lecture 16 - mitosis

• What does "ploidy" tell us about an organism?

  Ploidy indicates the number of unique sets of chromosomes or alleles an organism has.
• How does one parent cell give rise to two genetically identical offspring cells?

  Through the process of mitosis, where the cell divides to create two identical cells.

  
• What happens in the cell during mitosis?

  The cell distributes its duplicated chromosomes into two identical nuclei.

  
• How does the cell cycle relate to cancer?

  Mutations in genes that regulate the cell cycle can lead to uncontrolled cell division, resulting in cancer.
• What is the primary function of mitosis?

  To promote growth and tissue repair by creating two genetically identical cells.
• What are the four key ideas about mitosis?

  1. Mitosis promotes growth and tissue repair.
  2. Most specialized cells in adults cannot divide; only stem cells can.
  3. The goal is to create two cells with identical genetic information.
  4. Mitosis functions like a copy machine.
• What are stem cells capable of doing in adults?

  Stem cells can divide via mitosis to produce new cells.

  
• How often do stem cells in the epidermis replace the outer skin layer?

  Every 27 days.
• What is a chromosome made of?

  A chromosome is made of a single molecule of DNA or a pair of chromatids joined at the centromere.
• What does chromatin refer to?

  Chromatin refers to a mixture of DNA and proteins that form chromosomes.
• What happens to DNA before cell division?

  DNA is replicated, forming chromatids.
• What does homozygous mean?

  An organism has two identical alleles.
• What does heterozygous mean?

  An individual has two different alleles.
• How many base pairs and genes are present in humans?

  Humans have 81 million base pairs and 1200 to 1500 genes.
• What does "2n=46" mean for humans?

  It indicates that humans are diploid with 46 total chromosomes.
• What are the two types of chromosomes in humans?

  22 autosomes and 1 sex chromosome.

  
• What is the difference between haploid and diploid?

  • Haploid (1n): One set of chromosomes (e.g., gametes).
  • Diploid (2n): Two sets of chromosomes (e.g., somatic cells).
• How many alleles of ApoE does a person have?

  2 alleles, since humans are diploid.
• What occurs during the mitotic phase of the cell cycle?


  Mitosis distributes chromosomes into identical nuclei, followed by cytokinesis which divides the cytoplasm.
• What are the stages of mitosis?


  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
• What is a chromatid?


  A chromatid is one of the two identical halves of a chromosome.
• What is the function of the centromere?


  The centromere is the constricted region of the chromosome where replicate chromatids link together.
• How many centromeres are found in a diploid cell with three chromosome pairs during G2?


  6 centromeres.
• What characteristics do two chromosomes of an autosomal pair have in common?


  They share length, DNA sequence, alleles, loci, and centromere position.
• What are the checkpoints in the cell cycle?

  1. G1 checkpoint: Determines if the cell can proceed to the cell cycle; all cellular contents, excluding chromosomes, are duplicated
  2. S checkpoint: Each chromosome is duplicated
  3. G2 checkpoint: Ensures DNA is replicated correctly, making repairs if needed to prepare for cell division
  4. M Phase: mitosis & cytokinesis; chromosomes distributed into 2 identical nuclei, & division of cytoplasm producing 2 offspring cells
• What role do tumor suppressor genes play in cell division?


  Tumor suppressor genes detect errors in DNA replication and can initiate repair or programmed cell death.
• What is an example of a tumor suppressor protein?


  p53.
• What do proto-oncogenes do?


  Proto-oncogenes are normal genes that function to detect and respond to signals that stimulate a cell to divide.
• What happens when the function of p53 is altered?


  Cells may continue to divide even when there is an error in DNA.
• What is a mutation?


  A change in the DNA sequence that occurs during DNA replication, when cells are preparing to divide and go through cell division
• What is a DNA adduct?


  A DNA adduct is the chemical attachment of a mutagen to a nitrogenous base.
• How many mutations are typically required for a cell to become cancerous?

  At least two mutations are usually required.
• What must happen for a cell to become cancerous?


  • An accelerator on cell division must get stuck.
  • A brake on cell division must get broken.
  • This involves gain of function mutations in proto-oncogenes and loss of function mutations in tumor suppressor genes.
• Prophase


  Chromatin fibers condense and become more tightly coiled, condensing into discrete chromosomes and become visible under a light microscope.
• Metaphase


  Chromosomes align at metaphase plate (middle of the cell)
• Anaphase


  The two sister chromatids part ways, each becoming an independent chromosome. The 2 independent daughter chromosomes move towards opposite ends of the cell as their microtubules, attached to the centromeres, shorten.
• Telophase


  Two daughter nuclei form in the cells, nuclear envelopes arise from the fragments of the parent cell's nuc. env. & the chromosomes become less condensed

  Division of the cytoplasm is under way by late telophase, daughter cells appear shortly after
• Cytokinesis


  Occurs in animals cells & involves formation of cleavage furrow, which pinches the cell in two