Cells – the working units of life.

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Cells the working units of life.
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5.1 What Features Make Cells the Fundamental Unit
of Life?

• Life requires a structural compartment,
  separate from the external environment
• Cells are small (mostly).
• Exceptions bird eggs, neurons, some algae and
  bacteria cells

Elephant bird egg (extinct)
Ostrich egg
Chicken egg
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The Cell The Basic Unit of Life

• The cell theory states that
• Cells are the fundamental units of
  life.
• All organisms are composed of cells
• All cells come from preexisting cells

Robert Hooke's microscope. Hooke first described
cells in 1665.
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The Cell The Basic Unit of Life

• Cell size is limited by the surface
  area-to-volume ratio.
• The cell surface is what interfaces with the
  cells environment - Related to cells ability to
  exchange materials with environment
• Cell volume is a the space inside a cell. Volume
  is related to cells metabolic demands

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The Cell The Basic Unit of Life

• As volume increases, metabolic demands
• increase.
• For any given shape, increasing volume
• decreases the surface area-to-volume
• ratio.

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The Cell The Basic Unit of Life

• Microscopes are needed to visualize most cells.
• Normal human vision can resolve (i.e.,
  distinguished from one another) objects that are
  about 200 ?m (0.2 mm) in size.

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s/microscope.jpg
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The Cell The Basic Unit of Life

• Light microscopes use glass lenses to focus
  visible light and typically have a resolving
  power of 0.2 ?m.
• Electron microscopes have magnets to focus an
  electron beam have a resolving power 1
  million time X the human eye.

http//www.hcmc.org/a_z/images/newemmicroscope.jpg
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SEM ants head
TEM myeloma cell
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The Cell The Basic Unit of Life

• Every cell has a plasma membrane made of a
  phospholipid bilayer with proteins and other
  molecules Ch. 6.
• Is a selectively permeable barrier.
• Receives information from outside.
• Maintains a constant internal environment.
• Molecules that bind and adhere to adjacent cells.

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The Cell The Basic Unit of Life

• Cells show two organizational patterns
• Prokaryotes lack nucleus or other
  membrane-enclosed compartments and lack distinct
  organelles.

http//www.brooklyn.edu/bc/ahp/MBG/MBG3/CB.Prokary
oteCell.GIF
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The Cell The Basic Unit of Life

• Eukaryotes have a
• membrane-enclosed
• nucleus and other
• membrane-enclosed
• compartments or
• organelles..

http//www.brooklyn.edu/bc/ahp/MBG/MBG3/CB.Prokary
oteCell.GIF
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5.2 What features characterize prokaryotic cells?

• Prokaryotic cells inhabit many environments -
  hot springs, salt water etc.
• Each organism is single cell, but often found in
  chains or clusters
• Include Bacteria and Archaea

http//serc.carleton.edu/images/microbelife/Cyanob
acteria_1.jpg
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Prokaryotic Cells

• Features shared by all prokaryotic cells
• Enclosed by plasma membrane
• Nucleoid region where DNA is concentrated
• Cytoplasm (the plasma-membrane enclosed region)
  consists of nucleoid, ribosomes, and a liquid
  portion called the cytosol

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Prokaryotic Cells
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Prokaryotic Cells

• Specialized features of some prokaryotic cells
• Cell wall just outside plasma membrane
• An outermost slimy layer made of polysaccharides
  and referred to as a capsule
• Internal membranes for energy-related functions

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Prokaryotic Cells

• Some bacteria have flagella
• Some bacteria have pili, that help bacteria
  adhere to one another.
• Some also have cytoskeletal units of actin.

http//microvet.arizona.edu/Courses/MIC438/decker/
Biofilms/ecoli2
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Prokaryotic Cells
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5.3 What Features Characterize Eukaryotic Cells?

• Eukaryotes (animals, plants, fungi, and protists)
  have a membrane-enclosed nucleus in each of their
  cells.

http//www.brooklyn.edu/bc/ahp/MBG/MBG3/CB.Prokary
oteCell.GIF
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Eukaryotic Cells

• Compartmentalization is key to eukaryotic cell
  function
• Each organelle or compartment has a specific role
  defined by chemical processes
• Allows specialization of cells to form tissues
  and organs

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Organelles that Process Information

• The nucleus contains most of the cells DNA
• Site of DNA replication
• Site of DNA transcription.
• Nucleolus is specialized region where ribosomes
  are initially assembled

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Organelles that Process Information
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Organelles that Process Information

• Two lipid bilayers form nuclear envelope
• Perforated with nuclear pores which control
  passage of molecules

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Organelles that Process Information

• Nuclei contain chromatin - long, thin fibers of
  DNA is bound to proteins
• Before cell division chromatin condenses and
  organizes into chromosomes

http//faculty.jsd.claremont.edu/jarmstrong/images
/chromatin.gif
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Organelles that Process Information

• Nuclear lamina is a meshwork of proteins which
  maintains the shape of the nucleus

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Cytoplasm organelles cytosol

