12-04: Nucleic Acids

Nucleic Acids

• Nucleic acids: molecules that are polymers made of nucleotides   * When we link many nucleotides together, we get a nucleic acid
• They store hereditary information and can produce identical copies of themselves

     1. DNA, deoxyribonucleic acid: double stranded   2. RNA, ribonucleic acid: single stranded

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Nucleotides

• Nucleotides are made of 3 components (in a single nucleotide)

     1. Pentose      * 5 carbon sugar      * Either a ribose sugar in RNA or deoxyribose sugar in DNA   2. Phosphate group      * Bonded to C5 with a phosphate ester linkage   3. Nitrogenous base - 1 of 4:

           1. Adenine (A)      2. Guanine (G)      3. Cytosine (C)      4. Thymine (T) in DNA, or Uracil (U) in RNA         * a. b. and c. are possessed by both RNA and DNA

Phosphates can have OH’s, but in an aqueous environment, H and O ionize into H⁺ and O⁻ as H⁺ dissociates

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Formation:

• The sugar from one carbon and the phosphate from another carbon form a phosphodiester bonds to make a long backbone
• The phosphate has 2 ester linkages to 2 different carbons: C5 on the original/first sugar to C3 on the new/second sugar
• Covalent bonds between the phosphate group on nucleotide on the hydroxyl of the C3 hydroxyl of a sugar on the nucleotide

Nitrogenous bases

• Nitrogenous bases point towards the inside of the polymer, away from the backbone
• Two types of nitrogenous bases

     1. Pyrimidines      * Single ringed      * Cytosine (C), Uracil (U), Thymine (T)        * CUT are the pyrimidines since they are a double ringed “CUT” in half!   2. Purines      * Double ringed      * Adenine (A) and Guanine (G)

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DNA

• 2 strands of nucleotides together – bigger structure, ladder that twists into a helix
• Double stranded
• Bases point towards each other
• Cytosine (C) and Guanine (G) are complementary base pairs and join together with 3 hydrogen bonds (bonded to the N)
• Adenine (A) and Thymine (T) are complementary base pairs and join together with 2 hydrogen bonds
• Each strand of DNA has a free phosphate at one end and a free sugar at the other – one strand runs backwards relative to the other strand   * They run “anti-parallel” (parallel but in opposite directions)

\  Must be antiparallel in order for the H bonds to occur

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• Coils into a double helix   * Twisted ladder
• Phosphate sugar backbone around the outside and bases point towards the inside

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RNA

 Difference is on C2

RNA has many different functions (e.g. mRNA (Messenger RNA), tRNA, rRNA)

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Comparing DNA and RNA

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Other nucleotides

ATP

• ATP: adenosine triphosphate   * Has all of the features of a nucleotide but rather than 1 phosphate, it has a triphosphate (3)
• Adenine and ribose + 3 phosphates
• Cells use it as a source of energy – mitochondria synthesizes ATP which is useful for other cellular chemical processes
• Used for energy transport within the cell
• The only format of energy out cells can use (“currency”)   * The removal of 1 phosphate group releases energy to be used

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Nucleotide Derivatives

• Derivatives of nucleotides are used in the production of ATP
• Used to transport H⁺ and electrons from one reaction site to another

  e.g.   * nicotinamide adenine dinucleotide (NAD+)   * flavin adenine dinucleotide (FAD)   * cyclic adenosine monophosphate (cAMP)

\ Bottom line: not every nucleotide has to be in DNA & RNA

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