Biol 2430 Anatomy and Physiology

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Biol 2430 Anatomy and Physiology
Lect 2 Muse 5/9/12
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THE CELL

• The cell is the smallest structural and
  functional unit of the body. Most of the chemical
  reactions that sustain life occur inside cells.

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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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An Introduction to Cells

• A cell is surrounded by a watery medium known as
  the extracellular fluid (interstitial fluid)
• Plasma membrane (cell membrane) separates
  cytoplasm from the extracellular fluid
• Cytoplasm
• Cytosol liquid
• Intracellular structures collectively known as
  organelles

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Chapter 3Cells

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

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Cell functions are similar in all cells

• Cells maintain a selective barrier called the
  plasma membrane between their cytoplasm and the
  extracellular environment. All substances that
  enter or leave the cell must pass across the
  barrier.
• Cells contain hereditary material carrying
  encoded instructions for the synthesis of most of
  the cellular components. This hereditary
  material is duplicated prior to cell reproduction
  so that each new cell carries a full set of
  instructions.
• Cells carry out metabolic activities, which are
  catalyzed chemical reactions that result in the
  synthesis and breakdown of organic molecules.

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Components of a cell

• A generalized body cell has four principal
  divisions
• the plasma membrane
• the cytoplasm
• cytoplasmic organelles
• the nucleus.

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A Composite Cell

• hypothetical cell
• major parts
• nucleus
• cytoplasm
• cell 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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Cell Membrane

• outer limit of cell

• controls what moves in and out of cell

• selectively permeable

• phospholipid bilayer
• water-soluble heads form surfaces
• water-insoluble tails form interior
• permeable to lipid-soluble substances

• cholesterol stabilizes the membrane

• proteins
• receptors
• pores, channels, carriers
• enzymes
• CAMS (Cellular Adhesion Molecules)
• self-markers

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Cell Membrane
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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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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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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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The Nucleus is the largest organelle

• It is present in all cells of the body except
  mature red blood cells, which lost their nuclei
  as they developed.
• Generally, each cell has a single nucleus, but
  some giant cells, such as megakaryocytes of bone
  marrow, osteoclasts of bone, and skeletal muscle
  cells, may have several nuclei.

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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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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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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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Structural Components

• Centrioles
• Structure
• In a nondividing cell, two centrioles are located
  near the nucleus and Golgi apparatus in a
  specialized region called the centrosome.
• Function
• Centrioles function in cell division and also as
  the site of the formation of cilia and flagella.
• Centrioles are self-replicating and divide prior
  to cell division. Following replication, each
  original centriole and its duplicate migrate to
  opposite nuclear poles where they induce the
  formation of the spindle apparatus during cell
  division.

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Structural Components

• Cilia and flagella
• Structure
• Both cilia and flagella are motile processes that
  extend out from the cell surface.
• They are composed of longitudinal microtubules,
  which are arranged as two single tubules
  surrounded by a ring of nine regularly spaced
  double tubules.
• Function
• Both cilia and flagella function in movement.
• Cilia are able to move fluid or a layer of mucus
  over the surface of the cells on which they
  occur, while the flagellum of the sperm cell
  propels the cell.

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Cytoplasmic Organelles

• Endoplasmic Reticulum
• connected, membrane-bound sacs, canals, and
  vesicles
• transport system
• rough ER
• studded with ribosomes
• protein synthesis
• smooth ER
• lipid synthesis
• added to proteins arriving from rough ER
• break down of drugs

• Ribosomes
• free floating or connected to ER
• provide structural support

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Cytoplasmic Organelles

• Golgi apparatus
• stack of flattened, membranous sacs
• modifies, packages and delivers proteins

• Vesicles
• membranous sacs
• store substances

• Mitochondria
• membranous sacs with inner partitions
• generate energy

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Cytoplasmic Organelles

• Lysosomes
• enzyme-containing sacs
• digest worn out cell parts or unwanted substances

• Centrosome
• two rod-like centrioles
• used to produce cilia and flagella
• distributes chromosomes during cell division

• Peroxisomes
• enzyme-containing sacs
• break down organic molecules

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Cytoplasmic Organelles

• Cilia
• short hair-like projections
• propel substances on cell surface

• Flagellum
• long tail-like projection
• provides motility to sperm

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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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Cell Nucleus

• control center of cell

• nuclear envelope
• porous double membrane
• separates nucleoplasm from cytoplasm

• nucleolus
• dense collection of RNA and proteins
• site of ribosome production

• chromatin
• fibers of DNA and proteins
• stores information for synthesis of proteins

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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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Diffusion

• The random movement of particles (molecules or
  ions) under the influence of their own thermal
  energy, from an area of their higher
  concentration to an area of their lower
  concentration, or downhill.
• Diffusion of molecules or ions may take place in
  a liquid, gas, or solid or through nonliving or
  living membranes that are permeable to them.
• Diffusion in a liquid is the movement of solute
  and solvent particles in all directions through a
  solution, or in both directions through a
  permeable membrane.
• Net diffusion is the movement of particles from
  an area of their own high concentration to an
  area of lower concentration that is, along their
  own concentration gradients. Net diffusion means
  more particles are diffusing in one direction
  than in the other.

