L3_Biopolymers

Biopolymers Overview

  • Biopolymers include DNA, RNA, and proteins.

  • They are long polymers with specific sequences of subunits (monomers) that are crucial for their function.

  • Synthesis involves copying from a template.

Structure of Biopolymers

General Characteristics

  • Defined beginning and end with synthesis occurring in only one direction.

  • Conventionally written left-to-right.

Nucleic Acids

  • Building blocks: nucleotides composed of phosphate, sugar, and base.

    • Phosphate-sugar backbone is negatively charged and hydrophilic.

    • Two ends: 5' and 3' indicating directionality.

Protein Structure

  • Building blocks: amino acids linked by peptide bonds.

  • Common peptide backbone; side chains (R groups) differ across amino acids.

  • Peptides: short chains (<50 residues); proteins: longer chains (>50 residues).

Synthesis Mechanisms

Nucleotide Polymerization

  • Nucleotide monomers lose part of their structure during polymerization, forming residues in the growing chain.

  • Dehydration reactions required for synthesis, which is an anabolic process that consumes energy.

Peptide Bond Formation

  • Amino acids combine through a condensation mechanism to form dipeptides; energetically unfavorable without biological catalysts (ribosomes).

Characteristic Features of Biopolymers

Peptide Bonds

  • Peptide bonds are planar and rigid due to resonance, allowing rotation around other bonds.

  • Encourage hydrogen bonding crucial for protein structure and function.

Nucleic Acid Structures

  • Include variations in bases: adenine, guanine, cytosine, and thymine (in DNA) or uracil (in RNA).

  • Base pairing occurs through hydrogen bonds between complementary bases (e.g., A-T, C-G).

DNA and RNA

DNA Structure

  • Double helix model discovered in 1953 by Watson and Crick based on prior work by Franklin and Wilkins.

  • Features: antiparallel strands, major and minor grooves, phosphodiester bonds between sugar and phosphate.

RNA Structure

  • RNA typically does not form a B-type helix and can base-pair but is more prone to degradation due to the extra hydroxyl group.

Genetic Information

DNA's Role

  • DNA as genetic material established through various experiments, including those by Griffith and Avery in the early 20th century.

  • Chargaff’s rules for base composition included A=T and C=G ratios, leading to the understanding of DNA structure and function.

Functional Aspects of Nucleic Acids and Proteins

Electrophoresis and Ethanol Precipitation

  • Nucleic acids can be separated based on charge and size through electrophoresis.

  • Ethanol precipitation is a common method for nucleic acid purification.

Mutation and Stability

  • DNA has a lower mutation rate compared to RNA; uracil in RNA exists without repair mechanisms present in DNA to correct deaminated bases.

Glossary of Key Terms

Key Definitions

  • 5' and 3' ends: Orientation markers in nucleic acids.

  • Biopolymer: A polymeric substance in living organisms.

  • Peptide and phosphodiester bonds: covalent bonds that link amino acids and nucleotides, respectively.

  • Tm (Melting temperature): The temperature at which DNA strands separate.