles Lysosomes also recycle damaged organelles and fuse with food vacuoles to expose nutrients to lysosomal enzymes. Mitochondrion fragment TEM 42,500 Peroxisome fragment Figure 4.10C

30. When a cell is deprived of oxygen, its lysosomes tend to burst and release their contents into the cell. As a result of this, that cell will undergo self-digestion and die.

31. CONNECTION 4.11 Abnormal lysosomes can cause fatal diseases Lysosomal storage diseases interfere with various cellular functions Ex. Pompe’s & Tay-Sachs disease

32. Nucleus Chloroplast 4.12 Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole, Which has lysosomal and storage functions Centralvacuole Colorized TEM 8,700 Figure 4.12A

33. Nucleus Some protists have contractile vacuoles That pump out excess water Contractilevacuoles LM 650 Figure 4.12B

34. Transport vesicle fromGolgi to plasma membrane Transport vesiclefrom ER to Golgi Rough ER Plasmamembrane 4.13 A review of the endomembrane system The various organelles of the endomembrane system Are interconnected structurally and functionally Nucleus Vacuole Lysosome Figure 4.13 Nuclear envelope Smooth ER Golgi apparatus

35. ENERGY-CONVERTING ORGANELLES 4.14 Chloroplasts convert solar energy to chemical energy Chloroplasts, found in plants and some protists convert solar energy to chemical energy in sugars Stroma is the thick fluid enclosed by the inner chloroplast membrane. Chloroplast Stroma Inner and outermembranes TEM 9,750 Granum Intermembranespace Figure 4.14

36. Mitochondrion 4.15 Mitochondria harvest chemical energy from food Mitochondria carry out cellular respiration which uses the chemical energy in food to make ATP for cellular work Cristae-folds in the mitochondria that increase the surface area and enhance ability to produce ATP. Outermembrane Intermembranespace Innermembrane TEM 44,880 Figure 4.15 Cristae Matrix

37. THE CYTOSKELETON AND RELATED STRUCTURES 4.16 The cell’s internal skeleton helps organize its structure and activities A network of protein fibers Make up the cytoskeleton. Tubulin subunit Actin subunit Fibrous subunits 25 nm 10 nm 7 nm Microtubule Microfilament Intermediate filament Figure 4.16

38. Microfilaments of actin Enable cells to change shape and move Intermediate filaments Reinforce the cell and anchor certain organelles Microtubules of tubulin Give the cell rigidity and provide anchors for organelles and act as tracks for organelle movement

39. Microfilaments are mainly composed of actin whereas microtubules are composed of tubulin.

40. 4.17 Cilia and flagella move when microtubules bend Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells Flagella are longer and less numerous than cilia. Colorized SEM 4,100 LM 600 Figure 4.17A Figure 4.17B

41. Flagellum Electron micrographsof cross sections: Outer microtubuledoublet Clusters of microtubules drive the whipping action of these organelles Dynein arms are found on microtubules and cause movement by grabbing and pulling at adjacent microtubule doublets. Centralmicrotubules TEM 206,500 Radial spoke Dynein arms Flagellum Plasmamembrane TEM 206,500 Basal body(structurally identical to centriole) Figure 4.17C Basal body

42. CELL SURFACES AND JUNCTIONS 4.18 Cell surfaces protect, support, and join cells Cells interact with their environments and each other via their surfaces. Cell wall-made of cellulose

43. Walls of two adjacent plant cells Plant cells Are supported by rigid cell walls made largely of cellulose Connect by plasmodesmata, which are connecting channels Vacuole Plasmodesmata Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.18A

44. Plasmodesmata • Penetrate plant cell walls • Are one type of cell junction in plants • Carry chemical messages between plant cells • Carry nutrients between plant cells 4.18 Cell surfaces protect, support, and join cells

45. Animal cells are embedded in an extracellular matrix Which binds cells together in tissues

46. Tight junctions can bind cells together into leakproof sheets Line digestive tract Anchoring junctions link animal cells into strong tissues Heart & skin cells Gap junctions (communicating junctions) allow substances to flow from cell to cell Help heart cells have a coordinated beat Tight junctions Anchoring junction Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells

47. FUNCTIONAL CATEGORIES OF ORGANELLES 4.19 Eukaryotic organelles comprise four functional categories Eukaryotic organelles fall into four functional groups Manufacturing Breakdown Energy processing Support, movement, and communication between cells

48. Eukaryotic organelles and their functions Table 4.19

49. All cells on Earth • Are enclosed in a membrane that maintains internal conditions different from the surroundings. • Have DNA as the genetic material. • Can interconvert forms of energy. • Can interconvert chemical materials.