AJS_Jan13_lecture_4

Biological Macromolecules Overview

Date: Jan. 13, 2025Session: Lecture 4Source: ©2011 Pearson Education, Inc.

Isomer Types

• Cis isomer: The substituents (Xs) are on the same side of the double bond, which can impact the physical properties such as boiling point and solubility.

• Trans isomer: The substituents (Xs) are on opposite sides of the double bond, often resulting in different chemical and physical properties compared to cis isomers.

• Categories:

  • L isomer: Refers to the configuration of the amino acid that has its amino group on the left in the Fischer projection.

  • D isomer: Refers to the configuration where the amino group is on the right in the Fischer projection.

  • Structural isomers: Molecules that have the same molecular formula but differ in the connectivity of their atoms.

  • Enantiomers: Stereoisomers that are non-superimposable mirror images of each other, crucial in biochemical interactions.

Functional Groups

Definition: Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They add diversity to carbon skeletons and determine the properties of organic compounds.Discussion: Seven key functional groups will be explored throughout the course, including hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups. Each plays a unique role in biological processes and compound reactivity.

Major Biological Macromolecules

Carbohydrates

• Functions: Serve as primary energy sources and provide structural support in cell walls (e.g., cellulose in plants).

• Recognition: Know their basic structure (sugars and polysaccharides) and understand their role in energy storage (starch, glycogen) and cellular recognition (glycoproteins).

Lipids

• Functions:

  • Energy storage: Provide long-term energy storage in adipose tissues.

  • Signaling: Serve as hormones (steroids) and signaling molecules in cellular communication.

  • Structural components: Form lipid bilayers in cell membranes, contributing to cellular integrity and fluidity.

• Recognition: Distinguish between different types based on their properties, including saturated vs. unsaturated fats and the role of phospholipids in membrane structure.

Proteins

• Functions:

  • Enzymatic activity: Act as catalysts to accelerate biochemical reactions.

  • Structural support: Provide structure (e.g., collagen) and support for cells and tissues.

  • Transport: Carry molecules (e.g., hemoglobin transporting oxygen) within organisms.

  • Immune response: Play roles in immune response (e.g., antibodies).

• Recognition: Learn to identify different types of proteins (structural, enzymes) and their specific functions in cellular processes.

Nucleic Acids

• Types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

• Functions:

  • Storage: DNA stores genetic information essential for the development, functioning, growth, and reproduction of all living organisms.

  • Transmission: RNA plays a crucial role in translating genetic information into proteins.

• Recognition: Identify structural components including nucleotides, which consist of a sugar, a phosphate group, and nitrogenous bases (adenine, thymine, cytosine, guanine for DNA; uracil replaces thymine in RNA).

Polymers

• Polymers: Are formed from long chains of covalently linked monomers, which are building blocks of macromolecules.

• Dehydration synthesis: A process where two monomers are joined by the removal of a water molecule, forming a covalent bond.

  • Example:

    • Short polymer + Water (H2O) ⟶ Long polymer (bond formation).

• Hydrolysis: The breakdown of polymers into monomers by adding water, a critical reaction for digestion.

  • Example of hydrolysis process:

    • Long polymer + Water (H2O) ⟶ Short polymer (bond breaking).

Components of Nucleic Acids

• Nucleotide Structure:

  • Components: Consist of a nitrogenous base, a five-carbon sugar, and a phosphate group.

  • Nitrogenous Bases:

    • Pyrimidines: Include Cytosine (C), Thymine (T in DNA), and Uracil (U in RNA).

    • Purines: Include Adenine (A) and Guanine (G).

  • Sugars:

    • Deoxyribose (in DNA)

    • Ribose (in RNA).

  • Phosphate group: Joins the sugar and nucleobase to form a nucleotide, the building block of nucleic acids.

Peptide Bonds

• Peptide bond: A special covalent bond formed by dehydration synthesis among amino acids, linking them to create polypeptides which fold into functional proteins.

• Structure illustrated: Water (H2O) is removed to join two amino acids, resulting in a peptide bond.

Levels of Protein Structure

1. Primary Structure: The unique sequence of amino acids in a polypeptide chain.

2. Secondary Structure: Characterized by the formation of alpha helices and beta sheets, stabilized by hydrogen bonds between backbone components.

3. Tertiary Structure: The overall 3D shape of a polypeptide, formed by interactions among R groups and between R groups and the environment.

4. Quaternary Structure: Formed when multiple polypeptide chains (subunits) assemble into a functional complex.

Lipids:

Types:

• Fats (Triacylglycerols):

  • Consist of a glycerol molecule linked to three fatty acids via ester linkages formed through dehydration reactions.

• Phospholipids:

  • Composed of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails, critical for forming lipid bilayers in aqueous environments.

• Steroids:

  • Molecules characterized by a carbon skeleton consisting of four fused rings, functioning as hormones (e.g., testosterone, estrogen) and as structural components (e.g., cholesterol) in cell membranes.

Conclusion on Biological Macromolecules

• The structure of biological macromolecules is directly linked to their function in cellular processes. Understanding the importance of different macromolecules is crucial for insights into the formation, function, storage, and processing of biological information. Knowledge of these components allows for the exploration of various metabolic pathways and the intricate design of life at the molecular level.

Electronegativity and Polar Groups

• Sulfhydryl group: Considered weakly polar, which influences the interactions and structures of amino acids like cysteine, leading to the formation of disulfide bonds that stabilize protein structure.