The Cellular Level of Organization

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The Cellular Level of Organization

• Living things are constructed of cells.
• Cell structure is diverse but all cells share
  common characteristics.

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• The cell theory states
• All organisms are composed of one or more cells.
• Cells are the basic unit of structure and
  function in organisms.
• All cells come only from other cells.

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• Cells are small so they can exchange materials
  with their surroundings.

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Eukaryotic Cells

• Eukaryotic cells have a nucleus that controls the
  workings of the cell.
• All cells are surrounded by a plasma membrane
  made of phospholipids and proteins.

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• The plasma membrane regulates what enters and
  exits the cell.
• Inside the plasma membrane, the nucleus is
  surrounded by cytoplasm.
• Plant cells have a cell wall in addition to the
  plasma membrane.

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• Animal and plant cells have organelles.
• Organelles compartmentalize functions within the
  cell.
• The organelles of animal and plant cells are
  similar to each other except that centrioles are
  present only in animal cells, and chloroplasts
  are present only in plant cells.

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Animal cell anatomy
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Plant cell anatomy
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Animal cell anatomy
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Nucleus and nuclear envelope
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Structure of the Nucleus

• Chromatin DNA and proteins
• Nucleolus Chromatin and ribosomal subunits
• Nuclear envelope Double membrane with pores
• Nucleoplasm semifluid medium inside the nucleus.

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Animal cell anatomy
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Ribosomes

• Protein synthesis occurs at tiny organelles
  called ribosomes.
• Ribosomes are composed of a large subunit and a
  small subunit.
• Ribosomes can be found alone in the cytoplasm, in
  groups called polyribosomes, or attached to the
  endoplasmic reticulum.

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Animal cell anatomy
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The Endomembrane System

• The endomembrane system consists of
• Nuclear envelope
• Endoplasmic reticulum
• Golgi apparatus
• Vesicles

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The endoplasmic reticulum

• The endoplasmic reticulum (ER) is a system of
  membranous channels and saccules.
• Rough ER is studded with ribosomes and is the
  site of protein synthesis and processing.
• Smooth ER lacks ribosomes and is the site of
  synthesis of phospholipids and the packaging of
  proteins into vesicles, among other functions.

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The endoplasmic reticulum
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Animal cell anatomy
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The Golgi apparatus

• The Golgi apparatus consists of a stack of curved
  saccules.
• The Golgi apparatus receives protein and also
  lipid-filled vesicles from the ER, packages,
  processes, and distributes them within the cell.
• This organelle may also be involved in secretion.

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The Golgi apparatus
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Lysosomes and vacuoles

• Lysosomes are vesicles produced by the Golgi
  apparatus.
• Lysosomes contain hydrolytic enzymes and are
  involved in intracellular digestion.
• Vacuoles (large) and vesicles (small) are
  membranous sacs in the cell that store substances.

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Peroxisomes

• Peroxisomes are vesicles than contain enzymes.
• The enzymes in these organelles use up oxygen and
  produce hydrogen peroxide.
• Peroxisomes are abundant in the liver where they
  produce bile salts and cholesterol and break down
  fats.

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Animal cell anatomy
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Energy-Related Organelles

• The two energy-related organelles of eukaryotes
  are chloroplasts and mitochondria.

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Plant cell anatomy
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Chloroplast structure
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Chloroplasts

• A chloroplast is bounded by two membranes
  enclosing a fluid-filled stroma that contains
  enzymes.
• Membranes inside the stroma are organized into
  thylakoids that house chlorophyll.
• Chlorophyll absorbs solar energy and
  carbohydrates are made in the stroma.

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Plant cell anatomy
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Mitochondria

• Mitochondria are found in plant and animal cells.
• Mitochondria are bounded by a double membrane
  surrounding fluid-filled matrix.

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Mitochondrion structure
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The inner membranes of mitochondria are
cristae. The matrix contains enzymes that break
down carbohydrates and the cristae house protein
complexes that produce ATP.
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The Cytoskeleton

• The eukaryotic cytoskeleton is a network of
  filaments and tubules that extends from the
  nucleus to the plasma membrane.
• The cytoskeleton contains three types of elements
  responsible for cell shape, movement within the
  cell, and movement of the cell
• Actin filaments
• Microtubules
• Intermediate filaments

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Actin filaments
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• Actin filaments occur in bundles or mesh-like
  networks.
• Actin filaments play a structural role and
  interact with motor molecules, such as myosin.

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Microtubule structure
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• Microtubules small,hollow cylinders.
• Microtubules
• help maintain the shape of the cell
• act as tracks along which organelles and
  chromosomes can move.

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Structure of intermediate filaments
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• Intermediate filaments -ropelike assemblies of
  fibrous polypeptides
• support the plasma membrane
• support the nuclear envelope.

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Centrioles

• Centrioles are short cylinders with a 9 0
  pattern of microtubule triplets.
• May be involved in
• microtubule formation and disassembly
• organization of cilia and flagella.

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Centriole structure
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Cilia and flagella

• Cilia and flagella - 9 2 pattern of
  microtubules
• Involved in movement (cell, eggs, debris)
• Each cilium and flagellum has a basal body at its
  base.

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Structure of a flagellum or cilium
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Prokaryotic Cells

• Prokaryotic cells include the bacteria and
  archaea.
• Bacterial cells have these constant features
• Outer Boundary Cell wall
• Plasma membrane
• Cytoplasm Ribosomes
• Thylakoids
  (Cyanobacteria)
• Many enzymes
• Nucleoid Chromosome (DNA only)

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• Bacterial cells may have plasmids, small
  accessory rings of DNA.

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Evolution of the eukaryotic cell