Biological Macromolecules

Biological Macromolecules

  • Types of Macromolecules: Carbohydrates, Lipids, Nucleic Acids, Proteins

Carbohydrates

Structure and Function

  • Four Major Roles of Carbohydrates:
      - Source of Stored Energy: Carbohydrates serve as a reservoir of energy that can be converted into usable forms by organisms.
      - Transport of Stored Energy: They help in the distribution of energy resources within complex organisms.
      - Structural Molecules: Carbohydrates provide shape and support to organisms.
      - Recognition/Signaling Molecules: They can trigger specific biological responses, functioning in cell signaling.

Characteristics of Sugars

  • Functional Groups:
      - Multiple Hydroxyl Groups
      - 1 Carbonyl Group (C=O)
        - Aldehydes: Carbonyl at the end (e.g., Glucose)
        - Ketones: Carbonyl in the middle (e.g., Fructose)

  • Carbon Skeleton Size: Range from 3 to 7 Carbons
      - Trioses: 3 Carbons
      - Pentoses: 5 Carbons
      - Hexoses: 6 Carbons

  • Spatial Arrangement: Asymmetric carbons lead to different spatial configurations; e.g., glucose and galactose are enantiomers with distinct biochemical properties.

  • Formation of Ring Structures: Many sugars form ring structures when in solution.

Monosaccharides

  • Definition: "Simple sugars"

  • Common Examples:
      - Glucose, Galactose, Ribose
      - Other Pentoses: Deoxyribose, Fructose
      - Other Hexoses: Mannose

  • General Formula: C₁:H₂:O₁

  • Function in cells: Nutrient source; energy storage; raw material for other compounds.

Types of Monosaccharides:

  • Triose Sugars: C₃H₆O₃

  • Pentose Sugars: C₅H₁₀O₅

  • Hexose Sugars: C₆H₁₂O₆

Disaccharides

  • Definition: "Double sugars"

  • Examples:
      - Maltose (Glucose + Glucose)
      - Lactose (Glucose + Galactose)
      - Sucrose (Glucose + Fructose)

  • Formation: Created through dehydration synthesis, resulting in glycosidic linkages.

Polysaccharides

  • Definition: "Complex sugars"

  • Examples: Starch, Glycogen, Cellulose, Chitin

  • Functions: Energy storage and structural support.

  • Formation: Via dehydration synthesis of several monosaccharides; linked by glycosidic bonds and may also have functional groups.

  • Unique Properties: Glycogen is water-insoluble and often attached to proteins/lipids on cell surfaces, aiding in recognition signals (e.g., A/B/O blood types).

Storage Polysaccharides

  • Starch:
      - Polymer of glucose; energy storage in plants.
      - Forms:
        - Amylose (unbranched)
        - Amylopectin (branched)
      - Major source for humans: Potato & grains.

  • Glycogen:
      - Glucose polymer in animals, highly branched; primarily stored in muscle and liver.

Structural Polysaccharides

  • Cellulose:
      - Linear, unbranched polymer of D-glucose; major structural component of plant cell walls.
        - Glycosidic Linkages: 1-4 linkage (beta) differs from starch's 1-4 linkage (alpha).
      - Reinforces plant cell walls and forms microfibrils through H-bonds.
      - Indigestible for most organisms due to lacking enzymes.

  • Chitin:
      - An amino sugar structural polysaccharide; forms exoskeletons in arthropods and building material in some fungi.
      - Used in surgical threads; monomer consists of amino sugar.

Lipids

Definition and Characteristics

  • Polymers: Not considered true polymers.

  • Composition: Organic macromolecules containing carbon, hydrogen, and oxygen (CHO).
      - Few oxygen atoms compared to carbohydrates.

  • Examples:
      - Fats (solid form), Oils (liquid form), Waxes, Steroids (cholesterol, hormones), Triglycerides (glycerol + 3 fatty acids), Phospholipids.

Functional Properties

  • Non-polar: Share electrons equally, leading to no positive or negative pole.

  • Insoluble in Water: Lipids do not dissolve in water.

Functions of Lipids

  • Long-term Energy Storage: Compared to carbohydrates which provide quick energy.

  • Membrane Formation: Foundation of the phospholipid bilayer (cell membrane).

  • Protective Coatings: Example includes the protective surface of plant leaves.

Monomers of Lipids

  • Glycerol and Fatty Acids:
      - General structure of a fatty acid: CH3(CH2)nCOOHCH_3(CH_2)^nCOOH, where n ranges from 2 to 24.

  • Triglycerides: Composed of glycerol plus 3 chains of fatty acids.

Fatty Acids

  • Saturated Fatty Acids:
      - Long tail of hydrocarbons with single bonds; solid at room temperature.
      - Examples include Lard, Butter.

  • Unsaturated Fatty Acids:
      - Hydrocarbon tails contain double bonds; liquid at room temperature (e.g., Corn oil, Olive oil).

Lipid Reformation Process

  • Dehydration Synthesis:
      - Foods are digested via enzymes, resulting in hydrolysis to form monomers, which are then reformed into larger molecules.

  • Example Reactions:
      - Starch + Water → Glucose
      - Triglyceride + 3 Water → Glycerol + 3 Fatty Acids
      - Ester Linkage: Bonds formed between glycerol hydroxyl groups and fatty acids.

