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.