CELL DIVISION L2 PT. 1

• The cell cycle is an orderly sequence of events that describes the stage of a cell's life from the division of a single parent cell to the production of two new daughter cells. The mechanisms involved in the cell cycle are highly regulated
• Mitosis is part of the cell cycle that results in identical daughter nuclei that are also genetically identical to the original parent nucleus. In mitosis, both the parent and the daughter nuclei are at the same ploidy level - diploid for most plants and animals.
• Meiosis employs many of the same mechanisms as mitosis. However, the starting nucleus is always diploid and the nuclei that result at the end of a meiotic cell division are haploid.
• Mitosis

  • number of division : 1
  • number of daughter cells : 2
  • genetically identical : YES
  • chromosomes : same as parent (diploid)
  • where : somatic cells (body cells)
  • when : throughout life
  • role : growth and repair
• Meiosis

  • number of division : 2
  • number of daughter cells : 4
  • genetically identical : NO
  • chromosomes : half of parent (haploid)
  • where : sex cells (reproductive cells)
  • when : at sexual maturity
  • role : sexual reproduction
• MITOSIS

  The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and cell division that produce two identical (clone) cells
• The cell cycle has two major phases: the INTERPHASE and the MITOTIC PHASE

  • during interphase, the cell grows and DNA is replicated
  • during the mitotic phase, the replicated DNA and cytoplasmic contents are separated, and the cell divides.
• During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from the interphase into the mitotic phase, many internal and external conditions must be met. The three stages of interphase are called

  • G1 (Gap 1)
  • S (Synthesis)
  • G2 (Gap 2)
• The eukaryotic cell cycle is divided into 2 major phases:

  Interphase

  • Divided into 3 stages -> G1, G2, and S
  • DNA uncondensed

  Mitotic phase

  • 4 stages + cytokinesis
  • prophase, metaphase, anaphase, telophase, cytokinesis (PMAT)
  • nuclear division and division of cytoplasm
  • DNA condensed
• Three stages of interphase

  1. Gap 1 (G1) Phase

  • cell grows in size
  • organelles are replicated

  2. synthesis (S) Phase

  • replication of DNA
  • synthesis of proteins associated with DNA

  3. Gap 2 (G2) Phase

  • synthesis of proteins associated with mitosis
• Three stages of interphase

  1. Gap 1 (G1) Phase

  • cell grows in size
  • organelles are replicated

  2. synthesis (S) Phase

  • replication of DNA
  • synthesis of proteins associated with DNA

  3. Gap 2 (G2) Phase

  • synthesis of proteins associated with mitosis
• Cyclins regulate the cell cycle only when they are tightly bound to CDKs. To be fully active, the CDK / cyclin complex must also be phosphorylated in specific locations. Like all kinases, CDKs are enzymes (kinases) that phosphorylate other proteins.
• Cyclin-Dependent Kinase (CDK) - a family of protein kinase that are involved in regulating transcription, mRNA processing, and the differentiation of nerve cells.
• Cyclin-Dependent Kinase (CDK) - a family of protein kinase that are involved in regulating transcription, mRNA processing, and the differentiation of nerve cells.
• Cyclins - a group of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes.
• Karyokinesis, also known as mitosis, is divided into a series of phases - prophase, prometaphase, metaphase, anaphase, and telophase - that result in the division of the cell nucleus.
• STAGES OF THE MITOTIC PHASE

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
• Prophase

  • chromosomes condense and become visible
  • spindle fibers emerge from centrosomes (spindle fibers are specialized microtubules radiating out from centrioles)
  • nuclear envelope breaks down
  • nucleolus disappears
  • chromosomes are captured by spindle
• Prometaphase

  • chromosomes continue to condense
  • kinetochores appear at the centromeres
  • mitotic spindle microtubules attach to kinetochores
  • centrosomes move toward opposite poles
• Metaphase

  • Mitotic spindle is fully developed, centrosomes are at opposite poles of the cell
  • Chromosomes are lined up at the metaphase phase (equatorial plane) midway between the two poles of the cell
  • each sister chromatid is attached to a spindle fiber originating from opposite poles
  • the sister chromatids are still tightly attached to each other by cohesin proteins. At this time, the chromosomes are maximally condensed
• Anaphase

  • sister chromatids separate
  • spindle fibers shorten
  • spindle fibers attached to kinetochores shorten and pull chromatids toward the poles
  • free spindle fibers lengthen and push the poles of the cell apart
  • cohesin proteins binding the sister chromatids together break down
  • sister chromatids (now called chromosomes) are pulled toward opposite poles
  • non-kinetochore spindle fibers lengthen, elongating the cell
• Telophase

  • spindle fibers disintegrate
  • nuclear envelopes form around both groups of chromosomes
  • chromosomes revert to their extended state
  • cytokinesis occurs, enclosing each daughter nucleus into a separate cell
  • chromosomes arrive at opposite poles and begin to decondense
  • nuclear envelope material surrounds each set of chromosomes
  • the mitotic spindle breaks down
• Cytokinesis or cell motion is the second main stage of the mitotic phase during which cell division is completed via the physical separation of the cytoplasm components into two daughter cells

  • Animal cells undergo cytokinesis through the formation of a cleavage furrow. A ring of microtubules contracts, pinching the cell in half.
  • Plant cell undergo cytokinesis by forming a cell plate, between the two daughter nuclei
• uncontrolled mitosis

  • cancer caused by uncontrolled cell division. cancer cells form disorganized clumps are called tumors. tumors can be benign or malignant
  • does not follow proper regeneration/division
  • cancer does not mature/die
• benign tumor remain clustered and can be removed
• malignant tumors metastasize, or break away, and can form more tumors.
• oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell
• oncology is the study of cancer
• cell checkpoints are times when the cell is supposed to stop and check itself, these are DISABLED in cancer cells.
• tumor suppressor genes - are normal genes that slow down cell division repair, DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). when tumor suppressor genes don't work properly, cells can grow out of control, which can lead to cancer