1. Cell Structure and Function
Chapter 4 2-

2. The Cell Theory All living things are made of cells. A cell
The basic unit of all living things.
4-2
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3. The Historical Context of the Cell Theory
Robert Hooke coined the term “cell.”
Look at cork cells under a simple microscope.
Anton van Leeuwenhoek
Made better microscopes
Used them to look at a variety of substances and identified animalcules
4-3
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4. The Historical Context of the Cell Theory
Mathias Jakob Schleiden
Concluded that all plants were made of cells
Theodor Schwann
Concluded that all animals were made of cells
4-4
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5. Initial Observations of Cells
Cell wall
Outer non-living part of plant cells
Protoplasm
Interior living portion of the cell
Nucleus
Contains the genetic information of the cell
Cytoplasm
Fluid part of the protoplasm
Organelles
“Little organs” within the protoplasm
4-5
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6. Different Kinds of Cells
Prokaryotic
Structurally simple cells
Lack a nucleus
Lack most other organelles
Bacteria
Eukaryotic cells
More complex
Have a nucleus
Have a variety of organelles
Plants, animals, fungi, protozoa and algae
Typically much larger than prokaryotic cells
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7. Prokaryotic Cells Origin: ‘pro’-before; ‘karyote’ - nut
Lack a membrane-bound nucleus.
genetic material is present in the nucleoid
Two types of prokaryotes:
Bacteria
Archaea

8. Prokaryotic Cell Characteristics:
Simplest organisms - simple internal organization
Very small (1 to 10 microns across)
Genetic material in the nucleoid
No membrane-bound organelles
Capsules
Cytoplasm

9. 9

10. Eukaryotic Cells Origin: ‘eu’ - true, good; ‘karyote’ - nut
Possess a membrane-bound nucleus.
genetic material is highly organized within double-layer nuclear envelope
DNA never leaves the nuclear envelope
Types of eukaryotes divided into 4 kingdoms:1. Plantae Fungi Animalia 4. Protista

11. Eukaryotic Cell Characteristics:
More complex organisms
highly organized structure
Typically larger than prokaryote ( microns)
Genetic material in the membrane-bound nucleus
Many membrane-bound organelles
Cytoplasm
Cytoskeleton

12. Prokaryotes vs. Eukaryotes
4-7
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13. Eukaryotic and Prokaryotic Characteristics:
DNA, RNA
Ribosomes
Plasma membrane
Cytoplasm
Cell walls (plantae, fungi, protista, not present in animal cells)
Flagella

14. Eukaryotic Cells 14

15. Prokaryotic Cells 15

16. Cell Size Prokaryotic cells Eukaryotic cells
1-2 micrometers in diameter
Eukaryotic cells
micrometers in diameter
4-8
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17. Fig. 4.2

18. Cell Size is Limited Surface Area-to-Volume Ratio
Cells must get all of their nutrients from their environment through their cell membranes.
Volume increases more quickly than surface area.
Surface area-to-volume ratio must remain small.
4-9
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19. Surface Area-to-Volume Ratio19

20. The Structure of Cell Membranes
Thin sheets composed of phospholipids and proteins
Fluid-mosaic model
Two layers of phospholipids
Fluid
Has an oily consistency
Things can move laterally within the bilayer.
Mosaic
Proteins embedded within the phospholipid bilayer
4-10
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21. Phospholipids Phospholipid Structure (Chapter 3)
glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid
2 fatty acids attached to the glycerol
phosphate group attached to the glycerol

22. Nonpolar Hydrocarbon Tail
Phospholipids
Chapter 3: Phospholipids are Amphiphilic molecules
Polar Head Group
Nonpolar Hydrocarbon Tail
101

23. Phospholipids
The fatty acids are nonpolar chains of carbon and hydrogen.
Their nonpolar nature makes them hydrophobic (“water-fearing”).
The phosphate group is polar and hydrophilic (“water-loving”).

