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Bauman's Microbiology Chapter 7
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College: Second year
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microbiology
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1

What is the role of DNA helicase in DNA replication?

It uses the energy created by ATP to break the hydrogen bonds between two DNA strands, thereby "unzipping" the molecule.

2

The replication fork __________________.

is the point where DNA helicase is "unzipping" the double-stranded DNA molecule.

3

What is the function of stabilizing proteins?

They hold the separated strands apart and prevent their degredation.

4

The replication fork moves ___________.

ahead of the newly synthesized DNA.

5

What must occur for an organism to pass its genetic information on to its offspring?

The parent must copy its own DNA and provide a copy to its offspring.

6

The process of copying DNA prior to cell replication is known as _____________.

DNA replication.

7

What is meant by semiconservative replication?

The new copies of DNA contain one original strand of DNA and one new strand of DNA

8

What serves as the template for DNA replication?

each of the original DNA strands

9

Which enzyme(s) can synthesize new strands of DNA?

DNA polymerase

10

Why is primase essential for DNA replication?

It provides a 3' end of the newly synthesized strand, allowing DNA polymerase to begin copying DNA.

11

DNA synthesis occurs in which direction?

From 5' to 3' on both the leading and lagging strands.

12

How does the DNA polymerase know which nucleotide triphosphate to add to the growing strand?

It hydrogen-bonds the nucleotide to the parental strand, pairing adenines to thymines and guanines to cytosines.

13

What might happen if the cell does not have RNAse?

The newly made chromosome would consist of DNA and RNA molecules.

14

How many RNA primers are required for the leading strand of DNA replication?

How many for the lagging strand of DNA?

One RNA primer

multiple RNA primers

15

What is the function of the connector proteins?

They link the leading strand DNA polymerase and the lagging strand DNA polymerase together.

16

Okazaki fragments are typically ____ nucleotides in length and are found on the ______ strand of DNA replication.

1000 and Lagging

17

Name the 4 steps of lagging strand DNA replication.

1. Primase adds an RNA primer
2. DNA polymerase synthesizes new DNA strand in the
5' to 3' direction.
3. RNAse removes the RNA Primer.
4. Okazaki fragments are joined together.

18

Name the three products of transcription

mRNA, rRNA, tRNA

19

The role of transcription is ___________________.

to copy the information stored in DNA into RNA.

20

_______ is used to make ribosomes

rRNA

21

_______ is involved in bringing amino acids to the ribosomes

tRNA

22

_______ is a copy of a DNA sequence used to make protein

mRNA

23

In general, higher levels of transcription lead to ______________________.

higher amounts of protein.

24

Name three functions of RNA polymerase

It binds to the promoter region of the gene prior to starting RNA synthesis, adds nucleotides to the 3' end of the growing RNA molecule, and reads the template strand of DNA.

25

How does protein-dependent termination differ from protein-independent termination?

Protein-dependent termination involves the use of a protein to end transcription.

26

Translation

the process of making protein from RNA.

27

Ribosomes move along the mRNA in which direction?

5' to 3'

28

Name three things involved in translation

ribosomes, amino acids, and mRNA

29

What is the order of ribosomal sites that a charged tRNA molecule passes through?

A site, P site, E site

30

The anticodon sequence is found on the __________.

tRNA.

31

An amino acid is considered charged ____________.

when it is bound to its correct tRNA.

32

mRNA is not a part of the initiation process.

T or F?

True

33

Release factors _______________________and ________________________.

bind to the A site

are coded by stop codons

34

Name 3 genetic elements found in an operon

operator region, structural genes, and promoter

35

Where does the activation and repression of an operon occur?

operator region

36

Inducible operons are transcribed only ____________________.

when they are activated.

37

Repressible operons are always transcribed unless
_________________________________.

they are deactivated by a repressor

38

The structural genes of an operon typically have the same biochemical function in the cell.

T or F?

True

39

What does the inducer bind to in the lac operon system?

repressor proteins

40

Which genetic element codes for the repressor protein?

the regulatory gene

41

___________ _______ bind to the operator, preventing RNA polymerase from transcribing the structural genes.

Repressor proteins

42

When is the regulatory gene transcribed?

Always

43

What ceases when lactose is absent from the system.

Induction of the operon

44

The inducer acts by ________?

turning off the repressor

45

Allolactose serves as ___________?

an inducer

46

The trp operon is always activated unless __________________________________________.

deactivated by a repressor

47

What is the role of tryptophan in the trp operon?

It activates the repressor proteins.

48

Why is the transcription of structural genes of the trp operon turned off in the presence of tryptophan?

The structural genes are used to make tryptophan, which would not be needed if tryptophan is available.

49

What is the target of the activated repressor protein?

the operator region of the operon

50

The repressor gene is always _____________.

transcribed

51

Activated repressor proteins bind to the operator region, preventing ______________________________.

