Cell Structure and Function

1
Cell Structure and Function

• Chapter 4

2
Early Discoveries

• Mid 1600s - Robert Hooke observed and described
  cells in cork
• Late 1600s - Antony van Leeuwenhoek observed
  sperm, microorganisms
• 1820s - Robert Brown observed and named nucleus
  in plant cells

3
Developing Cell Theory

• Matthias Schleiden Plant cells
• Theodor Schwann- animal cells
• Rudolf Virchow summarized experiments by Redi
  Cells come from pre-existing cells

4
Formulation of the Cell Theory

• In 1838, Theodor Schwann and Matthias Schleiden
  were enjoying after-dinner coffee and talking
  about their studies on cells. It has been
  suggested that when Schwann heard Schleiden
  describe plant cells with nuclei, he was struck
  by the similarity of these plant cells to cells
  he had observed in animal tissues.

5
Hookes Cork (cells)
Fig. 4-2, p. 51
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Cell Theory

• 1) Every organism is composed of one or more
  cells
• 2) Cell is smallest unit having properties of
  life
• 3) Continuity of life arises from growth and
  division of single cells

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Cell

• Smallest unit of life
• Can survive on its own or has potential to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce

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Cells come from Pre-existing Cells
9
Structure of Cells

• All start out life with
• Plasma membrane
• Region where DNA is stored
• Cytoplasm

• Two types
• Prokaryotic
• Eukaryotic

10
Pasteurs Experiment to test Spontaneous
Generation
11
Fig. 4-1b, p. 50
12
Fig. 4-1c, p. 50
13
Lipid Bilayer

• Main component of cell membranes
• Gives the membrane its fluid properties
• Two layers of phospholipids

14
Fig. 4-4, p. 53
15
fluid
lipid bilayer
fluid
Fig. 4-4, p. 53
16
Fig. 4-10, p. 57
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Fluid Mosaic Model

• Membrane is a mosaic of
• Phospholipids
• Glycolipids
• Sterols
• Proteins
• Most phospholipids and some proteins can drift
  through membrane

18
Fig. 4-10, p. 57
19
Membrane Proteins

• Transport proteins
• Receptor proteins
• Recognition proteins
• Adhesion proteins

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Fig. 4-4, p. 53
21
Why Are Cells So Small?

• Surface-to-volume ratio
• The bigger a cell is, the less surface area there
  is per unit volume
• Above a certain size, material cannot be moved in
  or out of cell fast enough

22
Fig. 4-5, p. 53
23
Fig. 4-6, p. 54
24
Microscopes

• Create detailed images of something that is
  otherwise too small to see
• Light microscopes
• Simple or compound
• Advances in biochemistry, molecular biology have
  made imaging more useful
• Electron microscopes
• Transmission EM or Scanning EM

25
Limitations of Light Microscopy

• Wavelengths of light are 400-750 nm (visible
  light)
• If a structure is less than one-half of a
  wavelength long, it will not be visible
• Light microscopes can resolve objects down to
  about 200 nm in size

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Advantages of light microscope

• Video microscopy for live action viewings
• Fluorescence and other techniques to make
  subcellular organelles, proteins, lipids, etc.
  visible
• Microscopy U
• http//www.microscopyu.com/

27
Electron Microscopy

• Uses streams of accelerated electrons rather than
  light
• Electrons are focused by magnets rather than
  glass lenses
• Can resolve structures down to 0.5 nm

28
Prokaryotic Cells

• Archaebacteria and Eubacteria
• DNA is NOT enclosed in nucleus
• Generally the smallest, simplest cells
• No organelles

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Prokaryotic Structure
pilus
cytoplasm with ribosomes
DNA
flagellum
capsule
cell wall
plasma membrane
30
Fig. 4-11, p. 58
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Fig. 4-11, p. 58
32
Fig. 4-11, p. 58
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Eukaryotic Cells

• Have a nucleus and other organelles
• Eukaryotic organisms
• Plants
• Animals
• Protistans
• Fungi

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Fig. 4-19, p. 64
35
Table 4-2, p. 60
36
Table 4-3, p. 60
37
Fig. 4-14, p. 60
38
Fig. 4-15, p. 61
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Functions of Nucleus

• Keeps the DNA molecules of eukaryotic cells
  separated from metabolic machinery of cytoplasm
• Makes it easier to organize DNA and to copy it
  before parent cells divide into daughter cells

40
Components of Nucleus
Nuclear envelope Nucleoplasm Nucleolus Chromosome
Chromatin
41
Nuclear Envelope

• Two outer membranes (lipid bilayers)
• Innermost surface has DNA attachment sites
• Pores span bilayer

42
Nucleolus

• Dense mass of material in nucleus
• May be one or more
• Cluster of DNA and proteins
• Materials from which ribosomal subunits are built
• Subunits must pass through nuclear pores to reach
  cytoplasm

43
Chromatin

• Cells collection of DNA and associated proteins
• Chromosome is one DNA molecule and its
  associated proteins
• Appearance changes as cell divides

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Fig. 4-15, p. 61
45
Fig. 4-16, p. 62
46
Fig. 4-16, p. 62
47
Cytomembrane System

• Group of related organelles in which lipids are
  assembled and new polypeptide chains are modified
• Products are sorted and shipped to various
  destinations

