Structure of Nucleic Acids

What are the main nucleic acids and what are they made up of?

DNA: Deoxyribonucleic acid

RNA: Ribonucleic acid

• These are polymers made up of nucleotides (monomers)

What do the monomers of DNA consist of?

Nucleotides composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, guanine)

What is the chemical structure and role of the phosphate group?

• 1 central phosphorus atom bonded to 4 oxygen atoms

• Connects the 5' -carbon of one sugar to the 3' - carbon of the next sugar

How does the deoxyriboses’ chemical structure allow DNA to form?

• A 5 sided, 5-carbon ring

• Carbons numbered 1 to 5 going clockwise from the 1'-carbon connected to the nitrogenous base

• Deoxygenated because it lacks 1 oxygen atom at the 2'-carbon position compared to ribose sugar

What is the 5 prime end of the deoxyribose sugar?

• The end of a DNA strand where the 5'-carbon of the deoxyribose sugar is free

• The carbon only binds to the phosphate group without connecting to another sugar

What is the 3 prime end of the deoxyribose sugar?

• The end of the deoxyribose sugar that has a free hydroxyl group (-OH) at the 3'-carbon position

• Essential for DNA synthesis and pairing with the phosphate group of the next nucleotide

• Called the growing/tail end

What are some key differences between DNA and RNA?

Nitrogenous bases: RNA has Uracil, DNA has Thymine

Pentose sugar: Sugar of RNA is oxygenated (ribose), DNA is deoxygenated (deoxyribose)

Structure: RNA generally single strand, DNA double helix

What is the chemical structure and location of the nitrogenous bases?

• Attached to the 1'-carbon of the deoxyribose sugar

• Each contains: Nitrogen, carbon, hydrogen and oxygen

•  Come in two types: Purines and Pyrimidines

• Connected to each other via weak hydrogen bondds

What are purines and which bases are classified as these?

Purines: Adenine and Guanine

• Double-ringed

• Tip: Purines are pure, angles have halo rings that are pure

What are pyramidines and which bases are classified as these?

Pyrimidines: Cytosine, Thymine, Uracil

• Single ringed

• TIP: Pyramids are sharp and CUT (acronym for 3 base names)

How is the bond that connects the nitrogenous bases different to the bond that connects the sugar-phosphate backbone?

Sugar Phosphate: Covalent peptide bond

• Peptide bond between the phosphate group of one nucleotide and the ribose sugar of the next nucleotide

Nitrogenous base: Hydrogen bond

• Bases held together by weak hydrogen bonds

What are the complementary base pairs?

• Adenine pairs with Thymine (Uracil in RNA) via 2 hydrogen bonds

• Guanine pairs with Cytosine via 3 hydrogen bonds

• Purines always pair with pyramidines

How and why is there complementary base pairing?

Complemetary base pairing: The specific pairing of nitrogenous bases due to their complementary hydrogen-bonding sites

• Therefore only specific bases can form stable hydrogen bonds:

  • Adenine (A) pairs with Thymine (T) in DNA or Uracil (U) in RNA.

  • Cytosine (C) pairs with Guanine (G).

• This ensures accurate storage and transfer of genetic information