24. The Phospholipid Bilayer
Phospholipid structure
Hydrophobic tails
Hydrophilic heads
Bilayer
Hydrophobic tails of each layer associate with each other.
Hydrophilic heads on the surface of the bilayer
Cholesterol
Hydrophobic
Found within the hydrophobic tails
Keeps the membrane flexible
4-11
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25. Phospholipids
The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer:
fatty acids are on the inside
phosphate groups are on both surfaces of the bilayer

26. 26

27. Page 63

30. 30

31. Membrane Proteins Some are on the surface Some are partially embedded.
Protrude from one side
Some are completely embedded.
Protrude from both sides
Functions
Transport molecules across the membrane
Attachment points for other cells
Identity tags for cells
4-12
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32. Organelles Composed of Membranes
Plasma membrane (cell membrane)
Different cellular membranous structures serve different functions
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
Vacuoles and vesicles
Nuclear membrane
4-13
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33. The Plasma Membrane Composed of phospholipid bilayer
Separates the contents of the cell from the external environment
Important features
Metabolic activities
Moving molecules across the membrane
Structurally different inside and outside
Identification: Self vs. nonself
Attachment sites
Signal transduction
4-14
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34. The Endoplasmic Reticulum (ER)
Consists of folded membranes and tubes throughout the cell
Provides a large surface area for important chemical reactions
Because it is folded, it fits into a small space.
Two types of ER
Rough
Smooth
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35. The Endoplasmic Reticulum35

36. The Endoplasmic Reticulum
Rough Endoplasmic Reticulum (RER)
System of cytoplasmic membranes that create a network of channels throughout the cytoplasm
Ribosomes are attached to the outside of the RER membrane giving it a rough appearance under the microscope
Synthesis of proteins to be secreted out of the cell, or packaged and sent to lysosomes or plasma membrane
Proteins are synthesized into the RER channels (cisternal space)

37. The Endoplasmic Reticulum
Smooth Endoplasmic Reticulum (SER)
Relatively few associated ribosomes
Functions:
Synthesis of membrane lipids
Detoxification of foreign substances

38. CO 5

39. The Golgi Apparatus Stacks of flattened membrane sacs Functions
Modifies molecules that were made in other places
Manufactures some polysaccharides and lipids
Packages and ships molecules
4-16
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40. Fig. 4.12

41. Traffic Through the Golgi
Vesicles bring molecules from the ER that contain proteins.
Vesicles fuse with the Golgi apparatus.
The Golgi finishes the molecules and ships them out in other vesicles.
Some are transported to other membrane structures.
Some are transported to the plasma membrane.
Some vesicles become lysosomes.
4-17
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42. 42

43. Lysosomes Vesicles containing enzymes that digest macromolecules
Carbohydrates
Proteins
Lipids
Nucleic acids
Interior contains low pH
These enzymes only work at pH=5.
The cytoplasm is pH=7.
If the lysosome breaks open, these enzymes will inactivate and will not damage the cell.
4-18
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44. Functions of Lysosomes
Digestion
Of food taken into the cell
Destruction
Disease-causing organisms
Old organelles
4-19
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45. Peroxisomes Not formed from golgi membrane, but from ER membrane
Contain the enzyme catalase
Breaks down hydrogen peroxide
Breaks down long-chain fatty acids
Synthesizes cholesterol and bile salts
Synthesizes some lipids
4-20
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46. Fig. 4.15

47. Vacuoles and Vesicles Membrane-enclosed sacs Vacuoles Vesicles
Larger sacs
Contractile vacuoles found in many protozoa
Forcefully expel excess water from the cytoplasm
Vesicles
Smaller vesicles
4-21
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48. Vacuoles and Vesicles 4-22
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49. Fig. 4.16

