The Bacterial Genetics

8/2/2019 The Bacterial Genetics

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The Bacterial Genetic Page 1

THE BACTERIAL GENETICS

This lecture is the beginning of chapter 7, the doctor said that chapter 7 has 2different topics the first one is about metabolism of the bacteria and the other

topic is about the bacterial genetics. We are going to talk about genetics of

bacteria and in a general idea not very

deeply.

Bacterial Genetics

Genetics: the study of heredity.

DNA carries couple of genes it depends , if its human 46 chromosomes each

one of these chromosomes in numb real 1,2,3,4, each one of these

chromosomes carry number of genes , for bacteria ,the same thing, the

chromosome the genome of the bacteria carries genes and it depends on the

size of this microorganisms. And the numbers of genes that depends on the size

of chromosomes that carry genes and gives us treats that appears on bacteria, inthis case these traits can be :

Pigmentation The production of certain enzyme. The production of a certain product. The type of a growth of this M.O on surface of agar Media.

so we are going to call it a phenotype , An organisms phenotype refer to his

physical traits such as as hair, eye color in humans ,but in bacteria it is going tobe: The morphology ,the type of enzyme or the type of product it is producing.

An organisms phenotype is a manifestation ofthe organisms genotype:

whatever is carried on the gene is going to appear on appearance.

An organisms genotype:

it is complete collection of

genes; it is the genetics

information which carries onDNA.


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Genes rate all functions of the cell; In this case were going to talk aboutenzymes that catalyze certain reactions in the cell.

Ex: polymerase is very important for DNA replication

RNA polymerase is very important for transcription.

Particular segments of chromosome constitutes a gene, this segment consist of

couple of nucleotides, it maybe 20 of them maybe 500 of them maybe 1000 of

nucleotides long.

What do we mean by Mutations!

Mutations : A change in a DNA molecule we call it a genetic alteration.

So lets say it ACGAAGGCCTT.

If the one of these bases which make the gene changed this will lead to alteration

in the genetic (myocope)

Alteration it might be in this case leads to mutation , these mutation may affecton final product and it might not ,This final product might be a protein enzyme so

it will not work anymore dysfunction.

A change in a DNA molecule (genetic alteration) that is transmissible to offspringis called a mutation.


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Q: How it doesnt affect the final product which is a protein?

If we look at the universal codon table well final that we have many codons give

the same AA, so we might have a mutation that gives a different codon but still

have the same final product the same AA.

Categories of Mutations

3-Silent

mutations:basic maybe

change in the

bases but its not

going to go away

like there is no

mutation and it

doesnt effect on

the Final Product.

2-Harmful mutations

(some are lethal mutations):

Example: exposure to UVlight For A Long Time, It

Might Cause some kind of

alteration or mutations in

our DNA in the skin and it

might leads to a cancer

melanoma. The same

thing for bacteria some of

these mutations might be

lethal to the bacteria and

might kill the bacteria.

1-Beneficial

mutations: sometimes

these bacteria musthave a mutation

as result of environ-

mental stress .In this

case it can adapt itself

in a better way to the

changes in the envi-

ronment so in this case

this kind of mutation

will be beneficial

mutation for the


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Mutation rate (the rate at which mutations occur) can be increased byexposing cells to physical or chemical agents called mutagens and this

Mutagens could be environmental like exposing bacteria for Radiation,

certain chemicals. And this may Effect on bacterial genetic myocope and it

can cause mutations, so in this case the substance that cause mutations we

are going to call it mutagen.

The organism containing the mutation is called a mutantand it could be:

1) wild type bacteria: for example in the researches we said the wild type

bacteria its the normal bacteria, if it went through is kind of mutation then

its going to become a mutant, something happened to DNA, some

mutation happened in the structure of a DNA or the nucleotide sequence,

base change , then it led to a new type or a different type from a wild type

and were going to call it a mutant. This is the mutation

How the bacteria can acquire new genetic traits ?

If you exposed certain strains or species of staph aureus

for example: Gram positive bacteria its wall formed by a

thickpeptidoglycan layer, if it is exposed to penicillin, Penecillin works onthis peptidoglycan layer and it destroy it, but in this case bacteria acquired

weights by which it can produce an enzyme, penicillinase: can break downpenicillin .Penicillin is not anymore in the environment of this bacteria

anymore.

So By some kind of mutation now the bacteria are able to produce a substance

can break down penicillin, this is one way,another way maybe in the old day, for

example pseudomonas (gramve bacteria) it had gates in the outer membrane in

which they can introduce antibiotic that enter by these gates channelinto the

cell and they can kill the cell from inside.

But now the bacteria one way to resist antibiotics , now we have mutations that

doesnt make these gates , when these gates closed ,certain antibiotics are not

going to be able to be delivered or by pass the outer membrane to get inside the

cell, so its not going to be affected against pseudomonas .And we know that


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staph aureus and pseudomonas both of these a problem in the hospital, they are

nosocomial infection.

The problem of them that we cant use antibiotic that against them because those

type of bacteria they developed new ways to resist bacteria ( which havemutations ) so also in this case we have to develop new kinds of drugs or

treatment to kill this M.O or they are going to kill us .

