A Tour of the Cell

1. A Tour of the Cell Chapter 4

2. History of the Microscope • The microscope was invented in the 17th century • Using a microscope, Robert Hooke discovered cells in 1665 • Cell Theory- All living things are made of cells, and all cells come from other cells

3. The Microscope • Light Microscope (LM) • Pass visible light through a specimen • Magnification- an increase in the apparent size of an object • Resolving power- a measure of the clarity of an image • Light microscope cannot resolve detail finer than 0.2 micrometer (0.2/1000 mm) • Cannot show the details of the cell’s internal structure

4. Image seen by viewer Eyepiece Ocularlens Objective lens Specimen Condenser lens Light source Figure 4.1A The Light Microscope

5. Electron Microscopes • Electron microscopes were invented in the 1950s • They use a beam of electrons instead of light • The greater resolving power of electron microscopes • allows greater magnification • reveals cellular details

6. Scanning Electron Microscopy (SEM) • Used to study the architecture of cell surfaces • Object is covered with metal • Electrons are bounced off of the surface • “Bounced” electrons are collected and formed into an image

7. Transmission Electron Microscopy (TEM) • Used to study the details of internal cell structure • Object cut into extremely thin sections • Electron beam shot through the specimen • Electromagnets are used to focus and magnify the image

8. Electron Microscopy • Excellent tool for studying internal structures of cells • Good for studying 3D anatomy of cells and tissues at a greater magnification • Cannot replace the light microscope • Can’t use living specimens • Requires much prep time • Requires special training • Expensive

9. Cell Size • Cell size and shape are related to cell function • Chicken eggs are large because they hold nutrients • Muscle cells are long to help pull body parts together • Blood cells are small to help them navigate through tiny blood vessels

10. Natural Laws Limit Cell Size • At minimum, a cell must be large enough to house the parts it needs to survive and reproduce • The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes

11. 30 µm 10 µm Surface area of one large cube= 5,400 µm2 Total surface area of 27 small cubes= 16,200 µm2 Surface Area and Cell Size • A small cell has a greater ratio of surface area to volume than a large cell of the same shape • Muscle cells can be very thin because they are long and have more surface area

12. Prokaryotic Cells • Bacteria and Archaea • Most prokaryotic cells range from 2-8m in length • Lacks a nucleus, DNA is coiled into a nucleoid that does not have a membrane • Plasma membrane surrounds the cell, and a prokaryotic cell wall is outside the plasma membrane

13. Prokaryoticflagella Ribosomes Capsule Cell wall Plasma membrane Nucleoid region(DNA) Pili Figure 4.4 Prokaryotic Cells • May also contain a sticky outer coat called a capsule • Helps them stick to things • Some have pili to help stick • Some have flagella to aid in liquid movement

14. Eukaryotic Cells • All other life forms are made up of one or more eukaryotic cells • Plants, animals, fungi • These are larger and more complex than prokaryotic cells • Eukaryotes are distinguished by the presence of a true nucleus • Variety of structures (organelles) in the cytoplasm. Cytoplasm- fluid-filled region between the nucleus and the plasma membrane

15. Smooth endoplasmicreticulum Nucleus Roughendoplasmicreticulum Flagellum Not in most plant cells Lysosome Centriole Ribosomes Peroxisome Golgiapparatus Microtubule Plasmamembrane Cytoskeleton Intermediatefilament Microfilament Mitochondrion Figure 4.5A An Animal Cell

16. Cell Membranes • The plasma membrane controls the cell’s contact with the environment • The cytoplasm contains organelles • Many organelles have membranes as boundaries • These compartmentalize the interior of the cell • This allows the cell to carry out a variety of activities simultaneously • Increase total membrane area of the cell

17. A Plant Cell • All of the membrane-bound organelles present in animal cells are also in plant cells except the lysosome • No centriole or flagellum • Plant cells have structures that animal cells do not have: • Cell wall- protect cells and maintain shape • Chloroplasts – where photosynthesis occurs • Large central vacuole – carry out cellular digestion

18. Roughendoplasmicreticulum Nucleus Ribosomes Smoothendoplasmicreticulum Golgiapparatus Microtubule Centralvacuole Not inanimalcells Intermediatefilament Cytoskeleton Chloroplast Microfilament Cell wall Mitochondrion Peroxisome Plasma membrane Figure 4.5B A Plant Cell