48
Components of Cytomembrane System

• Endoplasmic reticulum
• Golgi bodies
• Vesicles

49
Endoplasmic Reticulum

• In animal cells, continuous with nuclear membrane
• Extends throughout cytoplasm
• Two regions - rough and smooth

50
Rough ER

• Arranged into flattened sacs
• Ribosomes on surface give it a rough appearance
• Some polypeptide chains enter rough ER and are
  modified
• Cells that specialize in secreting proteins have
  lots of rough ER

51
Smooth ER

• A series of interconnected tubules
• No ribosomes on surface
• Lipids assembled inside tubules
• Smooth ER of liver inactivates wastes, drugs
• Sarcoplasmic reticulum of muscle is a specialized
  form

52
Golgi Bodies

• Put finishing touches on proteins and lipids that
  arrive from ER
• Package finished material for shipment to final
  destinations
• Material arrives and leaves in vesicles

53
Vesicles

• Membranous sacs that move through the cytoplasm
• Lysosomes
• Peroxisomes

54
Mitochondria

• ATP-producing powerhouses
• Double-membrane system
• Carry out the most efficient energy-releasing
  reactions
• These reactions require oxygen

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Fig. 4-17, p. 63
56
Mitochondrial Structure

• Outer membrane faces cytoplasm
• Inner membrane folds back on itself
• Membranes form two distinct compartments
• ATP-making machinery is embedded in the inner
  mitochondrial membrane

57
Mitochondrial Origins

• Mitochondria resemble bacteria
• Have own DNA, ribosomes
• Divide on their own
• May have evolved from ancient bacteria that were
  engulfed but not digested

58
Cytoskeleton

• Present in all eukaryotic cells
• Basis for cell shape and internal organization
• Allows organelle movement within cells and, in
  some cases, cell motility

59
Cytoskeletal Elements
intermediate filament
microtubule
microfilament
60
Fig. 4-24, p. 68
61
Accessory Proteins

• Attach to tubulin and actin
• Motor proteins
• Crosslinking proteins

62
Microtubules

• Largest elements
• Composed of the protein tubulin
• Arise from microtubule organizing centers (MTOCs)
• Polar and dynamic
• Involved in shape, motility, cell division

63
Microfilaments

• Thinnest cytoskeletal elements
• Composed of the protein actin
• Polar and dynamic
• Take part in movement, formation and maintenance
  of cell shape

64
Intermediate Filaments

• Present only in animal cells of certain tissues
• Most stable cytoskeletal elements
• Six known groups
• Desmins, vimentins, lamins, etc.
• Different cell types usually have 1-2 different
  kinds

65
Fig. 4-24, p. 68
66
tubulin subunit
25 nm
Fig. 4-24, p. 68
67
Fig. 4-24, p. 68
68
Mechanisms of Movement

• Length of microtubules or microfilaments can
  change
• Parallel rows of microtubules or microfilaments
  actively slide in a specific direction
• Microtubules or microfilaments can shunt
  organelles to different parts of cell

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Fig. 4-25, p. 68
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Fig. 4-26, p. 69
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Fig. 4-13, p. 59
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actin subunit
57 nm
Fig. 4-24, p. 68
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Fig. 4-24, p. 68
74
Matrixes Between Animal Cells

• Animal cells have no cell walls
• Some are surrounded by a matrix of cell
  secretions and other material

75
Cell-to-Cell Junctions

• Plants
• Plasmodesmata
• Animals
• Tight junctions
• Adhering junctions
• Gap junctions

plasmodesma
76
Animal Cell Junctions
tight junctions
gap junction
adhering junction
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Fig. 4-19, p. 64
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Fig. 4-14, p. 60
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Flagella and Cilia
microtubule

• Structures for cell motility
• 9 2 internal structure

dynein
80
Fig. 4-27, p. 69
81
Fig. 4-27, p. 69
82
Plant Cell Features

• Cell wall
• Central vacuole
• Chloroplast

• Plasma membrane
• Nucleus
• Ribosomes
• Endoplasmic reticulum
• Golgi body
• Vesicles
• Mitochondria
• Cytoskeleton

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Fig. 4-18, p. 63
84
Fig. 4-20, p. 66
85
Fig. 4-21, p. 67
86
Fig. 4-23, p. 67
87
Specialized Plant Organelles

• Plastids
• Central Vacuole

88
Chloroplasts

• Convert sunlight energy to ATP through
  photosynthesis

89
Photosynthesis

• First stage
• Occurs at thylakoid membrane
• Light energy is trapped by pigments and stored as
  ATP
• Second stage
• Inside stroma, ATP energy is used to make sugars,
  then other carbohydrates

90
Central Vacuole

• Fluid-filled organelle
• Stores amino acids, sugars, wastes
• As cell grows, expansion of vacuole as a result
  of fluid pressure forces cell wall to expand
• In mature cell, central vacuole takes up 50-90
  percent of cell interior

91
Cell Wall
Plasma membrane

• Structural component that wraps around the plasma
  membrane
• Occurs in plants, some fungi, some protistans

Primary cell wall of a young plant
92
Fig. 4-20, p. 66
93
Plant Cell Walls
Secondary cell wall (3 layers)
Primary cell wall
94
Plant Cuticle

• Cell secretions and waxes accumulate at plant
  cell surface
• Semi-transparent
• Restricts water loss