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Cells

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Cells Chapter 3 Mitotic phase (M): dividing phase Prophase Metaphase Anaphase Telophase IPMAT Interphase: G1 , S and G2 phases. (90% of its time) G1 (gap 1 ... – PowerPoint PPT presentation

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Title: Cells


1
Cells
  • Chapter 3

2
  • I. Overview
  • Cell Membrane
  • Cytoplasm
  • Cytosol
  • Organelles
  • Nonmembranous Cytoskeleton, Microvilli,
    Centrioles, Cilia, Flagella, Ribosomes
  • Membranous Mitochondria, Nucleus, Endoplasmic
    Reticulum, Golgi Apparatus, Lysosomes,
    Peroxisomes, Vesicles

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  • II. Plasma Membrane (Cell Membrane)
  • "Fluid Mosaic Model" - plasma membrane is
    composed of a double layer (bilayer) of    
    phospholipid molecules with proteins that
    float/move among the phospholipids, yet the    
    plasma membrane is stable.
  • Proteins function....
  • As cell markers for recognition by immune system
  • As receptors (e.g for hormones)
  • As catalysts
  • Transportation

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  • Proteins in the membrane...
  • integral proteins (maintain selective transport)
  • peripheral proteins (catalyst and mechanical
    function)
  • The plasma membrane also contains a myriad of
    biological compounds such as glycoproteins,
    glycolipids, and proteoglycans (all referred to
    as glycocalyx) that extend outward from the
    plasma membrane

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  • III. Cytoplasm
  • Cytoplasm is the material found inside the cell
    and is divided into two subdivisions cytosol
        and organelles.
  • Cytosol (intracellular fluid) contains dissolved
    nutrients, ions, soluble and insoluble    
    proteins, and waste products.
  • Organelles are structures that perform specific
    functions within the cell and are classified as
        membranous and non-membranous.

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Mitochondria  Rod-like, double membrane, inner membrane folded into projections called cristae Site of ATP synthesis.
Ribosomes  Dense particles consisting of two subunits, each composed of ribosomal RNA and proteins can be free or it can be attached to ER site of protein synthesis
E. R. (rough)  Coiling membrane system with ribosomes attached proteins synthesized are packaged into vesicles for transport to the golgi apparatus
E. R. (smooth)  Coiling membrane system lacking ribosomes synthesizes lipids and carbohydrates
Golgi apparatus  Stack of smooth membrane sacs adjacent to the nucleus modifies synthesized proteins, then packages the proteins (e.g. lysosomes peroxisomes) in vesicles for transport around/out of cell
Lysosomes Membranous sacs containing hydrolytic enzymes used in cell digestion
Peroxisomes  Membranous sacs containing oxidative enzymes (e.g. peroxidase) that degrade toxic compounds such as hydrogen  peroxide
Vesicles  Membrane bound sac that transports cellular material
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Microfilaments Filaments containing the contractile protein actin part of the cytoskeleton and functions in intracellular movement
Intermediate filaments Protein fibers that provides strength, stabilize the position of organelles, and transport materials within the cytoplasm
Microtubules  Hollow tubes composed of the globular protein tubulin microtubules provide strength and rigidity and anchoring major organelles
Thick filaments    Large and long strands of myosin protein found in muscle cells that interact with thin actin filaments to produce muscle contraction
Centrioles   Cylindrical structure composed of nine triplets of microtubules centrioles direct the movement of DNA during cell division as well as form the bases of cilia and flagella
Microvilli   Small, finger-shaped projections of the cell membrane that actively absorb fluid and nutrients
Cilia Cell surface projections composed of microtubules cilia move to propel substance across the cell surface
Flagella  Larger and longer cilia that provides cellular locomotion (e.g. human sperm)
Nucleus  Structure housing genetic information and is surrounded by a membrane (nuclear envelope)
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Endoplasmic Reticulum
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  • IV. Membrane Transport Processes
  • Transportation of materials across the cell
    membrane is determined by the components in the
    membrane that impart permeability.
  • Most cells have selective permeability, free
    passage of some materials and restricts the
    passage of others.
  • Permeability may be based on size, electrical
    charge, molecular shape, solubility, etc...
    Passage across the membrane is classified as
    active (requiring energy) and passive (not
    requiring energy)

