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General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material

Building blocks of life

  • Carbon based: organic molecules
  • Carbohydrates: CHO
  • Lipids: CHO, water insoluble
  • Proteins: CHONS, structure/function in cells
  • Nucleic acids: CHONP, hereditary (genetic) information

Carbon

  • Can make 4 covalent bonds
    • Chains
      • Straight
      • Branched
      • Ring
    • Hydrocarbons (C, H): store energy
    • Functional groups
      • Attach to carbon
      • Alter chemical properties
      • Form macromolecules
      • Sapoteton

Carbohydrates

  • Principally CHO (rare N, S and P)
    • 1C:2H:1O ratio
    • Energy rich (many C-H bonds)
  • Monosaccharides (principal: glucose)
    • Simple sugars
    • Principle formula: C6H12O6
    • Form rings in water solution
  • Disaccharides (sucrose, lactose)
  • Polysaccharides (starch, glycogen, cellulose, chitin)

Stereoisomers

  • Bond angles of carbon point to corners of a tetrahedron
  • When 4 different groups are attached to a carbon, it is asymmetric, leading to various types of isomerism
    • Stereoisomers: (D, L)
  • Same chemical properties
  • Different biological properties
  • D sugars, L amino acids

Lipids

  • C-H bonds (nonpolar) instead of C-OH bonds as in carbohydrates
    • High energy
    • Hydrophobic (insoluble in water)
  • Categories
    • Fats: glycerol and three fatty acids
    • Phospholipids: primary component of membranes
    • Prostaglandins: chemical messengers (hormones)
    • Steroids: membrane component; hormones
    • Terpenes: pigments; structure

Fatty acids

  • Hydrocarbon chain
    • Even number of C, 14->20
    • Terminates in carboxyl group
  • Saturated: contain maximum number of hydrogens (all single bonds); maximum energy
  • Unsaturated: one or more double bonds
    • Usually higher melting point
    • Many common oils are polyunsaturated

Proteins

  • Polymer of amino acids
    • 21 different amino acids found in proteins
    • Sequence of amino acids determined by gene
  • Amino acid sequence determines shape of molecule
    • Linked by peptide bond (covalent)
  • Functions
    • regulate chemical reactions and cell processes [enzymes]
    • form bone and muscle; various other tissues
    • facilitate transport across cell membrane [carrier proteins]
    • fight disease [antibodies]
  • Motifs: folding patterns of secondary structure
  • Domains: structural, functional part of protein often independent of another part; often encoded by different exons
  • Shape determines protein's function

Amino acids

  • 21 commonly found in proteins
    • 21st is selenocysteine, not mentioned in text
  • Common structure
    • Amino group: NH2
    • Carboxyl group: COOH
    • R group- 4 different kinds of R groups
      • acidic
      • basic
      • hydrophilic (polar)
      • hydrophobic (nonpolar)
  • Confer individual properties on amino acids
  • List of amino acids

Structure

  • Primary structure: the amino acid sequence
    • Determines higher orders of structure
    • Critical for structure and function of protein
  • Secondary: stabilized by intramolecular hydrogen bonding
    • helix
    • sheet
  • Tertiary: folding, stabilized by ionic bonds (between R groups), hydrogen bonding, van der Waal's forces, hydrophobic interactions
  • Quaternary: _ 2 polypeptides

Function

  • Requires proper folding, cofactors, pH, temperature, etc.
  • Proteins are often modified after synthesis
    • Chemical modification
    • Addition of heme groups (hemoglobin, cytochrome)
  • Denatured proteins can not function properly
  • Proteins are degraded by proteosome as part of constant turnover of cell components

Hereditary (Genetic) information

  • Nucleic acids
    • DNA: deoxyribonucleic acid
  • Hereditary information of all cells
  • Hereditary information for many viruses
    • RNA: ribonucleic acid
  • Hereditary information of certain viruses (HIV)
  • Intermediate in gene expression
  • Composed of nucleotides
    • Ribonucleotides
    • Deoxyribonucleotides

RNA DNA origin

  • Which came first?
  • Paradox: DNA encodes protein necessary for its own replication
  • Discovery of catalytic RNA by Cech and Altman suggested that RNA might have been first self-replicating molecule
  • DNA evolved as more stable type of storage molecule

Proteins: Their building block is amino acids. The bond connecting 2 of the amino acids together are called peptide bonds. One of these bonds makes a monopeptide, two a dipeptide, and any more than that makes a polypeptide.

References

This text is based on notes very generously donated by Dr. Paul Doerder, Ph.D., of the Cleveland State University.

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