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Microbiology > Ch 08 Microbial Genetics > Flashcards

Ch 08 Microbial Genetics Flashcards

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1
Q

What is a base substitution?

A

A single DNA pair is altered.

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2
Q

What is a frame shift mutation?

A

A DNA pair is removed causing a shift in the meaning.

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3
Q

What are the chain of events in the central dogma?

A

DNA
mRNA
Protein
Function

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4
Q

What is an inducible operon?

A

A gene in the off mode that is expressed, turning it on.

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5
Q

What is a repressible operon?

A

A gene that is in the ON expressed mode that is turned off, not expressed.

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6
Q

What causes diseases?

A

Presence of toxic proteins the damaged tissue.

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7
Q

What causes antibiotic resistance?

A

Mutations the bacterial genome.

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8
Q

What is a biofilm?

A

Growth on a surface caused by altered bacterial gene expression.

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9
Q

What is biotechnology?

A

The application of microbes to make a useful product.

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10
Q

What is a genome?

A

The total genetic information inside a cell including chromosomes and plasmids.

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11
Q

What are chromosomes?

A

Structures containing DNA that carry hereditary information

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12
Q

What are genes?

A

Segments of DNA and RNA.

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13
Q

What is DNA made up of?

A

Repeating nucleotides consisting of a nucleobase, A, T, C, G, a deoxyribose (pentose sugar), and a phosphate group.

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14
Q

How do the base pairs pair up?

A

A-T

C-G

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15
Q

What is the genetic code?

A

The rules determined how a nucleotide sequence is converted into an amino acid sequence.

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16
Q

What does it mean when a gene has been expressed?

A

When the gene codes for a protein have been produced.

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17
Q

What does a genotype mean?

A

The genetic make up including all its DNA.

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18
Q

What does a phenotype mean?

A

The expressed DNA properties.

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19
Q

What are the two types of proteins in a microbe?

A

Enzymatic that catalyze reactions or structural that support the membrane.

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20
Q

What are short tandem repeats?

A

Non-coding regions

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21
Q

What is vertical and horizontal gene transfer

A

Transfer from one generation to another.

Transfer among same generations.

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22
Q

What does semi conservative replication mean?

A

When the original DNA and a new strand come together

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23
Q

Which end of the DNA strand can new nucleotides attached to?

A

3’

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24
Q

What is the name of the process that provides energy for adding a nucleotide to DNA?

A

Hydrolysis of the phosphate bonds.

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25
Q

What is transcription?

A

How are complementary strand from DNA forms RNA.

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26
Q

What does messenger RNA, mRNA, do?

A

Carries the information for making specific proteins from DNA to make RNA.

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27
Q

What are the two things that transcription requires

A

RNA polymerase

RNA nucleotides

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28
Q

Where on the DNA strand does RNA transcription begin?

A

At the promoter.

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29
Q

What is genetics?

A

Heredity of cell replication, expression, and transfer from on generation to another.

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30
Q

What do small nuclear ribonucleoproteins do?

A

Remove introns and splice exons together.

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31
Q

What does what does constitutive mean

A

Product produced at a fixed rate.

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32
Q

What is repression?

A

Inhibition of gene expression and enzyme synthesis.

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33
Q

What do repressors do?

A

Block the abilities RNA polymerase to initiate transcription. The default position of a repressible gene is on.

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34
Q

What is an inducer?

A

A substance that initiates transcription of a gene. The default position of an inducible gene is off.

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35
Q

What does cyclic AMP, cAMP, do?

A

cAMP binds to the allosteric site of catabolic activator protein then binds to the lac promoter which initiates transcription.

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36
Q

What is natural selection?

A

The survival of new genotypes.

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37
Q

What is a mutation?

A

A permanent change to the base sequence of DNA.

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38
Q

What is a missense mutation?

A

When a base substitution results in an unintended amino acid.

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39
Q

What is a nonsense mutation?

A

When a nonsense codon results.

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40
Q

What is a frameshift mutation?

A

When a point in the DNA sequence is removed or inserted and the line is shifted.