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  • Membrane transport processes
  • Passive
  • Diffusion - net movement of particles from an
    area of higher concentration to an area of lower
    concentration.
  • Osmosis - diffusion of water through a
    selectively permeable membrane
  • Facilitated diffusion - diffusion of a substance
    with the aid of a membrane carrier.
  • Filtration - movement of water and solutes
    through a semipermeable membrane from a region of
    higher hydrostatic pressure to a region of lower
    hydrostatic pressure

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  • b) Osmosis movement of a solvent (water)
    through a semi- permeable membrane down a
    concentration gradient (higher to lower)
  • Solutions
  • Isotonic
  • Hypertonic
  • Hypotonic

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  • A human red blood cell is composed of 0.9 salt
    and 99.1 water. If this cell is placed in a
    solution of 0.9 salt and 99.1 water (saline)
    the solution is isotonic and the blood cell will
    remain unchanged

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Isotonic
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  • The same RBC is placed in a beaker of distilled
    water (100 H2O and 0 salt), water will enter
    the cell and cause it to burst (lysis). Water
    goes from higher conc. to lower conc. This
    solution is hypotonic (hypoless salt in
    solution).

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Hypotonic
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  • The same RBC is placed in a beaker of 50 salt
    water (50 H2O and 50 salt), water will leave
    the cell and cause it to shrink (crenation).
    Water goes from higher conc. to lower conc. This
    solution is hypertonic (hypermore salt in
    solution).

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Hypertonic
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  • Active
  • Active transport - movement of a substance (with
    the aid of a membrane carrier) through a membrane
    against its concentration gradient.
  • Exocytosis - substances enclosed in a vesicle
    fuses with the plasma membrane, the vesicle then
    ruptures, releasing the substances outside the
    cell.
  • Endocytosis (types)
  • Phagocytosis - the cell membrane extends outward
    and encloses large particles which are then
    transported into the cell.
  • Pinocytosis - particles attach to the cell
    membranes which collapses, causing particles to
    be taken into the cell.
  • Receptor-mediated - pinocytotic movement
    initiated by protein receptors on the plasma
    membrane.

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  • Movement of particle may be....
  • Symport - movement of two or more different kinds
    of material in the same direction across the cell
    membrane.
  • Uniport - movement of one type of material in one
    direction across the cell membrane.
  • Antiport - moving two types of material across
    the cell membrane in opposite directions.

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  • V. Cell Division (Cell Life Cycle)
  • Multicellular organisms develop from a zygote,
    which is formed by the fusion of a sperm and an
    egg (gametes). Each gamete has half the
    compliment of chromosomes (haploid number) and
    when combined gives rise to a zygote with a
    complete set (diploid number) of chromosomes. In
    order for the zygote to develop into a
    multicellular organism, it must repeatedly
    undergo cellular divisions. The series of events
    a cell (or zygote) undergoes that ultimately
    produces a new cell is called the cell cycle.

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  • Nucleus
  • - located in the center of the cell
  • - controls all functions of organelles
  • - cell reproduction/division takes place
  • - DNA (Deoxyribonucleic Acid) is housed
  • - blueprint of heredity
  • - as cell divides the DNA coil tightly, called
    chromatin, to form chromosomes (46)
  • - bound by nuclear envelope double layered
    membrane enclosing nucleoplasm
  • Nucleoli are darkly stained areas within the
    nucleus that indicate rapid RNA synthesis.

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  • Cell Growth and reproduction produces two
    identical daughter cells from one parent cell
  • - cell life cycle has two major sections
  • Interphase (cell growth not dividing)
  • G1 phase growth
  • S phase growth and DNA synthesis
  • G2 phase growth and final preparation for
    cell division

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  • Mitotic phase (M) dividing phase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • IPMAT

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  • Interphase G1 , S and G2 phases. (90 of
    its time)
  • G1 (gap 1) cell grows vigorously and
    metabolically very active.
  • - depending on cell type, this phase may
    last minutes to years.
  • - centrioles begin replicating
  • S DNA replicates itself chromatin condenses.
    Ensures daughter cells receive identical genetic
    information.

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DNA replication (S phase)
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  • G2 phase is very brief.
  • - centriole replication is complete
  • - ready to divide

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  • Mitotic phase (M)
  • Prophase Chromosomes are visible.
  • - early prophase longest phase of mitosis.
  • - chromatin condenses to form chromosomes.
  • - centriole pairs start to separate/nuclear
    membrane breaks down.
  • - mitotic spindles (microtubules) start to
    develop

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  • late prophase
  • - centrioles migrate away from each to opposite
    poles of cell.

