Chapter 8 Flashcards
Microbial Genetics
1
Q
Genetics
A
The science of heredity
2
Q
What are the 2 circular chromosome in a bacterial cell
A
One large–> chromosome: DNA molecule with genetic information essential for continuous survival of org
One small–> plasmid: genetic information that could help org, but could survive without it
3
Q
Genome
A
The genetic information in a cell
4
Q
What does a cell’s genome include
A
Chromosomes and plasmids
5
Q
Chromosomes
A
Structures containing DNA that physically carry hereditary information
6
Q
What do chromosomes contain
A
Genes
7
Q
Genes
A
A linear sequence of nucleotides of DNA that form a functional unit of a chromosome or plasmid. These segments of DNA code for functional products (Except in some viruses in which they are made of RNA)
8
Q
What is DNA
A
Macromolecule composed of repeating units called nucleotides
9
Q
What does each nucleotide consist of
A
A nucleobase, deoxyribose (penrose sugar), a phosphate group
10
Q
What are the different nucleobases
A
Adenine
Thymine
Cytosine
Guanine
11
Q
How do base pairs occur
A
Adenine-Thymine
Cytosine-Guamine
12
Q
The DNA within a cell exist as
A
Long strands of nucleotide twisted together in pairs to form a double helix
13
Q
Each nucleotide strand of DNA is held together by
A
Hydrogen bonds between their nitrogenous bases
14
Q
The base sequence of one DNA strand determines the base sequence of the other strand. This is called
A
Complementary
15
Q
Genetic code
A
The set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein
16
Q
What 2 primary features of biological information storage does DNA structure help explain
A
- The linear sequence of bases provides the actual information.
- The complementary structure allows for the precise duplication of DNA during cell division
17
Q
How does the linear sequence of DNA provide actual information
A
Genetic information is encoded by the sequence of bases along a strand of DNA, in much the same way as our written language uses a linear sequence of letters to form words and sentences
18
Q
What does each offspring cell received from the parent cell
A
Each offspring cell receives one of the original strands from the parent cell. This ensures 1 strand that functions correctly
19
Q
Cellular metabolism deals mainly with
A
Translating the genetic messages of genes into specific proteins
20
Q
What does a gene usually code for
A
Messenger RNA molecule
21
Q
What does the coding of a messenger RNA molecule result in
A
The formation of a protein
22
Q
Alternatively to a protein what can a gene product be
A
ribosomal RNA, transfer RNA, micro RNA
23
Q
Are all RNA types involved in the process of protein synthesis
A
Yes
24
Q
Explain what “gene has been expressed” means
A
When the ultimate molecule for which a gene codes has been produced we say that the gene has been expressed
25
Genotype
The genetic make up of an organism, the information that codes for all particular characteristics of the organism. Potential properties. Not the properties itself.
26
Phenotype
Refers to actual expressed properties such as the organism's ability to perform a particularly chemical reaction
27
Phenotype is the manifestation of
Genotype
28
An organisms genotype is it's collection of
Genes, its entire DNA
29
An organisms phenotype is its collection of
Proteins
30
In most microbes most proteins are______________ and _____________
Enzymatic
| Structural
31
Describe the typical chromosome of bacteria
A single circular chromosome consisting of a single circular molecule of DNA with associated proteins
32
What is the chromosome attached to
At 1 or several points to the plasma membrane
33
How much of the cells volume the chromosome take up and why
10% because the DNA is twisted or super coiled
34
Short tandem repeat (STRs)
Non coding regions that occur in most genomes . They are repeating sequences of 2- to 5-base sequences.
35
What are STRs used for
DNA fingerprinting
36
Open reading frames
Regions of DNA that are likely to encode a protein
37
Genomics
The molecular study of genomes- the sequencing and molecular characterization of genomes
38
Name how genetic information flows
1. Vertically-->From one generation to the next; replication
2. Within each metabolizing cell, transcribed into mRNA and then translated into proteins needed for cell to function; expression
3. Genetic information can be transferred between cells of the same generation; recombination
39
Origin of replication (ORP)
A single location on the chromosome where dna synthesis is initiated. It consists of a specific sequence of about 300 bases that is recognized by specific initiation proteins.
