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3. Cells: The Living Units: Part D. Cell Cycle. Defines changes from formation of the cell until it reproduces Includes: Interphase Cell division ( mitotic phase). G 1 checkpoint (restriction point). S Growth and DNA synthesis. G 2 Growth and final preparations for division. G 1

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  1. 3 Cells: The Living Units: Part D

  2. Cell Cycle • Defines changes from formation of the cell until it reproduces • Includes: • Interphase • Cell division (mitotic phase)

  3. G1 checkpoint (restriction point) S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M G2 checkpoint Figure 3.31

  4. Nuclear envelope DNA Transcription RNA Processing Pre-mRNA mRNA Nuclear pores Ribosome Translation Polypeptide Figure 3.34

  5. Transcription • Transfers DNA gene base sequence to a complementary base sequence of an mRNA

  6. Translation • Converts base sequence of nucleic acids into the amino acid sequence of proteins • Involves mRNAs, tRNAs, and rRNAs

  7. Genetic Code • Each three-base sequence on DNA is represented by a codon • Codon—complementary three-base sequence on mRNA

  8. SECOND BASE U C A G U UUU UCU UAU UGU Tyr Cys Phe C UUC UCC UAC UGC U Ser A UUA UCA UAA Stop UGA Stop Leu G UUG UCG UAG Stop UGG Trp U CUU CCU CAU CGU His C CUC CCC CAC CGC C Leu Pro Arg A CUA CCA CAA CGA Gln G CUG CCG CAG CGG U AUU ACU AAU AGU Asn Ser C Ile AUC ACC AAC AGC A Thr A AUA ACA AAA AGA Lys Arg Met or G AUG ACG AAG AGG Start U GUU GCU GAU GGU Asp C GUC GCC GAC GGC G Val Ala Gly A GUA GCA GAA GGA Glu G GUG GCG GAG GGG Figure 3.36

  9. Mitosis vs. Meiosis • Mitosis for the regeneration and replacement of dead and dying cells with 2 new identical daughters which are in essence clones of a parent stem cell. • Daughter cells will differentiate into functional cell for the replacement of the dead cell(s) • Meiosis different from mitosis in that it serves to produce 4 sex cells (sperm and ova) call gametes with half the number of genes found in other body cells.

  10. Developmental Aspects of Cells • All cells of the body contain the same DNA but are not identical • Chemical signals in the embryo channel cells into specific developmental pathways by turning some genes off • Development of specific and distinctive features in cells is called cell differentiation • Elimination of excess, injured, or aged cells occurs through programmed rapid cell death (apoptosis) followed by phagocytosis

  11. 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 number of times a cell can divide.

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