steve.gb

1. Tour of the CellLecture 4 http://www.steve.gb.com

2. Much of the text material in the lecture notes is from our textbook, “Essential Biology with Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship. Other sources were sometimes used, and are noted.

3. Outline • Drugs that target cells • Microscopic world of cells • Microscopy • Cell types • Cell components and functions • Origin of membranes • Words and terms to know • Possible test items

4. American Civil War http://www.a2zcds.com http://nmhm.washingtondc.museum During the American Civil War, many soldiers died from infections in the treatment of their wounds (possibly as many as actually died on the battlefield).

5. Penicillin • Antibiotics derived from microorganisms disable or kill bacteria. • In the 1920s, Alexander Fleming discovered penicillin when he observed that mold prevented the growth of bacteria that he was trying to cultivate in bread. • Fleming recognized the value of an agent that inhibits bacterial growth, and the age of antibiotics was born. • The death rates from diseases such as bacterial pneumonia and surgical infection dropped substantially once antibiotics were introduced and then widely used. • The discovery of penicillin is a famous case of ‘serendipity.’

6. Bread Mold http://www.sciencemore.com

7. Antibiotic Actions • Antibiotics destroy bacteria or inhibit their growth. • Penicillin works by disrupting the synthesis of the cell walls in bacteria. • Erythromycin binds to a structure that synthesizes proteins found only in bacterial cells. • Ciprofloxacin, used in treating anthrax infections, targets an enzyme that helps maintain the genetic structure of bacteria. http://web.edu

8. Cell Theory • Cells were first described in 1665 by the British scientist, Robert Hooke, while examining a thin slice of cork through a microscope. • Over the next two centuries, cells were found in all organisms examined under a microscope. • By the mid-1800s the accumulation of evidence (through the process of inductive reasoning) led to the cell theory: all organisms are composed of cells. • The theory was later expanded to include observations that new cells arise from previously existing cells. Microscopic view of commercial cork obtained from Cork Oak http://instruct1.cit.cornell.edu

9. Cellular Structure of Cork http://farm1.static.flickr.com Robert Hooke’s drawing

10. Grove of Cork Oak http://www.isa.utl.pt http://cache.eb.com

11. Microscopic World of Cells • Each cell in a living organism is very complex. • Cells must be very small for materials to move in and out of the cell to meet its needs. • A modern jet aircraft, if it was reduced to the size of a cell, would seem simple in comparison. • Organisms are single-cellular, such as bacteria and protista, and multi-cellular as animals, plants, and most fungi. • The human body has many trillions of cells that work together to perform specific functions.

12. A Few Types of Neurons http:www.semaphorin.com

13. Light Microscope A portable microscope similar to the one Darwin used on the H.M.S Beagle http://www.meijitechno.com Modern lab and classroom version http://www.hps.cam.ac.uk

14. LM Operation • Light microscopes (LMs) were first developed during the Renaissance period. • Visible light passes through the specimen—the lens enlarges the image and projects it onto the human eye or camera. • Modern light microscopes have compound lenses to reduce chromatic (color) aberration and spherical aberration for improving the quality of the viewed image.

15. Magnification and Resolving Power • Two key aspects of microscopes are magnification and resolving power. • Magnification is the increase in an object’s apparent size compared to its actual size. • Resolving power is the ability to show two or more objects as distinct entities. • Due to limitations in resolving power, the maximum useful magnification is about 1000 times. The Big Dipper—an ancient eye test http://nightglories.com

16. LM Micrograph http://www.steve.gb.com Cross-section of bamboo showing its internal vasculature.

17. LM Micrograph http://marby.online.com Cell structure in an elodea leaf

18. LM Micrograph http://www7.ocn.ne.jp Cross section through a buttercup stem

19. LM Micrograph http://www.uwash.edu Red blood cells and a stained white blood cell

20. LM Micrograph http://www.emsdiasum.com Coronal cross-section of a rat brain

21. Electron Microscope http://www.usaft.af.mil An electron microscopy lab

22. EM Operation • The study of the structure of cells continued to advance once electron microscopes (EMs) were developed in the 1950s. • Electron microscopes use beams of electrons rather than light to explore the very small world. • The resolving power is much higher than for light microscopes, allowing for much higher useful magnifications. • Electron micrographs can be produced at magnifications of 100,000 or higher.

23. Types of Electron Microscopes • Scanning electron microscopes are used for studying the surfaces of cells. • Transmission electron microscopes are used for exploring the internal structure of cells. • Light microscopes can be used with live or prepared (dead) specimens, while electron microscopes can only be used with prepared specimens.

24. EM Micrograph http://www.allergy-details.com A ‘potpourri’ of pollens

25. EM Micrograph http://www.microscopy-uk.org Blood—neutrophils and lymphocytes

26. EM Micrograph http:www3.niaid.nih.gov Escherichia coli (E. coli)

27. EM Micrograph http://www.spaceref.com Microbes—specifically archaea

28. We now examine cells and their organelles

29. Cell Types • Prokaryotic cells—evolutionary much older cells, and much simpler in structure than eukaryotic cells. Bacteria, for example, are prokaryotes. • Eukaryotic cells—much more complex internal structure. All animal and plant cells are eukaryotes. • Prokaryotic cells are much smaller than eukaryotic cells and do not have a true nucleus—they have a nucleoid region containing genetic material.

