BV

Lecture Notes on Organic Compounds, Lipids, Proteins, and Nucleic Acids

Organic Compounds

  • Definition: Organic compounds are defined as any substance that contains both carbon (C) and hydrogen (H).
  • Example: Carbon Dioxide (CO₂) is not an organic compound because CO₂ lacks hydrogen.

Polymerization Reactions

  • Monomer + Monomer → Polymer + H₂O (this process is referred to as dehydration synthesis or condensation).
  • Polymer + H₂O → Monomer + Monomer (this process is known as hydrolysis).
  • Definition of a polymer (macromolecule): A long chain of repeating molecular units.
  • Organic compounds are also known as polymers.

Carbohydrates

Structure and Composition

  • Carbohydrates contain carbon (C), hydrogen (H), and oxygen (O).
  • Major classes: sugars and starches.
  • Carbohydrates are the most abundant group of organic compounds due to the presence of cellulose.

Major Functions of Carbohydrates

  1. Provides a readily available source of energy (e.g., glucose is used as a fuel in cell respiration).
  2. Short-term storage of energy (e.g., glucose is stored as glycogen in humans).

Types of Carbohydrates

Monosaccharides

  • Definition: Simple sugars; monomeric units of carbohydrates.
  • Example: Pentose sugars such as ribose and deoxyribose (found in RNA and DNA respectively).
  • Hexose: Glucose (C₆H₁₂O₆), a six-carbon sugar.

Isomers of Glucose (C₆H₁₂O₆)

  • Isomers include:
    • Glucose (aldehyde form - most abundant hexose).
    • Galactose (aldehyde).
    • Fructose (ketone).

Disaccharides

  • Definition: Formed by the combination of two monosaccharides.
  • Examples:
    1. Sucrose = glucose + fructose.
    2. Maltose = glucose + glucose.
    3. Lactose = glucose + galactose.

Polysaccharides (Polymers of Multiple Monomers)

  1. Starch - Principal storage polysaccharide in plants (Examples: potatoes, rice, grain) using α (alpha) covalent linkages.
  2. Glycogen - Principal storage polysaccharide in animals (about 1 pound stored in liver/skeletal muscle), also using α linkages.
  3. Cellulose - Found in plant cell walls, providing strength (humans lack the enzyme to digest cellulose).
    • Fiber constitutes a part of our diet and acts like brushes to stimulate goblet cells to secrete mucus. It is a glucose polymer bonded with β (beta) covalent linkages.

Lipids

Classification

  • Lipids are generally insoluble in water because they are nonpolar.

Types of Lipids

Neutral Fats (Triglycerides)

  • Definition: Formed from glycerol and 3 fatty acids.
  • Functions:
    1. Long-term energy storage (found in adipose tissue).
    2. Insulation and protection (also within adipose tissue).
  • Chemical Structure:
    • Fatty acids have a carboxyl group at one end and a long hydrocarbon chain that is nonpolar.
    • Hydrocarbon chains are typically 16-18 carbons long.
    • Glycerol contains 3 hydroxyl groups that react with the carboxyl groups of fatty acids to form ester linkages.

Saturated and Unsaturated Fatty Acids

  • Saturated fatty acids: All bonding sites filled with hydrogens; contain only single bonds between carbon atoms.
  • Unsaturated fatty acids: Some double bonds present, resulting in kinks in the molecular structure, which prevent solidification at room temperature (RT).
  • Polyunsaturated fatty acids: Have 2 or more double bonds (C=C).
  • Example Fats:
    • Unsaturated fats are typically liquid at RT (e.g., corn oil).
    • Saturated fats tend to be solid at RT (e.g., coconut oil).
    • Hydrogenation of vegetable oils can produce trans fatty acids.

Omega Fatty Acids

  1. Omega-3: Signals the body to “burn” fat (found in salmon, walnuts, flaxseeds).
  2. Omega-6: Signals the body to “store” fat (found in soy).
  3. Omega-9: Found in avocados, almonds, and olive oil.
  • Note: Omega refers to the position of the first double bond in the hydrocarbon chain.

