Nucleic acid

• Biomolecules


  Proteins and Nucleic acids
• BIO 101
• Adu, Oluwatosin B.
• Protein


  A large organic molecule constructed of a chain of amino acids. The word protein, derived from the Greek proteios, loosely means "holding first place"
• Proteins


  • They orchestrate the business of life by controlling multiple bioprocesses including metabolism, cell growth, and neurotransmission
  • They provide structure and can act as energy source
  • Their main role is as enzymes—enabling chemical reactions that are critical to life
• Amino acids


  Monomers that make up proteins, joined by peptide bonds
• Common amino acids

  • 20 different amino acids
• Amino acids


  • They have a carboxyl group and an amino group bonded to the same carbon atom (the α carbon)
  • They differ from each other in their side chains, or R groups, which vary in structure, size, and electric charge, and which influence the solubility of the amino acids in water
  • They have been assigned three letter abbreviations and one-letter symbols
• Amino acid structure


  • For all the common amino acids except glycine, the α carbon is bonded to four different groups: a carboxyl group, an amino group, an R group, and a hydrogen atom
  • The α-carbon atom is a chiral center, with two possible stereoisomers- D and L
  • The amino acid residues in protein molecules are exclusively L stereoisomers
• Zwitterions


  Amino acids in solution at neutral pH exist mainly as zwitterions, having both a positive and a negative charge
• Classification of amino acids

  • Based on nature of R-group: Nonpolar, aliphatic; Aromatic; Polar, uncharged; Positively charged (Acidic); Negatively charged (Basic)
  • Based on fate of carbon skeleton: Glucogenic; Ketogenic
  • Based on nutritional need: Essential; Nonessential
• Peptide bond


  The substituted amide linkage that joins two amino acid molecules to form a dipeptide
• Oligopeptide


  When a few amino acids are joined
• Polypeptide


  When many amino acids are joined, with molecular weights above 10,000
• Protein


  Molecules referred to as polypeptides generally have molecular weights below 10,000, and those called proteins have higher molecular weights
• 1. terminal and C-terminal residues


  In a peptide, the amino acid residue at the end with a free α-amino group is the amino-terminal (or N-terminal) residue; the residue at the other end, which has a free carboxyl group, is the carboxyl-terminal (C-terminal) residue
• Simple proteins


  Proteins that contain only amino acid residues and no other chemical constituents
• Conjugated proteins


  Proteins that contain associated chemical components in addition to amino acids, with the non-amino acid part being the prosthetic group
• Types of conjugated proteins

  • Glycoproteins = protein + sugar
• Protein structure


  • Primary structure is the linear sequence of amino acids
  • Secondary structure is formed by hydrogen bonding, taking the form of alpha helices or beta pleated sheets
  • Tertiary structure is the final 3D shape of the folded polypeptide chain, stabilized by various bonds
  • Quaternary structure is formed by the association of multiple polypeptide chains
• Primary structure


  The final 3-Dimensional shape of one folded amino acid chain
• The final shape of any polypeptide chain is unique and will have specific areas that are necessary for the function of the protein
• Tertiary structure


  • Stabilized by hydrogen bond, ionic bond, hydrophobic interactions and disulfide bonds
• Quaternary structure


  Formed from the association of two or more peptide strands
• Some proteins are large and complex, consisting of many polypeptide chains. These proteins have quaternary structure
• Proteins with quaternary structure

  • Hemoglobin (with four polypeptide chains)
  • Proteins (with three chains)
• The formation of disulfide bonds is important in the quaternary structure of many proteins
• Important functions of proteins

  • Enzymes - make chemical reactions happen faster
  • Reinforce structures - part of plasma membranes, cytoskeletal proteins, extracellular matrix
  • Transport materials into and out of the cell
  • Involved in cellular identity - glycoproteins on cell surfaces
  • Help cells move - cytoskeletal proteins power flagella and cell crawling
  • Help cells communicate - receptors for signals, signaling molecules like insulin
  • Organize molecules within the cell - chaperone proteins assist folding and guide proteins
• Nucleotides


  One of the most important classes of molecules in the body
• Nucleotides


  • Act as the basis for sources of energy (ATP, GTP) that drive biochemical reactions
  • Important constituent in several coenzymes
  • Component of the nucleic acids- RNA and DNA
• Nucleotide


  Has three characteristic components: (1) a nitrogenous base, (2) a pentose, and (3) one or more phosphates
• Nucleoside


  The molecule without a phosphate group
• Nitrogenous bases


  • Derivatives of two parent compounds, pyrimidine and purine
• Major purine and pyrimidine bases of nucleic acids

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T) in DNA
  • Uracil (U) in RNA
• Pentoses in nucleic acids

  Deoxyribonucleotide units of DNA contain 2'-deoxy-D-ribose, and the ribonucleotide units of RNA contain D-ribose
• Successive nucleotides of DNA and RNA

  Covalently linked through phosphodiester bond in which the 5'-phosphate group of one nucleotide unit is joined to the 3'-hydroxyl group of the next
• Covalent backbones of nucleic acids

  Consist of alternating phosphate and pentose residues, and the nitrogenous bases may be regarded as side groups joined to the backbone at regular intervals
• Oligonucleotides


  Polymers containing 50 or fewer nucleotides
• Polynucleotide


  A longer nucleic acid
• Primary structure


  The order and type of nucleotides in a polynucleotide strand