NT

Genes to Proteins

Chapter 8: Genes to Proteins

Authors: Michèle Shuster • Janet Vigna • Matthew Tontonoz

Driving Questions

  • What determines the shape of a protein molecule, and why is its shape important? The shape of a protein molecule is determined by the sequence and properties of its constituent amino acids, which dictate how the chain folds into a three-dimensional structure essential for its function.
  • What are the steps of gene expression, and where in the cell do they occur? The gene expression process comprises two main steps—transcription and translation. Transcription occurs in the nucleus, while translation occurs at the ribosomes in the cytoplasm.
  • How can organisms be genetically modified to produce recombinant proteins? Organisms can be genetically modified through genetic engineering, whereby specific genes are inserted into their genomes to produce desired proteins.
  • What are some pros and cons of genetically modified organisms? The advantages and disadvantages of GMOs include potential health benefits and biotechnological advances, alongside ethical and ecological concerns.

Spider Silk Characteristics

  • Strength Compared to Steel: Spider silk has higher toughness than steel or Kevlar, making it an attractive material for various applications.
  • Potential Applications of Genetically Modified Spider Silk: Uses include:
    • Bulletproof vests
    • Stronger skin grafts
    • Biocompatible and biodegradable scaffolds for tissue growth
    • Durable ecotextiles
    • Strong, elastic airbags
    • Screws and sutures for medical uses

What is a Protein?

  • Definition: A protein is a macromolecule composed of repeating amino acid subunits.
  • Functions: Proteins serve numerous essential roles in biological systems, including muscle contraction, catalyzing chemical reactions, and fighting infections.

Amino Acids

  • Characteristics: Amino acids are the building blocks of proteins, with 20 different types existing.
  • Structure: Each amino acid has a similar core structure but features a unique chemical side group, affecting its properties and the protein's ultimate shape.

Amino Acid Sequence and Protein Folding

  • Linear Chain Formation: Amino acids link together in a specific sequence to form a linear chain.
  • 3D Folding: This chain folds into a three-dimensional protein structure, which is determined by the amino acid sequence. Changes in this sequence can alter the protein's folding and, consequently, its function.

Gene Encoding and Protein Synthesis

  • Source of Proteins: Genes encode the instructions necessary for protein synthesis.
  • Gene Definition: A gene is a sequence of DNA that contains the instructions for producing one or more proteins.
  • Location on Chromosomes: Genes are located on chromosomes, each carrying a unique set of genes.
  • Process of Gene Expression: Gene expression is the overarching term for synthesizing a protein from a gene, consisting of two main steps: transcription and translation.

Steps of Gene Expression

  1. Transcription: Converting DNA to messenger RNA (mRNA).
    • Occurs in the nucleus (eukaryotic cells) and cytoplasm (prokaryotic cells).
  2. Translation: Converting mRNA to protein.
    • Occurs on the ribosomes in the cytoplasm.

Detailed Overview of Transcription

  • Process Overview: Transcription involves synthesizing mRNA from the DNA coding sequence.
  • Stepwise Breakdown:
    1. Initiation: RNA polymerase binds to the regulatory sequence of the gene's coding region.
    2. Elongation: RNA polymerase unwinds the DNA strands, exposing the gene's coding sequence and synthesizing mRNA by base pairing.
      • In RNA, adenine (A) pairs with uracil (U) instead of thymine (T).
    3. Termination: The mRNA strand detaches from the DNA, DNA reforms its double helix, and the completed mRNA molecule exits the nucleus.
    4. The original DNA sequence remains intact within the chromosome.

Detailed Overview of Translation

  • Process Overview: In translation, mRNA is read by ribosomes to synthesize proteins.
  • Stepwise Breakdown:
    1. The mRNA associates with a ribosome.
    2. The ribosome reads the mRNA in codons (groups of three nucleotides).
    3. Transfer RNA (tRNA) brings the corresponding amino acids to the ribosome, matching its anticodon with mRNA codons.
    4. The ribosome facilitates the addition of the specified amino acid to the growing polypeptide chain as it moves along the mRNA.
    5. Once the entire sequence is translated, the completed amino acid chain detaches and folds into its three-dimensional structure.

The Universal Genetic Code

  • Definition: A set of rules relating specific mRNA codons to specific amino acids.
  • Codons and Amino Acids: There are 64 possible codons which code for 20 different amino acids.

Genetic Engineering

  • Definition: Genetic engineering refers to the manipulation of the genome of a living organism through various techniques.
  • Transgenic Organisms: Organisms that have incorporated recombinant genes are termed genetically modified organisms (GMOs).

Examples of Genetic Engineering

  • Innovative Applications:
    • The Moon Parka winter coat utilizes genetically modified spider silk.
    • Crops like corn and soybeans contain genes from natural insecticides and herbicide resistance.
    • Genetically modified bacteria produce insulin for therapeutic use.

Spider Silk Production: Factories Model

  1. Step 1: Create a Recombinant Gene
    • A recombinant gene consists of parts from different genes that do not naturally occur together.
    • It may involve combining a yeast regulatory sequence with the spidroin coding sequence.
  2. Step 2: Insert the Recombinant Gene into Living Cells
    • A vector carrying the recombinant gene is inserted into a yeast cell.
  3. Step 3: Produce Protein Product
    • Transgenic yeast are cultivated under conditions optimal for large-scale spidroin protein production.

Pros and Cons of GMOs

Advantages:

  • Transgenic organisms have transformative applications in biotechnology and health including the production of insulin, ligaments, and materials for surgical applications.
  • Genetically modified crops demonstrate resistance to pests, improving agricultural viability.
  • Gene therapy offers hope for treating genetic disorders.

Disadvantages:

  • Concerns arise regarding health effects from GMOs.
  • Potential ecological impacts if transgenic organisms inadvertently spread or transfer genes to wild species.
  • Ethical dilemmas, particularly surrounding eugenics and genetic manipulation.
  • The CRISPR technique has raised significant ethical discussions, especially after controversies regarding its application in editing genetic diseases in embryos.

Summary of Key Points

  1. Shape of Proteins: Protein folding is governed by amino acid sequences; alterations to the gene can result in functional changes to the protein.
  2. Steps of Gene Expression: Gene expression includes transcription in the nucleus and translation in the cytoplasm, relying on both regulatory and coding sequences.
  3. Genetic Modification: Transgenic organisms can be created through genetic engineering, allowing for the production of recombinant proteins.
  4. Ethical and Practical Implications: While GMOs hold immense potential for various applications, they also pose risks and provoke ethical debates.