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41
Q

What is a mutagen?

A

An environmental agent that causes DNA mutations.

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42
Q

What is a thymine diner?

A

When UV forms a thymine dimer and a endonuclease cuts the damaged DNA, an exonuclease removes the damaged DNA, a DNA polymerase fills the gap, and a DNA ligase seals the strand.

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43
Q

What is an autotroph?

A

A mutant microbe that has different nutritional requirements than its parent.

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44
Q

What is a carcinogen?

A

A substance that causes cancer.

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45
Q

What is the Ames Test?

A

Uses bacteria as carcinogenic indicator.

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46
Q

What are reversions?

A

Substances that reverse the original mutation.

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47
Q

What is genetic recombination?

A

The exchange of genes between two DNA strands to form new combinations.

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48
Q

What was Griffith’s experiment?

A

Mice injected with nonvirulent rough strain, R cells, of pneumonia lived; injected with virulent smooth strain, S cells, died; injected with heat-killed S cells lived, but surprisingly injected with both R and heat-killed S cells died. Post mortem blood examination revealed that living S cells were created by transformation.
Conclusion: dead R cells caused a chemical transformation of some R cells into S cells.

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49
Q

What is F factor?

A

A fertility factor plasmid found in a donor cell in bacteria through a mating bridge.

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50
Q

What is a Hfr cell?

A

A high-frequency recombination cell bacteria when the F+ F factor has been conjugated with a F- cell into the chromosome. Remember sex pilli forms a bridge.

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51
Q

What is transduction?

A

DNA transferred from a donor to a recipient inside a virus called a bacteriophage.

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52
Q

What is specialized transduction?

A

When only certain genes are transferred.

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53
Q

What is a plasmid?

A

A small circular piece of DNA.

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54
Q

What is a sex pili?

A

Required for mating Gram-negative bacteria. Could be a bridge from an F cell or an Hfr cell. Involved in gene transfer and attachment onto surfaces.

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55
Q

What is dissimulation plasmid?

A

Enzymes that trigger catabolism of sugars and hydrocarbons.

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56
Q

What are bacteriocins?

A

Toxic proteins that kill other bacteria.

57
Q

What are resistance factors, R factors?

A

Genes that confer resistance to antibiotics, heavy metals, or toxins.

58
Q

What are transposons?

A

Small segments of DNA that can move to a different molecule.

59
Q

When does a cell do replication?

A

When making new cells.

60
Q

When does a cell do transcription?

A

All the time.

61
Q

How is RNA made?

A

Transcripiton

62
Q

What is a promoter?

A

The starting site on the DNA strand for transcription of RNA by RNA polymerase.

63
Q

What does DNA polymerase do?

A

Synthesizes DNA by copying a DNA strand.

64
Q

What does RNA polymerase do?

A

Produces primary transcript RNA.

65
Q

What does a ligase do?

A

Brings pieces of DNA together.

66
Q

What is a primer?

A

A strand of nucleic acid that serves as a starting point for DNA synthesis. It is required for DNA replication because the enzymes can only add new nucleotides to an existing strand of DNA.

67
Q

What is a plasmid?

A

A small circular piece of DNA that replicates independently of the chromosome.

68
Q

What is a bacteriophage?

A

A virus that infects bacteria DNA.

69
Q

What does genotype mean?

A

Genetic makeup of a specific allele. You can have the gene but not the trait.

70
Q

What did Watson and Crick do?

A

Discovered the double helix of DNA strands running in opposite directions, held by H bonds.

71
Q

What is a nucleotide?

A

A purine or pyrimidine base, five-carbon sugar, and a phosphate.

72
Q

What is semi-conserved replication?

A

Semi-conservative replication would produce two copies that each contained one of the original strands and one new strand. Conservative replication would leave the two original template DNA strands together to produce a copy composed of two new strands containing all of the new DNA base pairs.

73
Q

What is a helicase?

A

Helicases are enzymes that bind and may unwind nucleic acid or nucleic acid proteins.

