KH1

Introduction to Biopolymers

  • Lecture: BIOL 200 Aug 30, 2024 by Ken Hastings

  • Text Reference: Lodish Chapter 2.2, 5.1 (9th ed pp 44 - 50, 179-185)

DNA, RNA, and Proteins: The Informational Biopolymers

  • Definition of Polymer: A polymer is a covalent bond-linked chain of monomers.

  • Informational Polymers: Characterized by multiple types of monomers; the sequence of these monomers carries information (e.g., DNA sequence, RNA sequence, and protein sequence).

Structure of Informational Biopolymer Monomers

  • Common Generic Structure: All monomers in a class of informational biopolymer share a common element and a distinct characteristic element.

    • Common Element: Forms the polymer backbone through covalent bonding between monomers.

    • Characteristic Element: Forms side-chains protruding from the backbone.

Polymerization and Structure

Polymer Backbone and Side-Chains

  • Before Polymerization: The common and characteristic elements are distinct before the process commences.

  • After Polymerization: Covalent bonds form between monomers, establishing the backbone and side-chains.

Sequence as Information

  • Different sequences of monomer units result in different information encoded within the polymer (e.g., Yellow-Red-Green vs. Red-Red-Green).

Monomer Chemistry Determines Polymer Structure

  • If a monomer has ONE joining site, only two monomers can connect, preventing polymer formation.

  • If a monomer has TWO joining sites, linear polymers can form efficiently with exposed ends for further growth.

  • If a monomer has THREE joining sites, branched polymers can be produced.

Characteristics of Informational Biopolymers

  • Linear Nature: Informational biopolymers are linear, not branched. Some can form circular structures (e.g., genomic DNA in bacteria).

  • Efficiency: Linear molecules may be easier to package and handle than branched forms.

Asymmetrical Monomers and Polymer Growth

  • Informational biopolymer monomers are asymmetric, featuring two different joining sites (A and B).

    • Chemical Distinction: A joins only with B and vice versa, leading to a distinct directionality in polymer growth.

  • Growth is unidirectional, typically depicted to occur in the rightward direction with new monomers added at the right end.

Main Types of Monomer Units for Informational Biopolymers

Nucleotides and Amino Acids

  • Nucleic Acids: Composed of nucleotide monomers with varying chain lengths (e.g.,

    • DNA: ~10 to ~10

    • RNA: ~20 to ~10).

  • Proteins: Comprised of amino acid monomers, also with typical lengths (e.g., ~100 to ~10).

Nucleotide Structure

  • Common Elements: Include a pentose sugar, phosphate group, and heterocyclic base.

  • Polarity: The common elements provide orientation known as 5' and 3' ends; polymer growth occurs by adding monomers to the 3' end.

  • DNA and RNA Differences: DNA contains deoxyribose (lacking 2'-OH) which enhances stability compared to ribose found in RNA.

Nucleotide Bases and Their Properties

Purines vs. Pyrimidines

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

  • Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U).

  • Repair Mechanisms: Presence of T instead of U in DNA aids in damage repair.

Polarity in Nucleotide Chains

  • Phosphodiester Bonds: Links between adjacent nucleotides involve ester linkages joining phosphate to 5' and 3' OH groups.

Protein Structure

  • Common Elements: Comprise an alpha carbon connected to an amino group (NH2) and a carboxyl group (COOH).

  • Stereoisomers: Only L-amino acids participate in protein synthesis; polarity reflected in amino and carboxyl ends.

Amino Acid Classes

  • Hydrophobic (8): Comprised of nonpolar side chains.

  • Hydrophilic (9): Including acidic and basic side chains.

  • Special (3): Have unique properties.

Polymer Formation and Enzyme Mechanisms

  • Energizing Monomers: Nucleotides are activated into high-energy nucleoside triphosphates; linked to the growing chain through enzyme-catalyzed reactions.

  • Monomers: In the form of NTPs (ATP, CTP, GTP, UTP) and their deoxy variants.

RNA and Protein Synthesis

  • RNA as Template: Ribosomes utilize mRNA as a template for protein synthesis; amino acids linked through high-energy tRNA esters.

DNA Structure and Properties

  • Double-Stranded Nature: DNA usually exists as duplex DNA, held together by hydrogen bonds forming Watson-Crick base pairs.

  • Antiparallel Orientation: Two strands oriented 5' to 3' in opposite directions.

  • Helical Structure: Exists in a right-handed form termed "B" DNA.

Base Pairing and Interactions

  • Grooves: DNA-binding proteins contact specific sequences through major or minor grooves without needing to separate the strands.

DNA Denaturation and Renaturation

  • Denaturation: Separation of DNA strands occurs via heat (melting); denatured strands can re-associate, highlighting the stability of base pairing.

  • Biological Relevance: Crucial for DNA replication and transcription; exploited in molecular biology techniques.

Thermal Melting Behavior (Tm)

  • Tm's Dependence: Higher G-C content results in a higher melting temperature due to the strength of three hydrogen bonds in G-C pairs compared to two in A-T pairs.

DNA Bending and Structural Dynamics

  • Functional Importance: DNA can bend and compact, facilitating interactions with DNA-binding proteins.