Chapter 9: Gene Transfer, Genetic Engineering, and Genomics


11 Δεκ 2012 (πριν από 4 χρόνια και 8 μήνες)

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Chapter 9


Gene Transfer, Genetic Engineering, and Genomics


9.1 Genetic Recombination in Prokaryotes

Genetic Information in Prokaryotes Can Be Transferred Vertically and

Vertical gene transfer (VGT) is the transfer of gen
etic material from
parent cell to daughter cell

Horizontal gene transfer (HGT) is the transfer of DNA from a donor cell
to a recipient cell

Transformation Is the Uptake and Expression of DNA in a Recipient Cell

By integration of a new DNA fragment, the rec
ipient has gained some
ability it previously lacked

Transformation was first described by Frederick Griffith in 1928

Competence is the ability of a recipient cell to take up DNA from the

Conjugation Involved Cell
Cell Contact for Horizontal
Gene Transfer

In conjugation, a donor cell transfers DNA directly to the recipient

The donor cell forms a conjugation pilus to make contact with the

The F factor DNA in the donor replicates by the rolling
circle mechanism

Conjugation also Can Tra
nsfer Chromosomal DNA

High frequency of replication (Hfr) strains can donate chromosomal genes
rather than just the F plasmid

The F factor attaches to the chromosome using an insertion sequence

Conjugation is usually interrupted before the entire chromosom
e is

The recipient remains F

(called a recombinant F

If an integrated F plasmid breaks from the chromosome, taking a fragment
of chromosomal DNA, it is called an F' plasmid

Transduction Involves Viruses as Agents for Horizontal Transfer of


In transduction, a virus (bacteriophage) carries a chromosomal DNA
fragment from donor to recipient

In the lytic cycle, virulent phages

destroy the host chromosome

replicate themselves

destroy the cell

In the lysogenic cycle, temperate phages integrat
e their DNA into the host
chromosome (as a prophage)

Virulent phages perform generalized transduction

A fragment of host cell DNA ends up in the phage during
packaging, which they transfer to a new host cell

In the lysogenic cycle, the prophage eventuall
y excises itself from the host

Sometimes it takes a few flanking host genes and leaves a few
phage genes behind

9.2 Genetic Engineering and Biotechnology

Genetic Engineering Was Born from Genetic Recombination

Genetic engineering involves chang
ing the genetic material in an organism
to alter its traits or products

A recombinant DNA molecule contains DNA fragments spliced together
from 2 or more organisms

Specific fragments can be obtained by cutting short stretches of
nucleotides with a restric
tion endonuclease

The fragments are joined by DNA ligase

Genetic Engineering Has Many Commercial and Practical Applications

The genes responsible for producing human insulin can be cloned into

Bacteria could be genetically engineered to

break down

toxic wastes

produce antibiotics

Plants have been engineered using microbial genes for

herbicidal activity

viral resistance

Cows produce more milk when injected with bovine growth hormone produced
by engineered bacteria

Specific nucleotide sequences in
pathogens allow us to identify them using DNA

Recombinant vaccines can be safer than traditional vaccines using killed
or attenuated microbes

DNA vaccines are being developed in which a gene serves as the vaccine

8.3 Microbial Genomics

Many Microbia
l Genomes Have Been Sequenced

Hundreds of microbial genomes have been sequenced since the first in

Many of which are pathogens

Segments of the Human Genome May Have “Microbial Ancestors”

As many as 200 of the 35,000 human genes are essentially identic
al to
those of

They were passed down from early ancestors of humans

Microbial Genomics Will Advance Our Understanding of the Microbial World

Knowing genomes of bacteria that cause food
borne diseases can help us

develop detection methods

make food


It can help us identify microbes that cannot be cultured in the lab

Environmental genomics helps us understand how microbial communities

Improved biosensing

Comparative Genomics Brings a New Perspective to Defining Infectious Diseases
and S
tudying Evolution

Functional genomics attempts to discover

the function of proteins coded for in a genome

how the genes interact, allowing the microbe to grow and

Comparative genomics compares the DNA sequence of one microbe to
another similar or

dissimilar organism

Metagenomics is identifying the previously unseen microbial world

Techniques are now being developed to analyze and understand all the
genomes within a microbial community