50. The Nuclear Membrane
Separates the genetic material from the rest of the cell
Filled with nucleoplasm
Composed of two bilayers
Contains holes called nuclear pore complexes
Allow large molecules like RNA to pass through the membrane into the cytoplasm
4-23
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51. The Endomembrane System ̶ Interconversion of Membranes
Membranes are converted from one membranous organelle to another.
4-24
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52. Mitochondria Energy Converting Organelles Mitochondrion
A small bag with a large bag stuffed inside
Larger internal bag is folded into cristae
Cristae contain proteins for cellular respiration.
Releases the energy from food
Requires oxygen
Uses the energy to make ATP
4-25
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53. Mitochondria 53

54. Chloroplasts Energy Converting Organelles Chloroplasts 4-26
Sac-like organelle
Contain chlorophyll
Perform photosynthesis
Uses the energy in light to make sugar
Contain folded membranes called thylakoids
Thylakoids stacked into grana
Thylakoids contain chlorophyll and other photosynthetic proteins.
Thylakoids surrounded by stroma
4-26
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55. Chloroplasts 55

56. Nonmembranous Organelles
Ribosomes
Cytoskeleton
Centrioles
Cilia flagella
Inclusions
4-27
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57. Ribosomes Made of RNA and proteins Composed of two subunits
Large
Small
Are the sites of protein production
Found in two places
Free floating in the cytoplasm
Attached to endoplasmic reticulum
4-28
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58. Fig. 4.10
Ribosomes

59. Cytoskeleton Network of protein fibers found in all eukaryotic cells
Made up of
Microtubules
Microfilaments (actin filaments)
Intermediate filaments
4-29
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60. Cytoskeleton Functions: Supports the shape of the cell
Keeps organelles in fixed locations
Helps move materials within the cell

61. Cytoskeleton 61

62. Centrioles
Two sets of microtubules arranged at right angles to each other
Located in a region called the centrosome
Microtubule-organizing center near nucleus
Organize microtubules into spindles used in cell division
4-30
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63. Fig. 4.21

64. Cilia and Flagella Hair-like projections extending from the cell
Composed of microtubules covered by plasma membrane
Flagella
Long and few in number
Move with an undulating whip-like motion
Cilia
Small and numerous
Move back and forth like oars on a boat
9 + 2 arrangement of microtubules
Cell can control their activity
4-31
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65. Cilia and Flagella
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66. 66

67. Fig. 4.24b

68. Inclusions Collections of miscellaneous materials
Can be called granules
Temporary sites for the storage of nutrients and waste
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69. Glycogen Inclusions
Stryer's Biochemistry Fig. 23-2 82

70. Nuclear Components Contains chromatin
DNA + proteins
Becomes condensed during cell division into chromosomes
Surrounded by double layer of membrane
Nuclear membrane contains pores to control transport of materials in and out of nucleus
Contains one or more nucleoli
Site of ribosome synthesis
Contains nucleoplasm
Water, nucleic acids, etc.
4-34
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71. Nuclear Components 71

72. Getting Through Membranes
Membrane Transport
Motion of substances in and out of the cell
Cell membranes are Selectively Permeable
Two Types of Transport Mechanisms:
Passive Transport
Active Transport

73. Membrane Transport
Passive transport is movement of molecules through the membrane in which no energy is required from the cell
Active transport requires energy expenditure by the cell

74. 1. Passive Transport
Passive transport is movement of molecules through the membrane in which no energy is required from the cell
Molecules move in response to a concentration gradient
A concentration gradient is a difference between the concentration on one side of the membrane and that on the other side
Passive transport mechanisms only movement substances along the concentration gradient
From a higher concentration to a lower concentration

75. Types of Passive Transport:
Diffusion
movement of solute molecules from high solute concentration to low solute concentration
Osmosis
movement of solvent water from high solvent concentration to low solvent concentration

