Introduction to the Study of  Cell Biology <ul><li>Objectives </li></ul><ul><li>A brief outline of the early history of ce...
<ul><li>Biology  = science of life </li></ul><ul><ul><li>Characteristics, classification and behaviors of organisms,  </li...
<ul><li>Modern biology is divided into 2 categories based on primary level of focus: </li></ul><ul><ul><li>Organismic biol...
<ul><li>Cellular and molecular biology is  reductionist; i.e. </li></ul><ul><li>The knowledge of the parts of the whole ca...
Modern Cell Biology <ul><li>Involve interweaving of 3 historically distinct disciplines </li></ul><ul><ul><li>Cytology (th...
The Cell Biology Time Line
The Discovery of Cells  -  The cell theory   <ul><li>The term cell was first used by the English scientist  Robert Hooke  ...
<ul><ul><li>1839 - German zoologist  Theodor Schwann  (1810-1882) realized animals were also composed of fundamental cellu...
<ul><li>Size  –  pose challenge to understand cellular structure & organization  </li></ul><ul><li>Most cells and their or...
<ul><li>Cells are mostly microscopic in size </li></ul><ul><ul><li>Most eukaryotic cells have single nucleus with only 2 c...
 
Resolving Power of the Human Eye, the Light Microscope, and the Electron Microscope
<ul><li>Microscope </li></ul><ul><ul><li>Make small objects appear bigger </li></ul></ul><ul><ul><li>Magnification is only...
<ul><ul><li>Resolution: resolving power </li></ul></ul><ul><ul><ul><li>Ability to distinguish fine detail and structures  ...
<ul><ul><li>Magnification  </li></ul></ul><ul><ul><ul><li>Ability of the lens to enlarge or magnify the object </li></ul><...
<ul><ul><li>Visibility / contrast </li></ul></ul><ul><ul><ul><li>Features that allen a object actually to ….,larger determ...
<ul><li>Different types of light microscopy </li></ul><ul><li>Brightfield </li></ul><ul><li>Phase contrast </li></ul><ul><...
Table 1-1 Different Types of Light Microscopy: A Comparison
The paths taken by light rays that form the image of the specimen & those that form the background light of the field
A comparison of cells seen with different types of light microscope: brightfield, phase contrast, diffrential interference...
The light paths in a fluorescence confocal scanning light microscope
Confocal scanning micrographs of 3 optical sections 0.3 mm thick of a yeast nucleus stained with 2 different fluorescently...
<ul><li>Electron microscopy </li></ul><ul><ul><li>Types of electron microscopy: </li></ul></ul><ul><ul><li>~transmission e...
A comparison of the lens systems of a light and electron microscope
Streptococcus pyogenes   SEM TEM
Scanning Electron Microscopy
Basic properties of cells <ul><li>Life  –  most basic property of cells </li></ul><ul><li>Smallest unit to exhibit this pr...
<ul><li>Cells are highly complex and organized </li></ul><ul><li>Each level of structure in cells has a great level of con...
<ul><li>The information to build a cell is encoded in its genes </li></ul><ul><li>Genes - blueprints for constructing cell...
<ul><li>Cells capable of producing more of themselves  –  mitosis & meiosis </li></ul><ul><li>Cell reproduce by division <...
<ul><li>Cells acquire & use energy to develop & maintain complexity  –  photosynthesis, respiration </li></ul><ul><li>Virt...
<ul><li>Cells carry out a variety of chemical reactions </li></ul><ul><li>Sum total of the chemical reaction in a cell rep...
<ul><li>Cells engage in numerous mechanical activities </li></ul><ul><li>Based on dynamic, mechanical changed in cell </li...
<ul><li>Cells able to respond to stimuli </li></ul><ul><li>Most cells have receptors that sense environment & initiate res...
<ul><li>Cells respond to specific stimuli </li></ul><ul><ul><li>Altering metabolic activities </li></ul></ul><ul><ul><li>P...
<ul><li>Cells are capable of self-regulation  </li></ul><ul><li>Cell processes are a series of ordered steps </li></ul><ul...
Classification of cells <ul><li>Cells are classified by fundamental units of structure and by the way they obtain energy. ...
<ul><li>Cells are also defined according the need for energy. </li></ul><ul><ul><li>Autotrophs are ‘self feeders’ that use...
