anat and phys lecture 4

mitosis

the division of somatic cells (body cells) that have 2 copies of genetic material from 2 sources (2N 2n)

• produces daughter cells that are identical to the mother cell

Stages of Meiosis

• Prophase: nucleus + nuclear envelope disappear, chromatin condense and bind to scaffold molecule to become chromosome, cytoskeleton is repurposed for cell division where centrosomes have extended microtubules that act as spindle fibers where some of the spindles are bound to the kinetochores of the chromosome

• Metaphase: sister chromatids are lined up at the metaphase plate by the kinetochore spindles

• Anaphase: the shortening of the spindle fibers causes the sister chromatids to separate and to migrate to opposite poles of the cell

• Telophase: nucleus + nuclear envelope reform, chromosomes decondenses to revert back to chromatin

• Cytokinesis: peripheral microfilaments pinch at the cleavage furrow to squeeze/divide the cytoplasm to produce 2N 2n somatic cells

meiosis

two consecutive cell division that produces 4 haploid (1N 1n) cells (gametes) that are genetically unique from the diploid mother cell

Stages of Meiosis

• Prophase I: nucleus + nuclear envelope disappear, chromatin condenses to form chromosomes, cytoskeleton is repurposed for cell division (centrosomes migrate to opposite poles and fibers attach onto kinetochores)

  • synapsis: the process where homologous pairs of chromosomes come together and tightly align

  • crossing over: the exchange of maternal and paternal genetic material

  • chiasmata point: the point where crossing over occurs

• Metaphase I: homologous chromosome pairs are lined at the metaphase plate by kinetochore spindles

• Anaphase I: kinetochores shortening the fibers causes the maternal chromosomes and paternal chromosomes to separate at the chiasmata point and migrate to opposite poles of the cell, as a result carrying each others genetic material

• Telophase I: nuclear + nuclear envelope reform, chromosomes convert back to chromatin

• Cytokinesis: peripheral microfilament pinch at the cleavage furrow to squeeze/divide the cytoplasm in between the two new nuclei to produce two 2N 1n cells

Meiosis II: same process as mitosis I (in anaphase sister chromatids arbut DNA is not replicated before to produce four 1N 1n daughter cells

consequence if in anaphase I homologous chromosome pairs are separated at centromere and not the chiasmata point

ends up with 3 chromosomes in the first cell and 1 chromosome in the other cell

• cell with 3 chromosomes produces gametes with 2 copies and 1 copy chromosome

• cell with 1 chromosome will produce gametes with 1 copy and 0 chromosome

  • 50% of the eggs are either going to have no copies of the chromosome (null mutation) or will have 3 copies when they get fertilized (trisomy)

Difference between mitosis and meiosis

mitosis: maternal chromosomes and paternal chromosomes act independently from each other

meiosis: maternal chromosomes and paternal chromosomes form a molecular affiliation

neoplasia

making new cells

• when a new cell has different genetic characteristics than it is supposed to have and those characteristics alter the functionality/physiology of the cell it can become cancerous

dystrophy

abnormality in cell size

• atrophic: cell size is too small

• hypertrophy: cell size is too large

hyperplastic

too many cells

aplasia

too little amount of cells

consequence of genetically abnormal cell

a tumor: a population of abnormally growing cells

characteristics of tumor

• benign (not cancer): tumor grows very slowly, does not invade other tissue, cells have most of the characteristics that other cells have

• malignant (cancer): tumor is growing very rapidly, displaces neighboring cells (no contact inhibition), able to metastasis, is poorly differentiated

  • metastasis: the spread of tumor due to a tumor cell being displaced to another part of the body and that tumor cell creating another tumor at the new location

Two tissue types that are capable of dividing

epithelial and connective tissue

• muscle tissue and nervous tissue can’t divide

cancer based on origin

origin on epithelial tissue → carcinomas

origin on connective tissue → sarcomas

How is cancer formed

neoplastic transformation: the conversion of a normal cell into a cell with abnormal/uncontrolled growth and division

• change in DNA might lead to cancer: when new cells are created and DNA is replicated errors in DNA can occur → some errors are not edited out → concerned about the DNA sequences related to cell size, growth, replication rate, and repair (tumor repressor genes)

• proto-oncogenes: DNA sequences that are responsible for cell size and number

• when proto-oncogenes and tumor suppressor genes are damaged it could result in cancer (no tumor suppressor genes → damage will accumulate)