Cell Structure and Function

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Cell Structure and Function
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Cell Structure

• In 1655, the English scientist Robert Hooke
  coined the term cellulae for the small box-like
  structures he saw while examining a thin slice of
  cork under a microscope.

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Basic Cell Structure

• All cells have the following basic structure
• A thin, flexible plasma membrane surrounds the
  entire cell.
• The interior is filled with a semi-fluid material
  called the cytoplasm.
• Also inside are specialized structures called
  organelles and the cells genetic material.

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Generalized Eukaryotic Cell
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Visualizing Cells
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Prokaryotic Cells

• Simplest organisms
• Cytoplasm is surrounded by plasma membrane and
  encased in a rigid cell wall composed of
  peptidoglycan.
• No distinct interior compartments
• Some use flagellum for locomotion, threadlike
  structures protruding from cell surface

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Eukaryotic Cells

• Characterized by compartmentalization by an
  endomembrane system, and the presence of
  membrane-bound organelles.
• central vacuole
• vesicles
• chromosomes
• cytoskeleton
• cell walls

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Animal Cell
Animal cell anatomy
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Cell Membrane
Fluid Mosaic Model
Extracellular matrix protein
Extracellular fluid
Glycoprotein
Glycolipid
Carbohydrate
Cholesterol
Transmembrane proteins
Peripheral protein
Cytoplasm
Filaments of cytoskeleton
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The Nucleus And The Nuclear Envelope

• Repository for genetic material called chromatin
  - DNA and proteins
• Nucleolus holds chromatin and ribosomal
  subunits - region of intensive ribosomal RNA
  synthesis
• Nuclear envelope Surface of nucleus bound by two
  phospholipid bilayer membranes - Double membrane
  with pores
• Nucleoplasm semifluid medium inside the nucleus

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Chromosomes

• DNA of eukaryotes is divided into linear
  chromosomes.
• Exist as strands of chromatin, except during cell
  division
• Histones associated packaging proteins

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Ribosomes

• Ribosomes are RNA-protein complexes composed of
  two subunits that join and attach to messenger
  RNA.
• Site of protein synthesis
• Assembled in nucleoli

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Endomembrane System

• Compartmentalizes cell, channeling passage of
  molecules through cells interior.
• Endoplasmic reticulum
• Rough ER - studded with ribosomes
• Smooth ER - few ribosomes

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Rough ER

• Rough ER is especially abundant in cells that
  secrete proteins.
• As a polypeptide is synthesized on a ribosome
  attached to rough ER, it is threaded into the
  cisternal space through a pore formed by a
  protein complex in the ER membrane.
• As it enters the cisternal space, the new protein
  folds into its native conformation.
• Most secretory polypeptides are glycoproteins,
  proteins to which a carbohydrate is attached.
• Secretory proteins are packaged in transport
  vesicles that carry them to their next stage.
• Rough ER is also a membrane factory.
• Membrane-bound proteins are synthesized directly
  into the membrane.
• Enzymes in the rough ER also synthesize
  phospholipids from precursors in the cytosol.
• As the ER membrane expands, membrane can be
  transferred as transport vesicles to other
  components of the endomembrane system.

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Smooth ER

• The smooth ER is rich in enzymes and plays a role
  in a variety of metabolic processes.
• Enzymes of smooth ER synthesize lipids, including
  oils, phospholipids, and steroids.
• These include the sex hormones of vertebrates and
  adrenal steroids.
• In the smooth ER of the liver, enzymes help
  detoxify poisons and drugs such as alcohol and
  barbiturates.
• Smooth ER stores calcium ions.
• Muscle cells have a specialized smooth ER that
  pumps calcium ions from the cytosol and stores
  them in its cisternal space.
• When a nerve impulse stimulates a muscle cell,
  calcium ions rush from the ER into the cytosol,
  triggering contraction.

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The Golgi apparatus

• The Golgi apparatus is the shipping and receiving
  center for cell products.
• Many transport vesicles from the ER travel to the
  Golgi apparatus for modification of their
  contents.
• The Golgi is a center of manufacturing,
  warehousing, sorting, and shipping.
• The Golgi apparatus consists of flattened
  membranous sacscisternaelooking like a stack of
  pita bread.
• The Golgi sorts and packages materials into
  transport vesicles.

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Functions Of The Golgi Apparatus
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Membrane Bound Organelles

• Lysosomes vesicle containing digestive enzymes
  that break down food/foreign particles
• Vacuoles food storage and water regulation
• Peroxisomes - contain enzymes that catalyze the
  removal of electrons and associated hydrogen
  atoms

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Mitochondria

• Sites of cellular respiration, ATP synthesis
• Bound by a double membrane surrounding
  fluid-filled matrix.
• 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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Cytoskeleton

• The eukaryotic cytoskeleton is a network of
  filaments and tubules that extends from the
  nucleus to the plasma membrane that support cell
  shape and anchor organelles.
• Protein fibers
• Actin filaments
• cell movement
• Intermediate filaments
• Microtubules
• centrioles

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Centrioles

• Centrioles are short cylinders with a 9 0
  pattern of microtubule triplets.
• Centrioles may be involved in microtubule
  formation and disassembly during cell division
  and in the organization of cilia and flagella.

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Cilia and Flagella

• Contain specialized arrangements of microtubules
• Are locomotor appendages of some cells
• Cilia and flagella share a common ultrastructure

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Cilia and Flagella

• Cilia (small and numerous) and flagella (large
  and single) have a 9 2 pattern of microtubules
  and are involved in cell movement.
• Cilia and flagella move when the microtubule
  doublets slide past one another.
• Each cilium and flagellum has a basal body at its
  base.

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Cilia and Flagella
(a) Motion of flagella. A flagellum usually
undulates, its snakelike motion driving a
cell in the same direction as the axis of
the flagellum. Propulsion of a human
sperm cell is an example of
flagellatelocomotion (LM).
Direction of swimming
1 µm
(b) Motion of cilia. Cilia have a back-
and-forth motion that moves the cell in a
direction perpendicular to the axis of the
cilium. A dense nap of cilia, beating at a
rate of about 40 to 60 strokes a second,
covers this Colpidium, a freshwater
protozoan (SEM).
15 µm
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Cell Junctions

• Long-lasting or permanent connections between
  adjacent cells, 3 types of cell junctions