<ul><li>Prokaryotic  </li></ul><ul><ul><li>prokaryotes are surrounded by a membrane and cell wall.  </li></ul></ul><ul><ul...
baccillus
Structure of animals cell
Plant  Cel l
Differences between prokaryotic and eukaryotic cells Prokaryotes  Eukaryotes  Size Usually 1-2   m 5-100   m Nucleus  Ab...
Types of prokaryotic cells <ul><li>Divided into 2 major taxonomic groups/domains </li></ul><ul><ul><li>The Archaea/archaeb...
Types of eukaryotic cells <ul><li>Protists (single-cell)  –  do everything an organism must do to survive in single cell <...
<ul><li>Differentiation  – process by which a relatively unspecialized cell become highly specialized </li></ul><ul><li>Ce...
 
Viruses  <ul><li>Common virus properties  – not considered living since need host to reproduce and metabolize, etc </li></...
Tobacco mosaic virus Bacteriophage
<ul><li>Have surface proteins that bind to particular host cell surface component  </li></ul><ul><li>In the viral life cyc...
Conclusion  <ul><li>“ Long ago it became evident that the key to every biological problem must be finally sought in the ce...
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Cell Biology

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  • Biology - it is concerned with the characteristics and behaviors of organisms , how species and individuals come into existence, and the interactions they have with each other and with their environment . Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines.
  • Organismic biology - diversity of plants and animals on Earth - emphasize on biodiversity, evolutionary relationships, adaptations, and ecology of plants and animals.
  • Cell biology studies the physiological properties of cells , as well as their behaviors , interactions, and environment . This is done both on a microscopic and molecular level. Cell biology researches both single-celled organisms like bacteria and specialized cells in multicellular organisms like humans . Understanding cell composition and how they function is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important in the fields of cell and molecular biology . These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of &amp;quot;structure to function&amp;quot; is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology , but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species .
  • Cork = empty cell walls of dead plant tissues
  • Scheiden &amp; Schwann both agreed that cells could arise from noncellular materials (spontaneous generation)
  • Gases and food molecules dissolved in water must be absorbed and waste products must be eliminated. For most cells, this passage of all materials in and out of the cell must occur through the plasma membrane (see diagram above). Each internal region of the cell has to be served by part of the cell surface. As a cell grows bigger, its internal volume enlarges and the cell membrane expands. Unfortunately, the volume increases more rapidly than does the surface area, and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases. The important point is that the surface area to the volume ratio gets smaller as the cell gets larger . Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. When this happens, the cell must divide into smaller cells with favorable surface area/volume ratios, or cease to function. That is why cells are so small.
  • E.g. clear glass bead Under most conditions, against most b/grd, the bead is clearly visible If dropped into a beaker of imer
  • TEM - form images using electrons that are transmitted (pass) through a specimen SEM - utilize electrons that have bounced off the surface of the specimen
  • Complexity – order &amp; consistency Organization of atoms  molecules  polymers  sub cellular organelles  cells More complex a structure: The greater the number of parts that must be in their proper place The less tolerance of errors in the nature and interactions of the parts The more regulation or control that must be exerted to maintain the system
  • Just as individual organisms are generated by reproduction, so too are individual cells Prior to division, the genetic material is duplicated
  • Plant cells Energy of light trapped by light-absorbing pigments present in the membranes of photosynthetic cells  converted into chemical energy stored in energy-rich CHO i.e. sucrose, starch Animal cells Energy arrive prepackaged in the form of the sugar glucose
  • Cells function like miniaturized chemical plants Even the simplest bacterial cell is capable of hundreds of different chemical transformations
  • A cell’s receptor provide pathways through which external agents can evoke specific responses in target cells
  • In addition to acquiring energy, maintaining a complex, ordered state requires constant regulation
  • Distinction betw prokaryotic &amp; eukaryotic cells is based primarily on structural complexity and not on phylogenetic relationship
  • Multicellular organisms are created from a complex organization of cooperating cells. There must be new mechanisms for cell to cell communication and regulation. There also must be unique mechanisms for a single fertilized egg to develop into all the different kinds of tissues of the body. In humans, there are 1014 cells comprising 200 kinds of tissues!
