Chapter 6

1. Chapter 6 A Tour of the Cell

2. Cell theory: • All living organisms are made up of cells. • Cells are basic units of structure and function • All cells are produced from other cells. Robert Hooke- 1st person to view cells under microscope(compound); used thin slice of cork. Anton Von Leeuwenhook- 1st person to view single celled organisms in pond. (simple microscope) -Cell structure is correlated to cellular function

3. Microscopy • Scientists use microscopes to visualize cells too small to see with the naked eye • Light microscopes (LMs) • Pass visible light through a specimen • Magnify cellular structures with lenses • Different types of microscopes • Can be used to visualize different sized cellular structures

4. 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Light microscope Chicken egg 1 cm Frog egg 1 mm Most plant and Animal cells 100 µm Electron microscope 10 µ m NucleusMost bacteriaMitochondrion 1 µ m Smallest bacteria Electron microscope 100 nm Viruses 10 nm Ribosomes Proteins Lipids 1 nm Small molecules Figure 6.2 Atoms 0.1 nm Unaided eye Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 mm = 10–9 m

5. Brightfield(unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained Brightfield (stained specimen).Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved). Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells. • Use different methods for enhancing visualization of cellular structures

6. Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. It absorbs ultraviolet radiation and emit visible light Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry. Differential-interference-contrast (Nomarski). it uses optical modifications to exaggerate differences in density, making the image appear almost 3D.

7. Electron microscopes (EMs) • Focus a beam of electrons through a specimen (TEM) or onto its surface (SEM) • The scanning electron microscope (SEM) • Provides for detailed study of the surface of a specimen • The transmission electron microscope (TEM) • Provides for detailed study of the internal ultrastructure of cells

8. Isolating Organelles by Cell Fractionation • Cell fractionation • Takes cells apart and separates the major organelles from one another • First, cells are homogenized in a blender to break them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cell components, forming a series of pellets. • The centrifuge • Is used to fractionate cells into their component parts

9. Two types of cells make up every organism • Prokaryotic • Eukaryotic • All cells have several basic features in common • They are bounded by a plasma membrane • They contain a semifluid substance called the cytosol • They contain chromosomes • They all have ribosomes

10. Prokaryotic cells • Do not contain a nucleus • Have their DNA located in a region called the nucleoid • Eukaryotic cells • Contain a true nucleus, bounded by a membranous nuclear envelope • Are generally quite a bit bigger than prokaryotic cells

11. Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Bacterialchromosome Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes 0.5 µm (b) A thin section through the bacterium Bacillus coagulans (TEM) (a) A typical rod-shaped bacterium Flagella: locomotion organelles of some bacteria

12. A smaller cell • Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cell. • Eukaryotic cells • Have extensive and elaborately arranged internal membranes, which form organelles • Plant and animal cells • Have most of the same organelles

13. Hydrophilic region Hydrophilic region Proteins Phospholipid • The plasma membrane • Functions as a selective barrier • Allows sufficient passage of nutrients and waste Carbohydrate side chain

14. ENDOPLASMIC RETICULUM (ER) Nuclear envelope Nucleolus NUCLEUS Rough ER Smooth ER Chromatin Flagelium Plasma membrane Centrosome CYTOSKELETON Microfilaments Intermediate filaments Ribosomes Microtubules Microvilli Golgi apparatus Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Peroxisome Mitochondrion • A animal cell

15. In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Nuclear envelope Rough E NUCLEUS Chromatin Centrosome Smooth E Ribosomes Central vacuole Golgi apparatus Microfilaments Microtubules Mitochondrion Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell • A plant cell CYTOSKELETON:

16. -The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes. The Nucleus: Genetic Library of the Cell • The nucleus • Contains most of the genes in the eukaryotic cell • The nuclear envelope • Encloses the nucleus, separating its contents from the cytoplasm

17. Ribosomes: Protein Factories in the Cell • Ribosomes • Are particles made of ribosomal RNA and protein • Carry out protein synthesis The endomembrane system regulates protein traffic and performs metabolic functions in the cell • The endomembrane system • Includes many different structures

18. The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) • Accounts for more than half the total membrane in many eukaryotic cells • The ER membrane • Is continuous with the nuclear envelope • There are two distinct regions of ER • Smooth ER, which lacks ribosomes • Rough ER, which contains ribosomes

19. Functions ER • The smooth ER • Synthesizes lipids, Metabolizes carbohydrates, Stores calcium,Detoxifies poison • The rough ER • Has bound ribosomes • Produces proteins and membranes, which are distributed by transport vesicles • Has bound ribosomes • Produces proteins and membranes, which are distributed by transport vesicles

20. The Golgi Apparatus: Shipping and Receiving Center • The Golgi apparatus • Receives many of the transport vesicles produced in the rough ER • Consists of flattened membranous sacs called cisternae • Functions of the Golgi apparatus include • Modification of the products of the rough ER • Manufacture of certain macromolecules

21. Lysosomes: Digestive Compartments • A lysosome • Is a membranous sac of hydrolytic enzymes • Can digest all kinds of macromolecules • Lysosomes carry out intracellular digestion by: • Phagocytosis

22. Vacuoles: Diverse Maintenance Compartments • A plant or fungal cell • May have one or several vacuoles • Food vacuoles • Are formed by phagocytosis • Contractile vacuoles • Pump excess water out of protist cells • Central vacuoles • Are found in plant cells • Hold reserves of important organic compounds and water

