Chapter Nine Notes
Slide
1. Polymerase Chain Reaction (PCR) described in chapter 8 notes.
2. Chapter 9 will focus on how bacterial cells can change their genotype by getting DNA from other
microorganisms.
3. These are important terms you will want to know when discussing how bacterial cells acquire DNA
from other cells.
4. Transformation is one way that a microorganism can pick up free DNA that has been released in the
environment from a dying bacterial cell. The slide gives an overview of the basic steps involved.
5. This slide describes the original experiment performed which demonstrates that microorganisms
could have changes made to their original DNA if they could acquire DNA from another microorganism.
Two strains of Streptococcus pneumoniae were used with one making a capsule and the other strain was
a mutant and couldn’t make a capsule (nonvirulent). Only an infection with the capsulated strain would
cause a mouse to die. After injecting the two strains (dead capsulated strain with the living noncapsulated strain) into a mouse, there were mice that died. The scientists recovered the capsulated
strain from these mice. This experiment was performed before DNA was identified as containing the
genetic information in a cell. The scientists knew that something from the dead strain entered the living
nonvirulent strain and now allowed that strain to make a capsule. The nonvirulent strain was
transformed since it acquired DNA to make a capsule from the dead strain.
6. This slide summarizes the general steps needed for transformation to happen in a bacterial cell. Only
a certain size of DNA can actually get into a cell so that is why one can see that the DNA chromosome
gets cut into fragments. Also, the fragment will get incorporated into that recipient cell’s DNA for that
gene to bevexpressed in that cell. The genes in the fragment will undergo a recombination event in
which the fragment finds homologous genes on the recipient’s DNA and will recombine with that DNA.
Look at red “ab” genes on the fragment going into the purple recipient DNA replacing the purple “AB”
genes.
7. 8. Another method that a bacterial cell might acquire new genetic information is by a process called
transduction. In this case, a bacteriophage (virus) that can infect bacteria will carry DNA from a bacterial
cell that the bacteriophage last infected to a new bacterial cell. You will want to understand these terms
about bacteriophages (phages) and how some phages are considered lytic since they lyse the bacterial
cell so they can be released. Other types of phages (temperate) can enter the DNA of a bacterial cell
and remain there indefinitely until induced to pop out of that DNA.
9. The lytic phage go through a Lytic cycle in which they enter a host cell through a receptor on the
bacterial cell and ultimately assemble into new phage particles and are released from the cell by lysing
the bacterial cell. If a temperate phage infects a bacterial cell, the phage DNA gets incorporated into the
bacterial DNA (Lysogenic cycle) and remains there getting replicated along with the bacterial DNA. The
prophage can pop out of the bacterial DNA under certain conditions which can be seen on the next slide.
10. Most of the time when a phage DNA pops out of bacterial DNA that phage DNA will go through a
lytic cycle and get released like any lytic phage. Once it infects a new bacterial cell it will enter and
incorporate itself into the DNA of the new host. Some times when the prophage pops out of the host
cell a mistake is made and it takes some of the bacterial host DNA. You can see that in the figure as the
black phage DNA takes some of the red bacterial DNA. This phage can now go on to replicate as just
discussed but when it enters into a new bacterial host cell it will bring some of the red bacterial DNA to
the new purple host chromosome. This is referred to as specialized transduction since only certain
genes could be transferred to a new host. Those genes are the ones that are adjacent to the site in
which the prophage in incorporated into the host DNA since that DNA comes out with phage DNA.
11. In this slide once can see that when a lytic phage infects a bacterial cell, the phage will need to
package viral DNA into it’s capsid before being released from the bacteria. Sometimes, by accident, the
phage will package bacterial DNA along with viral DNA. When the phage enters a new host, it will now
bring in red bacterial DNA into the new host with green DNA. The genes on that red DNA can get
incorporated into the green bacterial chromosome through a recombination event so the genes on the
red DNA can be expressed. This is referred to as generalized transduction. Any fragment of bacterial
DNA can get packaged.
I will end here Monday and continue with the rest of the slides on Wednesday.