74
Q

Differentiate DNA polymerase from DNA ligase?

A

Polymerases: attaches new free nucleotides.
Ligases: seals new nucleotides into a strand.

75
Q

What are Okazawi fragments?

A

Short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication.

76
Q

Are nucleoside triphosphates endo or exogeneric?

A

Exergonic

77
Q

What is an operon?

Concept question.

A

The operator and promoter sites and the genes they control. An operon is a segment of DNA containing adjacent genes including structural genes, an operator gene, and a regulatory gene.

78
Q

List the differences between eukaryotes and prokaryotes.

A 
Eukaryotes - Prokaryotes
pos charge - neg charge
histones - supercoiled DNA
3 RNA polymerase - 1 RNA polymerase
complex regulation - operons
multi chromosomes - one chromo
multi origins on a chromo - one origin
      - polysomes in prokaryotes only
79
Q

RNA is made by which process?

A

Transcription

80
Q

What are the different forms of RNA?

A 
mRNA
miRNA
iRNA
rRNA
tRNA
81
Q

When is RNA polymerase used?

A

In transcription from DNA to RNA.

82
Q

How many chromosomes do humans have?

A

23 pairs

83
Q

What is the start codon?

A

AUG

84
Q

Remember, transcription is same language, translation a different language

A

-

85
Q

What does gene expression mean?

A

making protein polypeptide chains

86
Q

What does glycolyzation mean?

A

Adding a sugar

87
Q

What are trypanosomes?

A

Turns on only one.

A single-celled parasitic protozoan with a trailing flagellum, infesting the blood.

88
Q

Does lactose require an enzyme to be consumed? Does sugar?

A

Lactose needs an enzyme, lactose intolerant don’t have it.

Sugar does not need an enzyme.

89
Q

What does beta-galactosiadase do?

A

An enzyme that splits lactose into gluccose.

90
Q

Why does a cellular alarm (alarmone) sound involving cAMP?

A

Low glucose levels.
When glu is not avail, cAMP accumulates.
cAMP binds in allosteric site CRP protein.
When cAMP signals go up, cells need ATP.

91
Q

What does allosterase do?

A

Removes repressor

92
Q

What is an example of a chemical mutagen?

A

AZT

93
Q

Do chemical mutagens cause small or large mutations? Carcinogens?

A

Small

Large

94
Q

What is a disadvantage of not having a nucleus?

A

Bacterial DNA is more easily damaged

95
Q

Does ionizating or non-ionizating radiation cause more mutations?

A

Non-ioniziting causes more mutations.

Ionizing kills cells.

96
Q

What is the probability that a gene will mutate during normal cell division?

A

10 x 9 = one in one billion

97
Q

What does photolyase do?

A

Cell light repair after UV exposure.

98
Q

What is genomics?

A

The molecular study of genomes.

99
Q

What are R factors?

A

Carry resistance to antibiotics, heavy metals, or toxins.

100
Q

What are two groups of R factors?

A

Resistance Transfer Factor, RTF, genes for plasmid replication.
r-determinant codes for production of enzymes that inactivate certain drugs or toxins.

101
Q

What is R100?

A

Resistance plasmid R100 carries genes for resistance form sulfonamides, streptomycin, tetracycline and mercury. The plasmid can be transferred to genera including Escherichia, Klepsiella, and Salmonella.

102
Q

How does diphtheria cause a disease

A

If existing diphtheria bacteria inherits a virus. Without the bacteria, diphtheria is benign.

103
Q

1) Structure of a nucleotide. How do ribonucleotides differ from deoxyribonucleotides?