40
What acts as a template for the production of the other DNA strand
One strand. This happens because the bases along the 2 strands of double-helical DNA are complementary
41
The point at which replication occurs is called
The replication fork
42
Laws that govern DNA synthesis
1. DNA is copied by DNA polymerase; different ones: 1,2,3,etc. All have different functions: add on to nucleotides, proofread, etc
2. The new strands are always built in 5' to 3'
3. Initiated by an RNA primer
4. Leading strand is synthesized continuously
5. Lagging strand is synthesized discontinuesly by Okazaki fragments
6. The RNA primers are removed and Okazaki fragments joined by DNA polymerase and ligase
43
What happens when replication begins
The supercoiling is relaxed by enzymes; topoisomerase or gyrase, and the two strands of parental DNA are unwound by enzyme, Helicase, and separated from each other in one small DNA segment after another.
44
DNA is the ______________ for a cell's proteins including enzymes
Blueprint
45
DNA's obtained either from _________ _______in the _________ ________________or from a parent cell during cell division
Another cell
| Same generation
46
DNA can be expressed within a cell or transfer to another cell through ___________ and _____________
Recombination
| Replication
47
After replication begins, free nucleotides present in the cytoplasm of the cell are.....
Matched up to the exposed bases of the single stranded parental DNA
48
What happens to bases that are improperly base paired
They are removed and replaced by replication enzymes (DNA polymerase)
49
What does DNA polymerase do
Must have parent DNA used as template, manufacture a copy and adds nucleotides to open hydroxyl 3' end of existing parent strand. Antiparalelly, the new strand will be built 5' to 3'. Once the bases are properly aligned this enzyme joines the nucleotides to the growing DNA strand.
50
What happens as the replication fork moves along the parental DNA
Each of the unwound single strands combines with new nucleotides. The original strand and this newly synthesized daughter strand then rewind.
51
What is the process of replication refer to and why
Semiconservative replication, Because each new double stranded DNA molecule contains one original (conserved: 50% of original) strand and 1 new strand. Its starts with one DNA molecule and ends with 2 DNA molecules.
52
What is an important concept to understand about the paired DNA strands
That they are oriented in opposite directions relative to each other
53
What is the difference between transcription and translation in prokaryotes vs eukaryotes
▪︎In prokaryotes both transcription and translation occur in the cytoplasm. The whole cell has access to whatever is being produced and can access it immediately. The ribosomes can start reading the RNA right away, before its completely transcribed.
▪︎In eukaryotes transcription takes place where DNA is housed, in the nucleus and translation in cytoplasm where ribosomes are available. Everything is compartmentalized.
54
For paired bases to be next to each other the sugar components in one strand are ________ _________ relative to the other
Upside down
55
The end with the hydroxyl attached to the_______ carbon is called the _____ end of the DNA strand
3'
| 3'
56
The end having a phosphate attached to the ____ carbon is called the _____ end
5'
| 5'
57
The way in which the 2 strands fit together dictates that the ______ direction of one strand runs ___________ to the ______direction of the other strand.
5'--->3'
Counter
5'--->3'
58
As a replication fork moves along the parental DNA, the 2 new strands must grow in ____________ ___________
Different directions
59
What supplies the energy for DNA replication
Nucleotides which are actually nucleoside triphosphates
60
What provides the energy needed to synthesize DNA in DNA replication
Deoxyribose is the sugar in the nucleosides, 2 phosphate groups are removed by hydrolysis to add the nucleotide to a growing strand of DNA, providing energy to make the new bonds in the DNA strand
61
The DNA replication of some bacteria such as E. Coli moves directionally around the chromosome, what does this mean?
Teo replication forks move in opposite directions away from the origin of replication. Because the bacterial chromosome is a closed loop, the replication forks eventually meet when replication is completed.
62
What can be contributed to the large accuracy of DNA replication
Proofreading capabilities of DNA polymerase
63
How does DNA polymerase proofread DNA replication
As each new base is added, the enzyme evaluates whether it forms the proper complementary base pairing structure. If not the enzyme excises the improper base and replaces it with the correct one.
