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Chapter 04
Lecture Outline
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Cell StructureChapter 4
2
3
Cells
• Cells were discovered in 1665 by Robert Hooke
• Early studies of cells were conducted by– Mathias Schleiden (1838)– Theodor Schwann (1839)
• Schleiden and Schwann proposed the Cell Theory
4
Cell Theory
1. All organisms are composed of cells2. Cells are the smallest living things3. Cells arise only from pre-existing cells• All cells today represent a continuous line
of descent from the first living cells
5
Cell size is limited
• Most cells are relatively small due reliance on diffusion of substances in and out of cells
• Rate of diffusion affected by– Surface area available– Temperature– Concentration gradient– Distance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
4–3 πr3)
3
Cell radius (r)
Surface Area / Volume
Surace area (4πr2)
Volume ( 4.189 unit3
12.57 unit2
1 unit 10 unit
1257 unit2
4189 unit3
0.3
Surface area-to-volume ratio
• Organism made of many small cells has an advantage over an organism composed of fewer, larger cells
• As a cell’s size increases, its volume increases much more rapidly than its surface area
• Some cells overcome limitation by being long and skinny – like neurons
7
8
Microscopes
• Not many cells are visible to the naked eye– Most are less than 50 μm in diameter
• Resolution – minimum distance two points can be apart and still be distinguished as two separate points– Objects must be 100 μm apart for naked eye
to resolve them as two objects rather than one
2 types
• Light microscopes– Use magnifying lenses with visible light– Resolve structures that are 200 nm apart– Limit to resolution using light
• Electron microscopes– Use beam of electrons– Resolve structures that are 0.2 nm apart
9
• Electron microscopes– Transmission electron
microscopes transmit electrons through the material
– Scanning electron microscopes beam electrons onto the specimen surface
10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hum
an E
ye
Ligh
t Mic
rosc
ope
Elec
tron
Mic
rosc
ope
Hydrogen atom
Amino acid
Logarithmic scale
Protein
Ribosome
Large virus (HIV)
Human red blood cell
Prokaryote
Human egg
Paramecium
Chicken egg
Adult human
Frog egg
ChloroplastMitochondrion
1 m
10 cm
1 cm
1 mm
1 nm
0.1 nm (1 Å)
10 nm
100 nm
1 m
10 m
100 m
10 m
100 m
11
Basic structural similarities
1. Nucleoid or nucleus where DNA is located2. Cytoplasm
– Semifluid matrix of organelles and cytosol
3. Ribosomes– Synthesize proteins
4. Plasma membrane– Phospholipid bilayer
12
Prokaryotic Cells
• Simplest organisms• Lack a membrane-bound nucleus
– DNA is present in the nucleoid• Cell wall outside of plasma membrane• Do contain ribosomes (not membrane-
bound organelles)• Two domains of prokaryotes
– Archaea– Bacteria
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cytoplasm
Ribosomes
Nucleoid (DNA)
Plasma membrane
CapsuleCell wall
Pili
Flagellum
Pilus
0.3 µm
© Phototake
Bacterial cell walls
• Most bacterial cells are encased by a strong cell wall– composed of peptidoglycan– Cell walls of plants, fungi, and most protists different
• Protect the cell, maintain its shape, and prevent excessive uptake or loss of water
• Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls
• Archaea lack peptidoglycan
14
15
Flagella
• Present in some prokaryotic cells– May be one or more or none
• Used for locomotion• Rotary motion propels the cell
16
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Outer protein ring
Hook
Filament
Inner protein ringH+ H+
Peptidoglycanportion ofcell wall
Outermembrane
Plasmamembrane
a. b. c.
0.5 µm
a: © Eye of Science/Photo Researchers, Inc.
17
Eukaryotic Cells
• Possess a membrane-bound nucleus• More complex than prokaryotic cells• Hallmark is compartmentalization
– Achieved through use of membrane-bound organelles and endomembrane system
• Possess a cytoskeleton for support and to maintain cellular structure
18
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Nucleus
Nucleolus
Nuclear pore
Intermediate filament
Ribosomes
Ribosomes
Cytoplasm
Cytoskeleton
Microtubule
Centriole
Plasma membrane
Mitochondrion
Golgi apparatus
Exocytosis
Peroxisome
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Microvilli
Nuclear envelope
Actin filament(microfilament)
Intermediatefilament
Lysosome
Vesicle
19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
Nucleolus
Nuclear pore
Intermediate filament
Ribosome
Cytoplasm
Cytoskeleton
Microtubule
Plasma membrane
Mitochondrion
Peroxisome
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Nuclear envelope
Central vacuole
Plasmodesmata
Adjacent cell wall
Cell wall
Chloroplast
Golgiapparatus
Vesicle
Actin filament(microfilament)
Intermediatefilament
20
Nucleus
• Repository of the genetic information• Most eukaryotic cells possess a single nucleus• Nucleolus – region where ribosomal RNA
synthesis takes place• Nuclear envelope
– 2 phospholipid bilayers– Nuclear pores – control passage in and out
• In eukaryotes, the DNA is divided into multiple linear chromosomes– Chromatin is chromosomes plus protein
21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nuclearbasket
Nuclear pores
Nuclearenvelope
Nucleolus
Chromatin
Nucleoplasm
Nuclearlamina
Innermembrane
Outermembrane
Cytoplasmicfilaments
Nuclear porea.