A
  • structure: nucleobase(adenine, thymine, cytosine, guanine); deoxyribose (a pentose sugar); and a phosphate group.
  • RNA and DNA are nucleic acids, and composed of long chains of nucleotides, and each nucleotide is made out of a nucleobase, a phosphate, and a sugar. The sugar of RNA is ribose, and the sugar of DNA is deoxyribose, with only one oxygen distinguishing them: where a hydrogen (H) bonds in deoxyribose, a hydroxyl (OH) bonds in ribose. The partial negative charge of the hydroxyl in ribose repels the electrostatic negative charge of the phosphate, preventing the RNA chain from coiling in as tight a helix as it does in DNA. As a result DNA is more stable and RNA more flexible. This small difference has important consequences for the nucleic acids
104
Q

2) Structure of DNA:

A
  • long strand of nucleotides twisted together in pairs to form a double helix; each strand has a string of alternating sugar & phosphate groups (its sugar-phosphate backbone); the 2 strands are held together by hydrogen bonds between their nitrogenous bases;
105
Q

3) Nature of the chromosome in eubacteria:

A
  • bacteria typically have a single circular chromosome consisting of a single circular molecule of DNA with associated proteins
  • the chromosome is looped and folded and attached at one or several points to the plasma membrane
  • takes up only about 10% of the cell’s volume b/c twisted and supercoiled
106
Q

4) DNA Replication & semi conservative replication:

- DNA Replication:

A

one parental double-stranded DNA molecule is converted to 2 identical offspring molecules
- one strand acts as a template for the other strand
- requires the presence of several cellular proteins that direct a particular sequence of events
- in the beginning of replication… the supercoiling is relaxed by topoisomerase or gyrase
- the 2 strands of parental DNA unwind by helicase & separated from each other in one small
DNA segment after another
- binding proteins hold apart
- free nucleotides in the cytoplasm are matched up to the exposed bases of the single parental DNA strand
- where T was, only A can go; where C was, only G can go
- the nucleotide is joined to the DNA strand by DNA polymerase
- the parental DNA is unwound further to allow the addition of the next nucleotides
- point @ which replication occurs= replication fork
- as the replication fork moves along the parental DNA, each of the unwound single strands combines w/ new nucleotides
- the original strand & newly synthesized strand then rewind
- each new double stranded DNA molecule contains one original strand & one new strand, which is referred to as semiconservative replication

107
Q

5) Enzymes involved in replication & their function:

A
  • DNA Gyrase: relaxes supercoiling ahead of replication fork
  • DNA Ligase: seals new short stretches of nucleotides into continuous strand; makes covalent bonds to join DNA strands; okazaki fragments, new segments in excision repair
  • DNA polymerases: synthesize DNA; proofread/ repair DNA; attach free nucleotides to growing strand
  • Helicase: unwinds double-stranded DNA
  • topoisomerase: relaxes supercoiling ahead of the replication fork; separates DNA circles @ end of DNA replication
    Primase: RNA polymerase that makes RNA primers from a DNA template
108
Q

6) DNA synthesis on leading strand vs. lagging strand & why DNA synthesis occurs differently on the 2 parental templates:

A
  • leading strand: continuously synthesized by DNA polymerase
  • lagging strand: discontinuously synthesized; Primase (RNA polymerase), synthesizes a short RNA primer, which is extended by DNA polymerase; then DNA polymerase digests RNA primer & replaces it w/ DNA; then DNA ligase joins the discontinuous fragments of the lagging strand
  • because they break apart and form new strands
109
Q

7) 3 major types of RNA in cell & function/ structure of each:

A
  • RNA types:
    mRNA (messenger)
    tRNA (transfer) carries the complementary anticodon
    rRNA (forms integral part of ribosomes)
    Other types:
    iRNA (neutralize information that’s already there)
    miRNA (fine-tune regulation)
110
Q

8) Molecular structure of mRNA & DNA:

A
  • in RNA, the pentose is ribose; in DNA, it is deoxyribose
  • the bases adenine, guanine, and cytosine are found in both DNA and RNA
  • thymine is found only in DNA, and uracil is found only in RNA
111
Q

9) Identify the reaction sequence implied by the term “Central Dogma”

A
  • central dogma: describes how typically DNA is transcribed to mRNA, which is then translated into proteins that carry out vital cellular functions
  • mutations introduce change into this process, ultimately leading to new or lost functions
  • chain of events: DNA → mRNA → protein → function
    mutations alter genome: altered DNA → mutated mRNA → altered protein → altered function
112
Q