19. The Nucleus • Genetic control center of a eukaryotic cell • Nuclear DNA is attached to proteins forming very long fibers called chromatin, each fiber constitutes a chromosome • When cell reproduction occurs, the chromosome coils up

20. The Nucleus • The nucleus is enclosed by a nuclear envelope • Double membrane with pores to control in and outflow of material into the cell • Nucleolus- within the nucleus; mass of fibers and granules; where the components of ribosomes are made

21. NUCLEUS Chromatin Two membranesof nuclearenvelope Nucleolus Pore ROUGHENDOPLASMICRETICULUM Ribosomes Figure 4.6 The Nucleus

22. Endomembrane System • A biological membrane system in organelles that runs throughout the cell • Some of the membranes are connected, some are not • Many organelles work together in the synthesis, storage, and export of important molecules • Rough and smooth endoplasmic reticulum, the golgi aparatus, lysosomes, and vacuoles

23. Endoplasmic Reticulum • Two kinds of ER: • Rough ER and smooth ER • These two types of organelles differ in structure and function, but a continuous membrane runs between them • Membranes of rough ER are continuous with the plasma membrane • Space within the ER is separated from the cytoplasm

24. Transport vesiclebuds off 4 Ribosome Secretory(glyco-) proteininside transportvesicle Sugarchain 3 Glycoprotein 1 2 ROUGH ER Polypeptide Rough ER • Refers to the appearance of this organelle in electron micrographs • Roughness results from ribosomes which stud the membranes of the organelle • Two main functions: • Make more membrane • Make proteins that are secreted by the cell

25. Smooth ER • Continuous with rough ER • Lacks ribosomes embedded in the membrane • Activity results from enzymes embedded in the membrane • Synthesizes lipids (fatty acids, phospholipids, and steroids) • In some cells (liver), it regulates carbohydrate metabolism and breaks down toxins and drugs

26. SMOOTH ER ROUGHER Nuclearenvelope Ribosomes SMOOTH ER ROUGH ER Smooth ER • Drug Tolerance • When Liver cells respond to certain drugs over and over they make more ER and become tolerant to the drug • Becomes resistant to the drug and its relatives

27. Golgi Apparatus • Unconnected, flattened stacks • # of golgi sacks correlates with how active the cell is at secreting proteins • Works with ER by receiving and modifying substances manufactured by the ER • Modifies them and marks them for their destination • The golgi vesicles then bud off and the molecules are shipped to the plasma membrane

28. Golgi apparatus Golgiapparatus “Receiving” side ofGolgi apparatus Transportvesiclefrom ER Newvesicleforming “Shipping”side of Golgiapparatus Transport vesiclefrom the Golgi Figure 4.10 Golgi Apparatus

29. Lysosomes • Digestive enzymes enclosed in a membranous sac • Come from the golgi apparatus • Compartmentalize digestive enzymes so they won’t harm the cell • Digest food vacuoles in order to digest them • Destroy harmful bacteria • Recycle damaged organelles • Play important roles in embryonic development

30. Rough ER Transport vesicle(containing inactivehydrolytic enzymes) Plasmamembrane Golgiapparatus LYSOSOME Engulfmentof particle Lysosomeengulfingdamagedorganelle Nucleus “Food” LYSOSOMES Digestion Foodvacuole Lysozymes

31. Vacuoles • Membranous sacs that have a variety of functions • Food and chemical storage • Central vacuole of plants aids in plant growth, and chemical and waste storage • Also contain pigments for flower color and poisons that protect plants from predation • In protists they collect water to prevent dilution

32. Nucleus Centralvacuole Contractilevacuoles Nucleus Vacuoles Protists Plants

33. Transport vesiclefrom Golgi Transport vesiclefrom ER Rough ER Plasmamembrane Vacuole Nucleus Lysosome Golgiapparatus Nuclearenvelope Smooth ER Endomembrane System

34. Chloroplasts • The photosynthesizing organelles of plants and protists • Most of the living world runs on the energy provided by photosynthesis • Internal membranes partition the chloroplast into 3 compartments • Intermembrane space • Stroma • Granum

35. Chloroplast Stroma Inner and outer membranes Granum Intermembranespace Figure 4.15 Chloroplasts • Intermembrane space- between outer and inner membrane of the chloroplast • Stroma- Network of tubules and interconnected hollow disks formed of membranes • Granum- Stacks of hollow disks that are the chloroplasts solarpower packs

