Lipids, Phospholipids, Steroids, and Metabolism

Lipids

  • Lipids include fats, oils, and related compounds.
  • Examples: phospholipid bilayer (cell membranes), steroids.
  • Steroids are a class of lipids, not just muscle-building injections; they are essentially fatty acids with modifications.

Unique Properties of Lipids

  • Insoluble in water (hydrophobic).
  • Fatty acids vary in carbon chain length, leading to different types like MCT oil.
  • MCT Oil: Medium Chain Triglycerides.
    • Medium chain: 8-10 carbons.
    • Processed differently by the body.

Absorption of Lipids

  • Long Chain Triglycerides: Most dietary fats are longer than 10 carbons.
    • Absorbed into the lymphatic system.
    • Travel via chylomicrons.
    • Enter the bloodstream through the subclavian vein.
    • Bypass the liver initially.
  • Medium Chain Triglycerides: Go to the liver first after absorption and can be converted into a quick energy source.

Fatty Acid Structure

  • Carbon chain with hydrogens attached.
    • represented as spikes
  • Variations include single or double bonds within the hydrocarbon chain.

Saturated vs. Unsaturated Fatty Acids

  • Saturated Fatty Acids: All single bonds, fully saturated with hydrogen atoms.
  • Unsaturated Fatty Acids: Contain double bonds; require removal of two hydrogens per double-bonded carbon.
    • More likely to be liquids at room temperature due to kinks caused by double bonds.

Trans Fats

  • Formed during food processing when heat converts saturated fats into unsaturated fats.
  • The body lacks proper enzymes to break down trans fats effectively.
  • Considered unhealthy despite having double bonds.

Omega-3 Fatty Acids

  • Found in fish oil supplements.
  • Beneficial for heart and brain health.

Phospholipids

  • Similar to triglycerides.
    • Composed of a glycerol molecule. Two fatty acids coming off of it.
    • Two fatty acids + polar head (phosphatidylcholine group).
  • Polar Head: Contains a phosphate group and a nitrogen-containing group, making it polar (charged). *Prior examples, all lipids were non-polar.
    • Polar heads attracted to water; nonpolar tails repel water.

Cell Membrane Formation

  • Phospholipids self-assemble into a cell membrane due to their amphipathic nature (polar and nonpolar regions).
  • Cell membrane structure is maintained by the presence of water.
  • H_2O polarity is essential for cell membrane integrity.

Steroids

  • Cholesterol: Most important steroid; precursor to other steroids.

Cholesterol-Derived Hormones

  • Testosterone: Primary male sex hormone (androgen).
    • Increases metabolic rate.
    • Causes secondary sexual characteristics.
    • Can move through the cell membrane due to being steroids, and target all cells; receptors inside cells activate their function.
  • Cortisol: Glucocorticoid associated with stress levels.
    • Regulates blood glucose levels.
    • Cortisol levels are highest in the morning.

Cortisol Cycle

  • Cortisol levels naturally cycle throughout the day.
  • Stress can spike cortisol levels because the body believes it needs to release glucose for energy.
  • Progesterone: Important for female reproductive anatomy.
  • Aldosterone: Regulates sodium reabsorption and blood pressure.

Proteins

  • Collagen is a very abundant protein in the body. Is very high.

Structure

  • Amino acids organized into sequences.

Secondary structure

  • alpha helices

Additional Proteins and Structures

  • Keratin: Found in nails, skin, and hair.
  • Collagen: Structural framework for the heart, organs, and bones.

Tertiary Structures

  • Amino acids can form covalent bonds with other amino acids, leading to globular structures.
  • Example: Potassium channel in the cell membrane with alpha helices and varying R groups (red indicates positively charged or polar; blue indicates nonpolar).

Quaternary Structure

  • Multiple protein subunits come together to form structural fibers (e.g., collagen, keratin) or globular structures (e.g., enzymes, antibodies).
  • Environment influences protein folding and stability.

Nucleic Acids

RNA

  • RNA is single-stranded. Is not very stable.
  • RNA may bind to itself and have unique functions; it can possess enzymatic properties (ribozymes).

Ribozymes

  • Examples: Ribosomes, which synthesize proteins (stabilized by proteins).
    • Ribosomes composed of small and large subunits.
    • Messenger RNA (mRNA) enters, and a protein is produced.

History Nucleic Acids

  • Debate over which came first: DNA, RNA, or protein.
    • RNA can act as a ribozyme and may have come first.
    • DNA is more stable due to deoxyribose.

DNA

  • Made of sugar, phosphate, and a nucleobase.

ATP

  • ATP (Adenosine Triphosphate): Main energy currency of the cell.
    • Breaking off a phosphate group releases energy for cellular work.
  • Composition: Adenosine (ribose sugar + adenine base), with one to three phosphate groups.
    • AMP (one phosphate group): Also a base in RNA.
  • ATP is crucial for skeletal muscle contractions.
  • Regeneration of ATP through metabolism.

Metabolism

  • Metabolism is the sum of all chemical processes in the body.

ATP Production

  • ATP production is attained by breaking down food molecules like proteins, carbohydrates, and fats through glycolysis.

Glycolysis

  • Breaks things down to make ATP

Glycolysis Example

  • Glucose enters and requires ATP for double phosphorylation.
  • Kinase enzymes remove phosphate groups, generating ATP and pyruvate.
  • Energy Yield: Glycolysis nets two ATP molecules (four produced minus two invested).

Oxygen's Role in Metabolism

  • Oxygen is vital; without it, the mitochondrial processes shut down.

Citric Acid Cycle (Krebs Cycle)

  • A small amount of ATP is produced within the cycle.
  • Creates electron carriers for the electron transport system.

Oxidative Phosphorylation

  • Occurs via the electron transport system by pumping hydrogen protons.
  • If oxygen is present then the organism with undergo the Citric Acid Cycle, the aerobic pathway.
  • If a muscle doesn't have enough oxygen, it skips going into the mitochondria.

Electron Transport System

  • The oxygen acts as the final electron acceptor.
  • Electrons are transferred through enzymes, pumping hydrogen ions into an intermembrane space.

Starvation and Nutrient Breakdown

  • During starvation, the body breaks down proteins, fats, and carbohydrates.
  • Protein Catabolism: Releases ammonia, converted to urea and CO_2 excreted in urine.
  • Carbohydrate Metabolism: Includes gluconeogenesis (glucose synthesis) and glycogenolysis (glycogen breakdown).
  • Lipid Metabolism: Includes lipolysis (lipid breakdown) in adipose tissue and liver.

Lipid Breakdown (Lipolysis)

  • Breaks lipids into glycerol and fatty acids; glycerol can feed into glycolysis.

Fatty acids broken down into Acetyl CoA

  • Those hydrogen atoms can become electron transporters.
  • Occurs via beta oxidation in the liver.

Proteins Breakdown for Fuel

  • Not very efficient.
  • Involves deamination and transamination.

Dietary Restrictions

  • Restricting protein intake can lead to muscle breakdown.

GLP-1 Agonists:

  • mimics glucagon. Binds to receptors.
  • Makes you feel full and slows the rate your stomach empties.
  • Helpful for diabetes.

Exercise and Macronutrient Utilization

  • During exercise, carb storages deplete after about 60 minutes, then the body taps into fat storage.

Pronunciations

  • Gluconeogenesis