10) Process of transcription:

A

Prokaryotes:
- synthesis of a complementary strand of RNA from a DNA template
- all RNA made through transcription
- has a termination sequence
- ribosomal RNA (rRNA) forms an integral part of ribosomes
- messenger RNA (mRNA) carries the coded information for making specific proteins from DNA to ribosomes, where proteins are synthesized
- the genetic information stored in the sequence of nitrogenous bases of DNA is rewritten so that the same info, appears in the base sequence of mRNA
- ex: 3’ ATGCAT → 5’ UACGUA
- requires both an enzyme called RNA polymerase & a supply of RNA nucleotides
- begins when RNA polymerase binds to the DNA at a site called the promoter
- only one of the 2 DNA strands serves as the template for RNA synthesis for a given gene
- RNA is synthesized in the 5’ → 3’ direction
- RNA synthesis continues until RNA polymerase reaches a site on the DNA called the terminator
- allows the cell to produce short term copies of genes that can be used as the direct source of info, for protein synthesis
- messenger RNA acts as an intermediate between the permanent storage from, DNA & the process that uses the info, translation
Eukaryotes:
- takes place in nucleus
- mRNA must be completely synthesized & moved through the nuclear membrane to the cytoplasm before translation begins
- RNA undergoes processing before it leaves the nucleus
- regions of genes that code for proteins are often interrupted by noncoding DNA
- euk genes are composed of exons (regions of DNA expressed) & …
- introns (intervening regions of DNA) that do not encode protein
- in the nucleus, RNA polymerase synthesizes a molecule called an RNA transcript that contains copies of the introns
- small nuclear ribonucleoproteins (snRNP), “dsnurps”, remove the introns & splice the exons together

113
Q

11) Define the function of the promoter & Identify the molecular species on which it is
found:

A
  • begins transcription when RNA polymerase binds to the promoter on DNA
114
Q

12) What is the genetic code? & Discuss the significance of its universality:

A
  • 3 nucleotides in an mRNA codon are designated 1st position, 2nd position, 3rd position of the codon mRNA
  • each set of 3 nucleotides specifies a particular amino acid
  • AUG is methionine
  • start of protein synthesis
115
Q

13) Discuss the significance of the degeneracy of the genetic code:

A
  • amino acids make proteins, and they’re signaled by the alternative codons referred to the degeneracy of the code
  • if the amino acids aren’t signaled, proteins won’t be synthesized
116
Q

14) Translation:

A
  • protein synthesis
  • involves decoding “the language” of nucleic acids & converting it into the “language” of proteins
  • language is in the form of codons (groups of 3 nucleotides ex: AUG, GGC, AAA)
  • sequence of codons on an mRNA molecule determines the sequence of amino acids that will be in the protein being synthesized
  • codons are written in terms of their base sequence in mRNA
  • amino acids are signaled by several alternative codons, a situation referred to as the degeneracy of the code
  • 61 sense codons, 3 nonsense =64 codons
  • sense codons code for amino acids; nonsense (stop codons) do not
  • nonsense: UAA, UAG, UGA-signal the end of the proteins molecule synthesis
  • start codon: AUG codes for formylmethionine
  • codons of an mRNA are “read” sequentially and in response to each codon amino acids are assembled into a growing chain
  • site of translation is the ribosome
  • transfer RNA (tRNA) molecules both recognize the specific codons & transport the required amino acids
  • each tRNA molecule has an anticodon, sequence of 3 bases that is complementary to a codon
  • tRNA molecules base pair w/ associated codon
  • carry on its other end the amino acid encoded by the codon that the tRNA recognize
  • ribosomes direct the orderly binding of tRNA’s to codons & to assemble the amino acids brought there into a chain producing a protein
  • 2 ribosomal subunits: tRNA w/ anticodon UAC & mRNA to be translated & additional protein factors
  • this sets up the start codon AUG
  • ribosome joins the 1st 2 amino acids w/ a peptide bond, the 1st tRNA molecule leaves the ribosome
  • ribosome then moves along the mRNA to the next codon
  • amino acids are brought into the line one by one, peptide bonds are formed & a polypeptide chain results
  • it ends when one of the 3 nonsense codons in the mRNA is reached
  • ribosome then comes apart into 2 subunits, & mRNA & newly synthesized polypeptide chain are released
  • ribosome, mRNA, tRNA, are available to use again
  • ribosome moves along mRNA by 5’ → 3’
  • allows the start codon to be exposed
  • additional ribosomes can then assemble & begin synthesizing protein
  • there is a # of ribosomes attached to a single mRNA, all @ various stages of protein synthesis
  • prok cells, translation of mRNA into protein can begin even before transcription is complete
  • mRNA is produced in the cytoplasm in proks, start codons of an mRNA being transcribed are available to ribosomes before the entire mRNA molecule is made
117
Q

