Molecular biology

• DNA


  Deoxyribonucleic Acid
• DNA


  • Nucleotides are the basic building block
  • Pentose Sugar (Deoxyribose in DNA; Ribose in RNA), a Phosphate group, and a Nitrogenous base
  • The backbone of DNA are the phosphate group and the sugar
• Hereditary information


  Encoded in the DNA, then reproduced to all cells of the body
• Traits directed by DNA

  • Biochemical
  • Anatomical
  • Physiological
  • Behavioral (to some extent)
• Nitrogenous bases


  • Cytosine
  • Guanine
  • Adenine
  • Thymine (Uracil for RNA)
• Purines


  Adenine and Guanine
• Pyrimidines


  Cytosine, Thymine, and Uracil
• DNA and Protein were the two main chemical components of DNA that emerged as the leading candidates for the carriers of genetic material
• Transformation


  The phenomenon where a strain of bacteria is changed by a chemical component of another strain of bacteria
• Hershey and Chase's experiment found that only the DNA of the bacteriophage was transferred causing the infection of the bacteria and not the protein
• Chargaff reported that the base composition of DNA varies from one species to another
• Chargaff's rule


  • DNA base composition varies between species
  • The percentages of A and T bases are roughly equal, as are those of G and C bases
• Problem Solving: Determining DNA base percentages

  1. Given GC content

  2. Use Chargaff's rule to calculate A, T, G, C percentages
• DNA structure


  • Two antiparallel sugar phosphate backbones found at the exterior structure
  • Nitrogenous bases at the interior of the structure
• Watson and Crick deduced that DNA was a double helix based on Franklin's x-ray diffraction image
• DNA vs RNA


  • DNA is double stranded, RNA is single stranded
  • DNA has deoxyribose sugar, RNA has ribose sugar
  • DNA has thymine, RNA has uracil
  • DNA's primary function is to carry genetic information, RNA aids in protein synthesis
• RNA's primary function is to aid in the process of protein synthesis
• Rosalind Franklin produced an x-ray diffraction image of the DNA molecule unit
• Watson and Crick reasoned that there must be additional specificity of base pairing dictated by the structure of the nitrogenous bases
• DNA replication is a process in which a dividing cell generates a copy of its DNA
• Models of DNA replication

  • Conservative model
  • Semiconservative model
  • Dispersive model
• Enzyme


  Molecules that speed up the rate of chemical reactions
• Helicase


  • The "unzipping" enzyme that separates the double helix by breaking the hydrogen bonds between complementary bases
• DNA Polymerase


  • The "builder" enzyme that replicates the DNA molecules to build a new strand
• Primase


  • Enzyme that synthesizes RNA primers to initiate DNA replication
• Ligase


  • Enzyme that seals the gaps between Okazaki fragments during DNA replication
• Process of DNA replication

  1. Origins of replication

  2. Forming of replication fork

  3. Preparation stage

  4. Synthesizing of new DNA strand

  5. Antiparallel elongation

  6. Replacing RNA primers

  7. Proofreading and repairing DNA
• DNA replication in eukaryotic cells happens during the Interphase or S(Synthesis) Phase
• Semiconservative model


  Two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand. Half of the strand is conserved while the other is not. DNA replicates through this model.
• Dispersive model


  Each strand of both daughter molecules contains a mixture of an old and new synthesized DNA. Smaller fragments of original DNA are dispersed.
• Key enzymes of replication process

  • Helicase
  • DNA Polymerase
  • Primase
  • Ligase
• Helicase


  The "unzipping" enzyme that unzips/separates the double helix by breaking the hydrogen bonds between the complementary bases
• DNA Polymerase


  The "builder" enzyme that replicates the DNA molecules to build a new strand
• Primase


  The "initializer" enzyme that synthesizes short RNA sequences called "primers" to serve as a starting point for DNA synthesis
• Ligase


  The "gluer" enzyme that connects two strands of DNA together
• Process of DNA replication

  1. Origin of replication

  2. Forming of replication fork

  3. Preparation stage

  4. Synthesizing of new DNA strand

  5. Antiparallel elongation

  6. Replacing RNA primers

  7. Proofreading and correcting DNA
• Origin of replication


  Starting point of DNA replication where 2 DNA strands are separated and the opening up of replication bubbles
• Replication origin


  • Eukaryotic cell - multiple origins
  • Prokaryotic cell - one origin
• Replication fork


  A Y-shaped region where the parental strands of DNA are being unwound
• Helicase


  Enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands. Finds the origin of replication and starts the initiation process.