Protein Structure, Fatty Acids, and Metabolism: Key Concepts

Posted on Mar 20, 2025 in Biology

Protein Primary Structure

  • Consists of a sequence of amino acids.
  • Peptide bonds link amino acid residues.

Protein Secondary Structure

  • Stabilized by hydrogen bonds between amino and carboxyl groups of amino acids.
  • Composed of regular structures and repetitive polypeptide chains.

Protein Tertiary Structure

  • Stabilized by noncovalent interactions.
  • Disulfide bonds confer greater thermal stability.
  • Can be destabilized by chemical agents such as urea and β-mercaptoethanol.

Protein Domains

  • Domains are independent tertiary structures.
  • A protein domain often has separate functions.
  • A domain can be found in different proteins.

Myoglobin and Hemoglobin

Globular proteins with important physiological functions:

  • Both proteins have the same prosthetic group (heme).
  • The quaternary structure of hemoglobin makes its function and regulation more complex.

Collagen

A protein with important characteristics related to its functions:

  • Individual helices of collagen are associated in a triple helix stabilized by hydrogen bonds.
  • Hydroxyproline and hydroxylysine are important components in the collagen molecule, allowing greater stability of the fibers.
  • Collagen fibers are formed of tropocollagen associated in a regular array.

Keratin Characteristics

  • Rich in hydrophobic amino acids and cysteines.
  • Helices form dimers, which associate to form fiber cable structures.
  • Disulfide bridges stabilize fiber structures.

Fibrous Proteins

  • Actin filaments are formed by globular proteins.
  • Microfilaments are formed by globular proteins.

Fatty Acids

  • Linolenic acid is an ω-3 fatty acid.
  • Linoleic acid is an ω-6 fatty acid and is essential.

Nutritional Value of Fatty Acids

  • Linoleic and linolenic acids are components of phospholipids in cellular membranes.
  • Arachidonic acid is a precursor of metabolic regulators.

Membrane Lipids

  • Phosphatidylinositol participates in signal transduction.
  • A cerebroside is a ceramide with glucose or galactose as a polar group.

Substrate-Level Phosphorylation

  • Occurs in the synthesis reaction of pyruvate.
  • Occurs in fermentation processes.
  • Occurs in the citric acid cycle.

Glycogen

  • Glycogenolysis produces glucose when blood glucose is low.
  • Glycogenolysis directly produces glucose 1-phosphate.

Glycolysis

An important pathway in the body’s metabolism:

  • Occurs in the cytoplasm, not the mitochondrial matrix.
  • Various dehydrogenases catalyze reactions via different mechanisms.

Fermentation

Common but important processes:

  • Pyruvate is reduced.
  • Regenerates NAD+ in the cell.
  • Generates 2 ATP per molecule of glucose.

Acetyl-CoA

An important molecule in metabolism:

  • The pyruvate dehydrogenase complex yields acetyl-CoA.
  • Acetyl-CoA joins with oxaloacetate to produce citrate.
  • Acetyl-CoA can be used for the synthesis of lipids.

Electron Transport

  • Electrons are transported by complexes I, II, III, and IV in the inner mitochondrial membrane to reduce O2 to form water.
  • H+ are pumped by complexes I, III, and IV into the intermembrane space.

Oxidative Phosphorylation

  • An electrochemical gradient is generated by proton accumulation in the intermembrane space for ATP synthesis.
  • The ATP synthase complex uses the passage of H+ for ATP synthesis.
  • Approximately 2.5 ATP are generated for every NADH that is oxidized.

Gluconeogenesis

  • Glucose is synthesized from pyruvate.
  • Pyruvate carboxylase produces oxaloacetate from pyruvate.
  • 6 ATP are consumed per molecule of glucose synthesized.