The Structure and Function of Large Biological Molecules

Proteins

  • The Greek word for protein is “Proteios”, which means first or primary
  • 50% dry weight of cells
  • Contains: C, H, O, N, S
  • Play a major role in almost everything organisms do, such as storage, transport, and chemical reactions.

Protein Functions

  • Enzymes: speeding up chemical reactions
    • Example: lactase
  • Defense: protecting against diseases
    • Example: antibodies
  • Storage: storing amino acids
    • Example: milk protein = casein
  • Transport: transport of substances
    • Example: hemoglobin
  • Hormones: coordinating activities
    • Example: insulin
  • Receptors: responding to chemical signals, found in cell membranes for cell communication
  • Movement: motor proteins help muscles move
  • Structure: structure of skin, hair, nails
    • Example: keratin

Four Levels of Protein Structure

  1. Primary

   

  1. The primary structure of a protein consists of the amino acid sequence which are bound by covalent bonds called peptide bonds.
  2. Any slight change in this structure affects the protein’s conformation and ability to function regularly.
  3. 20 different AA’s
    1. Secondary

   

  1. The secondary structure of a protein is the bending and hydrogen bonding of a polypeptide backbone to form repeating patterns, resulting in a coiled or folded 3-D shape of the protein.
  2. Alpha (α) helix: the coiled structure in which hydrogen bonding occurs between every fourth amino acid.
  3. Beta (β) pleated sheet: a protein in which two or more of the polypeptide chains lie parallel to each other hydrogen bonds holding them in place. 
  4. Not dependent on amino acid sequence and R-groups, but the hydrogen bonding between backbone (amino and carboxyl group)
    1. Tertiary

   

  1. Bonding between side chains (R groups) of amino acids
  2. H bonds, ionic bonds, disulfide bridges, van der Waals interactions
    1. Quaternary

   

  1. 2+ polypeptides bond together

Amino Acid

  • R group: side chains
  • \
  • Properties:
    • hydrophobic
    • hydrophilic
    • ionic (acids & bases)
  • Amino acids are attached to an amino group, a carboxyl, a H atom (R group), and the skeleton (also considered an R group)
  • Amino group: -NH2
  • Acid: -COOH
  • When amino acids are joined together, a dehydration reaction takes place to remove the (OH) from the carboxyl and an H from the amino group

Protein Structure and Folding

  • Chaperonins: assist in proper folding of proteins by protecting them from “bad influences” like chemicals in the body, allowing the proteins to fold spontaneously and properly. 
  • The structure affects the function of the protein
  • A change in the structure will affect the function of the protein and easily can affect the body.
    • change in structure = change in function

Nucleic Acids

  • Function: store hereditary info
  • DNA
    • Double-stranded helix
    • N-bases: A, G, C, Thymine
    • Stores hereditary info
    • Longer/larger
    • Sugar: deoxyribose
  • RNA
    • Single-stranded
    • N-bases: A, G, C, Uracil
    • Carry info from DNA to ribosomes
    • tRNA, rRNA, mRNA, RNAi
    • Sugar: ribose
  • Nucleic acids: polymers of monomers called nucleotides
  • Each nucleotide is composed of a nitrogenous base, a five-carbon sugar, and a phosphate group. 
  • Nucleotides: monomer of DNA/RNA

Carbohydrates

  • Carbohydrates: serve as fuel and building material
  • Include simple sugars (fructose) and polymers (starch)
  • Ratio of 1 carbon: 2 hydrogen: 1 oxygen or CH2O
  • monosaccharide 🡪 disaccharide 🡪 polysaccharide
  • Monosaccharides: monomers (eg. glucose, ribose)
  • Polysaccharides:
    • Storage (plants-starch, animals-glycogen)
    • Structure (plant-cellulose, arthropod-chitin)

Lipids

  1. Fats (triglyceride): store energy

   

  1. Glycerol + 3 Fatty Acids
  2. saturated, unsaturated, polyunsaturated
    1. Steroids: cholesterol and hormones
    2. Phospholipids: lipid bilayer of cell membrane

   

  1. hydrophilic head, hydrophobic tails