Genes to Proteins - Translation / Genetic Engineering / Mutations

Codon Table and Supplemental Materials

  • Grab a codon table printout at the front of the room or in the back (plastic bins).

  • Alternatively, download the codon table (in color) from today's supplemental materials folder (102325) on the course Google Drive space.

Announcements and Reminders

  • COL#2 wrapper due Sunday 10/26/25 (ignore incorrect due date in the survey email).

  • Practice DNA to RNA to Protein (use the example with one simple codon on the non-template strand that will be done today).

  • A Halloween-themed practice assignment is coming soon to assist with gene expression (practicing transcription and translation) and mutations.

  • Today's focus: gene expression, mutations, and interesting considerations around genetic engineering.

Gene Definition and Characteristics

  • A gene is:

    • A protein that expresses other proteins.

    • A section of DNA that holds instructions for building at least one protein.

    • Comprised of mRNA.

    • Produced in a cell’s nucleus when gene expression is activated.

    • The aggregate of all DNA in an organism.

Location of Translation in Eukaryotes

  • Translation occurs in:

    • Ribosomes.

    • Often referenced locations that do not participate directly in translation (for clarity): nucleus, mitochondria, cell membrane.

Understanding Codons and Anticodons

  • Codons are found on

    • tRNA

  • Anticodons are found on

    • mRNA

The Genetic Code

  • Definition: The genetic code is the set of rules that convert a nucleotide sequence in RNA to an amino acid sequence.

  • Of the 64 triplets:

    • 61 code for amino acids.

    • 3 are stop codons, signaling to ribosomes to terminate polypeptide synthesis.

Key Characteristics of the Genetic Code

  • Redundant: All but two amino acids have multiple codons.

  • Unambiguous: Each codon corresponds to only one amino acid.

  • Non-overlapping: Codons are read sequentially, one at a time.

  • Nearly Universal: Codons specify the same amino acids across almost all organisms.

  • Conservative: If several codons code for one amino acid, the first two bases are often identical.

Structure and Function of Codons

  • Codons are three-nucleotide sequences in mRNA, coding for specific amino acids, with one codon acting as the start and others as stop codons.

  • There are 64 possible codons coding for only 20 amino acids, showcasing the redundancy in the genetic code.

Wobble Position in tRNA Pairing

  • Wobble Position: The third position in a tRNA-codon pairing may bind less stringently, allowing for variability without altering the amino acid.

Requirements for Translation

  • Translation necessitates:

    • mRNA

    • Ribosomes

    • Transfer RNA (tRNA)

    • Functions as a molecular interpreter, carrying amino acids and matching them with codons in mRNA using anticodons.

Role of Ribosomes

  • Ribosomes coordinate mRNA and tRNA functions.

  • Composed of two subunits made of proteins and ribosomal RNA (rRNA).

Translation Process Steps

  1. Newly transcribed mRNA binds to a ribosome.

  2. The ribosome translates mRNA in groups of three nucleotides (codons).

    • Each codon specifies an amino acid, delivered by tRNA via anticodons.

  3. When the right tRNA binds, its amino acid is added to the growing polypeptide chain, and the ribosome advances to the next codon.

  4. The completed amino acid chain detaches from the ribosome and folds into its functional shape.

    • mRNA and tRNA can be reused for multiple proteins.

Gene Expression Practice

  • Engage in exercises that require pairing of mRNA, tRNA (anticodon), and identifying amino acids using the codon table.

Genetic Code: Universal Implications

  • The universal nature of the genetic code enables programming of one species to produce proteins from another by transplanting foreign DNA (transgenic organisms).

  • Genetic engineering implies manipulating an organism's genome; organisms with recombinant genes are termed genetically modified organisms (GMOs).

Examples of Genetic Engineering

  • Moon Parka winter coat made of genetically modified spider silk.

  • Genetically modified corn and soybeans possess genes for natural insecticides.

  • Crops engineered for herbicide resistance.

  • Insulin produced by genetically modified bacteria.

Components of Genes

  • Genes consist of:

    • Regulatory Sequences: Dictate when and how much protein is synthesized.

    • Coding Sequences: Determine the amino acid sequence of the resulting protein.

Steps in Genetic Engineering

Step 1: Creating a Recombinant Gene

  • A recombinant gene combines segments from different genes not previously together in nature, e.g., joining yeast regulatory sequence with spidroin coding sequence.

Step 2: Inserting Recombinant Gene

  • Insert the recombinant gene into a vector (loop of DNA) and then into living cells, such as yeast.

Industrial Scaling in Genetic Engineering

  • Transferring genes for desired proteins to bacteria or yeast enables large-scale production of proteins that naturally occur in low quantities.

  • Example: Humulin (1982) was the first bioengineered pharmaceutical product aiding diabetes management and produced using a fermentation process.

How mRNA Vaccines Work

  • mRNA vaccines utilize the genetic sequence of a virus spike to create synthetic mRNA, instructing cells to produce the spike protein, stimulating an immune response.

Discussion on GMOs

  • Substantial debate on potential health effects of GMOs versus their role in combating world hunger.

  • Controversies regarding the safety of GMOs, with examples like "Roundup-ready" crops leading to increased herbicide use.

Consequences of Genetic Sequence Mistakes

  • Mutations: Changes in nucleotide sequences can arise from inheritance, random DNA replication errors, or environmental factors.

Types and Causes of Mutations

  • Inherited Mutations: E.g., mutations in the beta-globin gene leading to sickle cell disease.

  • Replication Errors: Occurs randomly during DNA replication, with 1 mutation per 10 billion base pairs.

  • Mutagens: Environmental factors (radiation, chemicals) that can induce mutations, such as UV radiation, smoking, and pollution.

Objectives for Next Week

  • Review content on mutations and their implications.

  • Compare normal gene alleles with sickle cell disease alleles.

  • Investigate gene therapy approaches for sickle cell disease and the CRISPR genetic engineering technique.