Molecular Biology

• The enzyme DNA polymerase plays a key role in DNA replication by adding nucleotides to the growing DNA strand.
• RNA polymerase binds to promoter sequences on DNA and transcribes genes into RNA.
• DNA replication occurs through semiconservative replication, where the two strands separate and serve as templates for new nucleotides to be added.
• DNA carries the instructions for building and maintaining an organism.
• The DNA double helix is held together by hydrogen bonds between complementary base pairs.
• Sex chromosomes


  The only non-homologous chromosomes. Y chromosome is inherited from a father and X chromosome from a mother
• Karyotype


  Display of human chromosomes. Full set of chromosomes of a cell arranged with respect to size, shape, and number
• A chromosome contains genes


  These genes contain exons and introns, exons are used to transcribe the protein
• Introns


  Non-coding parts, not useful
• Homologous chromosomes


  The maternal and paternal chromosomes. One of the two copies of a particular chromosome in a cell, each copy being derived from one of the progenitors
• Chromosome identification

  • Centromere
  • Size
  • Banding pattern
• Types of genomic instability

  • Deletion
  • Duplication
  • Inversion
  • Insertion
  • Translocation
  • Aneuploidy
• Genomic instability is a modification in chromosomes that might create cancer cells
• Genome size does not define the complexity of an organism. Coding regions are important for complexity as they transcribe into proteins
• Three types of DNA sequence are required to process eukaryotic chromosomes that can be replicated and then segregated in mitosis
• Types of DNA sequences required for eukaryotic chromosomes

  • Telomeres
  • Centromeres
• Centromere


  A DNA sequence that allows one copy of each duplicated chromosome to be pulled into the daughter cell when the cell divides
• Types of human chromosomes

  • Homologous chromosomes
  • Sex chromosomes
• Exons


  Coding sequences in genes that will be transcribed to mRNA. Important part for the sequencing of the protein
• Each human cell consists of 46 chromosomes
• Chromatin


  Consists of DNA bound to both histone and non-histone chromosomal proteins
• Histone tails cause the nucleosomes to be stacked between each other
• The human genome has approximately 30 X 10^9 nucleotide pairs
• Nucleosomes were discovered in 1974
• The 30 nm fiber is called "bead on the string". The string is the DNA and each bead is the "nucleosome core particle"
• Only a small percentage codes for proteins or functional RNA molecules
• Linker histone H1 helps to keep the nucleosomes together in a compact structure. The core of the H1 histone contains the 20 nucleotide pairs of DNA
• Chromatin


  • Consists of DNA bound to both histone and non-histone chromosomal proteins
  • In total, the chromosome is about ⅓ DNA and 2/3 protein by mass
• Nucleosomes are usually packed together in 30 nm fiber
• Replication origin, telomeres, and centromere are DNA sequences that are important for chromosomal DNA packaging
• Gene is a nucleotide sequence in the DNA molecule
• Structural organization of the nucleosome

  1. Isolation from unfolded chromatin by digestion with enzymes called nucleases

  2. The DNA linker is 80 nucleotides long

  3. Nuclease cuts the linker DNA so the nucleosome core particles can be released
• Every histone is dissociated by 4 different types of histones which create the DNA
• Structure of mitotic chromosomes


  • Three types of DNA sequence are required to process eukaryotic chromosome that can be replicated and then segregated in mitosis
  • Telomeres and centromeres are a very needed part to duplicate the chromosome
• In 1997, the structure of the nucleosome core was solved. All four histones create the DNA
• Chromosome is formed from DNA and a set of proteins
• DNA is tightly bound to an equal mass of histones which form nucleosomes
• Protein coding genes are composed of introns and exons
• Histones


  Responsible for the first and most basic level of chromosome packing = Nucleosome (protein-DNA complex)
• The human genome contains the 22 autosomes and 2 sex chromosomes