  • Cell Biology

    1. 1. Introduction to the Study of Cell Biology <ul><li>Objectives </li></ul><ul><li>A brief outline of the early history of cell biology. </li></ul><ul><li>Principle of microscopy </li></ul><ul><li>Familiarize with the basic properties of all cells. </li></ul><ul><li>Describe the differences between prokaryotic and eukaryotic cells. </li></ul>
    2. 2. <ul><li>Biology = science of life </li></ul><ul><ul><li>Characteristics, classification and behaviors of organisms, </li></ul></ul><ul><ul><li>how species and individuals come into existence, and </li></ul></ul><ul><ul><li>the interactions they have with each other and with their environment. </li></ul></ul>
    3. 3. <ul><li>Modern biology is divided into 2 categories based on primary level of focus: </li></ul><ul><ul><li>Organismic biology ~ emphasize on biodiversity, evolutionary relationships,adaptations,and ecology of plants & animals. </li></ul></ul><ul><ul><li>Molecular & cellular biology </li></ul></ul><ul><ul><ul><li>MB – concerns with interactions between the various systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and how these interactions are regulated. </li></ul></ul></ul><ul><ul><ul><li>CB –studies the physiological properties of cells, as well as their behaviors, interactions, and environment. </li></ul></ul></ul>
    4. 4. <ul><li>Cellular and molecular biology is reductionist; i.e. </li></ul><ul><li>The knowledge of the parts of the whole can explain the character of the whole </li></ul><ul><li>Create the need to explain the mechanisms of the living system cellular activity </li></ul>
    5. 5. Modern Cell Biology <ul><li>Involve interweaving of 3 historically distinct disciplines </li></ul><ul><ul><li>Cytology (the study of cells) </li></ul></ul><ul><ul><li>Microscopic study of cell structure organization </li></ul></ul><ul><ul><li>Biochemistry </li></ul></ul><ul><ul><li>chemistry of biological structure & function/cellular function </li></ul></ul><ul><ul><li>Genetics </li></ul></ul><ul><ul><li>Information flow </li></ul></ul>
    6. 6. The Cell Biology Time Line
    7. 7. The Discovery of Cells - The cell theory <ul><li>The term cell was first used by the English scientist Robert Hooke (1635-1703), who, in the mid-seventeenth century, used the term to describe the structure of cork. </li></ul><ul><li>The Dutch scientist Anton van Leeuwenhoek (1632-1723) made the first recorded observations of bacterial cells (termed &quot;animalcules&quot;) from pond water & tooth scrapings. </li></ul><ul><li>1830s – importance of cells realised </li></ul><ul><ul><li>1838 - German botanist Matthias Schleiden (1804-1881) observed that despite differences in tissue structure, all plants tissues were made of cells. </li></ul></ul>
    8. 8. <ul><ul><li>1839 - German zoologist Theodor Schwann (1810-1882) realized animals were also composed of fundamental cellular units or cells. </li></ul></ul><ul><ul><li>Schwann proposed first 2 principles of Cell Theory: </li></ul></ul><ul><ul><li>All organisms consist of 1 or more cells </li></ul></ul><ul><ul><li>The cell is the structural unit of life </li></ul></ul><ul><ul><li>Schleiden-Schwann view of cell origin was less insightful – i.e. cells could arise from noncellular materials </li></ul></ul><ul><ul><li>German physician Rudolph Virchow (1821-1902) demonstrated that living cells could arise only from other living cells (biogenesis), and not from inanimate matter (abiogenesis). </li></ul></ul>
    9. 9. <ul><li>Size – pose challenge to understand cellular structure & organization </li></ul><ul><li>Most cells and their organelles cannot be seen by the unaided eye </li></ul><ul><li>Size measured in micrometers (  m, where 1000  m = 1mm ), nanometers (nm, 10 -9 m) </li></ul>Principles of microscopy
    10. 10. <ul><li>Cells are mostly microscopic in size </li></ul><ul><ul><li>Most eukaryotic cells have single nucleus with only 2 copies of most genes </li></ul></ul><ul><ul><li>As a cell  in size, the surface area/vol. </li></ul></ul><ul><ul><li>ratio  </li></ul></ul><ul><ul><ul><li>Ability of a cell to exchange substances with its environment is proportional to its surface. </li></ul></ul></ul><ul><ul><li>Cells depend to a large degree on random movement of molecules (diffusion) </li></ul></ul>
