Biochemistry

Organic compounds contain carbon and hydrogen.  The carbons are frequently linked by covalent chemical bonds, which involve sharing pairs of electrons.  There are four categories of important organic compounds: carbohydrates, lipids, proteins and nucleic acids.  The number, type and spatial arrangement of the constituent atoms determines the functional properties of the compound.

Carbohydrates

• function as an important energy source for the body
• occur in a straight chain or ring form

Types of carbohydrates

1. Monosaccharide - simple sugar (3-7 C), cannot be split into simpler form. example:
   • 6-C: glucose, galactose, fructose
   • 5-C: ribose, deoxyribose
2. Disaccharide - double sugars, formed by combination of 2 monosaccharides by dehydration synthesis. example:
   • C₆H₁₂O_{6 +} C₆H₁₂O_{6 =} C₁₂H₂₂O_{11 +} H₂O
   • sucrose, lactose
3. Polysaccharide - multiple sugars.
   • glycogen, starch, cellulose

Lipids

• energy source (2x cal/gm of carbs or proteins), cell membrane component
• insoluble/slightly soluble in water (hydrophobic), soluble in organic solvents
• composed of glycerol backbone and fatty acid chains (type & number determine function)

Types of lipids

1. Glyceride - 1 glycerol + x fatty acids, mono-, di-, tri-
   • Saturated fats contain only single covalent bonds, max #H possible
   • Unsaturated fats contain double covalent bonds, reduces #H
2. Phospholipids - 1 fatty acid replaced by PO₄ & nonlipid group
   • Amphipathic molecules (polar & nonpolar regions) found in cell membranes
3. Steroids - large complex nonpolar C-ring molecules
   • ex. cholesterol, sex hormones, Vitamin D
4. Eicosanoids - derivatives of arachidonic acid (20 C)
   • ex. prostaglandins & leukotrienes act as local mediators, inflammatory response

 

Proteins

• structural, regulatory, transporter functions
• CHONS, chains of amino acids folded & coiled to form a particular configuration which determines its function
• 20 different common amino acids with an amino group (NH₂) & carboxyl group (COOH) and side chain (R group determines a.a. function)

Structural organization:

• Primary
  • linear amino acid sequence, formed by dehydration synthesis, peptide bonds (covalent bond) connecting amino acids
• Secondary
  • spatial arrangement of neighboring amino acids to form coils or pleats, H-bonds
• Tertiary
  • forms 3-dimensional structure of polypeptide, disulfide bonds
• Quaternary
  • arrangement of two or more polypeptides in protein
  • denaturation is loss of structural organization & function

Nucleic acids

• store biological information
• chains of nucleotides linked by dehydration synthesis
• ex. DNA & RNA

Nucleotide = N-base + pentose sugar + PO₄

• N-base
  • purine (double rings), adenine & guanine
  • pyrimidine (single ring), cytosine, thymine & uracil
• Pentose sugar
  • ribose or deoxyribose
• Phosphate group
   

RNA

single strand of A, G, C & U nucleotides containing ribose sugar

DNA

double strand of A, G, C & T nucleotides with deoxyribose wound in helix

High-energy molecules

• store & transfer chemical energy in form of high energy bonds
• Nucleotide + 2 phosphates attached by high energy bonds
• ex. ATP - adenosine triphosphate