Functions of Lipids Continued

  1. Energy Storage: More efficient than carbohydrates, providing twice the energy.

  2. Thermal Insulation: Adipose tissue reduces heat loss (e.g., blubber in cold climates).

  3. Buoyancy: Less dense than water, aiding in floating.

  4. Membrane Formation: Phospholipids form the core of cell membranes.

Steroids

  • Structure: Lipids made of four fused carbon rings with various functional groups.

  • Cholesterol:
      - Key steroid; a precursor for other steroid hormones and a common component in animal cell membranes.
      - Contributes to atherosclerosis when present in excess.

  • Health Statistics: About 10% of people aged 12-19 have blood cholesterol levels that may increase heart disease risk.

Nucleic Acids

Definition and Composition

  • Elements Present: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P).

  • Functions: Involved in heredity and information transmission.

  • Source in Diet: Found in any cellular material, essentially all foods.

  • Monomeric Units: Made of nucleotides, forming either oligonucleotides (e.g., RNA primers) or polynucleotides (e.g., DNA).

Types of Nucleic Acids

  1. Deoxyribonucleic Acid (DNA):
       - Master template of genetic code; self-replicating; contains instructions for protein synthesis.
       - Pentose sugar lacks the 2' OH group.

  2. Ribonucleic Acid (RNA):
       - Functions in protein synthesis, guided by DNA instructions.
       - Example: mRNA.

Structure of Nucleotides

  • Components of Nucleotides:
      - Phosphate Group
      - 5-Carbon Sugar
      - Nitrogenous Base

  • Nucleoside: Sugar + Base (i.e., nucleotide without the phosphate group).

Nitrogenous Bases

  • Four Types:
      - Cytosine (C)
      - Thymine (T)
      - Adenine (A)
      - Guanine (G)
      - In RNA: Uracil (U) replaces Thymine.

Families of Nitrogenous Bases

  1. Pyrimidines: One ringed structure (C, H, N).
       - Examples: Cytosine, Thymine, Uracil.

  2. Purines: Two-ring structure.
       - Examples: Adenine, Guanine.

Linking of DNA Nucleotides

  • Nucleotides are linked by dehydration synthesis/condensation reactions, forming phosphodiester bonds.

  • Orientation: 5'→3' (phosphate of one nucleotide links to the sugar of the next).

DNA Structure

  • Strands: Two sides formed of phosphates and deoxyribose sugars; steps made of nitrogenous bases.

  • Base Pairing:
      - A pairs with T (or U in RNA) via 2 hydrogen bonds.
      - G pairs with C via 3 hydrogen bonds.

  • Anti-parallel fashion: The two strands run in opposite directions.

Proteins

Nature and Composition

  • Elements Present: C, H, O, N, and sometimes S.

  • Functions in Organisms:
      - Storage, Transport, Regulatory functions, Movement, Structural roles, Catalyzing reactions, Cell to cell recognition.

  • Dietary Sources: Meat, fish, beans, eggs, nuts, dairy.

Functions of Proteins

  • Examples:
      - Hemoglobin: Transports oxygen in blood.
      - Actin/Myosin: Responsible for muscle movement.
      - Insulin: Hormone regulating glucose levels.
      - Immunoglobins: Antibodies combatting pathogens.
      - Amylase: Catalyzes starch hydrolysis.

Protein Structure

  • Amino Acids: Building blocks, 20 amino acids form countless proteins via peptide bonds into polypeptides.

  • Each amino acid:
      - Consists of an asymmetric carbon connected to an amino group, carboxyl group, hydrogen, and variable R group.

Proteins Formation

  • Peptide Bond: Formed by dehydration synthesis between an amino group and carboxyl group, releasing water.

Classification of Amino Acids

  • Groups:
      - Non-polar (hydrophobic; water-repelling).
      - Polar (hydrophilic; water-attracting).
        - Charged components:
          - Acidic (negative charge) and Basic (positive charge).

Four Levels of Protein Structure

  1. Primary Structure:
       - Specific sequence of amino acids; peptide bonds hold them together.

  2. Secondary Structure:
       - Hydrogen bonds form between amino acids, creating structures (alpha helix, beta-pleated sheet).

  3. Tertiary Structure:
       - 3D folded structure of a polypeptide caused by various interactions among side chains.

  4. Quaternary Structure:
       - Assembly of multiple polypeptides to form a functional protein.

Protein Misfolding and Denaturation

  • Denaturation disrupts secondary and tertiary structures, usually due to extreme conditions (e.g., heat, pH changes).

Types of Proteins

  • Fibrous Proteins: Long, narrow shapes; insoluble in water; provide structural support (e.g., collagen, keratin).

  • Globular Proteins: Round shapes; soluble; perform functions (e.g., enzymes, hemoglobin).

Functions of Proteins Recap

  1. Structural support (e.g., collagen)

  2. Storage (e.g., casein in milk)

  3. Transport (e.g., hemoglobin)

  4. Hormonal regulation (e.g., insulin)

  5. Movement (e.g., actin, myosin)

  6. Defense against disease (e.g., antibodies)

  7. Catalysis of biochemical reactions (e.g., digestive enzymes).

Conclusion

  • The roles and structures of various biological macromolecules are crucial for life processes, and understanding their functions contributes to knowledge in biochemistry, molecular biology, and genetics.