    11. 12. Resolving Power of the Human Eye, the Light Microscope, and the Electron Microscope
    12. 13. <ul><li>Microscope </li></ul><ul><ul><li>Make small objects appear bigger </li></ul></ul><ul><ul><li>Magnification is only better when more details are revealed </li></ul></ul><ul><li>Light microscope </li></ul><ul><ul><li>Has a series of lenses and uses light as its source of illumination </li></ul></ul><ul><ul><ul><li>Condenser lenses </li></ul></ul></ul><ul><ul><ul><li>Objective lens </li></ul></ul></ul><ul><ul><ul><li>Projector lens/eyepiece </li></ul></ul></ul><ul><ul><li>Components and their function (refer handout) </li></ul></ul>
    13. 14. <ul><ul><li>Resolution: resolving power </li></ul></ul><ul><ul><ul><li>Ability to distinguish fine detail and structures </li></ul></ul></ul><ul><ul><ul><li>i.e: to distinguish between 2 points at a specified distance </li></ul></ul></ul><ul><ul><ul><li>Limit of resolution  , resolving power  </li></ul></ul></ul><ul><ul><ul><li>Limit of resolution imposed by the wavelengths of illumination source e.g. visible light (400-700 nm) </li></ul></ul></ul><ul><ul><ul><li>Wavelength shorter, resolution  (resolution =  /2) </li></ul></ul></ul>
    14. 15. <ul><ul><li>Magnification </li></ul></ul><ul><ul><ul><li>Ability of the lens to enlarge or magnify the object </li></ul></ul></ul><ul><ul><ul><li>Total magnification = magnification of the objective lens x magnification of the ocular (eyepiece) lens </li></ul></ul></ul><ul><ul><ul><li>To achieve high magnification with good resolution – immersion oil between slide and objective lens </li></ul></ul></ul><ul><ul><ul><ul><li>Reduce lost of light rays after passed through the specimen </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Same refractive index as glass – same effect as increasing the diameter of objective lens </li></ul></ul></ul></ul>
    15. 16. <ul><ul><li>Visibility / contrast </li></ul></ul><ul><ul><ul><li>Features that allen a object actually to ….,larger determined by contrast </li></ul></ul></ul><ul><ul><ul><li>Difference between adjacent parts of an object or an object and its background </li></ul></ul></ul><ul><ul><ul><li>Staining with dye (mostly is metaline blue) </li></ul></ul></ul><ul><ul><ul><ul><li>Stained object to appear coloured </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Disadvantage: cannot be used with living cells because it will kill the cell and can’t see the cell movement </li></ul></ul></ul></ul>
    16. 17. <ul><li>Different types of light microscopy </li></ul><ul><li>Brightfield </li></ul><ul><li>Phase contrast </li></ul><ul><li>Differential interference contrast </li></ul><ul><li>Fluorescense </li></ul><ul><li>Confocal </li></ul>
    17. 18. Table 1-1 Different Types of Light Microscopy: A Comparison
    18. 19. The paths taken by light rays that form the image of the specimen & those that form the background light of the field
    19. 20. A comparison of cells seen with different types of light microscope: brightfield, phase contrast, diffrential interference contrast (DIC)
    20. 21. The light paths in a fluorescence confocal scanning light microscope
    21. 22. Confocal scanning micrographs of 3 optical sections 0.3 mm thick of a yeast nucleus stained with 2 different fluorescently labeled antibodies
    22. 23. <ul><li>Electron microscopy </li></ul><ul><ul><li>Types of electron microscopy: </li></ul></ul><ul><ul><li>~transmission electron microscopy (TEM) </li></ul></ul><ul><ul><li>~scanning electron microscopy (SEM) </li></ul></ul><ul><ul><li>Has a limit of resolution of about 0.2 – 0.5nm. </li></ul></ul><ul><ul><li>Looks at replicas of dead cells, after fixation and heavy metal ion staining </li></ul></ul><ul><ul><li>Transmission electron microscopes (TEMs) </li></ul></ul><ul><ul><ul><li>Electron are scattered as they pass through a thin section of the specimen, and then detected and projected </li></ul></ul></ul><ul><ul><li>Scanning electron microscopes (SEMs) </li></ul></ul>
    23. 24. A comparison of the lens systems of a light and electron microscope
    24. 25. Streptococcus pyogenes SEM TEM
    25. 26. Scanning Electron Microscopy
