Lecture Notes on Carbohydrates and Membrane Structure

Introduction to Biological Molecules

• Four main classes of biological molecules:
  • Proteins and amino acids
  • Nucleic acids
  • Carbohydrates (sugars)
  • Lipids

Carbohydrates Overview

• Key focus: carbohydrates (sugars)
• Introduction to carbohydrate structure, nomenclature, and basic membrane structure.
• Importance: critical energy storage molecules for cells, understanding metabolism, and understanding nucleic acid structure.
• Key points from the lecture:
  • Carbohydrates and lipids are essential for energy storage.
  • Membranes are essential for signal transduction.

Definition of Carbohydrates

• Carbohydrate formula: CnH2nOn
• Deviations can occur with added heteroatoms (phosphate, sulfur, nitrogen).
• Basic forms:
  • Monosaccharides: single sugar units.
  • Disaccharides: two sugars, e.g. sucrose (glucose + fructose).
  • Oligosaccharides: few sugar units;
  • Polysaccharides: many sugar units (e.g. starch).

Types of Carbohydrates

• Monosaccharides: simplest sugars, e.g. glucose.
• Disaccharides: e.g. sucrose (table sugar).
• Polysaccharides: e.g. starch (in potatoes).
• Isomers: same chemical formula but different structures (e.g. glyceraldehyde and dihydroxyacetone).
• Stereocenters: carbons with four different substituents, significant in biological activity.

Structure and Stereochemistry

• D and L forms:
  • Stereocenter furthest from the carbonyl determines D (right) or L (left).
  • Epimers: sugars differing at only one stereocenter.
• Common hexoses included:
  • Glucose: D-Glucose (aldose)
  • Fructose: D-Fructose (ketose)
  • Galactose and Mannose: important for nutrition and metabolism.

Pentoses

• Important pentoses include:
  • D-Ribose: Component of nucleic acids.
  • D-Ribulose and D-Xyulose: ketose epimers of ribose.

Ring Structures of Sugars

• Sugars in solution often form rings (e.g., pyranose and furanose forms).
• Alpha and Beta forms: determined by the orientation of the OH group at the anomeric carbon.
• Chair and Boat conformations: describe spatial arrangement of ring structures.

Importance of Carbohydrates

• Influence on taste and biological interactions is crucial.
• Structural differences impact how sugars are metabolized and utilized in the body.

Introduction to Lipids

• Lipids: Class of molecules including fats, phospholipids, and steroids.
• Formation of barriers (membranes) due to hydrophobic properties.
• Phospholipids: Composed of a fatty acid and glycerol, important for cell membrane structure.
• Different types of membrane lipids:
  • Phosphatidylcholine: common in membranes, important for emulsion stability.
  • Other phospholipids include phosphatidylserine and phosphatidylethanolamine.

Membrane Structure and Function

• Bilayer formation: Hydrophobic tails face inward, hydrophilic heads face outward.
• Membranes help compartmentalize biological processes and facilitate signal transduction.
• Different proteins can insert into membranes, impacting cellular processes.

Summary and Next Steps

• Review of carbohydrates, their structure, and biological relevance.
• Introduction to membranes and their lipid compositions.
• Prepare for more detailed discussions on metabolism and cell signaling after Spring Break.