1.5 Nucleic acids and their functions

• Nucleotides

  A nucleotide consists of a pentose sugar bonded to phosphate and a nitrogenous base.

  A nucleoside is a pentose sugar joined to a nitrogenous base: adenosine is composed of ribose bonded to adenine. This nucleoside is a component of ATP (adenosine triphosphate).

  
• DNA is an abbreviation for deoxyribonucleic acid. In DNA the sugar is deoxyribose, and the base is one of these four: adenine, thymine, guanine or cytosine.
• RNA is an abbreviation for ribonucleic acid. In RNA, the sugar is ribose, and the base is one of these four: adenine, uracil, guanine or cytosine.
• ATP is an abbreviation for adenosine triphosphate. In ATP, the sugar is ribose, the base is adenine and there are three phosphate groups.
• What type of reaction forms ATP?

  Endergonic reaction
• What are the components combined to form ATP?

  ADP and phosphate (Pi)
• Where does the energy to form ATP come from?

  Exergonic reactions in cellular respiration
• What type of reaction is involved in forming ATP?

  Condensation reaction
• What is eliminated when ATP is formed?

  Water
• What enzyme catalyzes the formation of ATP?

  ATP synthetase
• What happens during the hydrolysis of ATP?

  ATP is converted to ADP and Pi
• What enzyme catalyzes the hydrolysis of ATP?

  ATPase
• How much energy is released when ATP is converted to ADP and Pi?

  30.6 kJmol-1
• What does it mean that ATP is the 'universal energy currency'?

  It provides energy to all reactions in all cells
• Why is ATP important to organisms?

  It releases energy in small usable quantities
• How is energy released from ATP?

  By breaking the terminal phosphate bond
• Why can ATP be easily transported in cells?

  It is relatively small and soluble
• When is ATP synthesized?

  When energy is available
• What are the uses of energy derived from ATP in cells?

  • Active transport
  • Protein synthesis
  • Cell division
  • Muscle contraction
• What are the two main categories of bases in nucleic acids?

  Purines and pyrimidines
• Which bases are classified as purines?

  Guanine and adenine
• What structural characteristic do purine bases have?

  They have a double ring structure
• Which bases are classified as pyrimidines?

  Thymine, cytosine, and uracil
• What structural characteristic do pyrimidine bases have?

  They have a single ring structure
• Who investigated the proportions of bases in DNA?

  Edwin Chargaff
• What did Chargaff's results demonstrate about purines and pyrimidines?

  The percentage of purines equals that of pyrimidines
• According to Chargaff, what is the relationship between adenine and thymine?

  The percentage of adenine equals that of thymine
• According to Chargaff, what is the relationship between guanine and cytosine?

  The percentage of guanine equals that of cytosine
• How many hydrogen bonds link guanine and cytosine?

  Three hydrogen bonds
• How many hydrogen bonds link adenine and thymine?

  Two hydrogen bonds
• The base pairs are termed complementary base pairs.

  In RNA the proportions of adenine and uracil/ guanine and cytosine are not equal, as the molecules are single stranded. However, complementary base pairing takes place in some areas of transfer RNA (tRNA) to hold the 3D structure in place. C pairs to G, and A pairs to uracil (U) in RNA.

  
• What are the two functions of DNA in cells?

  Code for proteins and replicate before division
• How does DNA replicate before cell division?

  Each daughter cell receives equal DNA
• What is a polynucleotide?

  A polymer of nucleotides
• What forms the sugar-phosphate backbone of DNA?

  Condensation reactions create phosphodiester linkages
• What are the complementary base pairs in DNA?

  A-T and C-G
• Why do the deoxyribose components appear 'upside down' in the DNA structure?

  Because the strands are antiparallel
• What do the 3’ and 5’ refer to in DNA?

  Numbers of the carbons in the pentose
• How are the base and phosphate connected in DNA?

  The base is joined to C1 and phosphate to C5
• How do the strands of DNA run in relation to each other?

  They run in opposite directions, antiparallel