cell reproduction and differentiation

• the size of a cell is limited by the relationship of the cell's outer surface to its volume, or its surface area to volume ratio
• Plasma membrane


  structure all nutrients + waste products must pass
• small substances can transport materials much more efficiently than large cells
• cellular communication is more efficient in smaller cells
• When a cell is too large

  less efficient at moving nutrients/waste in the cell, increase in demand on its own DNA, Cytoskeleton less efficient
• cell size is important because materials + nutrients, oxygen, + waste (CO2) must pass into + out of the cell's surface
• Cells divide for:

  growth, repair/maintenance, reproduction
• once a cell becomes too large, a process called cell division begins
• Cell division

  when a single cell divides into two new daughter cells
• Process of cell division is called the cell cycle
• when a cell reaches it size limit, it must either stop growing or divide
• Interphase is the stage where:

  cell grows, carries out cellular functions, replicates/makes copies of its DNA
• Interphase is split into 3 sections:

  G1, S, G2
• Interphase makes up 90% of the cell cycle
• Proteins regulate the progress of cell division at certain points, called checkpoints; feedback signals from the cell can trigger proteins to initiate next phase or halt the cycle
• checkpoints stop the process if something goes wrong and can protect against duplicating DNA damage
• Gap 0 is for nondividing cells (check point). Cells not going to divide will exit the cell cycle
• checkpoints

  where proteins regulate the progress of cell division at certain points
• quality control checkpoints

  checkpoints that stop the process if things go wrong; protect against duplicating DNA damage
• Cancer

  uncontrolled growth and division of cells; a failure in the regulation of the cycle
• When unchecked, cancer cells can kill an organism by crowding normal cells and causing a loss of tissue function 
• Cancer cells spend less time in interphase than normal cells do
• causes of cancer

  mutations, environmental factors, carcinogens
• Apoptosis occurs during development, in cells that are damaged, and in cells that may lead to cancerous growths
• Apoptosis


  programmed cell death; cell shrinks and shrivels
• Eukaryotic cells reproduce through the Cell Cycle, Prokaryotic cells reproduce through Binary Fission
• Binary Fission

  Prokaryotes divide into 2 identical organisms (chromosomes duplicated, grow, and divide into 2 new cells)
• Chromosomes

  a structure in the nucleus that contains DNA
• each half of the chromosomes is called a sister chromatid, which contain identical copies of DNA
• the center of a chromosome where the sister chromatids meet are called the centromere 
• chromatin


  relaxed forms of DNA in the nucleus
• chromatin wraps around histone protein to maintain chromosome shape
• Mitosis


  the stage in the cell cycle where the cell's nucleus and nuclear material divide
• Mitosis is split into 4 sections:

  Prophase, Metaphase, Anaphase, Telophase
• Prophase


  Chromosomes form, nucleus expands
• Metaphase


  chromosomes line up in center of the cell
• Anaphase


  chromosomes split, sister chromatids go to opposite sides of the cell
• Telophase


  two new nuclei form around sister chromatids, cell not yet split in two
• Cytokinesis


  cells officially split into 2 new cells
• homologous chromosomes


  pairs of autosomes that have same genes in same order, but small differences in the DNA