DNA: the genetic material structure & replication

• DNA structure

  DNA is a nucleic acid composed of nucleotides
• nucleotides of DNA

  5-carbon sugar of nucleotides called deoxyribose, an attached phosphate group, the nitrogenous bases, and a free hydroxyl group attached at the 3 carbon of sugar
• Is DNA positively or negatively charged?

  Negatively charge because the phosphate groups are highly electronegative
• Pyrimidines

  2 nitrogen rings being cytosine, thymine, and uracil
• Purines

  1 nitrogen ring being adenine and guanine
• phosphodiester bond


  bond between adjacent nucleotides formed between the phosphate group of one nucleotide and the 3' -OH of the next nucleotide. The chain of nucleotides has a 5'-to3' orientation
• Double helix


  2 strands that are polymers of nucleotides arranged as a double helix, wrapped around 1 axis, antiparallel strands
• Complementarity of bases

  A forms 2 hydrogen bonds with T and G forms 3 hydrogen bonds with C. Gives consistent diameter
• DNA replication


  Requires 3 things; copying something which is our parental DNA molecule, something to do the copying which is our enzymes, building blocks to make copy which are our nucleotides triphosphate
• Stages of DNA replication

  initiation, elongation, termination
• Initiation of DNA replication


  ( 1 )When the replication begins
• Elongation of DNA replication

  ( 2 )When new strands of DNA are synthesized by DNA polymerase
• Termination of DNA replication


  ( 3 ) Replication is terminated
• Template strand


  The one we are copying
• DNA polymerase


  Matches existing DNA bases with complementary nucleotides and links them that all have several common feature
• 3 common features of DNA polymerase

  Adding new bases to 3' and of existing strands, synthesize in 5'-to-3' direction, require a primer of RNA
• Antiparellel


  one strand goes 3' to 5' the other goes 5' to 3
• Semidiscontinous DNA synthesis

  DNA polymerase can synthesize one in 1 direction, creating a leading strand and a lagging strand
• Leading strand of DNA

  Synthesized continuously form initial primer 5' to 3'. Just one RNA primer
• Lagging strand of DNA

  synthesized discontinuously with multiple priming events. Multiple RNA primers
• RNA primers


  a short strand of RNA, made by DNA primase, that is used to elongate a strand of DNA during DNA replication
• Okazaki fragments


  DNA fragments on the lagging strand
• The replication fork


  The partial opening of helix forming a replication fork. Later RNA will be removed and replaced with DNA
• old strand, new strand

  Semiconservative replication
• Leading strand synthesis


  Single priming event, strand extend by DNA pol 111, processivity; subunit that forms "sliding clamp" to keep it attached to DNA
• Lagging strand synthesis

  Discontinuous synthesis, DNA pol III, RNA primer made by primase for each Okazaki fragment. All RNA primers removed and replaced by DNA, DNA pol I

  - Backbone sealed by DNA ligase

  •Termination occurs at specific site - DNA gyrase unlinks 2 copies
• Temolemeres


  Specialized structures found on the ends of eukaryotic chromosomes, protect ends of chromosomes from nucleuses and maintain the integrity of linear chromosomes. Gradual shortening of chromosomes with each round of cell division - unable to replicate last section of lagging strand
• Telomeres maintenance

  Composed of short repeated sequence of DNA, telomerase; developmentally regulated and cancer cells generally show activation of telomerase
• Telomerase

  Enzyme makes telomere section of lagging strand using an internal RNA template ( not the DNA itself ). The leading strand can be replicated to the end
• DNA repair #1

  Errors due to replication. DNA polymerases have proofreading ability

  Mutagens - any agent that increases the number of mutations above background level; Radiation and chemicals.

  Importance of DNA repair is indicated by the multiplicity of repair systems that have been discovered
• 2 different kinds of DNA repair

  Specific repair; targets a single kind of lesion in DNA and repairs only that damage. And nonspecific repair; uses a single mechanism to repair multiple kinds of lesions in DNA
• Photo repair


  Specific repair mechanism for one particular form of damage caused by UV light. Thymine dimmers and photolyase
• Excision repair


  nonspecific repair, damaged region is removed and replaced by DNA synthesis in 3 steps; recognition f damage, removal of the damaged region, and resynthesis using wthe information on then damaged strand as a template
• After Morgan and fellow scientists developed the Chromosomal Theory of inheritance, the search was on for the chemical mechanism of inheritance. What are the two components of the chromosome?

  DNA and protein
• From initial logic which component would be the most likely candidate fro the genetic material?

  Protein was thought to be the genetic material because of its diversity and specificity of function.
• What did Frederick Griffith experiments show

  Transformation
• Define transformation


  the uptake of DNA directly from the environment
• What did the experiments of Oswald Avery, Colin Macleod and Marlyn Mccarty show?

  That DNA is the substance transferred between cells by transformation and indicated that the genetic material ( at least in their bacterial species ) is DNA.
• What did the experiments of Alfred Hershey and Martha Chase show?

  Showed/ proved that DNA, and not protein, constitute d the genetic information that viruses inject into bacteria
• The bonding within the molecule

  A phosphodiester bond