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The Cell: An Overview
Chapter 5
5.1 Basic Features of
Cell Structure and Function
 Cells are small and are visualized using a
microscope
 Cells have a DNA-containing central region
surrounded by cytoplasm
 Cells occur in prokaryotic an eukaryotic forms,
each with distinctive structures and organization
Microscopes and Cells
 Robert Hooke and Anton van Leeuwenhoek
 Robert Brown
 Mattias Schleiden and Theodore Schwann
 Rudolf Virchow
Microscopes and Cells
Fig. 5-1, p. 92
Cell Theory: Fundamental to Life
 All organisms are cellular
 Cell: the smallest unit of life
 Cells come only from preexisting cells
Examples of Cells
Fig. 5-2, p. 92
Units of Measure
Fig. 5-3, p. 93
Research Methods
Fig. 5-4, p. 94
Cells are Small
 No life is smaller than an intact cell
• Diffusion and surface area to volume ratios
 Cells viewed with microscopes
• Light and electron
 Magnification and resolution limit microscopes
Surface to Volume Ratios
All Cells Contain DNA
 All cells have a central region with DNA
• Stores hereditary information (connection to
evolution)
• Genes are located on DNA
• Proteins replicate DNA and copy information to
RNA
Cytoplasm
 Cytoplasm
• Surrounds the central region
 Cytosol
• Aqueous solution of cell
 Organelles
• Small organized structures within cytosol
Plasma Membrane
Fig. 5-6, p. 95
Plasma Membrane
 Plasma membrane defines cytoplasm
 Lipid bilayer and proteins
 Hydrophobic
• Selective passage hydrophilic
 Internal environment of cell different from
external
Prokaryotes and Eukaryotes
 Prokaryotes
• No boundary membrane in central region
• Nucleoid
• Domains: Archaea and Bacteria
 Eukaryotes
• Boundary membrane in central region
• True nucleus
• Domain: Eukarya
Components of Prokaryotic and
Eukaryotic Cells
Table 5-1, p. 96
5.2 Prokaryotic Cells
 Prokaryotic cells have little or no internal
membrane structure
Prokaryotic Cell Structure
Fig. 5-7, p. 97
Prokaryotic Internal Structure
 Small, little to no membrane structure
• Cell wall & capsule
 Plasma membrane allows metabolism
• ATP in mitochondria and chloroplasts
• Evolution by endosymbiosis
5.3 Eukaryotic Cells
 Eukaryotic cells have a membrane-enclosed
nucleus and cytoplasmic organelles
 Nucleus contains much more DNA than the
prokaryotic nucleoid
 Cytoplasm has endomembrane systems dividing
cell into functional and structural components
5.3 (cont.)
 Mitochondria are the powerhouses of the cell
 Microbodies carry out vital reactions that link
metabolic pathways
 The cytoskeleton supports and moves cell
structures
 Flagella and cilia are the propellers of eukaryotic
cells
Eukaryotic Cell Overview
 Domain Eukarya (true nucleus)
• Includes protists, fungi, plants and animals
 Eukaryotic plasma membrane function
• Regulate/recognize substances (immune system)
• Cell-to-cell binding
 Fungi, plants and many protists have cell walls
Typical Animal Cell
Fig. 5-8a, p. 99
Typical Plant Cell
Fig. 5-9a, p. 100
Eukaryotic Nucleus
 Nuclear envelope separates nucleus and
cytoplasm
• Two membranes and nuclear pores
 Nucleoplasm within nuclear envelope
• Chromatin and chromosomes
 Nucleolus
• Genes for ribosomal RNA
Nuclear Envelope
Fig. 5-10, p. 101
Endomembrane System
 Endomembrane system
•
•
•
•
Connects all membranes
Synthesizes/ modifies membrane proteins
Synthesizes lipids
Detoxification
 Vesicles exchange membrane throughout
endomembrane system
• ER, Golgi, nuclear envelope, lysosomes, vesicles,
plasma membrane
Endoplasmic Reticulum
Fig. 5-11, p. 102
Endoplasmic Reticulum
 Endoplasmic reticulum (ER)
• Interconnected network of membrane with
cisternae and lumen
 Rough ER
• Ribosomes bound to surface
• Membrane-associated protein synthesis
Endoplasmic Reticulum
 Smooth ER
• No ribosomes
• Synthesizes lipids and detoxifies
 Proportion rough/smooth ER reflect cell activities
Golgi Complex
Fig. 5-12, p. 103
Lysosomes
 Lysosomes
• Vesicles from Golgi complex
• Hydrolytic enzymes from ER; low pH
 Autophagy removes nonfunctional organelles
 Phagocytosis digests extracellular material
• Major function of immune systems
Endocytosis, Exocytosis
and Lysosomes
Fig. 5-13-14, p. 104
Vesicle Traffic