64
In DNA replication what is the energy source used to synthesize RNA
Nucleoside triphosphates with ribose
65
What happens in the process of transcription
Genetic information in DNA is copied or transcribed into a complementary base sequence of RNA
66
What does the cell use the transcribed information encoded in RNA for
To synthesize specific proteins through the process of translation
67
Transcription
The synthesis of a complementary strand of RNA from DNA template
68
What does Ribosomal RNA form
An integral part of ribosomes, the cellular machinery for protein synthesis
69
rRNA and __________ are involved in protein synthesis
tRNA
70
What does messenger RNA do
Carries the coded information for making specific proteins from DNA to ribosomes, where proteins are synthesized
71
What happens during transcription
A strand of mRNA is synthesized using a specific portion of the cell's DNA as a template. In other words DNA is rewritten so that the same information appears in the base sequence of mRNA.
72
What is the difference with base pairing of mRNA compared to DNA
A pairs with U, instead of T
73
What 2 things this the process of transcription require
1. An enzyme called RNA polymerase
| 2. A supply of RNA nucleotides
74
When does transcription begin
When RNA polymerase binds to the DNA at a site called the promoter
75
What serves as a template for RNA synthesis for a given gene
Only one of the 2 DNA strands
76
In what direction is RNA synthesized
5'--->3', like DNA
77
Up until when does RNA synthesis continue
Until RNA polymerase reaches a site on the DNA called the terminator.
78
What does the process of transcription allow the cell to produce
Short term copies of genes that can be used as a direct source of information for protein synthesis
79
What is messenger RNAs job
It acts as an intermediate between the permanent storage form, DNA, and the process that uses that information, translation
80
Translation
Protein synthesis. It involves decoding the language of nucleic acids" and converting that information into the language of proteins
81
What is the language of mRNA
In the form of codons
82
Codons
Groups of 3 nucleotides, such as AUG, GGC, AAA
83
What does a sequence of codons on an mRNA molecule determine
The sequence of amino acids that will be in the protein being synthesized. Each codon codes for a particular amino acid.
84
What is the genetic code
The coding of a particular amino acid
85
Degeneracy
A situation in which most amino acids are signaled by several alternative codons. This allows for certain amount of change, or mutation, in the DNA without affecting the protein ultimately produced.
86
How many codons are there
64
87
How many codons are sense codons ? How many are nonsense?
61
| 3
88
Sense codons
Code for amino acid
89
Nonsense codons
Also called stop codons, do not code for amino acids. They signal the end of the protein molecule's synthesis
90
What is the start codon that initiates the synthesis of the protein molecule
AUG
91
Through what process are codons of mRNA converted into protein
Through the process of translation. The codons are read sequentially and in response to each codon, the appropriate amino acid is assembled into a growing chain
92
Where is the site of translation
Ribosome
93
tRNA molecule's job
They act as translators. On one end of each tRNA recognizes the specific codon and transports the required amino acid on the other end
94
What does each tRNA molecule have
An anticodon
| An acceptor arm, the amino acid binding site
95
What is an anticodon
A sequence of 3 bases that is complementary to a codon
96
What is the function of the ribosome
To direct the orderly binding of transfer RNAs to codons and to assemble the amino acids brought into a chain, ultimately producing a protein
97
What are the components required to assemble a protein
Two ribosomal subunits, a tRNA with anticodon UAC, and the mRNA molecule to be translated, and additional protein factors
98
When does translation end
When one of the three nonsense codons in the mRNA is reached
99
What happens after translation ends
The 2 ribosomal subunits come apart and the mRNA and newly synthesized polypeptide chain are released
100
In what direction does ribosome move along the mRNA
5'-->3'
101
In prokaryotes where does transcription and translation occur and what benefit does this have
Occurs in the cytoplasm. The translation of mRNA into protein can begin even before transcription is complete. This happens because mRNA is available to ribosomes before the entire mRNA molecule is even made.
