Cells

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Lecture 8
Cells Structure A Tour of the Cell
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The Cell A basic unit of living matter
separated from its environment by a plasma
membrane. The smallest structural unit of
life.
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Discovery

• First observations of cells were made with light
  microscopes Robert Hooke (1665) Used primitive
  microscope to observe cork (dead plant cells).
  Coined the word cell.

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Cell Theory

• Developed 200 years ago.
• All living organisms are made up of one or more
  cells.
• The smallest living organisms are single cells,
  and cells are the functional units of
  multi-cellular organisms.
• All cells arise from pre-existing cells.

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Relative Sizes of Procaryotic and Eucaryotic
Cells and Viruses
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Different Classes of Cells

• Prokaryotic
• Eukaryotic
• - Animal
• - Plant
• All possess a cell membrane. Called the plasma
  membrane in bacterial cells and cytoplasmic
  membrane in animal/plant cells.

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The Cell Membrane

• Functions as a semi-permeable barrier, allowing a
  very few molecules across it while fencing the
  majority of organically produced chemicals inside
  the cell.
• Structure is a lipid bilayer (also referred to as
  the fluid-mosaic model).
• The most common molecule in the model is the
  phospholipid, which has a polar (hydrophilic)
  head and two nonpolar (hydrophobic) tails. These
  phospholipids are aligned tail to tail so the
  nonpolar areas form a hydrophobic region between
  the hydrophilic heads on the inner and outer
  surfaces of the membrane.

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Lipid Bilayer
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Functions of Cell Membranes

• Separate cell from nonliving environment. Form
  most organelles and partition cell into discrete
  compartments
• Regulate passage of materials in and out of the
  cell and organelles. Membrane is selectively
  permeable.
• Receive information that permits cell to sense
  and respond to environmental changes. Hormones
  Growth factors Neurotransmitters
• Communication with other cells and the organism
  as a whole. Surface proteins allow cells to
  recognize each other, adhere, and exchange
  materials.

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Prokaryotic Cells

• Bacteria and blue-green algae.
• Small size Range from 1- 10 micrometers in
  length. About one tenth the size of a eukaryotic
  cell.
• No nucleus DNA in cytoplasm or nucleoid region.
• Ribosomes are used to make proteins
• Cell wall Hard shell around membrane
• Other structures that may be present
• Capsule Protective, outer sticky layer. May be
  used for attachment or to evade immune system.
• Pili Hair-like projections (attachment)
• Flagellum Longer whip-like projection (movement)

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Prokaryotic Cells

• Bacteria and blue-green algae.
• Small size Range from 1- 10 micrometers in
  length. About one tenth the size of a eukaryotic
  cell.
• No nucleus DNA in cytoplasm or nucleoid region.
• Ribosomes are used to make proteins
• Cell wall Hard shell around membrane
• Other structures that may be present
• Capsule Protective, outer sticky layer. May be
  used for attachment or to evade immune system.
• Pili Hair-like projections (attachment)
• Flagellum Longer whip-like projection (movement)

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Prokaryotic Cells
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Prokaryotic Cell Wall

• Made up of peptidoglycans, molecules that have a
  carbohydrate (polysaccharide) attached to a
  polypeptide chain. The polysaccharide chains are
  liked by short amino acid chains.
• Forms a net like structure that surrounds the
  whole cell.
• Function support and prevention of lysis
• Use to identify different types of bacteria
• Gram positive and Gram negative

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Gram negative and Gram positive

• Gram because of inventor.
• Bacteria with small amounts of peptidoglycan and,
  characteristically, lipopolysaccharide, are
  Gram-negative. Cells are a pink colour after
  staining.
• Bacteria containing relatively large amounts of
  peptidoglycan and no lipopolysaccharide are
  Gram-positive. Cells are a purple colour after
  staining.

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Eukaryotic Cells

• E.g protists, fungi, plant, and animal cells.
• Nucleus Protects and houses DNA
• Membrane-bound Organelles Internal structures
  with specific functions such a Separate and
  store compounds
• Store energy
• Work surfaces
• Maintain concentration gradients

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Eukaryotic Cell Surfaces

• Cell wall Much thicker than cell membrane,
  (10 to 100 X thicker).
• Provides support and protects cell from lysis.
• Plant and algae cell wall Cellulose
• Fungi and bacteria have other polysaccharides.
• Not present in animal cells or protozoa.
• Breaks in surface Channels between adjacent
  plant cells form a circulatory and communication
  system between cells. Sharing of nutrients,
  water, and chemical messages

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Membrane-Bound Organelles of Eukaryotic Cells