So how they can acquire genetic traits?

For example Bacteria have resistance for antibiotics and other doesnt have it.

But the one that has resistance for antibiotic can give its gene to the one doesnt

have it so now both of them have antibiotic Resistance to a certain antibiotic

drug. How they can exchange genetic material ?so we have something named:

1-lysogenic conversion

2-transduction

3-transformation

4-conjngation

An extra chromosomal DNA molecule is called aplasmid. An organism thatacquires a plasmid acquires new genes. A plasmid can exist by itself or can

integrate into the chromosome is called an episome.

Its not really a part of chromosomal DNA. In bacteria the chromosomal DNA

which carries the genotype of the bacteria that is needed for metabolism and

structure of the cell replication..etc .there is also extra chromosomal DNA

found in the cytoplasm. It is smaller than the chromosomal DNA, which means the

numbers of genes that are carried on the plasmid are less than what carries on

the chromosomes.


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We have families of plasmid they have members, for example there are important

plasmid for antibiotic resistance also we have important plasmid for metabolism,

that makes a specific A.A.

So we have different kinds of plasmid.

Here the doctor showed a picture:

The left picture illustrates a plasmid that is expelled outside the E.coli bacteria.

The right picture illustrates a closer view of the plasmid, which can carry essential

genes

1- Lysogenic conversion:

There is something called bacteriophage; which is a virus that can infect the

bacteria. We have a type of bacteriophage that is called temprate phages. These

are considered a lysogenic phages; which means they can inject their DNA into

the bacterial cell and that DNA will be integrated into the bacterial chromosome.

Note that !Plasmid can either

exist by itself or it can

integrate itself into

the chromosome, we

call it an episome.


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It will not cause a lytic cycle, so we will have a bacteria that have the

bacteriophage DNA. That DNA may lay down there for a long time until the

environment inside and outside the cell will be improved, then they may excise

themselves from the chromosome, taking genes from the bacterial chromosome.

They will replicate inside the cell, synthesizing more and more DNA containing

the original bacteriophage DNA and some part of the bacterial DNA and protein

that will form the virus inside the bacteria.

They will form holes in the membranes of the bacteria cell and will come out of

the bacteria. And will attack another nearby bacteria by this it will transfer genes

from one bacteria to another. So this is another way which they can transfer

genes from one species to another.

These viruses if came from bacterial cell to another then they will carry some of

the genes from previous species to the next one and then we have lysogenic

conversion

A Phage is called prophage when it consists of the DNA without the virus coat

thereis no virus coat only the DNA. This prophage will integrate itself in the

bacterial chromosome, as mentioned previously, the bacteria that contains the

prophage is called lysogenic bacteria.

2-Transduction to carry a cross:

Also involves bacteriophage.

In transduction the bacteria genetic material came across from one bacteria cell

to another by a bacterial virus bacterium acquire new bacterial genes.

All the small amounts of genetic material are transferred by transduction which is

going to take, once it going to be excised from the chromosome, It will take

simple parts from bacteria DNA, from left and right which surround the Virus

DNA. From both slides, it takes simple parts from bacteria DNA, from left and


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right which surround the virus DNA.

Note how this differs from lysogenic conversion; where in bacteria acquire new

genetic information in the form of viral genes.

3-Transformation:

We have 2 types of transformation:-

1) Transformation by nature: it can happen by nature.

2) Transformation by force: that we use it in researches ofmicrobiology etc

were trying to introduce by force certain genes into the bacterial cell.

In the transformation: a bacterial cell becomes genetically transformed following

the uptake DNA fragments or naked DNA.

In transformation we will have a bacteria and a naked DNA floating around the

cell. This bacteria must be competent cell; that means it has all the chromosomes

and machinery that is required to take the nearby virus.

This naked DNA will be introduced in the chromosomal DNA of the bacteria, and

new characteristics will be acquired in that bacteria.

All the small amounts of genetic material are transferred by excise from thechromosome.

The ability to absorb naked DNA into the cell called competence and the bacteria

which has the ability to absorb DNA is called competent bacteria.

Not all species of bacteria are able to take in any kind of naked DNA around it

has to be competent , it has to be able to open up cell may to introduce this

named DNA.

for example, in molecular microbiology researches purposes we make the cell

competent by using different chemicals and we force certain DNA to get into the

cell and so introducing new traits that we are controlling into this bacterial cell

it will be under control and there for we can make a lot of researches , Ex: certain


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genes, what theyre producing . Etc a lot of things have been discovered by

that.

For example in microbiological researches for..purposes and etc we make the

cells competent by using different chemicals and techniques we make itcompetent and we force certain DNA to get into the cell and by this we are

introducing new traits that we are controlling into this bacterial cell and

depending on this we can do a lot of studies and a lot of things had been

discovered as a result of transformation.

Transformation properly is not widely in nature because not all the species that

you can find are competent to take naked DNA.