102
Where does transcription in eukaryotic cells take place
In the nucleus. The mRNA must be completely synthesized and moved through the nuclear membrane to the cytoplasm before translation can begin.
103
In eukaryotic cells, the regions of genes that code for proteins are often interrupted by
None coding DNA
104
Eukaryotic and archaea gene's are composed of
Exons and introns
105
Introns?
| Exons?
Introns-->The intervening regions of DNA that do not encode protein. They are cut out and then joined together for a finished ribosome RNA.
Exons-->code for proteins, expression. Needed for protein synthesis.
106
The starting codon molecule AUG intranslation is what code for bacteria ? Eukaryotes?
Formylmethionine
| Methionine
107
During translation, if methionine isn't needed, what happens to it?
It is removed later
108
What are the different stop codons
UAA
UAG
UGA
109
Exons
The regions of DNA expressed
110
Gene's are the units of __________ ____________
| encoded by a sequence of __________ _______ in DNA
Biological information
Nucleotide bases
111
A gene is____________ or turned into a _________ within the cell, through the process of ______________ and ___________
Expressed
Product
Transcription
Translation
112
Genetic information carried in DNA is transferred to a temporary ______ molecule by ______________
mRNA
| Transcription
113
Summarize what happens during translation
The mRNA directs the assembly of amino acids into a polypeptide chain, a ribosome attaches to mRNA, tRNAs deliver the amino acids to the ribosome as directed by the mRNA codon sequence, and the ribosome assembles the amino acids into the chain that will be the newly synthesized protein.
114
Constitutive
Products are constantly produced at a fixed rate
115
What percent of bacterial genes are constitutive
60 to 80%
116
When are constitutive genes turned on
They are turned on all the time, they code for enzymes that the cell needs in fairly large amounts for its major life processes
117
To genetic control mechanisms that regulate the transcription of mRNA
1. Induction
| 2. Repression
118
Repression
The regulatory mechanism that inhibits gene expression and decreases the synthesis of enzymes
119
What is repression a response to
An over abundance of an end product of a metabolic pathway
120
What mediates repression
Repressors
121
What are repressors
A regulatory protein, which block the ability of RNA polymerase to initiate transcription from the repressed genes.
122
What is the default position of a repressible gene
On
123
Induction
The process that turns on the transcription of a gene or genes
124
INDUCER
A substance that acts to induce transcription of a gene
125
Inducible enzymes
Enzymes that are synthesized in the presence of inducers
126
Name an inducible enzyme of E. coli and when it occurs
B-galactosidade
It is activated in the presence of lactose.
If E. coli is placed in a medium in which no lactose is present, the organism contains almost none of this enzyme. When this enzyme is added to the medium the bacterial cells produce a large quantity of the enzyme.
127
What is the inducer of B-galactosidase in E.coli
Lactose indirectly induces the cells to synthesize this enzyme. Lactose is converted to allolactose, which induces these genes.
128
Structural genes
Genes that determine the structures of proteins
129
What are the 2 short segments of DNA called located in the control region of the operon
1. Promoter
| 2. Operator
130
Promoter
A region of DNA where RNA polymerase initiates transcription
131
Operator
A region of DNA the acts as a go or stop signal for transcription of the structural genes
132
What is the structure on the operon made up of
It consists of the promoter and operator sites and structural genes that code for the protein.
133
What regulates the operon
The product of the regulatory gene
134
I gene
A regulatory gene that encodes a repressor protein that switches inducible and repressible opens on or off
135
The default position of an induce gene
Off
136
Using lactose explain how an inducible operon works
In absence of lactose, the repressor binds to the operator site, preventing transcriptions
In the presence of lactose, the repressor binds to a metabolite of lactose instead of to the operator and lactose digesting enzymes are transcribed
137
Repressible operons
The structural genes are transcribed until they are turned off or repressed
138
Explain how a repressible operon works, use tryptophan as an example
When excess tryptophan is present, the tryptophan acts as a corepressor binding to the repressor protein. The repressor protein can now bind to the operator, stopping further synthesis of tryptophan.
