Cell, Chromosome and Mitosis

• Cells


  The basic building block of all living organisms
• Types of cells

  • Somatic cells
  • Reproductive cells
• Reproductive/sex cells

  Also called germ cells or gametes, they are haploid
• Somatic cells


  Cells in the body other than reproductive cells, they are diploid
• Groups of living organisms

  • Prokaryotes
  • Eukaryotes
• Prokaryotes


  • Cells lack a nucleus, DNA floating loosely in the liquid center, divide by simple mitosis
• Eukaryotes


  • Have a well-defined nucleus to house and protect DNA, divide by mitosis for somatic cells and meiosis for sexual reproduction

  
• Prokaryotic cell


  Unicellular organism with a relatively simple cell structure
• Eukaryotic cell


  Has a compartmentalized cell structure with components bounded by intracellular membranes, can be unicellular or multicellular

  
• Similarities between prokaryotic and eukaryotic cells

  • Contain genetic material
  • Contain ribosomes
  • Have plasma membranes
  • Have cytoplasm

  
• Eukaryotic cell


  Has a nuclear envelope that surrounds the genetic material and separates the DNA from other cellular contents

  
• Prokaryotic cell


  Genetic material is in close contact with other components of the cell, which has important consequences for gene control
• Eukaryotic DNA

  Closely associated with histone proteins to form tightly packed chromosomes, the complex of DNA and histone protein is called chromatin

  
• Prokaryotic chromosome


  Single, circular molecule of DNA

  
• Eukaryotic chromosomes


  Multiple, usually linear DNA molecules

  
• Eukaryotic cells require mechanisms to ensure that a copy of each chromosome is faithfully transmitted to each new cell

  
• Cell reproduction

  1. Genetic information must be copied

  2. Copies of genetic information must be separated

  3. The cell must divide

  
• Prokaryotic cell reproduction

  1. Circular chromosome replicates and cell divides in binary fission

  2. Replication begins at origin of replication

  3. Two newly replicated chromosomes move to opposite ends

  4. New cell wall forms between two chromosomes, producing two cells

  
• Eukaryotic cell reproduction

  1. Requires DNA replication, copy separation, and division of cytoplasm

  2. Presence of multiple DNA molecules requires a more complex mechanism to ensure each new cell gets one copy of each molecule

  
• Eukaryotic chromosomes


  Separated from cytoplasm by nuclear envelope, have highly organized internal scaffolding called nuclear matrix

  
• Eukaryotic cells

  Usually have two sets of chromosomes, one set inherited from each parent, constituting homologous pairs

  
• Homologous chromosomes


  Usually alike in structure and size, each carrying genetic information for the same set of hereditary characteristics

  
• Alleles


  Different versions of the same gene
• Chromosome sets in cells

  • Haploid
  • Diploid
  • Polyploid

  
• Eukaryotic chromosomes


  • Large and complex, each consisting of a single molecule of highly folded and condensed DNA

  
• Centromere


  Attachment point for spindle microtubules, appears as constricted region
• Telomeres


  The natural ends, tips, of a linear chromosome, protect and stabilize the chromosome ends
• Origins of replication


  Sites where DNA synthesis begins, not easily observed under microscope

  
• Sister chromatids


  The two initially identical copies of a replicated chromosome, held together at the centromere

  
• Chromatin


  Substance in the cell nucleus composed primarily of DNA and proteins

  
• Euchromatin


  Undergoes normal process of condensation and decondensation in the cell cycle
• Heterochromatin

  Remains in a highly condensed state throughout the cell cycle, even during interphase

  
• Nucleosome


  The repeating core of protein and DNA produced by digestion with nuclease enzyme, the simplest level of chromatin structure

  
• Microtubules


  Composed of subunits of the protein tubulin, undergo repeated cycles of growth and shrinkage during prometaphase
• Centrosome


  Cellular structure involved in cell division, contains paired barrel-shaped organelles called centrioles
• Cell division is essential for growth, development, and injury repair
• Types of cell division

  • Mitosis
  • Meiosis
• Cell cycle


  The life story of a cell, the stages through which it passes from one division to the next
• Cell cycle

  1. New cell cycle begins after a cell has divided and produced two new cells

  2. Each new cell metabolizes, grows, and develops

  3. At the end of its cycle, the cell divides to produce two cells
• Cell cycle checkpoints


  Regulate progression through the cell cycle, allowing or prohibiting the cell's progression to the next stage