23. Central vacuole Cytosol Tonoplast Central vacuole Nucleus Cell wall Chloroplast 5 µm

24. The Endomembrane System: • The endomembrane system • Is a complex and dynamic player in the cell’s compartmental organization

25. Relationships among organelles of the endomembrane system • Nuclear envelope is connected to rough ER, which is also continuous with smooth ER • Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi 3) Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles 4) Lysosome available for fusion with another vesicle for digestion 5) Transport vesicle carries proteins to plasma membrane for secretion 6) Plasma membrane expands by fusion of vesicles; proteins are secreted from cell

26. Mitochondria and chloroplasts change energy from one form to another • Mitochondria • Are the sites of cellular respiration • Chloroplasts • Found only in plants, are the sites of photosynthesis

27. Mitochondria: Chemical Energy Conversion • Mitochondria • Are found in nearly all eukaryotic cells • Mitochondria are enclosed by two membranes • A smooth outer membrane • An inner membrane folded into cristae

28. Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA

29. Chloroplasts: Capture of Light Energy • The chloroplast • Is a specialized member of a family of closely related plant organelles called plastids • Contains chlorophyll • Chloroplasts • Are found in leaves and other green organs of plants and in algae • Chloroplast structure includes • Thylakoids, membranous sacs • Stroma, the internal fluid

30. Chloroplast Stroma Ribosomes Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid

31. Chloroplast Peroxisome Mitochondrion 1 µm Peroxisomes: Oxidation • Peroxisomes • Produce hydrogen peroxide and convert it to water

32. The cytoskeleton is a network of fibers that organizes structures and activities in the cell • The cytoskeleton • Is a network of fibers extending throughout the cytoplasm Roles of the Cytoskeleton: Support, Motility, and Regulation: • The cytoskeleton • Gives mechanical support to the cell • Is involved in cell motility, which utilizes motor proteins

33. Microtubule 0.25 µm Microfilaments

34. Components of the Cytoskeleton 1) Microtubules: Hollow tubes -Functions: maintain cell shape, cell motility, Chromosome movements in cell division, and organelle movements. 2)Microfilaments: 2 intertwined strands of actin. -Functions: keep cell shape, muscle contraction, cytoplasmic streaming, cell motility, & cell division. 3) Intermediate Filaments: Fibrous proteins supercoiled into thicker cables. -Functions: Keep cell shape, anchorage of nucleus and several other organelles, & formation of nuclear lamina.

35. Microtubules • Microtubules • Shape the cell • Guide movement of organelles • Help separate the chromosome copies in dividing cells Centrosomes and Centrioles: • The centrosome • Is considered to be a “microtubule-organizing center” • Contains a pair of centrioles

36. Centrosome Microtubule Centrioles Longitudinal section of one centriole Microtubules Cross section of the other centriole

37. Cilia and Flagella • Cilia and flagella • Contain specialized arrangements of microtubules • Are locomotor appendages of some cells • (a) Motion of flagella. A flagellum usually undulates, its snake like motion driving a cell in the same direction as the axis of the flagellum. Propulsion of a human sperm cell is an example of flagellatelocomotion (LM).

38. (b) Motion of cilia. Cilia have a back- and-forth motion that moves the cell in a direction perpendicular to the axis of the cilium. A dense nap of cilia, beating at a rate of about 40 to 60 strokes a second, covers this Colpidium, a freshwater protozoan (SEM).

39. Microtubule doublets ATP Dynein arm Powered by ATP, the dynein arms of one microtubule doublet grip the adjacent doublet, push it up, release, and then grip again. If the two microtubule doublets were not attached, they would slide relative to each other. • The protein dynein • Is responsible for the bending movement of cilia and flagella

40. ATP Outer doublets cross-linking proteins Anchorage in cell -In a cilium or flagellum, two adjacent doublets cannot slide far because they are physically restrained by proteins, so they bend. (Only two of the nine outer doublets in Figure 6.24b are shown here.)

41. 1 3 2 Localized, synchronized activation of many dynein arms probably causes a bend to begin at the base of the Cilium or flagellum and move outward toward the tip. Many successive bends, such as the ones shown here to the left and right, result in a wavelike motion. In this diagram, the two central microtubules and the cross-linking proteins are not shown. (c)

42. Microfilaments (Actin Filaments) • Microfilaments • Are built from molecules of the protein actin • Are found in microvilli • Microfilaments that function in cellular motility • Contain the protein myosin in addition to actin

43. Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments

44. Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium • Amoeboid movement • Involves the contraction of actin and myosin filaments

45. Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Parallel actin filaments Cell wall • Cytoplasmic streaming • Is another form of locomotion created by microfilaments

46. Intermediate Filaments • Intermediate filaments • Support cell shape • Fix organelles in place *Extracellular components and connections between cells help coordinate cellular activities

47. Cell Walls of Plants • The cell wall • Is an extracellular structure of plant cells that distinguishes them from animal cells • Plant cell walls • Are made of cellulose fibers embedded in other polysaccharides and protein • May have multiple layers • Animal cells • Lack cell walls • Are covered by an elaborate matrix, the ECM

48. A proteoglycan complex Collagen Polysaccharide molecule EXTRACELLULAR FLUID Carbo- hydrates Fibronectin Core protein Proteoglycan molecule Plasma membrane Integrins CYTOPLASM Micro- filaments Integrin • The ECM • Is made up of glycoproteins and other macromolecules

49. Functions of the ECM include • Support • Adhesion • Movement • Regulation *Cells rely on the integration of structures and organelles in order to function

50. Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes Plants: Plasmodesmata • Plasmodesmata • Are channels that perforate plant cell walls