Overview
This lecture covers the structure and function of nucleic acids (DNA, RNA, ATP, ADP) and proteins, explaining how genetic information is used to assemble proteins and emphasizing the critical importance of sequence and shape for protein function.
Relationship Between Nucleic Acids and Proteins
- DNA contains the genetic code that determines the amino acid sequence of proteins.
- The process of making proteins involves transcription (DNA to RNA) and translation (RNA to protein).
- Errors in DNA sequence can result in genetic disorders due to incorrect protein formation.
- A gene is a DNA segment coding for one protein.
- mRNA carries the DNA recipe to ribosomes for protein assembly.
Types and Structure of Nucleic Acids
- Types: DNA, RNA (mRNA, tRNA, rRNA), ATP, and ADP.
- Nucleic acids are made of nucleotide monomers.
- Each nucleotide consists of a pentose sugar (ribose/deoxyribose), phosphate group, and nitrogenous base.
- DNA uses deoxyribose, bases A, C, G, T; RNA uses ribose, bases A, C, G, U.
- DNA is double-stranded and antiparallel; RNA is single-stranded.
- ATP/ADP are nucleic acids used for energy, not genetic coding.
Structure and Formation of Proteins
- Proteins are polymers made up of 20 different amino acids.
- Amino acids have a central (alpha) carbon, amino group, carboxyl group, hydrogen, and variable R group.
- Polypeptide chains are formed by linking amino acids via dehydration reactions.
- The sequence of amino acids determines protein structure and function.
- The polypeptide folds into a specific three-dimensional shape to become functional.
Levels of Protein Structure
- Primary: amino acid sequence (most critical for function).
- Secondary: patterns formed by hydrogen bonds (alpha helix, beta-pleated sheet).
- Tertiary: overall 3D shape from R group interactions (conformation).
- Quaternary: assembly of multiple polypeptide chains (not present in all proteins).
Protein Shape and Function
- Correct amino acid sequence is crucial for proper folding and function.
- Protein denaturation occurs from changes in pH, temperature, or salinity, causing loss of function.
- One amino acid change (mutation) can cause diseases (e.g., sickle cell anemia).
Categories of Proteins and Their Functions
- Enzymes: catalyze chemical reactions (e.g., digestive enzymes).
- Storage proteins: store amino acids (e.g., egg white, milk protein).
- Structural proteins: provide support (e.g., collagen, keratin).
- Contractile proteins: enable movement (e.g., muscle proteins).
- Receptor proteins: receive signals at the cell surface.
- Transport proteins: move substances (e.g., hemoglobin).
- Hormones: chemical messengers (e.g., insulin, glucagon).
- Defensive proteins: protect against disease (e.g., antibodies).
Key Terms & Definitions
- Transcription — Process of copying DNA to messenger RNA.
- Translation — mRNA-directed protein assembly at the ribosome.
- Gene — DNA region coding for a protein.
- Nucleotide — Monomer unit of nucleic acids.
- Polypeptide — Chain of amino acids (not yet a functional protein).
- Denaturation — Structural change in a protein causing loss of function.
- Antiparallel — Two strands running in opposite directions (DNA).
- Complementary base pairing — A pairs with T (DNA) or U (RNA); C pairs with G.
Action Items / Next Steps
- Watch the linked video illustrating the DNA–RNA–protein relationship.
- Know the categories and examples of proteins.
- Familiarize with differences between DNA and RNA structure.
- Be able to identify a nucleotide and an amino acid structure.