189_2-24-25

Proteins

  • Folding of Proteins

    • Proteins exhibit various levels of structure:

      • Primary Structure: The sequence of amino acids.

      • Secondary Structure: Regular patterns of folds (e.g., alpha helices, beta pleated sheets).

      • Tertiary Structure: The overall three-dimensional shape of a protein due to interactions between amino acid side chains.

      • Quaternary Structure: The arrangement of multiple polypeptide chains into a single functional protein.

  • Proper folding is crucial for protein function.

Protein Denaturation

  • Denaturation: The process where proteins lose their structured shape due to the disruption of non-covalent bonds, leading to loss of function.

  • Normal Folded Protein: Refers to a protein in its proper functional shape.

  • Renaturation: The process of a denatured protein regaining its functional shape under certain conditions.

Factors Leading to Denaturation

  • Common denaturing agents include:

    • Heat: Elevated temperatures disrupt molecular interactions.

    • pH Changes: Alterations in acidity/alkalinity affect hydrogen bonding.

    • Ionic Strength Changes: Variability in salt concentrations disrupts ionic interactions.

    • General Note: Denaturation can be specific to each protein, as their structural integrity varies with environmental conditions.

Lipids

  • Types of Lipids:

      1. Fats:

      • Function in energy storage, insulation, and protection.

      1. Membrane Lipids: Major components of cell membranes.

      1. Steroids: Characterized by a structure of fused rings.

Composition of Fats

  • Fats are composed of two types of molecules:

      1. Fatty Acids:

      • Example: Palmitic acid.

      1. Glycerol:

      • Backbone structure that fatty acids attach to (OH groups).

Types of Fatty Acids

  • Saturated Fatty Acids: No double bonds; usually solid at room temperature.

  • Unsaturated Fatty Acids: Contain one or more double bonds; typically liquid at room temperature due to kinks preventing tight packing.

  • Examples:

    • Monounsaturated (ex. Oleic acid),

    • Polyunsaturated (ex. Linoleic acid).

Trans Fats and Health

  • Trans Fats: Formed when hydrogen is added to unsaturated fats, making them solid.

    • Introduces a rigid structure due to the molecular configuration.

    • Health Risks: Increase LDL ("bad" cholesterol) and decrease HDL ("good" cholesterol).

Triglycerides

  • Formed from glycerol and three fatty acids through dehydration synthesis.

  • Structural diagram for clarity.

Hydrolysis of Fats

  • Process where water is added to break fats into glycerol and fatty acids.

Phospholipids

  • Composition:

      1. Fatty Acids

      1. Glycerol

      1. Polar Group (for example, phosphocholine).

  • Characteristics: Amphiphilic; polar head groups and nonpolar tails allowing formation of bilayers in cell membranes.

Cholesterol and Steroids

  • Cholesterol: Most common steroid in humans, contributes to cell membrane structure and serves as a precursor for steroid hormones.

    • Generally insoluble in water.

  • Emulsifier in bile, aiding in the digestion of fats.

Carbohydrates

  • Basic Formula: C:H:O follows 1:2:1 ratio.

    • Example: Glucose (C6H12O6).

  • Two forms of sugars:

    • Aldose: Contains an aldehyde group.

    • Ketose: Contains a ketone group.

Monosaccharides to Polysaccharides

  • Monosaccharides combine via dehydration synthesis through glycosidic bonds to form disaccharides (example: maltose).

  • Examples of Polysaccharides:

    • Starch: Energy storage in plants, branched form is amylopectin.

    • Glycogen: Storage in animals, more frequent branching than starch.

Cellulose

  • Composed of β-1,4 glycosidic bonds between glucose.

    • Provides structural support in plant cell walls.

  • Only microorganisms can break down cellulose.

Chitin and Peptidoglycan

  • Chitin: Similar to cellulose but contains N-acetylglucosamine.

  • Peptidoglycan: Found in bacterial cell walls, with a structure that includes alternating N-acetyl-muramic acid subunits.

Nucleic Acids

  • Structure: Polymers of nucleotides, each consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group.

  • Functions:

    • Provide fast energy (ATP) and builder of nucleic acid polymers (DNA and RNA).

  • Nitrogenous Bases:

    • Adenine, Guanine (purines) and Thymine, Cytosine, Uracil (pyrimidines).

DNA vs. RNA

  • DNA has Thymine, while RNA has Uracil.

  • DNA comprises deoxyribose, RNA consists of ribose sugars.

  • DNA usually forms double-stranded structures, while RNA is typically single-stranded.

DNA Structure

  • Nitrogenous base pairing:

    • A with T (Apple Trees) and C with G (Chewing Gum).

  • The double helix structure is maintained by antiparallel strands.

The Cell Theory

  • States that cells are the fundamental building blocks of life

    • Cells arise from pre-existing cells and carry out all physiological processes.

  • Prokaryotic cells lack a nucleus, but all cells have plasma membrane, ribosomes, genetic material, and cytoplasm.