Major Functions of Triglycerides

  • Energy storage: 1g of fat provides 9 Kcal of energy, whereas 1g of carbohydrate provides just 4 Kcal.
  • Comparison: Plants store energy in bulky starch, while animals store energy in compact fat form.

Membrane Lipids (Phospholipids)

  • Structurally consist of glycerol, 2 fatty acids, and a phosphate group (which is negatively charged).
  • Arrangement: Phospholipids form a bilayer with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails inward.

Steroids

  • Important steroid: Cholesterol.
  • Functions: Cholesterol stabilizes cell membranes and is a precursor for the synthesis of other steroids.

Prostaglandins

  • Derived from fatty acids in cell membranes, mimicking hormones and controlling various functions such as blood pressure and pain response.

Vitamins as Lipids

  • Fat-soluble vitamins include:
    1. Vitamin A: Involved in vision; derived from carotene in orange fruits and vegetables.
    2. Vitamin D: Essential for various bodily functions.
    3. Vitamin E: Antioxidant, promotes wound healing.
    4. Vitamin K: Important for blood clotting.
  • Water-soluble vitamins: B and C.

Proteins

Definition and Composition

  • The most abundant organic molecule, making up 50% of an organism's dry weight.
  • Made of amino acids, which link to form polypeptide chains.
  • Proteins consist of C, H, O, N, and some S (notably containing nitrogen).

Categories of Proteins

  1. Structural proteins: Examples include collagen and keratin, making up major components of body structure.
  2. Regulatory proteins: Primarily hormones, including many that are polypeptides derived from amino acids.
  3. Contractile proteins: Important in muscle contractions, such as actin and myosin.
  4. Transport proteins: Including hemoglobin, which transports oxygen in red blood cells.
  5. Membrane-receptor proteins: Involved in cellular signaling and response mechanisms.
  6. Catalytic proteins: These are enzymes that facilitate biochemical reactions.

Amino Acids

  • There are 20 different amino acids.
  • Amino acids are linked by peptide bonds (a type of covalent bond).

Structure Levels of Proteins

  • Primary structure: Sequence of amino acids linked by peptide bonds.
  • Secondary structure: Includes alpha (helical) and beta (pleated sheet) configurations formed due to hydrogen bonds. Sensitive to pH and temperature.
  • Tertiary structure: Three-dimensional configuration due to interactions among R groups of amino acids.
  • Quaternary structure: Interaction between two or more polypeptide chains.
  • Examples: Fibrous protein (collagen) and globular proteins (enzymes, antibodies).

Enzymes

  • Enzymes are biological catalysts that lower activation energy for reactions.
  • Have an active site where substrates bind, leading to the formation of products.
  • Names of enzymes often include the suffix -ase (e.g., lactase).

Nucleic Acids

Structure and Function

  • Nucleic acids include DNA and RNA.
  • Monomer: Nucleotide, composed of:
    1. Phosphoric acid.
    2. Pentose sugar (ribose or deoxyribose).
    3. Nitrogenous base (either pyrimidines - cytosine, thymine [in DNA], uracil [in RNA] or purines - adenine and guanine).

Language of Nucleic Acids

  • DNA and RNA are polymers of nucleotides.
  • Language of proteins is based on the codons derived from amino acids.
  • Processes:
    1. Replication: Making an identical copy of DNA (DNA → DNA).
    2. Transcription: Changing DNA to RNA (DNA → mRNA, tRNA, rRNA).
    3. Translation: Converting RNA to protein (RNA → protein) using the codon dictionary.

ATP (Adenosine Triphosphate)

  • Structure: Composed of adenine, ribose, and three phosphate groups.
  • Synthesis via the addition of phosphate groups using energy captured from metabolic processes.

Genetic Code (Codon Dictionary)

  • Represents the genetic code of RNA by showing how nitrogenous bases encode amino acids.
  • Examples include:
    • UAU codes for the amino acid tyrosine.
    • Overall, the code is utilized during transcription and translation processes to synthesize proteins based on the genetic information in DNA.