76. 1. Diffusion Molecules are in constant, random motion.
Molecules move from where they are most concentrated to where they are less concentrated.
Involves a concentration gradient (diffusion gradient)
No concentration gradient=dynamic equilibrium
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77. The Rate of Diffusion Depends on The size of the molecule
Smaller molecules diffuse faster.
The size of the concentration gradient
The greater the concentration difference, the faster the diffusion.
4-37
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78. Diffusion in Cells
Diffusion can only happen if there is no barrier to the movement of molecules.
Can only happen across a membrane if the membrane is permeable to the molecule
Membranes are semi-permeable; they only allow certain molecules through.
Membrane permeability depends on the molecules size, charge, and solubility.
4-38
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79. Diffusion There are two types of diffusion Simple (Direct) Diffusion
Facilitated Diffusion

80. Simple Diffusion Substances pass directly through the cell membrane
The cell membrane has limited permeability to small polar molecules, water, and ions
Determined solely by the concentration gradient

81. Simple Diffusion Example: Oxygen diffusion 4-39
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82. Simple Diffusion
The rate (molecules/sec.) of simple diffusion depends on the degree of concentration gradient
As the gradient reaches equilibrium, diffusion slows
At equilibrium, substances pass in and out of the membrane at equal rates

83. Rate of Simple Diffusion vs Concentration83

84. Facilitated Diffusion
Substances must pass through transport proteins to get through the cell membrane
Facilitated diffusion is movement of a molecule from high to low concentration with the help of a carrier protein.
Facilitated Diffusion:
is specific
is passive
saturates when all carriers are occupied

85. Facilitated Diffusion
Some molecules have to be carried across the membrane.
Accomplished by carrier proteins
Still involves diffusion
Follows a concentration gradient
Is passive transport
4-44
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86. Facilitated Diffusion
Is Specific - a carrier protein transports only certain molecules or ions
Is Passive - the direction of net movement is determined by the relative concentrations on the substances inside an outside the cell
Has a Saturation Point - rate of facilitated diffusion (molecules/sec.) increases with gradient until all protein carriers are in use - saturation point

87. Saturation of Facilitated Diffusion
Rate
Concentration 87

88. 2. Osmosis
Osmosis is the movement of water from an area of high to low concentration of water
Movement of water toward an area of high solute concentration
In osmosis, only water is able to pass through the membrane

89. Osmosis
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90. Osmosis vs. Diffusion
The difference between osmosis and diffusion is the semipermeable membrane between the two solutions
If the membrane is permeable to the solute, then diffusion occurs
If the membrane is impermeable to the solute, but permeable to water (solvent) only, then osmosis occurs

91. Osmosis
Osmotic concentration is determined by the the concentration of all solutes in solution
All solutes displace water
Relative Osmotic Concentrations
Hypertonic solutions: have a higher relative solute concentration
Hypotonic solutions: have a lower relative solute concentration
Isotonic Solutions: have equal relative solute concentrations

92. Osmotic Influences on Cells
If a cell has less water (thus more solute) than its environment
It is hypertonic to its surroundings.
If a cell has more water (thus less solute) than its environment
It is hypotonic to its surroundings.
If a cell has equal amounts of water (and solute) as its environment
It is isotonic to its surroundings.
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93. Osmotic Influences on Cells
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94. 2. Active transport
Able to moves substances against the concentration gradient - from low to high concentration
Requires energy – ATP is used directly or indirectly to fuel active transport
allows cells to store concentrated substances
Requires the use of carrier proteins

95. Active Transport 4-45 http://www.youtube.com/watch?v=STzOiRqzzL4&NR=1
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96. Endocytosis Moves large molecules or sets of molecules into the cell
Phagocytosis
Cell eating
Food engulfed by the membrane
Material enters the cell in a vacuole.
Pinocytosis
Cell drinking
Just brings fluid into the cell
Receptor-mediated endocytosis
Molecules entering the cell bind to receptor proteins first.
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97. 97

98. 98

99. 99

100. Exocytosis Moves large molecules or sets of molecules out of the cell
Vesicles containing the molecules to be secreted fuse with the plasma membrane.
Contents are dumped outside the cell.
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101. 101

102. Endocytosis and Exocytosis
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