30. Prokaryotic Cell The bacteria E. coli dividing http://www.cod.edu A highly-stylized representation http://www.bio.mtu.edu

31. Eukaryotic Cell Electron micrograph—the nucleus and endoplasmic reticulum are prominent http://www.cod.edu A highly-stylized representation http://www.steve.gb.com

32. First Appearances • The age of the Earth based on scientific evidence is about 4.3 billion years. • Prokaryotic cells appeared about 3.5 billion years before present (bp). • The first eukaryotic cells evolved about 1.7 billion years bp. http://www.web.utah.edu

33. Components of Eukaryotic Cells Component Animal Cell Plant Cell Cytoplasm x x Plasma membrane x x Nucleus x x Chromosomes x x Ribosomes x x Endoplasmic reticulum x x Golgi apparatus x x Lysosomes x rare Mitochondria x x Cytoskeleton x x Vacuoles x x Flagella and cilia x rare Centrioles x x Cell wall -- x Chloroplasts -- x Central vacuole -- x

34. Cytoplasm Electron micrograph http://www.danforthcenter.org

35. Cytoplasm • The cytoplasm is the region of the cell between the nucleus and plasma membrane. • It contains various organelles suspended in a fluid known as the cytosol. • Each organelle is adapted to perform specific functions, as we will discuss. • Most organelles in eukaryotic cells are enclosed by their own membranes.

36. Plasma Membrane Computer-generated graphic http://www.sci-design.com

37. Plasma Membrane • Cells have a plasma membrane separating the interior and exterior of the cell—they arealso known as the intracellular and extracellular spaces. • The membrane consists primarily of phospholipids and proteins in a ‘fluid mosaic.’ • The plasma membrane regulates the traffic of molecules moving into and out of the cell. • It is selectively permeable—that is, the membrane allows some molecules to pass through while preventing the passage of others. • Transport proteins embedded in the plasma membrane allow the passage of other molecules such as glucose molecules.

38. Nucleus Electron micrograph http:.//www.science.org.au

39. Nucleus • The nucleus has a double membrane known as the nuclear envelope. • The double membrane is similar in structure to the plasma membrane. • Pores in the membrane allow the passage of material between nucleus and cytoplasm. • DNA molecules and associated proteins form long fibers in the nucleus called chromatin. • The nucleus also contains a ball-like mass (the nucleolus) that produces the component parts of ribosomes.

40. Chromatin and DNA Packed Unpacked Computer-generated graphics Both images from http://www.cgl.ucsf.edu

41. Ribosomes Computer-generated graphic http://rna.ucsc.edu

42. Ribosomes • Ribosomes are located in the cytoplasm, near the cell nucleus, where they synthesize proteins. • Some ribosomes make proteins that will be dissolved in the cytoplasm, while others make proteins for the plasma membrane or secretion by the cell. • DNA transfers genetic information via messenger RNA to the ribosomes to synthesize proteins. • We will discuss DNA and RNA in future lectures on the genetic basis of life.

43. Endoplasmic Reticulum Electron micrograph http://www.bu.edu

44. Endoplasmic Reticulum • The endoplasmic reticulum (ER) produces many types of molecules of life. • It is a complex system of tubes and sacs running through the cytoplasm. • Rough ER has the visual appearance of roughness due to ribosomes that stud its exterior surface. • The products of ribosomes are modified in the rough ER and sent on their way in transport vesicles. • Cells that secrete substantial amounts of protein, such as salivary glands, are rich in rough ER.

45. Smooth ER • Smooth ER synthesizes lipids, among other biological molecules. • It lacks the embedded ribosomes found in the membrane of rough ER. • Cells in the ovaries and testes are rich in smooth ER, and produce the steroids, estrogen and testosterone.

46. Detoxification • Smooth ER in the cells of the liver produce enzymes for the detoxification of drugs and poisons in the blood. • Smooth ER increases in liver cells when exposed to the chemicals in some drugs. • As a result, the body increases its tolerance to a chemical, requiring higher dosages to achieve the same effect. • An increase in tolerance to some drugs is a hallmark of addiction—it has a firm biological basis.

47. Golgi Apparatus Electron micrograph http://www.bu.edu

48. Golgi Apparatus • The Golgi apparatus is named for its discover, the Italian scientist, Camillo Golgi. • It works with the ER to refine, store, and distribute molecules synthesized in the cell. • Products manufactured in the ER reach the Golgi apparatus via transport vesicles. • Enzymes in the Golgi apparatus modify many of the products from the ER. • The Golgi apparatus tags proteins with ‘addresses’ for their destinations within the cell. • Containers known as vesicles budding from the Golgi apparatus distribute molecules to other organelles.

49. Lysosomes Electron micrograph http://biology.unm.edu

50. Lysosomes • A lysosome is a membrane-enclosed sac of enzymes needed for cellular digestion. • Lysosomes provide a compartment for chemical digestion to prevent self-destruction of the cell. • Enzymes breakdown macromolecules including proteins, glycogen, fats, and nucleic acids. • The molecules produced from the cellular digestive process nourish the cell.