Cell Structure and Function

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Cell Structure and Function

• Chapter 4

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History

• Anton van Leeuwenhoek (1674)
• Robert Hooke (1665)
• Coined the
• term cell

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Cell Theory

• States that all organisms are composed of cells
  and that cells come only from preexisting
• cells

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Organism sizes

• Most cells smaller than one millimeter some as
  small as one micrometer

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Cell size

• Surface-area-to-volume ratio
• Small cells likely have adequate surface area for
  exchanging wastes for nutrients
• Cells that specialize in absorption have
  modifications to increase the surface area per
  volume of the cell

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Surface to Volume Ratio
































TotalSurfaceArea (Height?Width?NumberOfSides?Numbe
rOfCubes) 96 cm2 192 cm2 384 cm2
TotalVolume (Height?Width?LengthXNumberOfCubes)
64 cm3 64 cm3 64 cm3 SurfaceAreaPerCube/Volume
PerCube (SurfaceArea/Volume) 1.5/1 3/1 6/1
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Prokaryotic Cells

• No membrane-bounded nucleus
• Structurally simple
• Small (1.1 to 1.5µm wide and 2 to 6 µm long)
• 2 domains
• Domain Bacteria
• Domain Archaea
• Found in all types of environments
• Air
• Water
• Soil
• Organisms

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Cell size
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Mycobacteria tuberculosis
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Bacterial Structure

• 3 basic shapes
• Bacillus rod-shaped
• Coccus spherical
• Spirilla - spirals

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Bacterial Organization

• Cell Envelope
• Plasma membrane
• Cell wall
• Glycocalyx

• Cytoplasm
• Nucleoid
• Ribosomes
• Thylakoids
• Appendages
• Flagella
• Sex Pili
• Fimbriae

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Cell Envelope

• Plasma membrane phospholipid bilayer with
  embedded and peripheral proteins
• Regulates passage
• Can form mesosomes to increase internal surface
• area

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Cell Envelope

• Cell wall maintains cell shape
• Strengthened by peptidoglycan
• Glycocalyx layer of polysaccharides outside of
  the cell wall
• Organized to form capsule
• Biofilms
• S. epidermidis

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Cytoplasm

• Semifluid solution encased by the plasma membrane
• Nucleoid region contains the bacterial
  chromosome
• Plasmid extrachromosomal DNA
• Ribosomes synthesize proteins
• Smaller than eukaryotic ribosomes
• Inclusion bodies store nutrients for later use
• Thylakoids in photosynthetic bacteria

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Appendages

• Flagella
• Filament
• Hook
• Basal body
• Sex pili
• Rigid tubular structures used to pass DNA
• Fimbriae
• Fibers on bacterial surface involved in
  attachment to surfaces

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Archaea

• More diverse in shape
• Cell walls contain polysaccharides and proteins
• Cell membrane has
• hydrocarbons in place
• of fatty acids
• Extreme environments
• Methanosarcina
• barkeri

http//www.ucmp.berkeley.edu/archaea/archaeamm.htm
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Eukaryotic Cells

• Larger than Prokaryotes
• Domain Eukarya
• Protists
• Fungi
• Plants
• Animals

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Eukaryotic Cells

• Contain
• Membrane-bounded nucleus
• Internal structures called Organelles
• Plasma membrane - phospholipid bilayer with
  embedded and peripheral proteins
• Regulates passage
• Cell wall plants different than bacterial cell
  wall

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Compartmentalization

• Compartmentalization
• Allows eukaryotic cells to be larger than
  prokaryotic cells
• Isolates reactions from others
• Organelles

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Organelles

• Two classes of organelles
• Endomembrane system
• Organelles that communicate with one another
• via membrane channels
• Via small vesicles
• Energy related organelles
• Mitochondria chloroplasts
• Basically independent self-sufficient

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Animal Cell Structure
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Plant Cell Structure
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Nucleus

• Contains chromatin in semifluid nucleoplasm
• Condense to form chromosomes
• Separated from cytoplasm by double-membrane
  nuclear envelope
• Nuclear pores permit passage in and out of the
  nucleus
• Dark nucleolus composed of rRNA
• Produces subunits of ribosomes

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Anatomy of the nucleus
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Ribosomes