15) Discuss the importance of base pairing in each of the processes, replication,
transcription and translation:

A

?

118
Q

16) Distinguish between DNA polymerase and RNA polymerase. Compare their error rates:

A
  • DNA polymerase: synthesizes DNA; proofreads & repairs DNA
  • RNA polymerase: copies RNA from DNA templat
119
Q

17) Discuss the significance of simultaneous transcription and translation in bacteria:

A
  • Unlike in eukaryotes, prokaryotic transcription and translation can occur simultaneously. This is impossible in eukaryotes, where transcription occurs in a membrane-bound nucleus while translation occurs outside the nucleus in the cytoplasm
120
Q

18) Define what is meant by the term constitutive gene expression:

A
  • Gene expression: mechanism that stops enzymes that aren’t needed from being catalyzed
  • constitutive: products are constantly produced at a fixed rate
  • code for enzymes that the cell needs in fairly large amounts for major processes
121
Q

19) Define operon & distinguish between promoter and operator, and between regulatory region and structural genes:

A
  • operon: set of operator & promoter sites, & the structural genes they control define an operon
  • promoter is segment where RNA polymerase initiates transcription
  • operator is traffic light that acts as a go or stop signal for transcription of the structural genes
  • 3 genes involved in lactose uptake & utilization are next to each other on the bacterial chromosome & regulated together; these genes determine structures of proteins= structural proteins
  • codes for repressor protein= regulatory region
122
Q

20) Compare and contrast the regulation of inducible and repressible operons. Give examples of substances under the control of each type of operon:

A
  • REPRESSIBLE OPERONS: structural genes are transcribed until they are turned off - repressed (normally open, then repressor protein comes in when you have too much of product → co-repressor → turn off system)
  • INDUCIBLE OPERONS: process that turns on transcription of a gene(S); inducer; enzymes that are produced inducible enzymes (normally OFF, need a particular thing, INDUCE IT/coax repressor off → bind to it and pull off operator to open the system) lac operon :
123
Q

21) Discuss how the catabolite activation system regulates a bacteria’s use of sugars in the medium:

A

-CATABOLITE ACTIVATION SYSTEM: when glucose is no longer available, cAMP binds to the allosteric site of CAP (catabolic activator protein) → binds to lac promoter, which initiates transcription by making it easier for RNA polymerase to bind to the promoter (THUS transcription of lac operon requires both presence of lactose and absence of glucose)

124
Q

22) Define the term mutation & Identify insertion, deletion, silent, missense, and nonsense mutations & Distinguish between point and frameshift mutations:

A
  • MUTATION: change in molecular structure of DNA, often a change in base sequence / spontaneous, mutagen-substances that chemically or physically reacts with DNA / alters DNA at random sites (unlikely… some spots are more vulnerable, but appears random)
    • insertion:
    • deletion:
    • silent:
    • missense: mRNA translated into protein, incorrect base may cause the insertion of an incorrect amino acid in the protein; if the base substitution results in an amino acid substitution in the synthesized protein
    • nonsense: base substitution resulting in a nonsense codon
  • point: (Base substitution ) missense mutation - change in amino acid (A-T, glutamic acid to valine hemoglobulin) / sickle cell
  • frameshift: few nucleotides inserted or deleted, sift reading frame, long stretch of altered amino acids, inactive protein (insertion of bases - Huntington’s disease) / carcinogenic things much more significant than point mutation
125
Q