• Nucleus
• Rough Endoplasmic Reticulum (RER)
• Smooth Endoplasmic Reticulum (SER)
• Golgi Apparatus
• Lysosomes Vacuoles
• Chloroplasts
• Mitochondria

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Membrane Bound Organelles
Nucleus
Processing and transport
Golgi Body
Rough ER
Smooth ER
Completed Protein
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Eucaryotic Cells Typical Animal Cell
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Eucaryotic Cells Typical Plant Cell
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Chloroplasts

• Site of photosynthesis in plants and algae.
• CO2 H2O Sun Light -----gt Sugar O2
• Number may range from 1 to over 100 per cell.
• Disc shaped structure with three different
  membrane systems
• 1. Outer membrane Covers chloroplast surface
• 2. Inner membrane Contains enzymes needed to
  make glucose during photosynthesis. Encloses
  stroma (liquid) and thylakoid membranes.
• 3. Thylakoid membranes Contain chlorophyll,
  green pigment that traps solar energy. Organized
  in stacks called grana.

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Chloroplasts Trap Solar Energy and Convert it to
Chemical Energy
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Chloroplasts

• Contain their own DNA, ribosomes, and make some
  proteins.
• Can divide to form daughter chloroplasts.
• Type of plastid Organelle that produces and
  stores food in plant and algae cells.
• Other plastids include Leukoplasts Store
  starch. Chromoplasts Store other pigments that
  give plants and flowers color.

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Mitochondria

• Change chemical energy of molecules into the
  useable energy of the ATP molecule.
• Oval or sausage shaped.
• Contain their own DNA, ribosomes, and make some
  proteins.
• Can divide to form daughter mitochondria.
• Structure
• Inner and outer membranes.
• Intermembrane space.
• Cristae (inner membrane extensions),
• Matrix (inner liquid)

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Mitochondria Harvest Chemical Energy From Food
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The Cytoskeleton

• Complex network of thread-like and tube-like
  structures.
• Functions Movement, structure, and structural
  support.
• Three Cytoskeleton Components
• 1. Microfilaments Smallest cytoskeleton fibres.
  Important for Muscle contraction Actin
  myosin fibres in muscle cells Amoeboid motion
  of white blood cells .
• 2. Intermediate filaments Medium sized fibres
  Anchor organelles (nucleus) and hold cytoskeleton
  in place. Abundant in cells with high mechanical
  stress.
• 3. Microtubules Largest cytoskeleton fibres.
  Found in structures that help move chromosomes
  during cell division (mitosis and meiosis).
  Found in animal cells, but not plant cells.
  Movement of flagella and cilia.

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Components of the Cytoskeleton are Important for
Structure and Movement
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The Cytoskeleton
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Cilia and Flagella

• Projections used for locomotion or to move
  substances along cell surface.
• Enclosed by plasma membrane and contain
  cytoplasm.
• Consist of 9 pairs of microtubules surrounding
  two single microtubules (9 2 arrangement).
• Flagella Large whip-like projections. Move in
  wavelike manner, used for locomotion. Example
  Sperm cell
• Cilia Short hair-like projections. Example
  Human respiratory system uses cilia to remove
  harmful objects from bronchial tubes and trachea.

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Lysosomes, Aging, and Disease

• As we get older, our lysosomes become leaky,
  releasing enzymes which cause tissue damage and
  inflammation. Example Cartilage damage in
  arthritis.
• Steroids or cortisone-like anti-inflammatory
  agents stabilize lysosomal membranes, but have
  other undesirable effects (affect immune
  function).

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Important Differences Between Plant and Animal
Cells

• Plant cells Animal cells
• Cell wall None
• Chloroplasts No chloroplasts
• Large central vacuole No central vacuole
• Flagella rare Flagella more usual
• No Lysosomes Lysosomes present
• No Centrioles Centrioles present

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Organelles and Function

• Manufacture Nucleus Ribosomes Rough ER Smooth ER
  Golgi Apparatus
• Breakdown Lysosomes Vacuoles
• Energy Processing Chloroplasts (Plants and algae)
  Mitochondria
• Support, Movement, Communication Cytoskeleton
  (Cilia, flagella, and centrioles) Cell walls
  (Plants, fungi, bacteria, and some protists)
  Extracellular matrix (Animals) Cell junctions

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Viruses are not cells!

• They are referred to as particles.
• They are the smallest living organisms on the
  planet.
• They are obligate parasites
• Core of nucleic acids surrounded by a protein
  coat (capsid)
• Some viruses have a DNA genome and others have an
  RNA genome.