• Cytoplasm - Material outside the nucleus and
  enclosed by plasma-membrane
• Consists of organelles suspended in the cytosol -
  mostly water, plus all proteins and other
  molecules of metabolism

http//www.puc.edu/Faculty/Gilbert_Muth/art0063.jp
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Organelles that Process Information

• Ribosomes sites of protein synthesis in both
  eukaryotes and prokaryotes
• In eukaryotes, ribosomes are found free in
  cytoplasm, bound to endoplasmic reticulum, and in
  mitochondria and chloroplasts

http//www.bu.edu/histology/i/21002loa.jpg
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The Endomembrane System

• The endomembrane
• a. Endoplasmic reticulum - network of
  interconnecting membranes
• b. Golgi apparatus

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The Endomembrane System

• At certain sites, ER membrane is continuous with
  outer nuclear envelope membrane

http//micro.magnet.fsu.edu/cells/endoplasmicretic
ulum/images/endoplasmicreticulumfigure1.jpg
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The Endomembrane System

• Rough ER (RER) has ribosomes attached.
• Makes proteins for secretion outside cytosol or
  embedded in plasma membrane

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The Endomembrane System

• Rough ER
• Receives and segregates newly synthesized
  proteins from cytoplasm.
• Chemically modifies and tags proteins for
  delivery.
• Ships proteins enclosed in vesicles to
  destinations.

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Figure 4.10 The Endoplasmic Reticulum
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The Endomembrane System

• Smooth ER (SER) lacks ribosomes
• Modifies proteins synthesized in RER
• Modifies molecules taken in by cell, e.g. drugs,
  pesticides
• Plays a role in detoxification
• Lipid steroid synthesis

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The Endomembrane System

• Hydrolysizes glycogen in animals cells
• Calcium storage in many cells

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The Endomembrane System

• Golgi apparatus
• Flattened membranous sacs and small
  membrane-enclosed vesicles
• Receives proteins from ER in membrane vesicles
  and further modifies them
• Concentrates, packages, and sorts proteins before
  they are sent to their destinations

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The Endomembrane System

• Makes some polysaccharides for plant cell walls

http//www.lifesci.sussex.ac.uk/home/Julian_Thorpe
/golgi.jpg
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Golgi Apparatus

• Golgi has 3 regions
• cis region receives vesicles
• Medial
• At trans region, vesicles bud off from Golgi
  moved

Flow of material
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The Endomembrane System

• Lysosomes
• Contain digestive enzymes that originate from
  Golgi
• For breakdown food and foreign material brought
  into cell by phagocytosis
• Autophagy - digest worn out cell components
• lysosomal storage diseases when this fails.
• Not in plants

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Lysosomes
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Organelles that Process Energy

• Mitochondria
• Converts potential chemical energy of fuel
  molecules into a form the cell can use (ATP)
• ATP production is called cellular respiration
• Cells requiring lots of energy have lots of
  mitochondria

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Organelles that Process Energy

• Mitochondria have an outer lipid bilayer and a
  highly folded inner membrane
• Cristae are inner folds for high surface area
  contain proteins used in cellular respiration
• Mitochondrial matrix is region enclosed by inner
  membrane contains DNA and ribosomes

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Organelles that Process Energy

• Plastids are found only in plants and some
  protists
• Chloroplasts, sites of photosynthesis
  conversion of light energy to chemical energy

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Organelles that Process Energy

• Chloroplasts have double membrane, and an
  internal membrane system
• Internal membranes (thylakoids) arranged in
  stacks (grana)
• Thylakoid membranes contain chlorophyll and other
  pigments
• Stroma is fluid in which grana are suspended
  contains ribosomes and DNA

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Other plastids

• Chromoplasts contain red, orange, and yellow
  pigments give color to flowers

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Other Organelles

• Peroxisomes small organelles specialized to
  compartmentalize toxic peroxides and break them
  down with specific enzymes

http//faculty.une.edu/com/abell/histo/peroxisome.
jpg
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Other Organelles

• Glyoxysomes structurally similar organelles
  found only in plants that convert lipids to
  carbohydrates for growth

http//faculty.une.edu/com/abell/histo/peroxisome.
jpg
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Other Organelles

• Vacuoles, found in plants and protists, are
  filled with an aqueous solution and are used to
  store wastes and toxins
• Functions include
• Store pigments, H2O
• Structure (tugor)
• Reproduction
• Digestion

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Other Organelles

• Central vacuole found in plants help plant cells
  hold their shape (tugor) and store water,
  minerals and ions

http//www.virtualsciencefair.org/2004/mcgo4s0/pub
lic_html/t4/plantcell.gif
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Other Organelles

• Freshwater protists may have contractile vacuoles
  to expel excess water

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7f8cfbe21c26e87498/paramecium.gif
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The Cytoskeleton

• Cytoskeleton
• Maintains cell shape and support
• Provides mechanisms for cell movement
• Positions organelles within cells

http//en.wikipedia.org/wiki/ImageFluorescentCell
s.jpg
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The Cytoskeleton

• Forms tracks for motor proteins that help move
  materials within cells
• Interacts with extracellular structures to anchor
  cell in place.

http//en.wikipedia.org/wiki/ImageFluorescentCell
s.jpg
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The Cytoskeleton