23) Give examples of chemical mutagens:

A
  • agents in the environment, chemicals, radiation, that directly or indirectly bring out mutations are mutagens
  • some result in resistance to antibiotics
  • nitrous acid→ exposing DNA to nitrous acid can convert the base adenine to a form that pairs w/ cytosine instead of the usual thymine
  • nitrous acid makes a specific base-pair change in DNA
  • nucleoside analog: given to growing cells, randomly incorporated into cellular DNA in place of normal bases; during DNA replication analogs cause mistakes in base pairing;
  • 2-aminopurine; 5-bromouracil; antiviral; antitumor
  • AZT: HIV medication; azidothymidine
  • radiation: x-ray/ gamma ray
  • Potent mutagens: electron emitted from orbit - ions, free radicals; Combine with DNA, break
126
Q

24) Define thymine dimerization & explain how this problem is caused and remedied in the cell:

A
  • creates issues when trying to replicate / transcribe DNA (issues for repair… )
    Non-ionizing UV radiation
    Most mutagenic 260nmn - screened out by ozone
    Cross linking of adjacent bases - dimers TT
    photolyase - light repair enzyme
    Nucleoside excision repair
127
Q

25) Discuss the evolutionary significance of mutations in bacteria:

A
  • genetic mutation & recombination provide diversity of organisms, and the process of natural selection allows the growth of those best adapted to a given environment
128
Q

26) Describe the process of replica plating and how auxotrophic mutants are identified by this process:

A
  • Process selects cell that cannot perform specific function;
  • ex: identify cell that lost ability to synthesize histidine
  • 100 bacteria cells inoculated on plate (master plate) → contains medium w/ histidine where all cells will grow → after 18-24 hrs, each cell reproduces & forms colonies → pad of sterile material is placed on master plate → material is placed on plate w/ histidine (nonmutant bacteria can grow) & w/o histidine → any bacteria that grows on medium w/histidine on master plate, but cannot synthesize its own histidine won’t grow on medium w/o histidine → colony can then be identified on master plate
  • mutant microorganism having a nutritional requirement that is absent in the parent= auxotrophic ex: may lack enzyme needed to synthesize a particular amino acid & will there for require that amino acid as a growth factor in its nutrient medium
129
Q

27) Describe the Ames test & discuss its significance:

A
  • uses bacteria as carcinogen indicators
  • based on observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effect of the original mutation
  • called reversion
  • measures reversions of histidine auxotrophs of Salmonella
  • his- cells, mutants that have lost ability to synthesize histidine to his+ cells histidine- synthesizing cells higher than spontaneous rate
  • 90% OF SUBSTANCES FOUND TO BE MUTAGENIC IN AMES TEST ARE CARCINOGENIC IN ANIMALS
    Genetic recombination - exchange of genes between 2 DNA molecules to form new combinations of genes on a chromosome
    Crossing over in Eukaryotic - prophase
    Vertical gene transfer - organism to offspring
    Horizontal gene transfer - transfer to organism of same generation, prokaryotic
130
Q

28) Distinguish between horizontal and vertical gene transfer:

A

Ex: plants & animals
Horizontal: bacteria transmit genes to offspring, & laterally to other microbes of same generation
- transformation; conjugation; transduction

131
Q

29) Describe the process of transformation. Describe Griffith’s experiment demonstrating transformation:

A
  • genes transferred from one bacterium to another as “naked” DNA in solution
  • Griffith’s experiment-rat liver extract →
    Streptococcus pneumoniae → virulent, encapsulated(prevents phagocytosis) strain= dz & avirulent, nonencapsulated strain= w/o dz
  • heat-killed encapsulated bacteria injected into mouse-mouse remained healthy & no colonies were isolated from mouse
  • (Bacillus, Haemophilus, Neisseria, Acinetobacter, some Streptococcus, Staphylococcus)
132
Q

