Carbohydrates, Lipids, and Proteins

Carbon Structure and Bonding

    Carbon Chains vs. Rings:

  • Chains can be straight or branched
  • Rings are closed-loop structures

    Tetravalence of Carbon:

  • Carbon forms four covalent bonds → creates complex 3D molecules essential for life

    Single, Double, and Triple Bonds:

  • Single = flexible, linear
  • Double = rigid, introduces kinks
  • Triple = shortest and strongest

    Strong Covalent Bonds:

  • Makes carbon-based molecules stable and durable (e.g. proteins, DNA)

Macromolecules and Polymers

    Macromolecules:

  • Large molecules made of monomers
  • Formed by condensation reactions (removes water)
  • Broken down by hydrolysis (adds water)

    ATP's Role in Polymer Formation:

  • Provides energy for synthesizing proteins, carbohydrates, and nucleic acids

    Hydrolysis and Energy:

  • Hydrolysis of ATP releases energy for cell activities

Carbohydrates

    Monosaccharides:

  • Simple sugars; building blocks of carbohydrates

    Polysaccharides:

  • Long chains of monosaccharides (e.g. starch, glycogen, cellulose)
  • Broken down by enzymes like amylase and maltase

    Functions:

  • Primary energy source
  • Structural support
  • Cell communication

    Ring vs. Linear Sugars:

  • Ring forms are more stable and biologically active

    Glucose Solubility:

  • Hydroxyl groups form hydrogen bonds → soluble in blood → easily transported for energy

Polysaccharide Structures and Functions

    Glycogen (animals):

  • Highly branched → rapid glucose release for energy

    Amylose (plants):

  • Helical and compact → efficient energy storage

    Cellulose (plants):

  • Straight, unbranched chains stack tightly → structural strength in cell walls

    Functional Comparison:

  • Cellulose = structure
  • Amylose/Glycogen = energy storage

Glycoproteins and Cell Recognition

    Definition:

  • Proteins with attached carbohydrate chains

    Functions:

  • Cell recognition
  • Communication
  • Adhesion

    Cell-to-Cell Recognition:

  • Help distinguish 'self' vs. 'non-self' (immune response, tissue integrity)

    Carbohydrate Chain Role:

  • Unique markers for each cell type → enables specific recognition

    Immune Function:

  • Errors can cause autoimmune diseases
  • Detect abnormal cells like cancer or infections

    Dynamic Nature:

  • Glycoproteins adapt via changing carbohydrate chains in response to conditions

Lipids

    Definition:

  • Nonpolar, hydrophobic molecules made of carbon and hydrogen

    Water Insolubility:

  • Hydrocarbon structure prevents hydrogen bonding with water

    Biological Roles:

  • Membrane structure
  • Energy storage
  • Waterproofing
  • Hormone transport

    4 Classes:

  • Triglycerides
  • Phospholipids
  • Waxes
  • Steroids

    Triglyceride Structure:

  • Three fatty acid chains + one glycerol

    Functions of Triglycerides:

  • Long-term energy
  • Insulation
  • Organ protection

    Lipid Formation:

  • Created through condensation reactions (water released when forming bonds)

Lipids – Structure and Function

    Thermal Insulation and Storage:

  • Triglycerides in adipose tissue form water-excluding droplets for thermal insulation
  • They trap heat and reduce body heat loss
  • They protect and cushion vital organs

    Fats vs. Oils:

  • Fats: Solid at room temperature; mostly saturated fatty acids
  • Oils: Liquid at room temperature; richer in unsaturated fatty acids

    Phospholipids and Cell Membranes:

  • Amphipathic: Hydrophilic (polar) head and hydrophobic (nonpolar) tails
  • In water, form a bilayer: heads face water, tails inward
  • Minimizes energy and creates stable membrane

    Functions of Bilayer:

  • Compartmentalization of cell contents
  • Selective permeability: allows certain substances through while blocking others
  • Fluidity (due to lateral movement of lipids/proteins)

    Dynamic Nature:

  • Phospholipids and embedded proteins move within the membrane

    Phospholipids vs. Triglycerides:

  • Triglycerides: 3 fatty acid chains + glycerol
  • Phospholipids: 2 fatty acid chains + phosphate group + glycerol

    Fatty Acid Types:

  • Saturated: No double bonds
  • Monounsaturated: One C=C double bond
  • Polyunsaturated: Multiple C=C double bonds

Other Lipids

    Waxes:

  • Waterproof, protective coatings (e.g. plant cuticles, bird feathers)

    Steroids:

  • Structure: 4 fused hydrocarbon rings with functional groups
  • Function: Hormone signaling (e.g. testosterone, cortisol)

    Hormone Transport:

  • Steroid hormones are nonpolar → easily pass through lipid bilayer
  • Functional groups give steroids their specific biological functions

Proteins – Structure and Function

    Basic Structure:

  • Proteins: Chains of amino acids (polymers)
  • Amino Acid Core - central carbon bonded to:
    • Amino group (–NH₂)
    • Carboxyl group (–COOH)
    • R-group (varies)

    R-Group Categories:

  • Polar: Partial charges (e.g. serine)
  • Nonpolar: Hydrocarbon chains (e.g. valine)
  • Negatively Charged (Acidic): Carboxyl groups (e.g. aspartic acid)
  • Positively Charged (Basic): Amine groups (e.g. lysine)
  • Diversity: 20 R-groups → diverse functions and properties in proteins

    Amino Acids and Roles:

  • Signaling: Some amino acids act as neurotransmitters
  • Transport: Contribute to active transport proteins, channels, etc.
  • Essential: Must be obtained through diet
  • Non-essential: Synthesized by the body
  • Conditional: Needed in special conditions (e.g. stress, pregnancy)

    Protein Deficiency Malnutrition:

  • Results from lack of essential amino acids
  • Common in strict vegan diets without supplementation
  • Symptoms: Fatigue, muscle loss, immune dysfunction

    Peptides and Polypeptides:

  • Peptides: Short chains of amino acids
  • Dipeptide: Two amino acids joined by a peptide bond
  • Polypeptides: Long chains that can fold into functioning proteins

    Peptides and Polypeptides - Bond Formation:

  • Via dehydration reaction (removal of water)

    Peptides and Polypeptides - Amino Acid Sequence:

  • Determines protein identity and properties
  • 20 amino acids → nearly infinite sequence combinations

Protein Folding and Structure

    Folding:

  • Polypeptide folds into a 3D shape essential for function

    Levels of Structure:

  • Primary: Amino acid sequence
  • Secondary: Alpha helices, beta sheets
  • Tertiary: 3D folding based on R-group interactions
  • Quaternary: Multiple polypeptides combined

    Final Shape:

  • Determined by amino acid sequence and interactions

Denaturation

    Definition:

  • Loss of functional 3D shape

    Causes:

  • High temperature: Breaks weak bonds by increasing vibrations
  • pH changes: Alters charges on R-groups, disrupting ionic/hydrogen bonds