Ribosomes
• Cell’s protein synthesis machinery• Found in all cell types in all 3 domains• Ribosomal RNA (rRNA)-protein complex• Protein synthesis also requires messenger
RNA (mRNA) and transfer RNA (tRNA)• Ribosomes may be free in cytoplasm or
associated with internal membranes
22
23
Endomembrane System
• Series of membranes throughout the cytoplasm
• Divides cell into compartments where different cellular functions occur
• One of the fundamental distinctions between eukaryotes and prokaryotes
24
Endoplasmic reticulum
• Rough endoplasmic reticulum (RER)– Attachment of ribosomes to the membrane gives a
rough appearance– Synthesis of proteins to be secreted, sent to
lysosomes or plasma membrane• Smooth endoplasmic reticulum (SER)
– Relatively few bound ribosomes– Variety of functions – synthesis, store Ca2+,
detoxification• Ratio of RER to SER depends on cell’s function
25
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ribosomes
Smoothendoplasmic
reticulum
Smoothendoplasmicreticulum
0.08 µm(inset): © Dr. Donald Fawcett & R. Bolender/Visuals Unlimited
Roughendoplasmicreticulum
Roughendoplasmicreticulum
26
Golgi apparatus
• Flattened stacks of interconnected membranes (Golgi bodies)
• Functions in packaging and distribution of molecules synthesized at one location and used at another within the cell or even outside of it
• Has cis and trans faces• Vesicles transport molecules to destination
27
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 µm
Secretoryvesicle
Formingvesicle
trans face
cis face
Fusingvesicle
Transport vesicle
(inset): © Dennis Kunkel/Phototake
28
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1.
2.
3.
Golgi membrane protein
Cisternae
Secretory vesicle
Cell membrane
Extracellular fluid
Roughendoplasmicreticulum
Membraneprotein
Newlysynthesizedprotein
Vesicle containingproteins buds fromthe rough endo-plasmic reticulum,diffuses through thecell, and fuses tothe cis face of theGolgi apparatus. Smooth
endoplasmicreticulumcis face
GolgiApparatus
trans faceThe proteins aremodified andpackaged intovesicles fortransport. Secreted
protein
The vesicle maytravel to the plasmamembrane,releasing itscontents to theextracellularenvironment.
Transportvesicle
Nucleus
Nuclear poreRibosome
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
29
Lysosomes
• Membrane-bounded digestive vesicles• Arise from Golgi apparatus• Enzymes catalyze breakdown of
macromolecules• Destroy cells or foreign matter that the cell
has engulfed by phagocytosis
30
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lysosome aiding in thebreakdown of an old organelle
Lysosome aiding in the digestion of phagocytized particles
Golgi membrane protein
Cisternae
Roughendoplasmicreticulum
Smoothendoplasmic
reticulum
cis face
GolgiApparatustrans face
Nucleus
Ribosome
Membrane protein
Hydrolytic enzyme
Transport vesicle
Breakdownof organelle
Lysosome
Lysosome DigestionOld or damaged
organelle
Food vesicle
Phagocytosis
Nuclear pore
Microbodies
• Variety of enzyme-bearing, membrane-enclosed vesicles
• Peroxisomes– Contain enzymes
involved in the oxidation of fatty acids
– Hydrogen peroxide produced as by-product – rendered harmless by catalase
31
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
0.2 µm(inset): From S.E. Frederick and E.H. Newcomb, “Microbody-like organelles in leaf cells,” Science,
163:1353-5. © 21 March 1969. Reprinted with permission from AAAS
32
Vacuoles
• Membrane-bounded structures in plants• Various functions depending on the cell
type
• There are different types of vacuoles:– Central vacuole in plant cells– Contractile vacuole of some fungi and protists– Storage vacuoles
33
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(inset): © Henry Aldrich/Visuals Unlimited
Nucleus
ChloroplastTonoplast
Centralvacuole
1.5 µm
Cellwall
34
Mitochondria
• Found in all types of eukaryotic cells• Bound by membranes
– Outer membrane– Intermembrane space– Inner membrane has cristae– Matrix
• On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism
• Have their own DNA
35
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
IntermembranespaceInner membrane
Outer membrane
RibosomeMatrix
DNACrista
0.2 µm(inset): © Dr. Donald Fawcett & Dr. Porter/Visuals Unlimited
36
Chloroplasts
• Organelles present in cells of plants and some other eukaryotes
• Contain chlorophyll for photosynthesis• Surrounded by 2 membranes• Thylakoids are membranous sacs within
the inner membrane– Grana are stacks of thylakoids
• Have their own DNA
37
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ribosome DNA
Stroma
Stroma
ThylakoidmembraneOutermembraneInnermembrane
Thylakoid diskGranum
Granum
1.5 µm(inset): © Dr. Jeremy Burgess/Photo Researchers, Inc.