30) Discuss the role that the discovery of the transforming substance had in the identification of DNA as the hereditary material:

A
  • DNA was carrier of genetic info
  • some bacteria, after death & cell lysis, release their DNA into the environment
  • other bacteria can then encounter the DNA & depending on particular species & growth conditions, take up fragments of DNA & integrate them into their own chromosomes by recombination
  • protein: RecA, binds to donor DNA causing the exchange of strands
133
Q

31) Describe conjugation & discuss how conjugation with an F bacterium differs from conjugation with an Hfr bacterium:

A
  • CONJUGATION: the direct transfer of DNA from one bacterial cell to another bacterial cell / the transferred DNA is a plasmid, a circle of DNA that is distinct from the main bacterial chromosome. /// mediated by plasmid / direct cell-cell contact / opposite mating type … “M & F” / donor must carry plasmid & recipient do not have gene / GRAM - plasmid carried gene for sex pilli / GRAM + produce sticky surface molecules that cause cell to come into direct contact / within same type of bacteria →E. Coli F factor (fertility factor) / some F+ cell the factor is integrated into chromosomes becoming Hfr cell (high frequency of recombination) / Conjugation F- and Hfr cell Hfr cell’s chromosome replicated and a parental strand is transferred to recipient cell → begins in the middle of the integrated F factor and a small piece of F factor leads the chromosomal genes into the F- cell / chromosome usually breaks before completely transferred / recipient remains F- didn’t receive complete F factor / mapping
134
Q

32) Describe the process of generalized transduction.

A
  • GENERALIZED TRANSDUCTION: the process by which DNA is transferred from one bacterium to another by a virus / refers to the process whereby foreign DNA is introduced into another cell via a viral vector
  • bacterial DNA is transferred from donor to recipient cell inside a virus / phage attachment, injects DNA into bacteria / phage DNA replicated, transcribed, translated / bacterial chromosomes broken down by phage enzymes / some of bacterial DNA packaged inside phage protein coat / phage P22 Salmonella, P1 E. coli

Specialized transduction: all genes equally likely to be packaged in a phage coat and transferred
-only certain bacterial genes are transferred adjacent genes to prophage
TOXIN → Corynebacterium diptheria, E. coli, Streptococcus pyogenes

135
Q

33) Define plasmid. Discuss their significance in antibiotic resistance and disease process:

A
  • PLASMID: small DNA molecule within a cell that is physically separated from a chromosomal DNA and can replicate independently
  • self-replicating circular pieces of DNA
  • 1-5% of chromosomes
  • Prokaryotic, some eukaryotic Saccharomyces cerevisiae
  • Enzymes for catabolism of certain exotic substrates - Pseudomonas
  • TOXIN: E. coli, Staphylococcus aureus. Clostridium tetani, Bacillus anthracis
  • Bacteriocins
  • R factor = resistance to ABX, heavy metals, cellular toxins / resistance transfer factor (RTF) - include genes for plasmid replication and conjugation / R-determinant - resistance genes / R100 - resistance to sulfonamides, streptomycin, chloramphenicol, tetracycline, mercury /transferred btwn E. coli, Klebsiella, Salmonella / antibiotic feed
136
Q

34) Define transposons:

A

-TRANSPOSONS: (or transposable element) is a small piece of DNA that inserts itself into another place in the genome → (will NOT be on exam)

137
Q

List the prokaryote and eukaryote ribosomal subunits.

A 
Prokaryotic 70S
30S site of inhibition for tetracycline
50S site of inhibition for macrolides
Eukaryotic 80S
40S
60S
138
Q

What is a TATA box?

A

A DNA sequence that indicates where a genetic sequence can be read and decoded. It is a type of promoter sequence, which specifies to other molecules where transcription begins. Transcription is a process that produces an RNA molecule from a DNA sequence.

139
Q

What is a alamone?

A

An intracellular signal molecule that is produced due to harsh environmental factors. They regulate the gene expression at transcription level.

Microbiology (23 decks)

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