    26. 27. Basic properties of cells <ul><li>Life – most basic property of cells </li></ul><ul><li>Smallest unit to exhibit this properties </li></ul><ul><li>Can be removed from organism and cultured in lab </li></ul>
    27. 28. <ul><li>Cells are highly complex and organized </li></ul><ul><li>Each level of structure in cells has a great level of consistency from cell to cell </li></ul><ul><ul><li>Organelles have a particular shape & location in all individuals of species  consistent appearance in the electron microscope </li></ul></ul><ul><li>Organelles have consistent macromolecules composition arranged in a predictable pattern </li></ul><ul><li>Cell structure is similar from organism to organism despite differences in higher anatomical features </li></ul>
    28. 29. <ul><li>The information to build a cell is encoded in its genes </li></ul><ul><li>Genes - blueprints for constructing cellular structures </li></ul><ul><li>Give direction for running cellular activities program for cell reproduction </li></ul><ul><li>Changes in genetic information from generation to generation lead variation </li></ul>
    29. 30. <ul><li>Cells capable of producing more of themselves – mitosis & meiosis </li></ul><ul><li>Cell reproduce by division </li></ul><ul><ul><li>The content of a ‘mother’ cell are distributed into 2 ‘daughter’ cells. </li></ul></ul><ul><li>Before division, genetic material is copied  each daughter cell get complete and equal share of genetic information. (preexisting theory) </li></ul>
    30. 31. <ul><li>Cells acquire & use energy to develop & maintain complexity – photosynthesis, respiration </li></ul><ul><li>Virtually all energy needed by life on Earth comes from sun </li></ul><ul><li>Light energy is turned to chemical energy by photosynthesis; stored in energy-rich CHO i.e. sucrose, starch </li></ul><ul><li>Most animal cells get energy prepackaged, often as glucose </li></ul><ul><li>Once in cell, glucose disassembled; energy is stored as ATP & use to run cell activities </li></ul>
    31. 32. <ul><li>Cells carry out a variety of chemical reactions </li></ul><ul><li>Sum total of the chemical reaction in a cell represents that cell ’ s metabolism </li></ul><ul><li>Chemical changes that take place in cells require enzymes (increase rate of chemical reactions) </li></ul>
    32. 33. <ul><li>Cells engage in numerous mechanical activities </li></ul><ul><li>Based on dynamic, mechanical changed in cell </li></ul><ul><li>Mostly initiated in the shape of ‘ motor ’ proteins (require constant energy to keep working) </li></ul><ul><ul><li>Materials are transported from place to place </li></ul></ul><ul><ul><li>Structures are assembled and then rapidly disassembled </li></ul></ul><ul><ul><li>The entire cell moves itself from one site to another </li></ul></ul>
    33. 34. <ul><li>Cells able to respond to stimuli </li></ul><ul><li>Most cells have receptors that sense environment & initiate responses </li></ul><ul><li>Cells posses receptors to bind </li></ul><ul><ul><li>Hormones </li></ul></ul><ul><ul><li>growth factors </li></ul></ul><ul><ul><li>extracellular materials </li></ul></ul><ul><ul><li>surfaces of others cells </li></ul></ul>
    34. 35. <ul><li>Cells respond to specific stimuli </li></ul><ul><ul><li>Altering metabolic activities </li></ul></ul><ul><ul><li>Preparing for cell division </li></ul></ul><ul><ul><li>Moving from 1 place to another </li></ul></ul><ul><ul><li>Committing suicide </li></ul></ul>
    35. 36. <ul><li>Cells are capable of self-regulation </li></ul><ul><li>Cell processes are a series of ordered steps </li></ul><ul><li>The importance of a cell ’ s regulatory mechanisms becomes most evident when they break down </li></ul><ul><li>Examples </li></ul><ul><ul><li>Failure of a cell to correct error in DNA replication  mutation </li></ul></ul><ul><ul><li>Breakdown in growth control  may lead to cancer cell (unable to control) </li></ul></ul>
    36. 37. Classification of cells <ul><li>Cells are classified by fundamental units of structure and by the way they obtain energy. </li></ul><ul><li>Cells are either </li></ul><ul><ul><li>Prokaryotic~archaebacteria and eubacteria </li></ul></ul><ul><ul><li>Eukaryotic~protists, fungi, plants and animals </li></ul></ul><ul><li>Distinguish by their size and the types of internal structures (organelles) </li></ul>
