Chapter 9 BSC 1005 Mr Tidwell Cells reproduce by cell division in which a parent cell normally gives rise to 2 daughter cells o Each daughter receives a complete set of hereditary information from the parent cell and about half its cytoplasm The hereditary information is usually identical with that of the parent cell The hereditary information in all cells is usually based on the blueprint of deoxyribonucleic acid DNA o Each DNA molecule consists of a long chain like a spiral staircase composed of smaller subunits called nucleotides o Each nucleotide consists of a phosphate a sugar deoxyribose and one of four nitrogen containing bases adenine A thymine T guanine G or cytosine C o The subunits of inheritance called genes are segments of DNA The cell division of eukaryotic cells by which organisms grow or increase in number is called mitotic cell division o After cell division the daughter cells may differentiate and become specialized o The repeating pattern of divide grow and differentiate then divide again is for specific functions called the Cell Cycle Most cellular organisms have 3 categories of cells o Stem cells Stem cells differentiate into a variety of cell types have the important characteristics of self renewal and to Stem cells self renew because they retain the ability to divide perhaps for the entire life of the organism Stem cells include most of the daughter cells formed by the first few cell divisions of a fertilized egg as well as a few adult cells o Some stem cells in early embryos can produce any of the specialized cell types of the entire body When a stem cell divides usually one daughter remains a stem cell and the other differentiates o Other cells capable of dividing o Permanently differentiated cells Permanently differentiated cells differentiate and never divide again Example brain cells heart cells Sexual reproduction fusion of gametes from two adults in eukaryotic organisms occurs when offspring are produced by the o Cells in the adult s reproductive system undergo a specialized type of cell division called meiotic cell division Page 1 of 6 Chapter 9 BSC 1005 Mr Tidwell o Products of meiotic cell division have exactly the genetic information of their parent cells and reestablish the full genetic complement when they fuse Reproduction in which offspring are formed from a single parent without having a sperm fertilize an egg is called asexual reproduction The prokaryotic cell cycle consists of a relatively long period of growth followed by binary fission splitting in two are longer and have more DNA than prokaryotic Eukaryotic chromosomes chromosomes DNA o Human chromosomes are 10 to 80 times longer and have 10 to 50 times more o Each human chromosome contains a single DNA double helix about 50 million to 250 million nucleotides long Genes are segments of the DNA of a chromosome o Genes are sequences of DNA from hundreds to thousands of nucleotides long o Each gene occupies a specific place or locus plural loci on the chromosome o The largest human chromosome chromosome 1 has 3000 genes o The smallest human chromosome chromosome 22 has 600 genes Every chromosome has specialized regions that are crucial to its structure and function o 2 Telomeres o 1 Centromere The two ends of a chromosome consist of repeated nucleotide sequences called telomeres which are essential for chromosome stability It temporarily holds two daughter DNA double helices together after DNA replication It is the attachment site for microtubules that move the chromosomes during cell division At the end of DNA replication a duplicated chromosome consists of two identical DNA double helices called sister chromatids which are attached to each other at the centromere Eukaryotic chromosomes usually occur in pairs with similar genetic information o When an entire set of stained chromosomes from a single cell are examined its Karyotype we see that most cells contain pairs of chromosomes o Both members of each pair are the same length and shape and have the same staining pattern o These similarities occur because each chromosome in a pair carries the same genes arranged in the same order Page 2 of 6 Chapter 9 BSC 1005 Mr Tidwell Chromosomes that contain the same genes are called Homologous chromosomes or Homologues Cells with pairs of homologous chromosomes are called Diploid which means double Changes in the nucleotide sequence in DNA of one homologous chromosome may not occur in the other in the pair These changes are called mutations and make one homologue different genetically than the other Mutations in DNA are the ultimate source of genetic variability Most mutations are neutral or harmful Mutations give rise to new alleles alternative gene forms that may produce differences in structure or function These changes in nucleotide sequence can be passed from generation to generation In some cases a single mutation can have negative consequences for the whole organism In some cases the changes may be beneficial to the organism carrying it A human cell has 23 pairs of chromosomes for a total of 46 o 22 out of the 23 pairs are called autosomes Autosomes paired in diploid cells of both sexes have similar appearance and similar DNA sequences and are o The 23rd pairs are called sex chromosomes and are different in the male and female The female has two X chromosomes that usually look similar The male has an X and a Y chromosome that appear very different However in a male the X and Y chromosomes act as a pair during meiotic cell division Not all cells have paired chromosomes o Cells in the ovaries and testes undergo meiotic division and produce gametes that only have one member of each chromosome pair o These kinds of cells are Haploid o A haploid has the number of chromosomes of a diploid cell When a sperm fertilizes an egg fusion of the two haploid cells produces a diploid cell with two copies of each type of chromosome o The copy from the egg is the maternal chromosome o The copy from the sperm is the paternal chromosome Interphase is a time for acquisition of nutrients growth and chromosome duplication o Interphase has three phases Page 3 of 6 Chapter 9 BSC 1005 Mr Tidwell G1 growth phase 1 is a time for acquisition of nutrients growth to proper size differentiates decides to divide or not S synthesis phase chromosome is replicated for division of the cell into daughter cells G2 growth phase 2 include completion of cell growth and preparation is characterized by DNA synthesis during which