General Biology/Getting Started/Chemical Building Blocks of Life

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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.

Reference

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