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The rate of net diffusion of particles in a
solution is increased by the following factors

• A higher concentration gradient because there are
  more particles
• A low molecular weight because large particles
  are not as easily moved by colliding with each
  other
• An increase in temperature because higher
  temperature increases random particle movement.

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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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Facilitated Diffusion

• diffusion across a membrane with the help of a
  channel or carrier molecule
• glucose and
• amino acids

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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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Endocytosis (endo inner)

• Means taking into the cell.
• It includes phagocytosis and pinocytosis.
• Phagocytosis (phago to eat) is the engulfing of
  large solid substances by foldings of the plasma
  membrane to form a phagocytic vesicle.
• The phagocytic vesicle fuses with a lysosome and
  the lysosomal enzymes destroy the contents.
• Specialized phagocytic cells in the body remove
  disintegrating cells, foreign matter, and
  bacteria.
• Pinocytosis (pino to drink) is the engulfing of
  small drops of extracellular fluid, which may
  contain dissolved nutrients, and incorporating
  them into the cell.
• Receptor-mediated endocytosis refers to the
  binding of receptor molecules on the cell surface
  with specific substances known as ligands. The
  receptor-ligand complex then undergoes
  endocytosis for transport into the cell.

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Endocytosis

• cell engulfs a substance by forming a vesicle
  around the substance
• three types
• pinocytosis substance is mostly water
• phagocytosis substance is a solid
• receptor-mediated endocytosis requires the
  substance to bind to a membrane-bound receptor

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Endocytosis
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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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Transcytosis

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

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Stages of replication

• The two strands of DNA are unwound and separated
  (unzipped) by unwinding enzymes, which cause the
  weak hydrogen bonds between the paired bases to
  break.
• The enzyme DNA polymerase, using the four kinds
  of complementary nucleotides freely present in
  the nucleus, matches and attaches the
  nucleotides to the exposed bases on each
  unzipped, single stranded DNA.
• Two complete DNA double helices are formed, each
  identical in nucleotide sequence to the original
  DNA helix that served as the templates. Thus, the
  genetic information is copied exactly.
• Such replication is termed semiconservative
  because it conserves each strand of the original
  DNA double helix while each also receives a newly
  synthesized matching partner strand.

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DNA Replication

• hydrogen bonds break between bases
• double strands unwind and pull apart
• new nucleotides pair with exposed bases
• controlled by DNA polymerase

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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

• series of changes a cell undergoes from the time
  it forms until the time it divides
• stages
• interphase
• mitosis
• cytoplasmic division

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The Cell Cycle
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Interphase

• very active period
• cell grows
• cell maintains routine functions
• cell replicates genetic material to prepare for
  nuclear division
• cell synthesizes new organelles to prepare for
  cytoplasmic division
• phases
• G phases cell grows and synthesizes structures
  other than DNA
• S phase cell replicates DNA

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Mitosis

• produces two daughter cells from an original
  somatic cell
• nucleus divides karyokinesis
• cytoplasm divides cytokinesis
• stages
• prophase chromosomes form nuclear envelope
  disappears
• metaphase chromosomes align midway between
  centrioles
• anaphase chromosomes separate and move to
  centrioles
• telophase chromatin forms nuclear envelope
  forms

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Mitosis
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Control of Cell Division

• cell division capacities vary greatly among cell
  types
• skin and blood cells divide often and
  continually
• neuron cells divide a specific number of times
  then cease

• chromosome tips (telomeres) that shorten with
  each mitosis provide a mitotic clock

• cells divide to provide a more favorable surface
  area to volume relationship

• growth factors and hormones stimulate cell
  division
• hormones stimulate mitosis of smooth muscle
  cells in uterus
• epidermal growth factor stimulates growth of new
  skin

• contact (density dependent) inhibition

• tumors are the consequence of a loss of cell
  cycle control

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Stem and Progenitor Cells

• Stem cell
• can divide to form two new stem cells
• self-renewal
• can divide to form a stem cell and a progenitor
  cell
• totipotent can give rise to every cell type
• pluripotent can give rise to a restricted
  number of cell types

• Progenitor cell
• committed cell
• can divide to become any of a restricted number
  of cells
• pluripotent

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Stem and Progenitor Cells
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The telomere paradox