139
What are the enzymes needed for lactose catabolism
B-galactosidase, Permease, Transacetylase
140
The transcription of the lac operon requires the presence of what 2 things
1. Presence of lactose
| 2. Absence of glucose
141
Cyclic AMP (cAMP)
A substance derived from ATP that serves as a cellular alarm signal
142
When does cAMP accumulate
When glucose is no longer available
143
Enzymes that metabolize glucose are ______________
Constitutive
144
cAMP binds the ________ ____ of ________
| that binds to the lac promoter, which initiates transcription
Allosteric site
| Catabolic activator protein (CAP)
145
Catabolite repression
Inhibition of the metabolism of alternative carbon sources by glucose. When glucose is available, the level of cAMP in the cell is low and CAP is not bound.
146
microRNAs
Single stranded RNA molecules of approximately 22 nucleotide, Inhibit protein production in eukaryotic cells
147
Short RNAs
In bacteria enable the cell to cope with environmental stresses such as low temperature or oxydative damage
148
Mutation
A permanent change in the base sequence of DNA
149
What happens when a mutation occurs
This will cause some type of change in the product encoded by the gene. An enzyme may become inactive or less active. It can be beneficial, such as an enhanced or new activity or it can be detrimental on that ot loses a phenotypic trait it needs or can even die.
150
Silent mutation
Is simple mutation that causes no change in the activity of the product encoded by the gene. Occurs when one nucleotide is substituted for another in the DNA.
151
Explain how the degeneracy of a mutation occurs
1. The new codon might still code for the same amino acid
2. If the amino acid is changed, its function might not change or is a nonvital portion
3. It can be chemically similar to the original amino acid
152
Types of mutations
```
1. Base substitution or point mutation
•Missense mutation
•Nonsense mutation
2.Frameshift mutations
3. Spontaneous mutations--> base substitution/frameshift
```
153
Base substitution
Most common type of mutation.
A single base at 1 point in the DNA sequence is replaced with a different base. When the DNA replicates the result is a substituted base pair.
154
What are 2 types of base substitution mutations
1. Missense mutation
| 2. Nonsense mutation
155
Missense mutation
A change in the DNA resulting from a base substitution that resulted in a substitution of an amino acid of a synthesized protein
156
Example of missense mutation
Sickle cell disease is caused by a single change in the gene for globin, changing the shape of hemoglobin molecule and RBCs
157
Nonsense codon
A base substitution resulting in a nonsense codon
158
By creating a nonsense codon in the middle of an mRNA molecule, some substitutions effectively prevent the
Synthesis of a complete functional protein, only a fragment is synthesized
159
Frameshift mutations
One or a few nucleotide pairs are deleted or inserted in the DNA
160
What does frameshift mutations do
The mutation can shift that translational reading frame, the 3 by 3 grouping of nucleotides recognized as codons by tRNAs during translation.
161
What happens when nucleotide pairs are delete in frameshift mutations
This causes changes in many amino acids downstream from the site of the original mutation. They almost always result in a long stretch of altered amino acids and the production of an active protein.
162
It's spontaneous mutation
Base substitutions and frameshift mutation that occurs spontaneously because of occasional mistakes made during DNA replication. They occur in the absence of any mutation causing agents.
163
What are examples of mutation causing agents
Agents in the environment such a certain chemicals and radiation
164
Mutagens
Agents in the environment, such a certain chemicals and radiation that directly or indirectly bring about mutations
165
Mutations can result in resistance to
Antibiotics
166
Nitrous acid
A chemical known to be a mutagen shows how exposure of DNA to nitrous acid can convert the base adenine to a form that no longer pairs with thymine but instead pairs with cytosine. The DNA is altered at random locations.
167
Nucleoside analog
A chemical mutagen. Analogs or randomly incorporated into cellular DNA in place of the normal bases. During DNA replication the analogs cause mistakes and base pairing. This will result in base pair substitutions in the progeny cells.