Fig. 5-15, p. 105
Mitochondria
 Cellular respiration yields ATP
 Mitochondria have two membranes
• Outer membrane smooth
• Inner membrane folded (cristae)
• Mitochondrial matrix
 Mitochondria have own genome
• Endosymbiosis
Mitochondria
Fig. 5-16, p. 106
Microbodies
 Microbodies
• Single membrane organelles
• Not part of endomembrane system
 Microbody enzymes link biochemical pathways
 Examples
• Peroxisomes, glyoxysomes or glycosomes
Microbodies
Fig. 5-17, p. 107
Cytoskeleton
 Cytoskeleton
• Maintains shape and organization
• Interconnected protein fibers and tubes
 Most prominent in animal cells
• Plants and fungi also use cell walls and central
vacuole
Cytoskeleton Examples
Fig. 5-18, p. 107
Cytoskeleton Components
 Main elements of animal cytoskeletons
• Microtubules are supportive
• Intermediate fibers thinner, interconnected with
microtubules
• Microfilaments thinnest
Cytoskeleton Components
 Each element assembled from proteins
• Microtubules from tubulin
• Intermediate fibers from intermediate filaments
• Microfilaments from actins
Major Components of Cytoskeleton
Fig. 5-19, p. 108
Microtubules
 Many microtubules originate from centrosome
• Originate from centrioles
• Anchor major organelles
• Microtubules provide tracks for mobile organelles
Microtubules
 Organelle movement by motor proteins
• Vesicle attached to motor protein “walks” along
microtubule
• Requires ATP
 Cytoskeleton allows large cellular movement
• Amoeboid motion, cytoplasmic streaming, cell
division
Kinesin
Fig. 5-20a,b, p. 108
Flagella and Cilia
 Flagella and cilia for cell motion
• Identical structure; cilia shorter/greater in number
 Structures are 9+2
• Motor proteins
• From centrioles and basal body
 Prokaryotes have analogous (not homologous)
flagella and cilia
Flagellar Structure
Fig. 5-21, p. 109
Flagellar and Ciliary Beating Patterns
Fig. 5-22, p. 110
Centrioles
Fig. 5-23, p. 110
5.4 Specialized Structures of Plant Cells
 Chloroplasts are biochemical factories powered
by sunlight
 Central vacuoles have diverse roles in storage,
structural support, and cell growth
 Cell walls support and protect plant cells
Chloroplasts
 Chloroplasts have multiple membranes for
photosynthesis
• Outer smooth, inner folded; stroma inside both
• Thylakoids and grana inside stroma
• Endosymbiosis
 Plastids are plant organelles that include
chloroplasts, amlyoplasts and chromoplasts
Plastids
 Plant organelles including
• Chloroplasts
• Amyloplasts
• Chromoplasts
Chloroplast Structure
Fig. 5-24, p. 111
Central Vacuoles
 Central vacuoles
•
•
•
•
Large vesicles in plants
90% of many plant cell’s volume
Turgor pressure from water
Other functions
 Tonoplast
• Membrane surrounding central vacuole
Cell Walls
 Cell walls
• Extracellular structures
• Provide structure and contain pressure
• Cellulose fibers for tensile strength, other organic
molecules for compression resistance
 Two types of cells walls
• Primary
• Secondary
Cell Walls
 Middle lamella holds adjacent cell walls together
 Plasmodesmata provide cellular connections
• No cell wall passage
Cell Wall Structure
Fig. 5-25, p. 112
5.5 The Animal Cell Surface
 Cell adhesion molecules organize animal cells
into tissues and organs
 Cell junctions reinforce cell adhesions and
provide avenues of communication
 The extracellular matrix organizes the cell
exterior
Cell Adhesion and Junctions
 Cell adhesion molecules bind cells together
nonpermanently
• Glycoproteins bind to specific molecules on other
cells
 Cell junctions seal spaces between cells
permanently
• Direct cellular communication
Functions of Cellular Junction
 Anchoring junctions “weld” cells together
• Desmosomes and adherens
 Tight junctions prevent small ion movement
• Seal spaces and fuse membranes
 Gap junctions allow passage without membrane
control
• Same tissue
Animal Cell Connections
Fig. 5-26, p. 114
Extracellular Matrix
 Collagen proteins
• Tensile strength and elasticity
 Proteoglycans
• Interlinkage
• Changes consistency (jellylike to hard and elastic)
 Fibronectins
• Connect cells via integrins
Extracellular Matrix
Fig. 5-27, p. 115
Animation: Fluid mosaic model
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ANIMATION