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[4] BACTERIAL GENETICS > BACTERIAL GENETICS - MODULE > Flashcards

BACTERIAL GENETICS - MODULE Flashcards

1
Q

DNA is a macromolecule composed of repeating units called

A

nucleotides,

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2
Q

Each nucleotide consists of a

A

pentose sugar (deoxyribose)
phosphate group
nitrogen-containing nucleobase [adenine (A), and guanine (G) or a pyrimidine base — cytosine (C), and thymine (T)]

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3
Q

The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphateof the next, resulting in an alternating [?]

A

sugar-phosphate backbone

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4
Q

The DNA molecule consists of two strands of nucleotides resembling a

A

ladder with a sugar-phosphate backbone

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5
Q

Each rung of the ladder consists of a of pair bases, which combine in specific pairs

A

(A with T, and C with G)

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6
Q

According to base pairing rules, hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to
make a

A

double-stranded DNA

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7
Q

the sequence on one strand is [?] to that on the other.

A

complementary

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8
Q

The two strands of nucleotides are coiled around each other to form a [?], a structure like a spiral ladder forming a double-stranded DNA that is helical

A

double helix

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9
Q

are small sections of the DNA molecule that codes for production of proteins; These are the fundamental units of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring

A

Genes

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10
Q

is the sum total of genes present in cell or organism; Each contains all of the information needed to build and maintain that organism

A

Genome

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11
Q

The genome size is expressed in [?]. For example, in humans, 3 billion base pairs (3 gbp) is are contained in all cells that have a nucleus.

A

base pairs

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12
Q

is the inheritable genetic makeup of an organism that codes for a particular trait.

A

Genotype

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13
Q

refers to actual, expressed or observable trait; governed by the genotype; may be affected by environmental factors thus, its
expression differs in different situations

A

Phenotype

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14
Q

Among the bacteria, [4 answers] are some of the environmental influences that may dictate whether the genetic trait may be expressed or not. For example, Serratia marcescens form red colonies at 24 oC, and white colonies at 37 oC.

A

temperature, ph, age, humidity

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15
Q

Different types of DNA may be found in a bacterial cell. The genes are carried on:

A

bacterial chromosome, (2) plasmid, (3) phage, or (4) transposon

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16
Q

Bacterial cell has how many chromosome/s

A

one (1) chromosome

  • consists of double stranded DNA
  • arranged in a circular form
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17
Q

Bacterial chromosome is found in the region of the cytoplasm called

A

nucleoid

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18
Q

carry most bacterial genes

A

Chromosomes

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19
Q

During cell division, duplication of chromosome occurs so that each daughter cell receives an

A

identical set

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20
Q

are circular, double-stranded DNA. They are small ranging from 1.5 to 400 kbp; extra-chromosomal; can replicate
autonomously in bacterial cells

A

PLASMIDS

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21
Q

They carry genes that code for specialized functions, e.g, fertility genes that direct conjugation, many of the genes for antibiotic resistance, and most bacterial exotoxins.

A

PLASMIDS

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22
Q

process where table pieces of phage (prophage) DNA may be inserted into the bacterial chromosome and replicates with the bacterial DNA following infection with a temperate phage

A

lysogeny

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23
Q

a repressed virus — carried passively without replication and causing lysis of the infected bacterium

A

temperate phage

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24
Q

Besides the repressor protein, this prophage DNA may also direct synthesis of
another protein. Most notable are gene products that make bacteria more
pathogenic. This enhanced virulence is called

A

lysogenic conversion

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25
Q

are large, mobile genetic elements, with DNA sequences of several kbp , that can move themselves or a copy from one molecule of DNA to another, so are referred j to as “jumping genes”

A

Transposons

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26
Q

carry genes for specialized functions but do not contain genetic information for replication

A

transposons

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27
Q

is the unilateral transfer of genetic information from a donor cell to a recipient cell

A

Genetic exchange

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28
Q

is not an essential step in the life cycle of bacteria. But, it is beneficial and may bring together combination of genes that enables the recombinant bacteria to carry out a valuable new function

A

genetic exchange

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29
Q

is the gene transfer from one bacterial cell to another involving direct cell-to-cell contact

A

Conjugation

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30
Q

Conjugation is controlled by [?] that carries the genes that code for sex pili formation which bring the two cells in physical contact

A

F factor (fertility plasmid)

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31
Q

have F factor, therefore form sex pili

A

Donor (male) cells

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32
Q

lack F factors and are called F- cells

A

Recipient (female) cells

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33
Q

have F factor in its free state (not incorporated into the bacterial chromosome)

A

F+ cells

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34
Q

have F factor that is integrated into the bacterial chromosome

A

Hfr cells

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35
Q

denotes high frequency of recombination, referring to the fact that Hfr cells donate copies of genes on the bacterial chromosome

A

“Hfr”

