Cells ch3

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  1. cell cycle
    defines the changes from the formation of the cell until it (the cell) reproduces

    This includes: Interphase and Cell division (mitotic phase)
  2. interphase
    • -period from cell formation to cell division
    • -thought of as "resting" only from dividing
    • -nuclear material is called chromatin

    • Four Subphases:
    • -G1 (gap 1) = vigorous growth and metabolism
    • -G0 = gap phase in cells that permanently cease dividing
    • -S (synthetic) = DNA replication
    • -G2 (gap 2) = preparation for division

  3. DNA replication
    • DNA helices begin unwinding from the nucleosomes
    • helicase untwists the double helix and exposes complementary chains
    • the Y-shaped site of replication fork
    • each nucleotide strand serves as a template for building a new complementary strand
  4. DNA replication --- DNA polymerase
    • only works in one direction
    • continuous leading strand is synthesized
    • discontinuous lagging strand is synthesized in segments
    • DNA ligase splices together short segments of discontinuous strand
    • End Result: two DNA molecules formed from the original
    • this process is called semiconservative replication
  5. cell division (mitosis)
    • -Mitotic (M) phase of the cell cycle
    • -essential for body growth and tissue repair
    • -does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle

    Includes 2 distinct events: Mitosis and Cytokenesis

    Mitosis: four stages of nuclear division

    • 1) Prophase =
    • -chromosomes become visible, each with 2 chromatids joined at centromere
    • -centrosomes separate and migrate toward opposite poles
    • -mitotic spindles and asters form
    • -nuclear envelope fragments
    • -kinetochore microtubules attach to kinetochore of centromeres and draw them toward equator
    • -polar microtubules assist in forcing poles apart

    • 2) Metaphase=
    • -centromeres of chromosomes are aligned at equator
    • -this plane midway b/w poles is called the metaphase plate

    • 3) Anaphase=
    • -shortest phase
    • -centromeres of chromosomes split at same time; each chromatid now becomes a chromosome
    • -chromosomes (V shaped) are pulled toward poles by motor proteins of kinetochores
    • -polar microtubules continue forcing poles apart

    • 4) Telophase=
    • -begins when chromosome movement stops
    • - the 2 sets of chromosomes uncoil to form chromatin
    • -new nuclear membrane forms around each chromatin mass
    • -nucleoli reappear
    • -spindle disappears

    • -- Cytokinesis
    • -begins during late anaphase
    • -ring of actin microfilaments contracts to form a cleavage furrow
    • -two daughter cells are pinched apart, each containing a nucleus identical to the original
  6. control of cell division
    • "Go" signals:
    • -critical volume of cell when area of membrane is inadequate for exchange
    • -chemicals (eg growth factors, hormones, cyclins...)

    • "Stop" signals:
    • -contact inhibition
    • -growth-inhibiting factors produced by repressor genes
  7. protein synthesis
    • DNA is the master blueprint for protein synthesis
    • Gene: segment of DNA with blueprint for one polypeptide
    • triplets of nucleotide bases form genetic library
    • each triplet specifies coding for an amino acid
  8. protein synthesis

    roles of the 3 main types of RNA
    • Messenger RNA (mRNA)
    • -carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm

    • Ribosomal RNA (rRNA)
    • -a structural component of ribosomes that, along with tRNA, helps translate message from mRNA

    • Transfer RNAs (tRNAs)
    • -bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis
  9. protein synthesis

    transfers DNA gene base sequence to a complementary base sequence of an mRNA

    • 3 basic phases:
    • initiation, elongation, and termination

    1) initiation - once properly positioned, RNA polymerase pulls apart strands of DNA double helix so transcription can begin at the start point in promoter

    • 2) elongation - RNA aligns nucleotides w/complementary DNA bases on template strand and links them together.  RNA polymerase elongates the mRNA strand one base at a time, unwinds the DNA helix and rewinds helix behind it. At any given time, 16-18 base pairs of DNA are unwound
    • DNA-RNA hybrid is up to 12 pairs long

    3) termination - transcription ends and newly formed mRNA separates from DNA template

  10. protein synthesis

    Transcription factor
    • loosens histones from DNA in area to be transcribed
    • binds to promoter, a DNA sequence specifying start site of gene to be transcribed
    • mediates the binding of RNA polymerase to promoter
  11. protein synthesis

    transcription - RNA polymerase
    • enzyme that oversees synthesis of mRNA
    • unwinds DNA template
    • adds complementary RNA nucleotides on DNA template and joins them together
    • stops when it reaches termination signal
    • mRNA pulls off the DNA template, is further processed by enzymes, and enters cytosol
  12. protein synthesis

    Transcription: DNA-RNA hybrid
    at any given moment, 16-18 base pairs of DNA are unwound and the most recently made RNA is still bound to DNA
  13. protein synthesis

    • converts base sequence of nuceic acids into the amino acid sequence of proteins
    • involves mRNA, tRNAs, and rRNAs
    • mRNA attaches to a small ribosomal subunit that moves along the mRNA to the start codon
    • large ribosomal unit attaches, forming a functional ribosome
    • anticodon of a tRNA binds to its complementary codon and adds its amino acid to the forming protein
    •  chain
    • new amino acids are added by other tRNAs as ribosome moves along rRNA, until stop codon is reached
  14. role of the rough ER in protein synthesis
    • mRNA/ribosome complex is directed to rough ER by a singal-recognition particle (SRP)
    • forming protein enters the ER
    • sugar groups may be added to the protein, and its shape may be altered
    • protein is enclosed in a vesicle for transport to Golgi apparatus
  15. cytosolic protein degradation
    • nonfunctional organelle proteins are degraded by lysosomes
    • ubiquitin tags damaged or unneeded soluble proteins in cytosol; they are digested by enzymes of proteasomes
  16. extracellular materials
    • body fluids = interstitial fluid, blood plasma, and cerebrospinal fluid
    • cellular secretions = intestinal and gastric fluids, saliva, mucus, and serous fluids
    • extracellular matrix = abundant jellylike mesh containing proteins and polysaccharides in contact with cells
  17. developmental aspects of cells
    • all cells of the body contain the same DNA but are not identical
    • chemical signals in the emryo channel cells into specific development pathways by turning some genes off
    • development of specific and distinctive features in cell is called cell differentiation
    • elimination of excess, injured, or aged cells occurs through programmed rapid cell death (apoptosis) followed by phagocytosis
  18. theories of cell aging
    • wear and tear theory = little chemical insults and free radicals have cumulative effects
    • immune system disorders = autoimmune responses and progressive weakening of the immune response
    • genetic theory = cessation of mitosis and cell aging are programmed into genes.  Telomeres (strings of nucleotides on the ends of chromosomes) may determine the # of times a cell can divide
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Cells ch3
2013-02-01 14:51:28
Cell growth reproduction

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