• Three major types of cytoskeletal components
• microfilaments
• intermediate filaments
• microtubules

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The Cytoskeleton

• Microfilaments
• Actin based protein
• Needed for cell
• contraction with myosin
• pinching off
• Stabilize cell shape
• Involved in cytoplasmic
• streaming, and formation
• of pseudopodia

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The Cytoskeleton

• Intermediate filaments
• 50 kinds made of fibrous proteins of keratin
  family ?
• Stabilize cell structure
• Organize organelles

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The Cytoskeleton

• Microtubules
• Hollow cylinders made of tubulin protein dimer
  subunits
• Provide rigid intracellular skeleton for some
  cells
• Function as tracks that motor proteins can move
  along in cell

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The Cytoskeleton

• Regularly form and disassemble as needs change
• Have and ends
• Framework along which motor proteins can move
  structures.

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The Cytoskeleton

• Cilia and eukaryotic flagella, appendages of
  cells for movement, are made of microtubules

http//biology.unm.edu/ccouncil/Biology_203/Images
/Protists/euglenaflag.jpeg
http//www.mie.utoronto.ca/labs/lcdlab/biopic/fig/
47.03.jpg
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The Cytoskeleton

• Flagella
• longer than cilia
• Cells usually have only one or two
• Move in undulating manner

Euglena
http//biology.unm.edu/ccouncil/Biology_203/Images
/Protists/euglenaflag.jpeg
http//www.mie.utoronto.ca/labs/lcdlab/biopic/fig/
47.03.jpg
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The Cytoskeleton

• Cilia
• Shorter than flagella
• Usually present in great numbers
• Provide coordinated beating movement

http//www.mie.utoronto.ca/labs/lcdlab/biopic/fig/
47.03.jpg
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The Cytoskeleton

• Microtubules in cilia and flagella arranged in 9
  2 array
• At the base of each is a basal body.
• The nine doublets extend into basal body, adding
  another microtuble ? 9 tiplets

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The Cytoskeleton

• Centrioles
• similar to basal bodies, but located in cell
  center
• involved in mitotic spindle formation

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The Cytoskeleton

• Motor proteins - move along microtubules
• In cilia and flagella, microtubules are
  cross-linked by spokes of the motor protein
  dynein
• Dynein reversibly changes shape when ATP energy
  is released

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The Cytoskeleton

• Kinesin binds to vesicles and walks them along
  by changing shape

Harvard University Inner Life of Cells
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5.4 What Are the Roles of Extracellular
Structures?

• Extracellular structures are outside plasma
  membrane
• Example peptidoglycan cell wall of bacteria

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4.4 What Are the Roles of Extracellular
Structures?
http//micro.magnet.fsu.edu/cells/plants/images/ce
llwallfigure1.jpg

• Plant cell wall
• made of cellulose fibers embedded in
  polysaccharides and proteins
• Plasmodesmata gap junctions that interconnect
  cells

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Figure 4.24 The Plant Cell Wall
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Extracellular Structures

• provides rigid structure for plasma membrane
  under turgor pressure, giving important support
• acts as barrier to many organisms that may cause
  plant diseases

http//botit.botany.wisc.edu/images/130/Plant_Cell
/Elodea/Chloroplasts_face_side_MC.jpg
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Extracellular Structures

• Multicellular animals have an extracellular
  matrix
• Mainly collagen, and proteoglycans
  (glycoproteins)
• May take many forms, from fluid to rigid
• Basement membrane in epithelial tissues and the
  hard material in bones are examples.

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Extracellular Structures

• Extracellular matrix
• Holds cells together
• Contributes to structure of bone, cartilage,
  skin, etc.
• Filters
• Plays role in chemical signaling

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Origin of Eukaryotic Cells

• Continuing evolution
• Believed that eukaryotes evolved from
  prokaryotes. share many features, similar
  biochemistry, same molecular genetic material,
  progression to increasing complexity.
•  

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Origin of Eukaryotic Cells

• Endosymbiosis Theory
• Some prokaryotic cells ingested others,
  benefitted from their presence and passed the
  offspring of the ingested organism to their own
  offspring.

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Origin of Eukaryotic Cells

• Evidence
• DNA in chloroplasts and mitochondria similar
  to that found in free-living organism of similar
  structure function.

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Harvard Inner Life of the Cellhttp//aimediaserve
r4.com/studiodaily/videoplayer/?srcai4/harvard/ha
rvard.swfwidth640height520
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Try This

• 1. In biology, we call the basic unit of life the
  _______.
• 2. Membranous compartments with distinctive
  shapes and functions are termed _______.

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Try This

• 3. The DNA of prokaryotic cells is found in the
• a. plasma membrane.
• b. nucleus.
• c. ribosome.
• d. nucleoid region.

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Try This

• 4. An organelle found only in plant cells is the
• a. cilium.
• b. nucleus.
• c. mitochondrion.
• d. chloroplast
• e. ribosome

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Try This

• 5. The idea that eukaryotic cells are derived
  from prokaryotic cells living together in a
  mutualistic relationship is the
• a. endosymbiotic theory.
• b. cell theory.
• c. evolutionary theory.
• d. parasite theory.