C

Biology: Chap. 3

Monomers of Carbohydrates

  • Monosaccharides: Monomers of carbohydrates (simple sugars) composed of six carbons; primarily hexoses.
    • Common hexoses include:
    • Glucose
    • Fructose
    • Galactose
    • These are isomers (same chemical formula, different structures).

Dimers of Carbohydrates

  • Disaccharides: Formed from two monosaccharides connected by a covalent bond.
    • Examples:
    • Sucrose: Composed of glucose and fructose, linked via dehydration synthesis.
    • Lactose: Composed of glucose and galactose, linked similarly.
    • Sometimes collectively referred to as simple sugars alongside monosaccharides.

Polymers of Carbohydrates

  • Polysaccharides: Large chains of monosaccharides.
  • Oligosaccharides: Medium-length chains that can be difficult to digest.
  • Primary polysaccharides discussed:
    • Chains of glucose:
    • Amylose: Linear with few branches.
    • Amylopectin: Branched structure.
    • Glycogen: Highly branched, mainly in animals for energy storage (1-6 linkages every so often).

Linkages

  • α(1→4) Glycosidic Linkages: Most common form between glucose units in starch.
  • α(1→6) Glycosidic Linkages: Create branches in starch, less frequent.

Starch

  • Purpose: Long-term energy storage in plants (e.g., potatoes, grains).
  • Composition tends to be about 70-80% amylopectin, and the rest amylose.
  • Cooking impacts texture based on the balance of amylopectin and amylose.
  • Glutinous rice: Contains no amylose, used in sushi, sticky rice dishes.

High Fructose Corn Syrup (HFCS)

  • Derived from corn starch (amylose and amylopectin).
  • Process: 1) Hydrolysis by amylase (breaks starch into glucose); 2) Conversion of glucose to fructose by isomerase.
  • Composition: Typically a 50/50 blend of glucose and fructose.

Cellulose

  • Polysaccharide composed of β(1→4) glycosidic linkages, making it structurally different from starch.
  • Provides rigidity to plant cell walls; most organisms cannot digest cellulose, acting as fiber in the human diet.

Lipids

Types of Lipids

  1. Triglycerides (Fats)

    • Composed of glycerol and three fatty acids (saturated or unsaturated).
    • Function: Long-term energy storage.

  2. Phospholipids

    • Similar structure as triglycerides but with two fatty acids and a phosphate group.
    • Form cell membranes (phospholipid bilayer); hydrophilic head and hydrophobic tail.

Steroids

  • Medium-sized hydrophobic molecules with a structure of carbon rings.
  • Example: Cholesterol, crucial for cell membrane fluidity and as a precursor for hormones.

Hormonal Steroids

  • Include hormones like testosterone and cortisol, playing roles in cellular communication.
  • Most hormones in the body are proteins; a minority are steroids.

Proteins

  • Composed of amino acids (20 types) linked by peptide bonds formed through dehydration synthesis.
  • Protein function is determined by shape, which is determined by the amino acid sequence.
  • Proteins can be hundreds to thousands of amino acids long.

Amino Acid Structure

  • Contains a central carbon bonded to:
    • An amino group (NH2)
    • A carboxylic acid group (COOH)
    • A hydrogen atom
    • A variable R group (side chain), which defines the amino acid's identity and properties.

Building Proteins

  • Amino acids are joined by peptide bonds, creating polypeptide chains.
  • Protein shape influences its function, leading to different functional roles in the body.