Lecture 2 (II) F24 (PL + Analysis of Lipids + Simple Sugars)

Phosphate Derivatives in Biochemistry

• Phosphoric acid (H3PO4)

  • Triprotic acid: can donate three protons (H+).

  • At neutral pH, it exists as an equilibrium mixture of H2PO4- and HPO4^2-

  • Notation for this mixture is Pi.

  • Phosphorylation process adds negative charges to molecules, increasing their water solubility.

    • Examples include: phospholipids, DNA, RNA, and proteins.

  • pKa = 7.2

Reactions of Phosphoric Acid

• Phosphoric acid reacts with alcohols and acids to form:

  • Phosphate esters

  • Phosphoanhydrides

  • Diagrams indicate the reaction mechanisms:

    • Mixed anhydride formation involves various components returning to phosphate groups plus water.

    • Phosphate ester formation depicted similarly.

Glycerophospholipids

• Also referred to as phosphoglycerides.

• Key components of biological membranes.

• Structure:

  • Glycerol: carbon atoms 1 and 2 are esterified to two fatty acids (tail).

  • A highly polar or charged group (X) attaches to the third carbon via a phosphodiester linkage (head).

  • Amphipathic nature:

    • Hydrophilic head and hydrophobic tail properties allow them to form lipid bilayers.

Classes of Glycerophospholipids

• Major classes categorized by head-group properties.

  • Examples:

    • Phosphatidic Acid: Net charge at pH 7 = -2

    • Phosphatidylcholine (Lecithin): No charge at neutral pH.

    • Phosphatidylethanolamine: No charge at neutral pH.

    • Phosphatidylserine: Net charge = -1.

    • Phosphatidylglycerol: Net charge = -1.

  • Note: Phosphatidylcholine and phosphatidylethanolamine are primary membrane constituents.

Structure of Phosphatidylcholine (Lecithin)

• Represents a class of lipids rather than a singular entity.

• Different combinations of fatty acids yield various phosphatidylcholine molecules.

  • Diagrams show structural variation with global formulas for clarity.

Hydrolysis of Phosphatidylethanolamine

• Complete hydrolysis yields:

  • Glycerol

  • Fatty acid

  • Phosphate

  • Ethanolamine

  • Molar ratio inquiries:

    • Various options presented: A (2:1:1:1), B (1:2:1:1), C (1:1:2:1), D (1:2:1:2)

Lipid Aggregation in Water

• Lipids aggregate spontaneously:

  • Formation of micelles occurs with fatty acids and some other lipids.

  • Phospholipids do not form tight micelles due to bulky hydrophobic tails.

  • Instead, they form lipid bilayers, folding into liposomes or vesicles (key for cell membrane structure).

Functional Groups of Biomolecules

• Overview of common functional groups applicable in biomolecular chemistry, including:

  • Methyl, Ether, Ester, Phosphoryl, Hydroxyl among others with respective representations.

Cold-water Fish Adaptation

• Fish like ice-fish live in sub-zero temperatures:

  • Differences in fatty acids compared to warm-water fish may be:

    • More unsaturated fatty acids in cold-water fish for membrane fluidity.

Lipid Analysis Techniques

• Separation methods include:

  • Column chromatography on silica gel to assess lipid polarity.

  • Thin Layer Chromatography (TLC) for observing lipid movement based on polarity.

• Trans-esterification:

  • Identifies separated fatty acids definitively via mass spectrometry, observing chain length and saturation levels.

Carbohydrates Overview

• Sugars: most abundant biomolecules, vital for energy metabolism and nucleic acid components.

• Classifications:

  • Monosaccharides: single sugar units (e.g., glucose).

  • Oligosaccharides: short chains of monosaccharides (disaccharides, trisaccharides).

  • Polysaccharides: long polymer chains (e.g., glycogen, cellulose).

Chemical Properties of Monosaccharides

• Characteristics include:

  • High solubility in water, low solubility in organic solvents.

  • Colorless and sweet-tasting.

  • General formula: (CH2O)n.

Functional Groups in Monosaccharides

• Presence of carbonyl groups (aldehyde/ketone) and hydroxyl groups (-C-OH).

• Defined as polyhydroxy-aldehydes (aldoses) or polyhydroxy-ketones (ketoses).

Diversity of Monosaccharides

• Simplest monosaccharides: Trioses.

• Variants include:

  • Tetroses, Pentoses, Hexoses, Heptoses.

  • Hexoses (e.g., D-glucose, D-fructose) most common in nature.

Emil Fischer's Contributions

• Fischer’s work in the late 19th century revolutionized understanding of carbohydrate chemistry.

• His contributions to analysis, synthesis, and understanding stereochemistry remain foundational in biochemistry.

Representing Sugar Structures

• Fischer projection: Represents 3D structures on paper (vertical = behind, horizontal = forward).

• Perspective formula: Another representation method using wedge bonds showing 3D orientation.