168
What are some chemical mutations that cause frameshifts
Benzopyrene--> from smoke and soot
| Aflatoxin--> mold that grows and peanuts and grain
169
How are frameshift mutagens able to slip between the stacked base pairs of DNA double helix
They have the right size and chemical properties, They offset the 2 strands of DNA leaving a gap or bulge in one strand or the other, When the staggered DNA strands are copied during dna synthesis one or more base pairs can be inserted or deleted in the new double strand DNA
170
Frame shift mutagens are often
Potent carcinogens
171
How is it that x-rays and gamma rays are forms of radiation that are potent to mutagens
They ionize atoms and molecules, The resulting ions and free radicals are very reactive, Some of these ions oxidize bases in DNA, resulting in errors in DNA replication and repair that produce mutations. There's also breakage of covalent bonds in the sugar phosphate backbone of DNA, which causes physical breaks in chromosomes .
172
How is UV light another form of mutagenic radiation
Direct UV light exposure on DNA causes the formation of harmful covalent bonds between certain bases. Adjacent thymines in DNA strand can cross link to form thymine dimers. This could cause serious damage or death to the cell because it cannot properly transcribe or replicate such DNA
173
What are some bacterial enzymes that can repair UV damage
Photolyases, aka light repair
| Nucleotide excision repair
174
Photolyases
Also known as light repair enzymes
| Say youse visible light energy to separate the dimer back to the original 2 thymines
175
Nucleotide excision repair
* It is not restricted to UV damage, it can repair mutations from other causes.
* Enzymes cut out the incorrect base and fill in the gap with newly synthesized DNA that is complementary to the correct strand
176
How are incorrect basis distinguished from correct basis in the nucleotide excision repair mechanism
The enzyme, methylased. These enzymes add a methyl group to selected bases soon after DNA strand is made. A repair endonuclease then cuts the non methylated strand and an exonuclease removes the damaged DNA
177
How is the DNA strand repaired on nucleotide excision repair
DNA polymerase fills the gap by synthesizing new DNA, using an intact strand as a template. DNA ligase seals the remaining gap by joining the old and new DNA
178
Mutation rate
The probability that a gene will mutate when a cell divides. Stated as power of 10. 10-5 or 10-3 per replicated gene
179
Are mutations common
| Spontaneous mistakes?
No they're rare. Spontaneous mistakes and DNA replication occur at a very low rate--> 1:10 9 in replicated base pairs or 1:10 6 replicated genes
180
The occurrence of random mutations
Occur at low frequency, is an essential aspect of the adaptation of species to their environment, occur randomly along chromosome
181
Positive selection
Direct selection. The detection of mutant cells by rejection of the unmutated parents cell.
182
Example of positive (direct) selection
Mutant bacteria resistant to PNC:
Plate bacterial cells on medium containing penicillin. Those that grow are identified as mutants, those that dont grow are normal.
183
Negative selection
Indirect. Used to identify mutations in other kinds of genes. This process selects a cell that cannot perform a certain function.
184
What kind of technique is used for negative selection
Replica plating
185
Discuss replica plating
1. Sterile velvet is pressed on the grown colonies on the master plate
2. Cells from each colony are transferred from the velvet to new plates, one containing histamine and one lacking it.
3. Plates are incubated
4. Growth on plates is compared. A colony that grows on the medium with histidine but could not grow on the medium without histidine is auxotrophic
186
Replica play teen is a very effective means of isolating mutants that require one or more
New growth factors
187
Auxotroph
Any mutant microorganism having a nutritional requirement that is absent in the parent
188
Carcinogens
Substances that cause cancer in animals including human. Many known mutagens have been found to cause this.
189
Ames test
Uses bacteria as carcinogen indicators. It is based on the observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effect of the original mutation
190
Reversion
This occurs when a mutation occurs when a second mutation restores the function that was lost as a result of the first mutation. The second mutation causes a change in the dNA that either reverses the original alteration or compensates for it.
