BIOM1050/BIOM1070 Module 1: Cell Biology DNA, Protein & the Central Dogma

Overview of Cell Biology, DNA, Protein, and the Central Dogma

• Course: BIOM1050/BIOM1070

• Lecturer: Dr. Henry de Malmanche

• Key Concept: Understand the central dogma of molecular biology, including DNA, RNA, and protein synthesis.

Learning Objectives

• Explain the directionality of DNA and its relation to leading and lagging strands during replication.

• Match DNA replication enzymes to their specific functions.

• Define key terms:

  • Central Dogma: The flow of genetic information from DNA to RNA to protein.

  • Transcription: The process of copying a segment of DNA into RNA.

  • Translation: The synthesis of a protein from the mRNA sequence.

• Translate mRNA sequences into corresponding proteins using the genetic code.

• Describe the roles of proteins within cells (e.g., structure, function, movement).

• Draw and understand the structure of amino acids and their role in protein diversity.

• Interpret various representations of protein structure (1o, 2o, 3o, 4o).

• Discuss the implications of mutant protein sequences on function and health.

Structure of DNA and RNA

• Directionality: DNA and RNA strands have polarity; they run in a 5' to 3' direction.

• Leading Strand: Synthesized continuously towards the replication fork.

• Lagging Strand: Synthesized in fragments away from the replication fork.

DNA Replication Enzymes

• DNA Polymerase: Synthesizes new DNA strands.

• Helicase: Unwinds the DNA double helix.

• Primase: Synthesizes a short RNA primer.

• Ligase: Joins Okazaki fragments on the lagging strand.

The Process of Transcription

1. Initiation: RNA polymerase binds to the promoter region of DNA.

2. Elongation: RNA strand is synthesized from the DNA template.

3. Termination: RNA polymerase detaches when it reaches a termination signal.

4. Processing: In eukaryotes, pre-mRNA undergoes capping, polyadenylation, and splicing (removal of introns).

The Process of Translation

1. Initiation: The small ribosomal subunit binds to mRNA and the start codon.

2. Elongation: tRNAs bring amino acids to the ribosome; peptide bonds form between adjacent amino acids.

   • Sites in Ribosome:

     • A site: Accepts the incoming tRNA.

     • P site: Holds the growing polypeptide chain.

     • E site: Exit site for tRNAs.

3. Termination: Completion occurs when a stop codon is encountered, and release factors promote disassembly of the ribosome and release of the polypeptide.

Transfer RNA (tRNA)

• Functions as an adaptor between mRNA codons and amino acids.

• Each tRNA has an anticodon complementary to its associated codon on mRNA.

• Synthesized by aminoacyl tRNA synthetases which attach the correct amino acid to its corresponding tRNA.

Protein Structure

• Primary Structure (1°): Linear sequence of amino acids linked by peptide bonds.

• Secondary Structure (2°): Includes alpha helices and beta sheets formed via hydrogen bonding.

• Tertiary Structure (3°): The overall 3D shape of a polypeptide due to interactions among side chains.

• Quaternary Structure (4°): The assembly of multiple polypeptide subunits.

Mutations and Their Effects

• Types of Mutations:

  • Point Mutation: A single nucleotide change can lead to missense (different amino acid) or nonsense (stop codon) mutations.

  • Frameshift Mutation: Caused by insertion or deletion of nucleotides, altering the reading frame and affecting downstream protein structure.

  • Silent Mutation: No change in amino acid sequence.

• Mutations in the p53 gene can lead to cancer susceptibility; over 50% of cancer patients have a mutated version.

Function of Proteins

• Proteins have diverse roles including:

  • Catalyzing biochemical reactions (enzymes).

  • Transporting substances across membranes.

  • Providing structural support.

  • Facilitating movement and cellular communication.

Summary of Key Terms

• Ribosome: Site of protein synthesis, made of RNA and proteins.

• Codon: A sequence of three nucleotides on mRNA that codes for an amino acid.

• Anticodon: A sequence of three nucleotides on tRNA that pairs with a codon on mRNA.

• Peptide Bond: The bond formed between amino acids during protein synthesis.

This overview encapsulates the essential concepts needed to understand the central dogma of molecular biology, structure and function of proteins, and the implications of mutations in genes.