MCB UNIT 1

Unsaturated Fatty Acids and Molecular Structure

• Unsaturated fatty acids contain double bonds between carbon atoms.

• Forming a double bond leads to a kinked structure in the molecule rather than a straight one. This affects the three-dimensional shape of the molecule.

• If additional double bonds are introduced at near identical locations, the kink increases further, affecting interactions between fatty acid molecules.

Biological Implications of Kinking

• Interactions and Fluidity: Tight packing of straight hydrocarbon tails allows for stable structures. In contrast, kinked structures (due to double bonds) create space, leading to increased fluidity and decreased stability.

• Stability vs. Fluidity: More interactions (due to straight tails) increase stability, while fewer interactions (due to kinks) increase fluidity. These are opposing principles.

Adaptations in Cold Environments

• In cold conditions, increased stability is not desirable; less fluidity leads to too tight packing of membrane structures.

• Tail Length: Longer tails increase interaction surface area, enhancing stability. In cold environments, shorter tails are preferable to reduce interactions and maintain fluidity.

  • Example: Prefer tail lengths of 14 carbons over 24.

• Saturation Levels: Introducing more unsaturation (kinks) reduces packing efficiency, allowing for greater fluidity. In cold environments, increased unsaturation is advantageous.

• For optimal conditions in cold temperatures, aim for shorter (14) and unsaturated fatty acids, fostering fluidity.

Role of Peptide Bonds in Protein Structure

• The peptide bond is formed between the carboxyl group of one amino acid and the amino group of another.

• The formation of peptide bonds creates partial double bond character, preventing free rotation about the bond—this is crucial for maintaining structural integrity in proteins.

• This restriction allows for hydrogen bonding between neighboring amino acids, facilitating the formation of secondary structures like alpha helices and beta sheets. Without this, proteins would have less defined structures and functions.

Hydrolysis and Glycosidic Bonds

• Condensation Reaction: When forming disaccharides, two hydrogens and an oxygen are removed (water is released).

• Hydrolysis Reaction: Water is added to break glycosidic bonds, regenerating two monosaccharides. Water acts as a reactant in this process, emphasizing the importance of hydration in breaking down complex carbohydrates.

Stability vs. Strength in Chemical Bonds

• Recognize the distinction:

  • Stability: Refers to the effort needed to form or break a bond, influenced by environmental factors (e.g., heat, pH).

  • Strength: The physical bonding energy itself.

• Ionic bonds are identified as strong but easy to form, requiring no special effort beyond initial conditions. The strength may be high, but stability can be altered by external actions like heat or changes in acidity.