Cells!

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Cells!

• Muse 2430 Lecture 2
• 5/8/13

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Chapter 3Cells

• vary in size
• possess distinctive shapes
• measured in micrometers

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An Introduction to Cells

• Sex cells (germ cells)
• Reproductive cells
• Male sperm
• Female oocyte (a cell that develops into an egg)
• Somatic cells (soma body)
• All body cells except sex cells

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Cell Membrane
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The Plasma Membrane
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Cell Membrane

• The proteins are divided into two categories
  integral and peripheral.
• The integral proteins form the majority of
  membrane proteins. They penetrate and are
  embedded in the bilayer, bound to the nonpolar
  tail regions.
• The transmembrane proteins span the bilayer
  completely and may form channels (pores) for
  transport of substances across the membrane.
• Integral proteins also may lie partly submerged
  in one side or the other. They have several
  functions.
• Some integral proteins serve as cell surface
  enzymes.
• Integral proteins bound to carbohydrates may form
  receptor sites for chemical messages from other
  cells, such as endocrine glands.
• Some also function as markers, or antigens, which
  identify cell types.
• The peripheral proteins are loosely bound to the
  membrane surface and can be easily removed from
  it. Their functions are not as well known as
  those of integral proteins. They may be involved
  in structural support and changes in membrane
  shape during cell division or cell movement.

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Structure of the Plasma Membrane
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Intercellular Junctions

• Tight junctions
• close space between cells
• located among cells that form linings

• Desmosomes
• form spot welds between cells
• located among outer skin cells

• Gap junctions
• tubular channels between cells
• located in cardiac muscle cells

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The cytoplasm contains a complex network of
structural components

• Microfilaments
• Structure
• Microfilaments are solid thread-like cylinders
  made of protein and found in a variety of sites
  within the cell.
• Function
• Microfilaments are responsible for contractility
  of cells, which is a property of all cells but is
  especially well developed in muscle cells.
• Contractility is responsible for cell locomotion
  and movements associated with phagocytosis,
  pinocytosis, and cell division.

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Cell Adhesion Molecules

• guide cells on the move

• selectin allows white blood cells to anchor

• integrin guides white blood cells through
  capillary walls

• important for growth of embryonic tissue

• important for growth of nerve cells

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Structural Components

• Microtubules
• Structure
• Microtubules are hollow tubes present everywhere
  in the cytoplasm in all cells.
• They are composed of protein tubulin molecules.
• Function
• Microtubules contribute to the cytoskeleton, or
  supporting elements, of the cell.
• They also are involved in cell division, cell
  movements, and the transport of materials from
  one area of the cell to another.

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Cytoplasmic Organelles

• Microfilaments and microtubules
• thin rods and tubules
• support cytoplasm
• allows for movement of organelles

• Inclusions
• temporary nutrients and pigments

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Movements Into and Out of the Cell

• Passive (Physical) Processes
• require no cellular energy
• simple diffusion
• facilitated diffusion
• osmosis
• filtration

• Active (Physiological) Processes
• require cellular energy
• active transport
• endocytosis
• exocytosis
• transcytosis

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Simple Diffusion

• movement of substances from regions of higher
  concentration to regions of lower concentration
• oxygen, carbon dioxide and lipid-soluble
  substances

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Osmosis

• movement of water through a selectively
  permeable membrane from regions of higher
  concentration to regions of lower concentration
• water moves toward a higher concentration of
  solutes

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Osmosis
Osmotic Pressure ability of osmosis to generate
enough pressure to move a volume of water
Osmotic pressure increases as the concentration
of nonpermeable solutes increases

• hypertonic higher osmotic pressure
• hypotonic lower osmotic pressure
• isotonic same osmotic pressure

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Facilitated Diffusion

• In facilitated diffusion, the carrier substance
  combines with the solute molecules to form a
  solute-carrier complex, which is soluble in the
  lipid-bilayer, and thus transports the solute
  across the membrane.
• Once on the other side, the solute is released.
  The carrier breaks away from the complex, returns
  to the exterior of the membrane, and repeats the
  process.
• The carriers exhibit specificity i.e. they are
  highly selective in distinguishing between
  closely related molecules.
• Facilitated diffusion can be inhibited by
  competitive and noncompetitive inhibitor
  molecules, which closely resemble the solute
  molecules.
• The rate of passage of a solute through
  facilitated diffusion depends on
• its concentration difference on both sides of
  the membrane
• the number of carrier molecules available
• how rapidly the solute-carrier complex formation
  takes place.