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36
Q

Types of conjugal crosses:

A

F+ x F- conjugation

Hfr x F- conjugation

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37
Q

It is mediated by the sex pilus that forms the conjugative tube through which the F factor passes

A

Attachment between F+ and F- cells

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38
Q

Only a single strand of the DNA duplex is transferred. The area that is lost is reduplicated so the donor always stays the same genotype. The transfer of the plasmid is fairly quick so that it is transferred in its entirety. No bacterial genes are transferred

A

Transfer of the F factor from the F+ cell to the F- cell

39
Q

The donor cell remains F+ cell. The recipient cell is converted to F+ cell

Only the F factor has been transferred and it remains a free element in the cytoplasm. The F factor will replicated independently of the chromosome, thus, there is no genetic recombination

A

Separation of both cells

40
Q

Other plasmids are transferred by similar mechanisms with F+ x F- conjugation

A

R (resistance) plasmids
Col plasmids (bacteriocinogenic plasmids)
virulence plasmids

41
Q

It is facilitated by the sex pilus

A

Attachment of the Hfr cell to an F- cell

42
Q

The first half of F factor will be transferred first and then the bacterial genes in the linear order. Most of the integrated F factor enters the recipient cell last

Only a single strand of the DNA duplex is
transferred. The area that is lost is reduplicated so that the donor always stays the same genotype. It takes approximately 90 minutes for a complete transfer to occur. Because the conjugative bridge is so fine, mating is normally interrupted, so the entire genome of the donor cell is not transferred

A

Transfer of the F factor from the Hfr cell to the F- cell

43
Q

The donor cell remains Hfr. The recipient gets some donor chromosomal genes
that can recombine with its own chromosome, but does not become Hfr since the complete F factor is not transferred. It becomes a recombinant F- cell

A

Separation of cells

44
Q

Destruction of cell does not necessarily destroy its

A

genetic material

45
Q

When bacteria [?], they often release their DNA into the surrounding medium.

A

lyse

46
Q

When this DNA is introduced into another viable cell, it retains its ability to
direct the

A

synthesis of specific proteins

47
Q

The uptake of free (or naked) extracellular DNA in the environment by a competent cell and subsequent integration into its chromosome by a competent is called

A

transformation

48
Q

The [?] cell often acquires new characteristics as a result.

A

recipient

49
Q

Competency is dependent on several factors:

A
  • Stage of growth — logarithmic phase
  • Alterations in the cell membrane that makes it permeable to the DNA molecule
  • Synthesis of receptor sites on the bacterial cell surface
50
Q

Only a few bacterial species are capable of

A

natural transformation

51
Q

Naturally competent transformable bacteria, of medical importance, are found in several genera and include

A

Haemophilus influenzae
Neisseria gonorrhoeae
Neisseria meningitidis
Streptococcus pneumoniae

52
Q

Specific DNA sequences are required for uptake of the DNA, thus restricting genetic
exchange to a [?] or closely related species.

A

single species

53
Q

is induced in the laboratory by a variety of techniques. The procedure involves
extraction of the DNA, and treatment of cells with high salt (e.g., CaCl2 ) and temperature shock to render the cell membrane more permeable to DNA and make them readily take up DNA. This is fundamental in genetic engineering.

A

Artificial (or forced) transformation

54
Q

is the transfer of DNA between bacteria by means of a phage (bacteriophage)

A

Transduction

55
Q

Phages come in two major types:

A

Virulent phage

Temperate phage

56
Q

infects bacterial cells, replicates, and and kills the host bacteria, usually by lysing — lytic cycle

A

Virulent phage

57
Q

often have repressor genes to prevent phage replication; integrates their DNA into the bacterial chromosome where it stably stays as a prophage without lysing the host bacteria. — lysogeny

A

Temperate phage

58
Q

In the absence of [?] they also may replicate lytically.

A

functional repressor protein,

59
Q

two (2) types of transduction

A

generalized and specialized

60
Q

is mediated virulent phages

A

Generalized transduction

61
Q

steps in Generalized transduction

A
  1. Attachment and infection
  2. Replication of the phage DNA
  3. Assembly and package
  4. Lysis of the host bacterium
62
Q

The virulent phage DNA is injected into the bacterium

A
  1. Attachment and infection
63
Q

This directs synthesis of the phage components and the in disintegration of the bacterial chromosome into small pieces

A
  1. Replication of the phage DNA
64
Q

Phage DNA and protein coat (capsid) are packaged into phages . Occasionally, bacterial DNA are packaged in a phage capsid by mistake — these are called transducing particles.

A
  1. Assembly and package
65
Q

This releases the phages and transducing particles.

A
  1. Lysis of the host bacterium
66
Q

When the transducing particle infects a new bacterium, it injects the DNA from the [?], rather than viral nucleic acid.