• Composed of large and small subunits that serve
  in protein synthesis
• Subunits made in nucleolus
• Subunits are mix of protein and rRNA
• Occur singly and in groups, polyribosomes,
• May become attached to endoplasmic reticulum,
  rough ER

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Nucleus, ribosomes, and ER
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Endomembrane System

• Consists of nuclear envelope, membranes of
  endoplasmic reticulum, Golgi apparatus, and
  several types of vesicles
• Restrict enzymatic reactions to specific
  compartments within cell

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Endoplasmic Reticulum

• Rough studded with ribosomes
• Synthesizes proteins
• Modifies proteins
• Adds sugar to protein
• Results in glycoproteins
• Smooth no ribosomes
• Synthesizes lipids

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Endoplasmic Reticulum
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Endomembrane System

• Golgi Apparatus
• Consists of flattened, curved saccules
• Modifies proteins and lipids and packages them in
  vesicles

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Endomembrane System

• Lysosomes
• Membrane-bounded vesicles produced by the Golgi
  apparatus
• Engage in digestion of molecules and apoptosis
  (programmed cell death)
• Some genetic diseases
• Caused by defect in lysosomal enzyme
• Lysosomal storage diseases (Tay-Sachs)

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Peroxisomes

• Peroxisomes are membrane-bounded vesicles that
  enclose enzymes
• Similar to lysosomes
• Enzymes are cell-specific
• Enzymes synthesized by free ribosomes in
  cytoplasm (instead of ER)
• Active in lipid metabolism
• Catalyze reactions that produce hydrogen peroxide
  H2O2
• Toxic
• Broken down to water O2 by catalase

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Peroxisomes
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Vacuoles

• Vacuoles are membranous sacs that are larger than
  vesicles
• Plants cells typically have a central vacuole
  that functions in storage of nutrients and waste
  products
• Up to 90 volume of some cells
• Functions in
• Storage of water, nutrients, pigments, and waste
  products
• Development of turgor pressure
• Some functions performed by lysosomes in other
  eukaryotes

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Vacuoles
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Energy-Related Organelles

• Chloroplasts
• Mitochondria

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Chloroplasts

• Chloroplasts use solar energy to synthesize
  carbohydrates
• Photosynthesis
• Cellular Respiration
• Adenosine triphosphate (ATP) is used for all
  energy-requiring processes in cells
• Chloroplasts are green due to the green pigment
  chlorophyll
• Stroma contains concentrated mixture of enzymes
• Granum stack of thalakoids

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Chloroplast Structure
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Mitochondria

• Mitochondria are involved in cellular respiration
• Produce most of ATP utilized by the cell
• Cristae inner membrane that encloses matrix
• Matrix contains enzymes that break down
  nutrient molecules also contains mitochondrial
  DNA and ribosomes

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Mitochondrion Structure
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Cytoskeleton

• Cytoskeleton serves as internal skeleton that
  maintains cell shape and assists in movement of
  its parts
• Actin Filaments
• Pseudopods
• Intermediate Filaments
• Microtubules

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Actin Filaments

• Extremely thin filaments like twisted pearl
  necklace
• Responsible for maintainance of cell shape
• Support for microvilli in intestinal cells
• Intracellular traffic control
• Cytoplasmic streaming
• Pseudopods
• Involved in mitosis
• Important component in muscle contraction (other
  is myosin)

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Intermediate Filaments

• Intermediate in size between actin filaments and
  microtubules
• Rope-like assembly of fibrous polypeptides
• Functions
• Support nuclear envelope
• Cell-cell junctions, like those holding skin
  cells tightly together

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Microtubules

• Hollow cylinders - a and b tubulin in dimers
• Dimers arrange themselves into tubular spirals of
  13 dimers
• Interacts with proteins kinesin and dynein to
  cause movement of organelles

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Centrioles

• Centrioles are short cylinders with a 9 0
  pattern of microtubule triplets that may give
  rise to basal bodies of cilia and flagella

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Cilia, and Flagella

• Cilia and flagella are hair-like projections that
  aid in movement
• Outer covering of plasma membrane
• Inside this is a cylinder of 18 microtubules
  arranged in 9 pairs
• In center are two single microtubules
• This 9 2 pattern of microtubules used by all
  cilia flagella
• Differ from prokaryote flagella
• Flagella move like a propeller or cork screw
• In eukaryotes, cilia are much shorter than
  flagella
• Cilia move in coordinated waves like oars

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