Ch. 27- Bacteria & Archaea Guided Notes
Warm Up Questions:
1. What was Frederick Griffith’s contribution to our understanding of DNA? (Refer back to Ch. 16)
2. How do bacteria replicate?
What you need to know:
 Mechanisms that contribute to genetic diversity in prokaryotes, including transformation, conjugation,
transduction, and mutation.
1. Genetic Diversity in Prokaryotes
Factors:
1. Rapid reproduction (binary fission)
2. Mutations – errors in replication
3. Genetic recombination
2. Genetic Recombination in Bacteria
 Transformation: uptake of foreign DNA
from surroundings
 Transduction: viruses transfer genes
between prokaryotes
 Conjugation: DNA transferred from one
to another
3. Transformation
 Uptake of foreign DNA from surroundings
 Observed by Griffith (bacteria & mice)
4.
Transduction
 Viruses (bacteriophages) carry
bacterial genes from one host cell to
another
 Recombine DNA of donor and
recipient cell
5.
Conjugation
 One cell donates DNA to another
 Donors cell extends a sex pilus
(“mating bridge”) through which DNA is
transferred
 Requires the presence of a piece of
DNA called the F factor to produce the pilus
6. Plasmids
 Small ring of DNA that carries a few genes
 Replicates separately from bacterial chromosome
 Can carry genes for antibiotic resistance
 Used frequently in genetic engineering for gene cloning
In this section you will continue your exploration of the genomes of bacteria. Click on the links listed below to
watch the animations and make annotations in your notes. After each animation there are several quiz questions
to check your understanding. It is your responsibility to understand this information!
Bacterial Genome:
What is the main
component of most
bacterial genomes?
How is the DNA arranged
in the nucleoid region of the
bacterial genome?
What is a plasmid?
Describe the process of
binary fission.
-Double stranded, circular DNA with small amount of associated protein
-Certain proteins cause chromosomes to tightly coil and supercoil densely packing
into nucleoid region
-Smaller circles of DNA separate from cells large circular DNA
-Asexual process
-Replication at origin of replication, enzymes split circular chromosome.
-Enzymes reassemble to form new DNA
-Cell splits into two new cells
http://glencoe.mcgraw-hill.com/sites/9834092339/student_view0/chapter10/animation_-_cell_division.html
Importance of Mutations:
Why do mutations make
such a large contribution to
bacterial genetic variation
as compared to humans?
What is the process of
alteration of a bacterial
cell’s genotype by the
uptake of naked, foreign
DNA from the surrounding
environment?
What famous experiment in
the previous unit described
this process?
What is transduction?
List the generalized steps of
transduction.
-Bacteria reproduce so quickly that it quickly increases genetic diversity compared
to humans slow rate of reproduction
-Genetic recombination (exchange of DNA segments by crossing over) caused by
transformation
1. When harmless bacteria takes up a piece of DNA from a disease causing
bacteria that has broken open.
2. Incorporates DNA of pathogenic bacteria into its own harmless DNA
3. Causing the harmless bacteria to turn pathogenic because it can now create a
protein coat protecting it from your body’s immune system
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter13/animation_quiz_1.html
-Griffith with his experiment of harmless/ harmful bacteria on mice
-When phages carry bacterial DNA from one host cell to another bacterial cell
1. Phage infects bacterial cell
2. Host DNA fragmented and phage DNA and proteins made
3. Bacterial DNA fragments get encased in phages capsid
4. Phage infects other bacteria—DNA of both bacteria cross over resulting in
genetic recombination
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html
What is the process of
direct transfer of genetic
material between two
bacterial cells that are
temporarily joined?
Conjugation
1. Dna to be transferred is cut by enzyme relaxosome at the origin of
transfer on the plasmid
2. Cut T DNA is pumped through pili to the other bacterial cell
3. Once in recipient cell will be replicated to become double stranded
4. Pili released and now both cells are F+ cells
http://glencoe.mcgrawhill.com/sites/9834092339/student_view0/chapter28/bacterial_conjugation.html
What structure joins them?
Sex pili- brings the bacterial cells closer together
What generally must be
Cytoplasmic mating bridge—Need a piece of DNA called the f-factor (fertility
present for the sex pili to
factor)
donate DNA during
F+ = contains f-factor and will produce sex pili (donor)
conjugation?
F- = contains no f-factor and will not produce sex pili (recipient)
What are plasmids?
-small circular, self replicating DNA molecule that separates from the bacterial
chromosome (DNA)
-Not required for the survival or reproduction under normal conditions
-Advantages- help bacteria living in stressful conditions
-Example: F plamid facilitates genetic recombination—which helps during
unfavorable conditions in changing environment
What is special about the F Contains f-factor and plasmid—create sex pili
plasmid?
Donor cell during conjugation
What is an episome?
-A genetic element that can replicate either as part of the bacterial chromosome
or independently
-Plasmids and temperate viruses qualify as episomes
What are R plasmids and
-R plasmids are bacteria that carry genes that are antibiotic resistance
why are they problematic to -Antibiotics are used to kill bacteria in humans
humans?
How does this relate to
-R plasmids shows that organisms will adapt to their environment. The R plasmids
natural selection?
have learned how to avoid being killed by antibiotics making them more fit for
survival.
What are transposable
-DNA of a single cell can also undergo recombination
elements?
-Transposable genes exist independently—not part of chromosome or plasmid
DNA
-Transposase is the enzyme that removes the transposable element from one
bacterial DNA and splices it into another bacterial DNA
-Common name is Jumping Genes
-Allows bacteria to adapt to new environments—resistance to antibiotics
http://highered.mcgrawhill.com/sites/dl/free/0072835125/126997/animation36.html