The Chemistry of DNA and RNA

Question 1

Chemistry of DNA

Answer 1

Each monomer consists of:
- 5 carbon sugar (deoxyribose - has a H instead of -OH group)
- Nitrogenous base attached to 1’ position
- Phosphate group

Question 2

DNA’s 4 different bases

Answer 2

• Purine (double-ringed) nucleotides: Adenine (A) and Guanine(G)
• Pyrimidine (1 ring) nucleotides: Cytosine (C) and Thymine (T)

Question 3

Direction of DNA

Answer 3

• Phosphate residue links each monomer between 3’-hydroxyl of one deoxyribose + 5’-hydroxyl of the next
• Links are a phosphodiester bond

Question 4

RNA - Similar to DNA

Answer 4

• Four bases: Adenine, Guanine, Cytosine & Uracil (similar to T but without -CH3 group)
  
  • more susceptible to breakdown due to the hydroxyl group in the ribose, less chemically stable
  • is energetically expensive for RNA to have T which is short-lived
  • thus RNA is not chemically stable
• Ribose, a pentose sugar
• Phosphate

Question 5

Oxidative deamination

Answer 5

• NH3 replaced by carbonyl group
• How cytosine becomes uracil

Question 6

RNA & DNA similarities

Answer 6

• Their chains have a sense of direction, 5’ to 3’
• Same bases (except for Uracil)

Question 7

RNA & DNA Differences

Answer 7

• RNA has ribose while DNA has deoxyribose
• RNA is labile, single-stranded normally and doesn’t form a stable secondary structure like a double helix normally
• DNA is longer than RNA

Question 8

Nucleotides & Nucleosides

Answer 8

Nucleotides - phosphate group + sugar + nitrogenous base

Nucleosides - sugar + nitrogenous base

Question 9

Nomenclatures concerning Phosphates

Answer 9

• 1 phosphate = monophosphate
• 2 phosphates = diphosphate
• 3 phosphates = triphosphate