    37. 38. <ul><li>Cells are also defined according the need for energy. </li></ul><ul><ul><li>Autotrophs are ‘self feeders’ that use light or chemical energy to make food, e.g : plant </li></ul></ul><ul><ul><li>In contrast, heterotrophs (&quot;other feeders&quot;) obtain energy from other autotrophs or heterotrophs </li></ul></ul><ul><ul><li>e.g : many bacteria and animals </li></ul></ul>
    38. 39. <ul><li>Prokaryotic </li></ul><ul><ul><li>prokaryotes are surrounded by a membrane and cell wall. </li></ul></ul><ul><ul><li>cells lack characteristic eukaryotic subcellular membrane enclosed &quot;organelles,&quot; but may contain membrane systems inside a cell wall. </li></ul></ul><ul><ul><li>Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria (&quot;blue bacteria&quot;). </li></ul></ul><ul><ul><li>Some prokaryotic cells have external whip-like flagella for locomotion or hair like pili for adhesion. </li></ul></ul><ul><ul><li>Prokaryotic cells come in multiple shapes: </li></ul></ul><ul><ul><li>cocci (round), baccilli (roots) and spirilla or spirochetes (helical shapes). </li></ul></ul>
    39. 40. baccillus
    40. 41. Structure of animals cell
    41. 42. Plant Cel l
    42. 43. Differences between prokaryotic and eukaryotic cells Prokaryotes Eukaryotes Size Usually 1-2  m 5-100  m Nucleus Absent Presence, bounded by nuclear envelope DNA Usually a single, circular molecule (chromosome) Multiple molecules, linear, associated with protein Cell division Simple fission Mitosis & meiosis Internal membranes Rare Complex (nuclear envelope, Golgi apparatus, endoplasmic reticulum, etc) Ribosome 70S 80S (70S in mitochondria & chloroplasts) Cytoskeleton Absent Microtubules, microfilaments, intermediate filaments Motility Rotary motor (drives bacterial flagelum) Dynein (drives cilia & eukaryote flagellum), kinesin, myosin
    43. 44. Types of prokaryotic cells <ul><li>Divided into 2 major taxonomic groups/domains </li></ul><ul><ul><li>The Archaea/archaebacteria </li></ul></ul><ul><ul><ul><li>Live in extremely inhospitable environment/extremophiles </li></ul></ul></ul><ul><ul><ul><li>Methanogens, convert CO 2 and H 2 into CH 3 methane gas </li></ul></ul></ul><ul><ul><ul><li>Halophiles, extreme salty environment </li></ul></ul></ul><ul><ul><ul><li>Acidophiles, acid loving </li></ul></ul></ul><ul><ul><ul><li>Thermophiles, extreme high temperature </li></ul></ul></ul><ul><ul><li>The bacteria/eubacteria </li></ul></ul><ul><ul><ul><li>Present in every conceivable habitat on Earth </li></ul></ul></ul>
    44. 45. Types of eukaryotic cells <ul><li>Protists (single-cell) – do everything an organism must do to survive in single cell </li></ul><ul><li>Multicellular organisms (fungi, plants, animals) exhibit differentiation – different activities conducted by different types of specialized cells </li></ul>
    45. 46. <ul><li>Differentiation – process by which a relatively unspecialized cell become highly specialized </li></ul><ul><li>Cells specialized for varied functions, have distinctive appearance, carry unique materials </li></ul><ul><ul><ul><li>E.g. skeletal muscle, cartilage cells, red blood cells </li></ul></ul></ul><ul><ul><li>Cells have similar organelles but their no., appearance & location may differ and correlate with cell activities </li></ul></ul>
    46. 48. Viruses <ul><li>Common virus properties – not considered living since need host to reproduce and metabolize, etc </li></ul><ul><li>All are obligatory intracellular parasites </li></ul><ul><li>Outside the living cell, it exists as particle or virion </li></ul><ul><li>Genetic material is surrounded by protein capsule or coat (capsid) </li></ul>
    47. 49. Tobacco mosaic virus Bacteriophage
    48. 50. <ul><li>Have surface proteins that bind to particular host cell surface component </li></ul><ul><li>In the viral life cycle, a virus infects a cell, allowing the viral genetic information to direct the synthesis of new virus particles by the cell . </li></ul>
    49. 51. Conclusion <ul><li>“ Long ago it became evident that the key to every biological problem must be finally sought in the cell; for every living organism is, or at some time, has been a cell ” </li></ul><ul><li>(Wilson, E.B) </li></ul>
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