38
Endosymbiosis
• Proposes that some of today’s eukaryotic organelles evolved by a symbiosis arising between two cells that were each free-living
• One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes
• Mitochondria and chloroplasts
39
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chloroplast
Chloroplast
Modern Eukaryote
Unknown Bacterium
Unknown ArchaeonMitochondrion
Protobacterium
Modern EukaryoteCyanobacterium
Cyanobacterium
Unknown Archaeon
ProtobacteriumMitochondrion
Nucleus
Nucleus
40
Cytoskeleton
• Network of protein fibers found in all eukaryotic cells– Supports the shape of the cell – Keeps organelles in fixed locations
• Dynamic system – constantly forming and disassembling
41
3 types of fibers
• Microfilaments (actin filaments)– Two protein chains loosely twined together– Movements like contraction, crawling, “pinching”
• Microtubules– Largest of the cytoskeletal elements– Dimers of α- and β-tubulin subunits– Facilitate movement of cell and materials within cell
• Intermediate filaments– Between the size of actin filaments and microtubules– Very stable – usually not broken down
42
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microtubule
Intermediate filament
Actin filament
Cell membrane
a. Actin filaments
b. Microtubules
c. Intermediate filament
Centrosomes
• Region surrounding centrioles in almost all animal cells
• Microtubule-organizing center– Can nucleate the assembly of microtubules
• Animal cells and most protists have centrioles – pair of organelles
• Plants and fungi usually lack centrioles
43
Centrioles
44
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Microtubule triplet
45
Cell Movement
• Essentially all cell motion is tied to the movement of actin filaments, microtubules, or both
• Some cells crawl using actin microfilaments
• Flagella and cilia have 9 + 2 arrangement of microtubules– Not like prokaryotic flagella– Cilia are shorter and more numerous
46
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Flagellum
Basal body
Microtubuletriplet
Centralmicrotubule pair
Plasmamembrane
Radial spokeDynein arm
Doublet microtubule
0.1 µm
0.1 µm(top & bottom insets): © William Dentler, University of Kansas
• Eukaryotic cell walls– Plants, fungi, and
many protists– Different from
prokaryote– Plants and protists
– cellulose– Fungi – chitin– Plants – primary
and secondary cell walls
47
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plant cell
Plasmodesmata Primary wallSecondary wall
Cell 1
Cell 2
Primary wall
Secondary wall
Plasma membrane
Middle lamella
Middlelamella
Plasmamembrane
© Biophoto Associates/Photo Researchers, Inc.0.4 µm
48
Extracellular matrix (ECM)
• Animal cells lack cell walls• Secrete an elaborate mixture of
glycoproteins into the space around them• Collagen may be abundant• Form a protective layer over the cell
surface• Integrins link ECM to cell’s cytoskeleton
– Influence cell behavior
49
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Cytoplasm
Actin filament
Integrin
Fibronectin
Collagen Elastin
Proteoglycan
50
Cell-to-cell interactions
• Surface proteins give cells identity– Cells make contact, “read” each other, and
react– Glycolipids – most tissue-specific cell surface
markers– MHC proteins – recognition of “self” and
“nonself” cells by the immune system
51
Cell connections
• 3 categories based on function1.Tight junction
– Connect the plasma membranes of adjacent cells in a sheet – no leakage
2.Anchoring junction– Mechanically attaches cytoskeletons of neighboring
cells (desmosomes)
3.Communicating junction– Chemical or electrical signal passes directly from one
cell to an adjacent one (gap junction, plasmodesmata)
52
53
a.
Tight junction
Adjacent plasmamembranes
Tight junctionproteins
Intercellularspace
Microvilli
Basal lamina
Adhesivejunction(desmosome)
Tightjunction
Intermediatefilament
Communicatingjunction
2.5 µm
Intercellular space
b.
Adjacent plasmamembranesCadherin
Cytoplasmicprotein plaque
Cytoskeletal filamentsanchored to plaque
Anchoring junction (desmosome)
0.1 µm
c.
Intercellular space
Channel (diameter 1.5 nm)
Communicating junction
ConnexonTwo adjacent connexonsforming an open channelbetween cells
Adjacent plasmamembranes
1.4 µm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: Courtesy of Daniel Goodenough; b: © Dr. Donald Fawcett/Visuals Unlimited; c: © Dr. Donald Fawcett/D. Albertini/Visuals Unlimited
Plasmodesmata
54
•Plant cells• Plasmodesmata
• Specialized openings in their cell walls
• Cytoplasm of adjoining cells are connected
• Function similar to gap junctions in animal cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
PrimaryCell wall
Middle lamella Plasmamembrane
PlasmodesmaSmoothER
Centraltubule
Cell 2Cell 1