Amino Acid Chemistry Quiz

Amino Acid Chemistry

• Amino acids are composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and small amounts of sulfur (S) – often abbreviated as CHONS.
• The alpha-carbon in amino acids is asymmetric (except glycine).
• This asymmetry leads to two optically active forms: D-form and L-form.
• Only L-amino acids are used to make proteins.
• Glycine lacks an asymmetric carbon.
• Amino acids are dipolar ions (zwitterions) in solution.
  • The amino group (NH2) gains a positive charge, and the carboxyl group (COOH) gains a negative charge.
  • Dipolar ions have zero mobility in electrophoresis.
• Amino acids exhibit amphoteric behavior.
  • There is no pH where a.a have no ionic character.
  • The isoelectric point (pI) is the pH at which the number of cations equals anions.
  • Each amino acid has a specific pI depending on its structure.
    • Acidic amino acids have lower pI values (e.g., aspartic acid 2.8, glutamic acid 3.2).
    • Neutral amino acids have pI values between 5.0 and 6.3.
    • Basic amino acids have higher pI values (e.g., lysine 9.7, arginine 10.8, histidine 7.6).
• Electrophoresis separates amino acids based on their isoelectric points.
  • A mixture of amino acids is placed on a gel or paper.
  • An electric field is applied.
  • Positively charged amino acids move towards the negative electrode (cathode), negatively charged amino acids towards the positive electrode (anode).
  • Amino acids with no net charge at a given pH stay in place.
• Twenty amino acids make up proteins.
  • Nine are essential amino acids; the body doesn't produce them, so they must be obtained through diet.
  • Eleven are nonessential; the body can synthesize them.
• Amino acids are grouped based on the R-group properties:
  • Nonpolar
  • Polar uncharged
  • Acidic (negatively charged)
  • Basic (positively charged).
• Peptides are formed from amino acids linked via peptide bonds (condensation reactions).
  • A molecule of water is removed when forming a peptide bond.
• The terminal ends of peptides are identified as N-terminal and C-terminal.
• Peptides are important in biological processes, as intermediates in protein synthesis, antibacterial agents (e.g., penicillin), growth factors (e.g., folic acid), hormones (e.g., insulin, angiotensin), antioxidants (e.g., glutathione) and in diseases (neurological disorders).
• Glutathione (γ-Glu-Cys-Gly) is a natural antioxidant.
• Angiotensin is a potent vasodilator/constrictor.
• Peptides have industrial uses, particularly in pharmaceutical, cosmetic and medical applications.
• Peptide-based drugs.
• Cancer-detection agents.
• Skin care products.
• Food additives/sweeteners.
• Proteins are large polypeptides.
• Proteins have important biological functions including catalysis (enzymes), transport (hemoglobin), structural support (collagen), regulation of the immune response, transmission of nerve signals (receptors).
• Proteins are classified based on source (animal or plant), and shape (globular or fibrous).
  • Globular proteins generally have spherical shapes and tertiary/quaternary structures.

Protein Structure

• Proteins are composed of amino acids linked together by peptide bonds.
• Proteins have four levels of structure:
  1. Primary structure: linear sequence of amino acids.
     • Determines a protein's overall structure and function.
     • Example of how small changes in amino acid sequence can affect function is Sickle Cell Anemia.
  2. Secondary structure: local folding patterns (α-helices, β-sheets, β-bends) stabilized by hydrogen bonds.
  3. Tertiary structure: 3D shape of the entire polypeptide chain, stabilized by various bonds (hydrogen bonds, disulfide bonds, ionic bonds, hydrophobic interactions). This determines the protein's specific shape and function.
  4. Quaternary structure: arrangement of multiple polypeptide chains in a protein, stabilized by the same bonds as tertiary structures.
  • Haemoglobin is an example of a protein that has a quaternary structure and made up of both α and β chains.
  • Myoglobin is another example of a protein that has a tertiary structure composed of a polypeptide chain.

Protein Chemical Bonds

• Disulfide bridges form between cysteine residues in specific cases.
• Hydrogen bonds stabilize secondary and tertiary structures.
• Nonpolar/hydrophobic interactions are important in tertiary structures.
• Ionic/electrostatic interactions occur between charged amino acid side chains.

Protein Methods

• Electrophoresis and Western Blotting are used to separate and identify proteins.

Protein Quantification

• Methods used to determine protein amounts include immunological techniques (ELISA, Western Blotting) and protein-specific tools like mass spectrometry.

Protein Denaturation

• Denaturation disrupts the three-dimensional structure of a protein, causing it to lose its biological activity.
• It results from physical agents (heat, shaking, radiation etc) and chemical agents (organic solvents, detergents, etc).
• Denaturation often results from changes caused by alterations in pH levels, change in temperature, or the addition of chemicals.
• Denaturation is commonly a reversible process.

Industrial Importance of Proteins

• These important roles extend to pharmaceutical, cosmetic and agricultural applications.
• Proteins and peptides in these industries range from the formation of gelatin for food products, to uses in medical treatment.