36. Mitochondria • Organelles that convert energy from one chemical form to another • Carry out cellular respiration • Sugars are converted to the chemical energy of a molecule of ATP • Enclosed by two membranes • Composed of two compartments: • Intermembrane space • Mitochondrial matrix

37. MITOCHONDRION Outermembrane Intermembranespace Innermembrane Cristae Matrix Mitochondria • Intermembrane space • Fluid-filled compartment • Encloses mitochondrial matrix • Mitochondrial matrix- • Many of the rxns of cellular respiration occur here • Inner membrane highly folded into christae that increase the surface area • Embedded in the cristae are the enzymes that make ATP

38. Cytoskeleton • Cytoskeleton- A supportive meshwork of fine fibers contained in eukaryotic cells • Fibers extend throughout the cell • Also involved in cell movement • May help regulate cellular activity by transmitting signals from the cells exterior to the interior • Three main types of fibers: • Microfiliments, intermediate filiments, microtubules

39. MICROFILAMENT Actin subunit 7 nm INTERMEDIATE FILAMENT Fibrous subunits 10 nm Cytoskeleton • Microfilaments • Solid helical rods composed mainly of actin • Twisted double chain • Can help cells change shape by assembling and disassembling • Interact with other protein filaments to make cells contract • Intermediate filaments • Fibrous proteins with a rope-like structure • Reinforcing rods and anchor organelles

40. MICROTUBULE Tubulinsubunit 25 nm Cytoskeleton • Microtubules- straight, hollow tubes composed of globular proteins called tubulin • May disassemble and reassemble to provide rigidity and shape to the cell • Anchorage for organelles and tracks for organelle movement within the cytoplasm

41. Cilia and Flagella • Cilia- short, numerous appendages • Flagella- longer, less numerous appendages • Core of microtubules wrapped in an extension of the plasma membrane • 9 microtubule doublets surrounds a central pair (9+2) • At the base microtubules form an anchoring structure called the basal body where the central core mt’s disappear • Cilia and flagella provide support and contribute to movement

42. FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasmamembrane Flagellum Centralmicrotubules Outer microtubule doublet Plasmamembrane Basal body Basal body(structurally identical to centriole)

43. Microtubule doublet Slidingforce Dynein arm Locomotion with Cilia and Flagella • Protein knobs (dynein arms) attached to each microtubule doublet • Bending is done by the dynein arms grabbing onto the adjacent mt and ‘walking’ along it so that the arms slide along each other

44. Cell surfaces • Most cells have an additional surface coating surrounding the plasma membrane • Prokaryotes-capsules • Interact mainly with non-cellular surroundings • Plants- cell walls • Protect cells and provide structural support • Eukaryotes- composed of many cells organized into a single, functional organism

45. Plant cell walls • Consist of fibers of the polysaccharide cellulose embedded in a matrix of other polysaccharides and proteins • Cell walls are multi-layered • Between the walls of adjacent cells is a layer of sticky polysaccharides that bonds the cells together

46. Plant cell walls • Cell walls are not totally isolated they have cell junctions called plasmodesmata that connect them to one another • Plasmodesmata are channels between adjacent cells that form a circulatory and communication system connecting the cells in plant tissues

47. Walls of two adjacent plant cells Vacuole PLASMODESMATA Layers of one plant cell wall Cytoplasm Plasma membrane Plant cell walls • Cytoplasmic fluid of the cells extends through the plasmadesmata so that water and small molecules can pass from cell to cell • Nourishment, water, chemical signals

48. Animal cells • Animal cells secrete and are embedded in a sticky layer of glycoproteins called the extracellular matrix • Helps hold cells together • Protective and supportive functions • Regulates cell behavior • Adjacent cells in many tissues also connect by cell junctions

49. Three general types of Cell Junctions • Tight junctions- bind cells together forming a leak-proof sheet • Digestive tract • Anchoring junctions- attach cells together in the extracellular matrix • Muscle cells • Communicating junctions- channels similar to plasmodesmata • Animal embryos

50. TIGHTJUNCTION ANCHORING JUNCTION COMMUNICATING JUNCTION Plasma membranes ofadjacent cells Extracellularmatrix Figure 4.19B Three general types of Cell Junctions