A

donor bacterium

67
Q

The recipient bacterium receives the donated DNA and incorporates it into its own chromosome, producing a [?] with a new genotype.

A

recombinant cell

68
Q

Because the virus is defective (biologically inactive as a virus), it is unable to initiate lytic cycle. The [?] survives and can use the new genetic material

A

transduced cell

69
Q

Generalized transduction is so-called because any bacterial DNA fragment can be [?] within the phage and can be [?] from one cell to another.

A

packaged; transferred

70
Q

is mediated by temperate phages

A

Specialized transduction

71
Q

steps in Specialized transduction

A
  1. Attachment and infection
  2. Lysogeny and lysogenic conversion
  3. Replication
  4. Most cells continue to divide
  5. Spontaneous induction
  6. Reactivation of phage DNA, assembly and package
  7. Lysis of the host bacterium
72
Q

The temperate phage DNA is injected into the bacterium, and represses its own replication (R, repressor molecules).

A
  1. Attachment and infection
73
Q

Lysogeny - - - t h e p h a g e D N A integrates into the chromosome of the host bacterium. The integrated phage DNA is now called prophage. Ly s o g e n i c c o n v e r s i o n — t h e bacterium (lysogenic cell) acquires new traits.

A
  1. Lysogeny and lysogenic conversion
74
Q

Prophage is replicated with the host chromosome. All daughter cells are lysogenic cells qnd have the potential for producing temperate phages.

A
  1. Replication
75
Q

showing no evidence of viral infection

A
  1. Most cells continue to divide
76
Q

In a small percentage of lysogenic cells, prophage DNA excises from the bacterial chromosome. This occurs spontaneously but is enhanced by irradiation with UV light or exposure to agents that inter fere with DNA replication.

A
  1. Spontaneous induction
77
Q

Following excision, phage DNA replicates and progeny temperate phages assemble and become packaged within a capsid.When prophage separates from the bacterial chromosome, it carries with it a segment of bacterial DNA in the same capsid, becoming a specialized transducing particle.

A
  1. Reactivation of phage DNA, assembly and package
78
Q

The induced cell lyses and infectious temperate phages are released.

A
  1. Lysis of the host bacterium
79
Q

Because prophages are inserted only at special site on the bacterial chromosome, only bacterial DNA [?] to this site can be transferred in specialized transduction

A

adjacent

80
Q

The medical significance of lysogenic conversion is illustrated by its role in the [?] of certain bacteria

A

pathogenesis

81
Q

Phage-coded pathogenic
factors:
• [1] of Salmonella
• [2] of Clostridium botulinum (causing botulism)
• [3] of Streptococcus pyogenes (causing scarlet fever)
• [4] of Corynebacterium diphtheriae

A

[1] O antigen
[2] Botulinum toxin
[3] Erythrogenic toxins
[4] Diphtheria toxin

82
Q

is a permanent alteration in the base sequence of the gene (DNA) resulting in phenotypic change; genetic variation in bacteria may result from this

A

Mutation

83
Q

Mechanisms of mutation:

A

Insertion
Deletion
Substitution

84
Q

takes place when a nitrogenous base (nucleobase) is added to the nucleotide sequence

A

Insertion

85
Q

is the removal of a nucleobase from the nucleotide chain

A

Deletion

86
Q

arise when there is mispairing between complementary bases. It occurs when one or more nucleobases in a nucleotide sequence is replaced with another base

A

Substitution

87
Q

Mutations can be [?] by a mutagen in the environment.

A

spontaneous, or induced

88
Q

is a random, undirected alteration of the DNA base sequence that arise as a consequence of mistakes in DNA replication. This type of mutation occurs naturally in the environment.

A

Spontaneous mutation

89
Q

are caused by exposure to external influences or agents that result in the DNA to breakdown. Such external influences include chemicals, radiation, viruses, diet and lifestyle

A

Induced mutation

90
Q

agents that induce mutations causing the DNA to break down

A

mutagens

91
Q

converts the nucleobase adenine (A) to a form that no longer pairs with thymine (T) but cytosine (C). Thus, when DNA containing such modified adenines replicates, one daughter DNA molecule will have a base-pair sequence different from that of the parent DNA.

A

Nitrous acid (HNO2)

92
Q

ionize atoms and molecules with the formation of highly reactive ions and free radicals. Some of these ions can combine with bases in DNA, resulting in errors in DNA replication and repair that produce mutations

A

X rays and gamma rays

93
Q

is a non-ionizing component of ordinary sunlight. Its most important effect on DNA is the formation of harmful covalent bonds between certain bases. Adjacent thymines in a DNA strand can cross-link to form thymine dimers. Such dimers, unless repaired, may cause serious damage or death to the cell because it cannot properly transcribe or replicate such DNA

A

Ultraviolet (UV) light

[4] BACTERIAL GENETICS (2 decks)

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