Bio 205 Chapter 9 S24

Chapter 9: Gene Transfer and Genetic Engineering

Gene Transfer

• Prokaryotic DNA Transfer

  • Prokaryotic cells can transfer DNA from donors to recipients.

  • This combining of DNA is referred to as recombination.

  • Resultant cells from recombination are called recombinants.

• Types of Gene Transfer

  • Vertical Gene Transfer: Transmission of genetic material from parent to offspring in humans.

  • Horizontal Gene Transfer: Prokaryotes transfer DNA between organisms of the same generation.

Transformation

• Definition

  • The process where genetic material is taken up from a bacterium’s environment.

• Historical Background

  • First discovered in the context of Streptococcus pneumoniae with smooth (virulent) versus rough (non-virulent) colonies.

  • Smooth colonies have a capsule, making them virulent; rough colonies lack a capsule and do not cause disease.

Bacterial Competence

• Competence Factors

  • Not all bacteria can take up naked DNA; only those with a competence factor released into the medium can do so.

  • Competent bacteria uptake single-stranded DNA fragments; these fragments get inserted into their chromosome.

  • Molecular biologists can procure competent bacteria for laboratory transformations.

Transduction

• Overview

  • Genetic material is transferred using bacteriophages (viruses that infect bacteria).

• Types of Bacteriophages

  • Virulent Phages: Cause infection and lysis of bacterial cells.

  • Temperate Phages: Enter a lysogenic phase, inserting their DNA into the bacterial chromosome (prophage) without immediate lysis.

  • Temperate phages can later switch to a lytic phase, leading to cell lysis, replication, and further infection of neighboring bacterial cells.

• DNA Transfer

  • During prophage excision, bacterial DNA can be transferred to other bacterial cells during subsequent phage infections.

Conjugation

• Definition

  • The process where bacterial cells take up genetic material from neighboring cells through direct contact.

• Mechanism

  • Requires a structure known as the F pilus, also referred to as the sex pilus or conjugation pilus.

  • Can transfer large pieces of DNA, including entire chromosomes.

  • F plasmids:

    • F+ is the donor cell (male), and F- is the recipient cell (female).

Plasmid Functions

• Functionality

  • Direct synthesis of conjugation pili.

  • Provide resistance to specific antibiotics.

Antibiotic Resistance

• Definitions

  • Resistant: Able to live and grow in the presence of antibiotics.

  • Susceptible: Cannot grow or survives in the presence of antibiotics.

• Mechanism of Resistance

  • Bacteria with resistant genes survive on media containing antibiotics, while those without die.

High Frequency Recombinations

• Derived from F+ strains where the F plasmid is integrated into the bacterial chromosome, potentially initiating the transfer of chromosomal DNA along with the F plasmid.

F’ Plasmids

• Definition

  • An F plasmid that can detach from the chromosome and return to plasmid form, but if it carries chromosomal DNA, it is termed an F' plasmid.

Transposons

• Characteristics

  • Often located on resistance plasmids, with the ability to move between plasmids and integrate into the bacterial chromosome.

  • Transposition: The movement of genes from one location to another.

• Components of Transposable Elements

  • Code for transposase (enzyme aiding in transposition).

  • Surrounded by inverted repeats.

  • Transposons can carry unrelated genes that are also moved around.

Genetic Engineering

• Definition

  • The deliberate manipulation of genetic material to modify organism characteristics.

  • Laboratory transfer of genes between different species is achievable.

Genetic Fusion

• Process of moving DNA from one chromosome location to another, affecting gene operon regulation when control genes are repositioned.

Gene Amplification

• Mechanism for rapid plasmid or bacteriophage replication within bacterial cells, useful for large-scale production of antibiotics and enzymes.

Recombinant DNA Technology

• Overview

  • Involves DNA containing sequences from two different species, integrating into germ cells for transgenic offspring.

  • Key Requirements:

    1. In vitro manipulation of DNA.

    2. Recombination of DNA from another species within a phage or plasmid (vector).

    3. Cloning to produce genetically identical offspring.

The Process of Creating Recombinant DNA

1. DNA from the donor organism is cut into small segments using restriction endonucleases.

2. The same enzyme is used to cut the vector (plasmid/phage).

3. New DNA segments are ligated into the vector using ligase.

4. The finished vector is utilized to transform bacterial cells via heat-shock or electroporation.

Medical Applications of Recombinant DNA

1. Production of important human substances (e.g., insulin, interferon).

2. Diagnostic applications for genetic fetal defects.

3. Gene therapy: inserting functional genes to cure genetic diseases.

4. Forensic science applications.

Industrial Applications of Recombinant DNA

• Roles in:

  • Fermentation processes (wine and beer).

  • Degradation of plant materials for resource utilization.

  • Fuel manufacturing.

  • Environmental cleanup efforts.

  • Metal extraction processes from ores.

Agricultural Applications of Recombinant DNA

• Applications include:

  • Insect resistance in crops.

  • Creation of high-yield and herbicide-resistant seeds.

  • Introduction of nitrogen-fixing capabilities.

Safety of Recombinant DNA Research

1. No incidents of illness in lab workers due to known recombinant organisms.

2. Lab strains of E. coli used do not infect humans.

3. Mammalian genes integrated into bacterial strains reduce adaptability.

4. Standard lab safety protocols are effective in managing mutant E. coli strains.