Chemical building blocks nucleic acids nucleic acids

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Chemical Building Blocks: Nucleic Acids Nucleic acids: composed of nucleotides (i.e. organic molecules that are the basic structural units for DNA and RNA) Each nucleotide consists of three key components: 1. A nitrogenous base i. Purines: have two rings within their structure (adenine [A] and guanine [G]) ii. Pyrimidines: have only one ring in their structure (cytosine [C], thymine [T], and uracil [U]) 2 A pentose (i.e. five-carbon) sugar; ribose or deoxyribose 3 At least one phosphate group i. If the molecule lacks one or more phosphate groups, it is a nucleoside Three fundamental differences between DNA and RNA: 1 DNA is double-stranded; RNA is generally single-stranded 2 DNA nucleotides contain deoxyribose; RNA nucleotides contain ribose (the difference is a hydroxyl group on the 2' carbon, present in ribose only)
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3 DNA contains the base thymine; RNA contains the base uracil (the difference is a methyl group on carbon 5 of the base in uracil) Individual nucleotides within DNA and RNA are linked together to form polynucleotides; this occurs through their pentose sugar groups. Phosphodiester bonds : chemical bonds joining successive sugar molecules in a polynucleotide o Formed between the 5' phosphate on one nucleotide and the 3' hydroxyl of the adjacent nucleotide Nucleic acids have directionality based on their free ends (termini ) : 5' -> 3' Chemical Building Blocks: Proteins All 20 common amino acids have a similar structure; a central carbon atom (the carbon atom) bonded to four different chemical groups: 1 Amino group o Can have 1-3 hydrogens depending on the pH of the solution and if the nitrogen is participating in a peptide bond 2 Carboxyl group o Can lose the hydrogen from the carboxylic acid, giving it a negative charge at physiological pH; a hydroxyl is lost if it participates in a peptide bond 3 R group o Vary in structure, size, electrical charge, and hydrophobicity 4 Lone hydrogen atom Once incorporated into a polypeptide chain, the individual amino acids are referred to as amino acid residues . Peptide bonds: covalent bonds linking two consecutive amino acid monomers along a peptide chain o Formed between the amino group of one amino acid and the carboxyl group of the adjacent amino acid o Polypeptide chains also have directionality at their termini: amino to carboxyl (i.e. N-terminus to C-terminus) Chemical Properties: Strong Chemical Bonds Strong bonds (i.e. covalent bonds and ionic bonds) involve short distance interactions between atoms, and generally require a catalyst to break them; play major roles in the formation and stability of nucleic acid and amino acid polymers Electronegativity: the propensity of an atom within a molecule to attract electrons to itself Atoms with a tendency to gain electrons are referred to as electronegative atoms; those with a propensity to lose electrons as electropositive atoms
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Valence: maximum number of covalent bonds a particular atom can form Some bonds may have partial double character (i.e. there is restriction of rotation around the
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  • Winter '13
  • DNA

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