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  • Metaphase (meta middle)
  • - chromosomes cluster toward the center of
    cell.
  • - centromeres align along the equator of the
    spindle
  • - enzyme separase will separate the chromatid.

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  • Anaphase (apart) shortest phase.
  • - centromeres of the chromosomes split
  • - each chromatid becomes its own chromosome
  • - Each chromosome is pulled to opposite pole

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  • Telophase begins when chromosomal movement
    stops.
  • - chromosomes uncoil goes back to fine threads
    of chromatin.
  • - new nuclear envelope forms
  • - cytoplasm pinches inward forming a cleavage
    furrow (cytokinesis)

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  • Somatic (body) cells contain a diploid number of
    chromosomes.
  • Human cells contain two sets of chromosomes (one
    member from each pair is inherited from each
    parent) homologous chromosomes
  • 2n (n of different chromosomes). n23 in
    humans
  • 2(23) 46
  • 22 pairs are called autosomes while the last pair
    determines the sex of the individual sex
    chromosomes (X and Y)
  • Mapping of chromosomes is called a karyotype

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  • What can cause abnormal cell division?
  • - radiation UV light, x-ray
  • - viruses
  • - organic chemicals pesticide, nicotine
  • Teratogens substances that can cause severe
    congenital abnormalities.
  • Carcinogens chemical or environmental agent that
    produces cancer

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  • Cancer
  •   - The p53 gene prevents these mutations from
    causing problems.
  • - p53 is present in all DNA
  • - p53 is responsible for cell division to stop
    so that mutated DNA can be repaired.
  • - If DNA cannot be repaired the cell undergoes
    apoptosis in which the cell is programmed to
    die.
  • - Defective or missing p53 can result in the
    cell mutating uncontrollably causing a tumor.
  • - Normal cells will divide on average about 50
    times then the cell dies. While tumors divide
    without stopping.

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  • Benign tumors are cell masses that do not
    fragment or spread beyond its original area of
    growth.
  •     
  • Malignant tumors are cell masses that break
    apart and spread or invade other parts of the
    body.  This movement is metastasis.            
                                             
  • Cancer is the term used to refer to any tumor
    that has the potential to become malignant.

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  • VI. Protein Synthesis
  • Ribonucleic acid (RNA) links DNA's genetic
    instructions for making proteins to the process
    of protein synthesis
  • It copies or transcribes the message from DNA and
    then translates that message into a protein.
  • RNA, like DNA, is a nucleic acid or polymer of
    nucleotides
  • RNA structure differs from DNA in the following
    ways
  • The five carbon sugar in RNA nucleotides is
    ribose rather than deoxyribose
  • The nitrogenous base uracil is found in place of
    thymine

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PROTEIN SYNTHESIS
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  • The linear sequence of nucleotides in DNA
    ultimately determines the linear sequence of
    amino acids in a protein.
  • Nucleic acids are made of four types of
    nucleotides which differ in their nitrogenous
    bases
  • Hundreds or thousands of nucleotides long, each
    gene has a specific linear sequence of the four
    possible bases.
  • Proteins are made of twenty types of amino acids
    linked in a particular linear sequence (the
    protein's primary structure).
  • Information flows from gene to protein through
    two major processes, transcription and
    translation.

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  • Transcription - the synthesis of RNA using DNA as
    a template
  • A gene's unique nucleotide sequence is
    transcribed from DNA to a complimentary
    nucleotide sequence in messenger RNA (mRNA).
  • The resulting mRNA caries this transcript of
    protein-building instructions to the cell's
    protein-synthesizing machinery.

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  • Translation - synthesis of a polypeptide, which
    occurs under the direction of messenger RNA
    (mRNA)
  • During this process, the linear sequence of bases
    in mRNA is translated into the linear sequence of
    amino acids in a polypeptide.
  • Translation occurs on ribosomes, complex
    particles composed of ribosomal RNA (rRNA) and
    protein that facilitate the orderly linking of
    amino acids into polypeptide chains.
  • Signals are contained in the RNA to start and
    stop translation.

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SUMMARY OF PROTEIN SYNTHESIS
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GENETIC CODE
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Translation
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