191
What substitute for animal enzyme is used when performing Ames test? Why
The chemical to be tested and the mutant bacteria are incubated together with rat liver extract . Animal enzymes activate many chemicals into forms that are chemically reactive for mutagenic or carcinogenic activity to appear
192
How do you know a substance is mutagenic in the Ames test
It will cause the reversion of his- bacteria to his+ bacteria at a rate higher than the spontaneous reversion rate
193
The number of observed revertants indicate the degree to which a substance is
Mutagenic and therefore possibly carcinogenic
194
Genetic recombination
Refers to the exchange of genes between 2 DNA molecules to form new combinations of genes on a chromosome
195
Crossing over
A process in which a cell picks up a foreign DNA, called a donor DNA, some of it could insert into the cells chromosome. The DNA has recombined. The chromosome now carries a portion of the donor's DNA.
196
Between mutation and recombination which is more likely to be beneficial
Recombination. Because it is less likely to destroy a gene's function and may bring together combinations of genes
197
Vertical gene transfer
Occurs when genes are passed from an organism to its offspring
198
Horizontal gene transfer
Also known as lateral transfer. The transfer involves a donor cell that gives a portion of its total DNA to a recipient cell.
199
Recombinant
The recipient cell that incorporates donor DNA into its own dna.
200
Transformation
The process and which genes are transferred from one bacterium to another as naked DNA in solution. It involves the direct uptake, incorporation and expression of exogenous genetic material (exogenous DNA) from its surroundings and taken up through the cell membrane(s).
201
Is transformation of bacteria a natural process
Yes. It occurs naturally among the very few genera of bacteria.
202
Competent cell means
A state in whicn a recipient cell is in a physiological state in which it can take up the donor DNA
203
What does competence result from
From alterations in the cell wall that make it permeable to large DNA molecules
204
Conjugation
Another mechanism by which genetic material is transferred from one bacterium to another. It is mediated by one kind of plasmid.
205
Plasmid
A circular piece of DNA that replicates independently from the cells chromosome. Their Gene's are usually not essential for the growth of the cell under normal conditions
206
How is conjugation different from transformation
Conjugation requires direct cell to cell contact, 2 cells. Conjugating cells must be of opposite mating type. Transfer of DNA comes from donor.
Transformation requires only 1 cell, no cell to cell contact required, uptake is from surroundings.
207
Conjugation between gram negative bacteria
Plasmids carry Gene's that code for synthesis of sex pili. The plasmid is replicated during transfer of a single stranded copy of the plasmid DNA to the recipient, where the complementary strand is synthesized.
208
Sex Pili
Projections from the donor cell surface that contact the recipient and help bring the 2 cells into direct contact
209
Conjugation of gram positive bacteria
They produce sticky surface molecules that cause cells to come in direct contact with each other
210
When a F factor is transferred from a donor to a recipient, the recipient becomes a
F+ cell
211
When an F factor becomes integrated into the chromosome of and F+ cell, it makes the cell a
High frequency of recombination (Hfr) cell
212
When an Hfr donor passes a portion of its chromosome into an F- recipient, the recipient becomes a
Recombinant F- cell
213
Why is it that conjugation from an Hfr cell to a F- cell, results in an F- cell remaining an F- cell
The chromosome from a Hfr cell breaks before it is completely transferred. Just as in transformation, an F- cell may acquire new versions of chromosome or genes. However because it did not receive a complete F factor during conjugation it remains an F- cell.
214
Transduction in bacteria
A mechanism of genetic transfer between bacteria in which bacterial DNA is transferred from a donor cell to a recipient cell inside a virus that infects bacteria.
215
Bacteriophage
Aka phage. A virus that infects bacteria.
216
Generalized transduction
All genes contained within a bacterium infected by a generalized transduction phage are equally likely to be package in a phage coat and transferred. This includes phage DNA, but most importantly; *bacterial DNA, *plasmid DNA, or even DNA of another virus.
217
Specialized transduction
Only certain bacterial genes are transferred, such as for certain toxins produced by bacteria host
218
What are genetic elements that provide additional mechanisms for genetic change
Plasmids
| Transposons
219
Plasmids
Self replicating, gene-containing circular pieces of DNA, about 1-5% the size of the bacterial chromosome.