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Filtration

• smaller molecules are forced through porous
  membranes
• hydrostatic pressure important in the body
• molecules leaving blood capillaries

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Active Transport

• carrier molecules transport substances across a
  membrane from regions of lower concentration to
  regions of higher concentration
• sugars, amino acids, sodium ions, potassium
  ions, etc.

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Transport in Vesicles

• Vesicle - a small spherical sac formed by budding
  off from a membrane
• Endocytosis - materials move into a cell in a
  vesicle formed from the plasma membrane
• three types receptor-mediated endocytosis
  
• phagocytosis
• bulk-phase endocytosis (pinocytosis)
• Exocytosis - vesicles fuse with the plasma
  membrane, releasing their contents into the
  extracellular fluid
• Transcytosis - a combination of endocytosis and
  exocytosis

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Phagocytosis
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Endocytosis
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Transcytosis

• endocytosis followed by exocytosis
• transports a substance rapidly through a cell
• HIV crossing a cell layer

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Exocytosis

• reverse of endocytosis
• substances in a vesicle fuse with cell membrane
• contents released outside the cell
• release of neurotransmitters from nerve cells

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Nucleus

• Structure
• The nuclear envelope consists of a double
  membrane separated by the perinuclear space.
• The inner membrane is smooth. The outer membrane
  often contains ribosomes and is continuous with
  the surrounding ER.
• The inner and outer membranes fuse at irregular
  intervals around the nucleus to form nuclear
  pores, which allow for exchange of materials
  between the nucleus and the cytoplasm.
• Chromatin appears as irregular clumps or granules
  material dispersed throughout the nucleus.
• Chromatin is composed of coiled strands of DNA
  bound to basic proteins called histones, varying
  amounts of RNA, and other nonhistone proteins and
  enzyme systems.
• In a dividing cell, the chromatin is condensed
  and coiled into discrete units, the chromosomes.
  Human cells contain 23 pairs of chromosomes.
• The nucleoplasm is the matrix that surrounds the
  chromatin. It is composed of proteins,
  metabolites, and ions.
• The nucleolus is a spherical structure composed
  of RNA and protein. The size of the nucleolus and
  the number present vary in different cell types.
  It is missing in cells that do not synthesize
  protein, such as spermatozoa. It is the site of
  ribosome production

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Ribosomes

• Structure
• Ribosomes are small granules composed of
  ribosomal RNA and almost 80 different proteins.
• They occur as individual granules or in clusters
  called polyribosomes.
• They may be free in the cytoplasm (free
  ribosomes) or attached to the membranes of the
  endoplasmic reticulum.
• Function
• Ribosomes are the site of protein synthesis.
• Free ribosomes are involved in the synthesis of
  proteins for the cells own use for example, in
  the renewal of enzymes and membranes.
• Attached ribosomes are the site of synthesis of
  proteins that are secretory products to be
  released from the cell.

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Golgi Apparatus

• Function
• The Golgi apparatus is the site of accumulation,
  concentration, packaging, and chemical
  modification of the secretory products
  synthesized on the rough ER.
• The transport vesicles pinch off from the ER and
  carry the secretions to the Golgi apparatus,
  where the secretions fuse with its cisternae.
• The large condensing vacuoles concentrate the
  secretion and package them to become secretory
  granules.
• Secretory granules, which are large, densely
  packed, membrane-bounded structures, unload their
  contents via exocytosis upon nervous or hormonal
  stimulation.
• The Golgi apparatus also chemically modifies the
  molecules synthesized in the ER for incorporation
  into the plasma membrane. It adds fatty acid
  residues to certain proteins to convert them to
  lipoproteins, and it synthesizes and attaches
  carbohydrate side chains to proteins to form
  glvcoproteins.
• The Golgi apparatus processes proteins that
  function intracellularly, such as the lysosome
  enzymes.

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Golgi Complex
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The cell cycle and mitosis

• The cell cycle, in cells that are capable of
  dividing, refers to the events in a cells life
  span in the period between the time it was formed
  by cell division to the beginning of the next
  cell division.
• The greatest portion of the cycle (about 90) is
  devoted to growth and synthesis, called
  interphase, with a smaller portion devoted to
  nuclear and cell division, or mitosis.

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The Cell Cycle
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Stem and Progenitor Cells
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Mitosis cell copying
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The End