DNA Structure

• Nucleotides


  Basic units of DNA molecule, composed of a 5-carbon sugar (deoxyribose for DNA or ribose for RNA), a phosphate, and a nitrogenous base

  
• Where is the nitrogenous base attached to?


  1' carbon of sugar

  
• Where is the phosphate group attached to?

  5' carbon of sugar

  
• nitrogenous bases


  Adenine, Thymine (uracil in RNA), Cytosine, Guanine

  
• Pyrimidines


  cytosine, thymine, uracil

  
• Purines


  Adenine and Guanine

  
• complementary base pairing


  Hydrogen bonding between particular bases of nucleotides, purines always pair with pyrimidines

  
• complementary base pairs


  A-T G-C

  
• How many bonds between guanine and cytosine?

  3 hydrogen bonds (wider and stronger due to more hydrogen bonds)

  
• How many bonds between adenine and thymine?

  2 hydrogen bonds (tighter and weaker due to less hydrogen bonds)

  
• Why does adenine always pair with thymine and guanine with cytosine in DNA?

  because adenine has a compatible chemical structure with thymine, so they can form a complete bond, same reason for guanine and cytosine

  
• What would happen if adenine bonded with cytosine?

  the strand would be too wide due to a higher amount of hydrogen bonds
• What would happen if guanine bonded with thymine?

  not enough hydrogen bonds, since thymine can have 2 hydrogen bonds, while guanine can provide 3 hydrogen bonds
• Double helix structure


  The structure of DNA

  
• Are the strands complementary?

  yes, because the other strand can be found out if one strand is given
• antiparallel


  Parallel, but running in opposite directions. The 5' end of one strand of DNA aligns with the 3' end of the other strand in a double-helix.

  
• How is DNA antiparallel?

  they are not identical and they run in opposite directions (one end runs from 5' to 3' while the other runs from 3' to 5')

  
• 5' end


  the end of a strand containing a 5' phosphate group

  
• 3' end


  the end of a strand containing a sugar

  
• DNA is written as the

  5' to 3
• 5' to 3' direction


  starts with phosphate and ends with sugar, which allows it to be decoded by technology for DNA replication (antiparallel strand is 3' to 5')

  
• difference between RNA and DNA

  RNA replaces Thymine with Uracil

  
• difference between a gene and allele


  a gene is a stretch of DNA that determines a trait and an allele is an alternate form of a gene