4-Conjugation:

The other way by which bacteria can acquire new traits, new genetic and

chromosomes: Conjugation. It Is a widely used way, it is a phenomena in the

bacteria and we manipulated this procedure tonature to our own benefits on

molecular microbiology laboratory tubes.

Conjugation: means mating between 2 bacteria.

In this case it involves specialized type of pillus called a sex pilus we have two

types of pillus: sex pillus and attachment pillus

Bacteria that have the sex pillus: donor cell

Attaches by a means of the sex pilus to another Bacterial cell called the recipient

cell.

The donor cell is going to extend its sex pillus to the recipient cell.

In this case they have close contact they have to be in close, close to each other.

Structure of this pillus is tubes and the bacteria that have got the Pilli also contain

plasmid. The plasmid carries certain genes on it. It Does replication and give a


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copy in the donor cell and another copy that pass by the Pilli to the recipient cell.

And at the end of this both of these they are going to have the same plasmid.

So the donor cell and the recipient cell have the plasmid and both plasmid carry

certain genes of them depends on the type of the plasmid.

If we have R plasmid which is one of plasmid types: resistance plasmid which

can carry genes which can resist certain antibiotics. It might be penicillinase,

tetracyclonase.

Plasmid that contains multiple genes for antibiotic resistance IS known as a

resistance factor or R-factor.

The bacterial cell that receives an r factor becomes a super bulk it is not going to

care if this antibiotic surrounding it or not, because it has the gene that can break

down this antibiotic and that what happens in the pseudomonas bacteria, that

causes a nosocomial infection.

Here the doctor started to talk about nosocomial infection:Nosocomial infection is the infection that is acquired while the patient is in the

hospital. There are a lot of bacteria responsible for it:

1) Pseudomonas bacteria.2) Acinitobacter this bacteria has acquired a resistance for multiple

antibiotics and that can cause the death of the patient whom infected

by it

3) Klebsiella4) Staph aureus, esp. the MRSA type MRSA: methicillin resistance staph

aureus.

All of these bacteria have resistance for multiple antibiotics, esp. the

pseudomonas and staph aureus. So if an immunocomprimised patient

got infected by these microorganisms, he might die.


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You have a picture in the slides that show the conjugation process of the E.coli

bacteria, and it illustrates the sex, and attachment Pilli.

Genetic engineering:

Genetic engineering or recombinant DNA technologyinvolves techniques to

transfer eukaryotic genes (particularly human genes) into easily cultured cells

to manufacture important gene products (mostly proteins).

A recombinant gene has been used in different fields:

1) Production of vaccines, like hepatitis b, tetanus:Lets take how the recombinant gene technology has been utilized to produce

the vaccine against hepatitis b virus: This vaccine is composed of the surface

antigen of hepatitis b virus, not the whole virus, (it is a subunit vaccine).once

introduced to the body, our body will produce antibodies against this surface

antigen, these antibodies will remain in our body to prevent the infection of

hepatitis b virus.


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How did we make that surface antigen of hepatitis b virus?

We took the gene that encodes the hepatitis b surface antigen from the

hepatitis b virus, and then we put it in the vaccine virus. Vaccina virus is not

harmful. So we have vaccina virus that has hepatitis b surface antigen.

Hepatitis b virus vaccines are taken in 3 booster doses.

A note from a question that has been asked in the lecture: vaccines can rarely

cause a disease in the human.

2) Production of insulin to treat DM: Plasmids are frequently used as vehiclesfor inserting genes into cells: In labs we can manipulate the plasmids and

inject a certain gene inside it by a process that requires a lot of enzymatic

action, (lets suppose that gene is the gene responsible for the production

of insulin.) Then we let the E.coli bacteria takes that plasmid in the process

of transformation, now we have an E.coli bacteria that has the plasmid

containing the insulin gene inside it. Now we let the bacteria multiply and

produce the insulin. We take the bacteria and remove the cell wall and take

the insulin. Buy this we have produced a lot of amount of insulin

3) Production of clotting factor to treat hemophilia, production of growthhormones.

4) Antibiotics: many antibiotics that are found in the markets are produced byusing the streptomycin bacteria.

5) Synthesis of antibodies: some antibodies are important to neutralizecertain toxins, other antibodies are used in research; for example the

antibodies can be tagged by florescent or radioactive material, in this case

we can identify the antigen that the antibody will bind to.


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Gene therapy:

Gene therapy of human diseases involves the insertion of a normal gene into cells

to correct a specific genetic disorder caused by a defective gene.

A cell can have an abnormal gene, which causes a disease, here we can inject the

normal gene into a virus and then we inject that virus in the body. It will go to the

cell and then there will be an exchange of the gene material. The cell will take the

normal gene. And by this we can cure the disease. Not all viruses can be used to

do that, for example we can use adeno viruses or vaccina viruses.

Genes may someday be regularly prescribed as drugs in the treatment of

diseases (e.g., autoimmune diseases, sickle cell anemia, cancer, cystic fibrosis,

heart disease, etc.)

This Script is Done by:

Jumana Ali Al-shawabke.

Rana Ahmed Al-Otom.

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The Bacterial Genetics