220
Where are plasmids found
They are found mainly in bacteria but also in some eukaryotic microorganisms such as Saccharomyces cerevisiae
221
F factor
A conjugative plasmid that carries genes for sex pili and for the transfer of the plasmid to another cell
222
For plasmids dispensable
Yes, but they may be crucial to the survival and growth of the cell
223
Dissimilation plasmids
The code for and enzymes that trigger the catabolism of certain unusual sugars and hydrocarbons. These can be used as primary carbon and energy sources. They may permit the survival of microorganisms in very diverse and challenging environments.
224
Give examples of how plasmids code for proteins that enhance the pathogenicity of a bacterium
E.coli-->toxin production and attachment to intestinal cell wall
S.aureas--> exfoliative toxin
C.tetani-->neurotoxin
B.anthracis-->toxins
225
Bacteriocins
Toxic proteins that kill other bacteria, genes for synthesis contained in plasmids
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R factors
Resistance factors. Plasmid's that contain genes that offer cell resistance to antibiotics, heavy metals, or cellular toxins
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For factor groups of genes
1. Resistance transfer factor (RTF)
| 2. r-determinant
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Resistance transfer factor
Genes for plasmid replication and conjugation
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R- Determinant
Plasmid with the resistance genes, codes for the production of enzymes that inactivate certain drugs or toxic substances
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How does transformation occur
DNA from dead cells gets cut into fragments and exits the cell. The free-floating DNA can then be picked up by competent cells. The exogenous DNA is incorporated into the host cell’s chromosome via recombination.
231
How does the transfer of resistance between bacteria or organisms happen
Bacterial species can conjugate and transfer plasmid to other species or plant cells, Non conjugative plasmids transfer from one cell to another by inserting themselves into a conjugative plasmid or a chromosome or by transformation
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Tranposons
Small segments of DNA that can move from one region of a DNA molecule to another. They contain information for their own transposition.
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Discuss how transposons move around
They may move from one site to another site on the same chromosome or to another chromosome or plasmid. They may insert themselves within genes, inactivating them. They can cause havoc within the cell.
234
How often does transposons occur
Relatively rare, it is comparable to the frequency of spontaneous mutation rate in bacteria: 10 -5️⃣ to
10 -7️⃣ per generation
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Insertion sequences (IS)
The simplest transposons, contains only a gene that codes for an enzyme and recognition sites
236
What enzyme does IS code for and what does it do
Transposase
| Catalyzes the cutting and resealing of DNA that occurs and transposition
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Recognition sites
Short inverted repeat sequences of DNA that the enzyme recognizes as recombination sites between the tranposon and the chromosome.
238
What types of genes do complex transposons carry
Other genes not connected with the transposition process. Such as genes for enterotoxin or for antibiotic resistance. Plasmid such as R factors are frequently made up of a collection of tranposons.
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Why are transposons with antibiotic resistant of practical interest
1. Because there is no limitation on the kinds of genes that they can have
2. They provide a natural mechanism for the movement of genes from one to another
3. They may be carried between cells on plasmids or viruses
4. They can also spread from one organism or even species to another
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A single, circular chromosome contains a single dna molecule measuring _________ when stretched out.
How does it fit in the cell nucleoid?
```
1mm long (1000× longer than cell)
It fits compactly into the cell nucleiod by twisting around itself (supercoiling).
```
241
What is RNA primers function in DNA synthesis
It's a sequence of about 10 nucleotides that are complementary to the parent DNA, this then allows DNA polymerase III to add deoxyribonucleotides to synthesize the new complementary strand to the parent strand.
242
Transcription involves
1. DNA is transcribed to make RNA ( m, t, r)
2. Transcription begins when RNA polymerase binds to the promoter sequence
3. Transcription proceeds and the 5' to 3' direction
4. Transcription stops when it reaches the terminator sequence
243
What is the 1st step in transcription
DNA molecule must be transcribed into RNA so ribosomes can read and understand.
244
What does a codon express
Each codon makes a building block (amino acid) for a protein
245
Where are amino acids located
In the cell
246
What RNA is required for translation
All 3; messenger, transfer, ribosomal
247
tRNA has a __________ codon to what is presen6on RNA
Complementary
248
What base is different on RNA
There is no thymine, instead there is uracil
