Lecture 1 - Cell Division

• Humans begin life as one cell, and grow into about 200 trillion cells through cell division
• What is the purpose of cell division?

  • growth
  • development
  • repair
  • Asexual reproduction
  • Sexual reproduction
• How much cell division is occuring in us (adult humans)?

  Cell division occurs at a high rate in some cell types, and rarely in others
• A crucial function of most cell division is the distribution of identical genetic material to the two daughter cells.
• Cell division is remarkably accurate in passing DNA from one generation to the next
• The life of a cell?

  • Divide - produce identical daughter cells
  • Differentiate - cells stop dividing to specialize in structure or function
  • Apoptosis - programed cell death
• What is the purpose of Apoptosis?

  Eliminates unnecessary cells, removes damaged or unhealthy cells
• A fertilized egg, or zygote, divides by mitosis. The fetus grows and develops into a mature adult consisting of countless cells with identical DNA
• Each mature individual produces sex cells by another form of cell division called meiosis. Sex cells combine at fertilization.
• DNA = deoxyribonucleic acid, a molecule that carries genetic information
• DNA is found in every cell in an organism‘s body
• DNA must be replicated and passed to new cells during division.
• DNA can take on various forms inside the cell.
• Interphase: The cell grows in preparation for cell division, the chromosomes are duplicated, with the DNA copied precisely.
• Mitosis: The chromosome copies are separated from each other and moved to opposite ends of the cell.
• Cytokinesis: The Cell divides into two daughter cells, genetically identical to each other and to the parent cell.
• How does one parent cell give rise to two genetically identical daughter cells?

  • Duplicate DNA
  • Separate DNA into two nuclei
  • Two Daughter cells
• When a cell divides, it must first duplicate its genome
• Genome: All the DNA in a cell
• Chromosomes: One long DNA strand packaged tightly
• Prokaryotic cells: Single DNA molecule
• Eukaryotic cells: Commonly multiple DNA
• The DNA molecule of a chromosome carries several hundred to a few thousand genes
• Homologous chromosomes have the same genes, but the genes may be mutated compared to the other chromosome.
• Each version of a chromosome is called an allele.
• The location of a gene on a chromosome is called the locus.
• Cells that have all the pairs of chromosomes are called diploid.
• Cells that have only 1 set (no pairs) of chromosomes are called haploids.
• Duplicated chromosomes can still have 1 chromosome, but with 2 chromatids.
• Somatic cells (nonreproductive cells) are diploids.
• Gametes (reproductive cells) are haploid
• Diplods have 2 sets of chromosomes: 46 chromosomes
• Haploids have half as many chromosomes as somatic cells: 23 chromosomes.
• Examples of somatic cells: Neurons, skin cells
• Examples of Gametes: Egg cells, Sperm cells.
• Karyotypes are human chromosomes. They are used to determine the sex of an individual.
• What is interphase?

  Cell growth and copying of chromosomes to prepare for cell division
• Mitosis is a type of cell division that promotes growth and tissue repair/renewal.
• Mitosis creates two cells with identical genetic information.
• What are the 3 intervals in interphase?

  • G1 Phase (Gap 1) - Cell growth and prep for DNA replication
  • S Phase (synthesis) - Replication of cell’s DNA molecules
  • G2 Phase (Gap 2) - Additional growth and prep for division