12. This figure demonstrates that two microorganisms can come together and exchange DNA. One can
follow the 6 genes involved A, B, C, D, E, F and the (+) means that it is a wild type gene and the (-) means
that the gene has a mutation. All the wild type genes need to be in a bacterial cell for the organism to be
able to grow on the selection agar plates. This could happen if the (+) D,E,F genes moved into the (+)
A,B,C strain. This experiment was the first indication that conjugation can occur between two closely
related strains of bacteria.
13. One of the bacterial strains needs to have a F pilus (conjugation pilus) which will allow the transfer of
genetic material into another bacterial strain that does not make a F pilus.
14. The genetic information to make a pilus is carried on a plasmid called the F plasmid (F stands for
fertility). This slide is to remind you that a plasmid is extrachromosomal DNA which is circular.
15. This slide states some facts about the transfer of these plasmids.
16. This figure demonstrates the transfer of the F plasmid into a cell that doesn’t have the F plasmid.
The recipient cell is now said to be F+. Notice that the plasmid comes into the recipient cell as a single
strand and that strand will be copied so the double stranded plasmid DNA will be restored. The original
F+ strain will also need to copy the single stranded plasmid to restore the plasmid to a double strand
plasmid.
17. Sometimes the F plasmid integrates in the chromosome of a cell. Conjugation can still happen but
this time some chromosomal DNA will also come in with the plasmid. Strains with a F plasmid
integrated into the host chromosome are referred to as Hfr strains for High Frequency Recombinants.
18. This figure demonstrates the Hfr strain conjugating with a strain that doesn’t have a plasmid. The
result of this conjugation is the recipient cell getting some blue DNA which can recombine with the
green DNA in the recipient. The recipient cell didn’t receive a whole copy of the plasmid so the cell
doesn’t become an Hfr strain. It is extremely rare that the cells would stay together long enough to
transfer the whole chromosome and the integrated plasmid.
19. Sometimes the plasmid from the Hfr strain pops out the chromosome and takes some adjacent DNA
with it. This is referred to as a F’ (prime) plasmid. If this plasmid conjugates with a cell, extra copies of
genes on the plasmid can be passed into the recipient cell. This is an example where the recipient cell
has become F’ and contains an extra copy of the A and B genes in this case.
20. F plasmids can also contain genetic information for other things besides the ability to make a pilus.
This is the list of some of the things that might be found on a plasmid. In the medical field, the plasmids
that contain genetic information to make a microorganism resistant to antibiotics are a major concern.
And then these plasmids can be passed onto to bacterial cells that don’t already have that plasmid.
21. This is just an example of the genetic information that might be found on a plasmid. Many plasmids
contain genes that have information to cause a microorganism to be resistant to many antibiotics.
22. Microorganisms may also acquire genetic information from a transposable DNA element. The
transposase enzyme allows the genetic sequence to move itself to other locations on DNA. Often the
transposable element has genes to make an organism resistant to antibiotics. The transposable element
may also insert itself into a gene on a chromosome causing the gene to no longer function.
23.This slide shows that a typical transposon has the gene for the transposase as well as unique
sequences that allows it to insert itself into different locations on DNA. In this transposon, there is also
a gene for ampicillin resistance.
24. Scientists took the information that was known about how microorganisms exchange DNA and
manipulated microorganisms so that they would express human proteins such as insulin. This was the
start of recombinant DNA technology which started back in the late 1960’s.
25. This figure demonstrates the steps needed to get a human gene of interest into a plasmid. The
plasmid will be taken up by a microorganism and the human protein will be expressed. With the use of
restriction enzymes that cut specific sequences in DNA, one can cut the human gene of interest out of
DNA and place it into a plasmid that was cut with the same restriction enzyme. The restriction enzyme
cuts DNA leaving overlaps (sticky ends) which allows the human gene of interest to base pair with the
plasmid that was cut with the same enzyme and has the same sticky ends. The plasmid now has the
human gene and the plasmid to put into a microorganism through a transformation event.
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