RNA polymerase from transcribing the structural genes

52

Which mutation is the least likely to be harmful to a cell?

silent mutation

53

A mutation that results in the presence of a stop codon in the middle of the genetic code is a _____________.

nonsense mutation

54

What type of mutation can change all subsequent amino acids following it?

fragment mutation

55

A chemical that can increase the rate of mutations.

mutagen

56

Base pair substitutions that can result in what 3 types of mutations

silent, nonsense, and missense

57

How frequently does an error occur in DNA replication in the absence of a mutagen?

one error for every 1,000,000,000 nucleotides copied

58

What is a potential source of mutations from ionizing radiation?

The resulting Ions and free radicals can break chromosomes.

59

Ethidium bromide can result in _________________.

frameshift mutations via insertion or deletion of nucleotides.

60

X-rays would be considered which type of mutagen?

ionizing radiation

61

5-bromouracil is an example of a ___________ _______.

nucleoside analog

62

Enzymes known as photolyases are involved in which type of repair?

light repair mechanism

63

How can a mismatch repair enzyme detect which strand contains the correct DNA sequence?

The original strand will likely have a methyl group attached, while the newly mutated strand will not.

64

Name the 2 repair mechanisms that require assistance from DNA polymerase to make the correction?

excision-repair mechanism AND mismatch-repair mechanism

65

Light repair mechanism does not involve the removal of nucleotides?

T or F

True

66

Name 2 repair mechanisms that might be involved in repairing a mutation that results from exposure to UV light

light-repair mechanism AND

excision-repair mechanism

67

The transfer of DNA from one bacterium to another is an example of ______________ _________ _____________.

Horizontal gene transfer

68

Transcription is NOT a type of horizontal gene transfer.

T or F

True

69

Name 3 types of horizontal gene transfer.

conjugation, transformation, and transduction

70

Recombinant

A cell that has incorporated new DNA as part of its own

71

Cells that are naturally able to take up DNA from their environment

competent

72

Why do S strains escape killing by host phagocytes?

They are encapsulated.

73

What reason most likely explains the recovery of S strain from a mouse injected with heat-killed S strain mixed with living R strain?

The R strain picked up the S-strain DNA, enabling it to produce capsules.

74

T or F?

S strains are capable of causing disease in mice.

True

75

___________ are unable to cause disease in mice.

R strains

76

R strains do not produce a _________.

capsule

77

Generalized transduction is initiated by ___________.

the lytic cycle of viral replication

78

Transduction

the transfer of bacterial DNA from one host to another via a bacteriophage

79

What would be a fate of a bacterium infected by a generalized transducing bacteriophage?

integration of the packaged DNA into the host chromosome

80

The process of generalized transduction requires a _______ ______________.

lytic bacteriophage

81

The process of generalized transduction utilizes any fragment of the bacterial chromosome.

T or F?

True

82

Generalized transduction is the result of ________________________?

Sloppy packaging of the DNA by bacteriophage

83

What 2 things initiate specialized phage transduction?

Prophage integrates into the host genome

AND

bacteriophage enters lysogeny

84

Two terms that could describe the newly infected host of a specialized transducing bacteriophage

recipient cell AND

recombinant cell

85

What is packaged by the bacteriophage during induction?

the phage DNA with some of the host DNA

86

What is the purpose of bacterial conjugation?

to transfer DNA between two living cells

87

Why is E. coli considered the model of bacterial conjugation?

The process of conjugation is best characterized in E. coli.

88

T or F?

After conjugation, each cell involved has a copy of the shared DNA.

True

89

What is unique about the DNA transferred between two cells during conjugation?

It is transferred by a single strand

90

3 chronological events of conjugation

Pulling of donor and recipient cells together,
Fusion of the cell membranes, Transfer of the DNA

91

What characteristics do F+ and F- cells share?

each contain a chromosome

92

Following conjugation between a donor and a recipient, what cell types are present?

two F+ cells

93

F plasmid

fertility factor

94

What DNA molecule is transferred between cells during conjugation between an F+ and an F- cell?

a single stranded F plasmid

95

The 4 chronological events of conjugation

Attachment of the sex pilus,
Pulling of donor and recipient cells together
Fusion of the cell membranes
Transfer of the F factor

96

How does an F+ cell become an Hfr cell?

By integrating the F plasmid into the chromosome

97

What typically results from conjugation between an Hfr cell and an F- cell?

one Hfr cell and one F- cell

98

What does Hfr stand for?

high frequency of recombination

99

Why are F- cells unable to spread the fertility factor?

F- cells rarely receive a complete copy of the fertility factor during conjugation.

100

Name 3 characteristics of an F- cell

Cannot synthesize a sex pili
absence of fertility factor
Cannot mate with another F- cell

101

How long does it take an Hfr strain of E. coli to transfer its complete chromosome?

100 minutes

102

Approximately how long would it take for the serA gene to transfer?

62 minutes

103

If conjugation was allowed to be carried out for 42 minutes, which genes would be transferred to the recipient strain?

trp

104

Which gene would transfer quickest during conjugation for this Hfr strain?

Fertility factor

105

If gene X transferred at 99 minutes, what conclusion could you make about gene X?

Gene X is close to the fertility factor on the Hfr chromosome, but it is near the end of the chromosome transfer.

106

Transposons

DNA fragments that can move from one location in the DNA to another

107

Which type of transposon would contain an antibiotic resistance gene?

complex transposons

108

Insertion sequences are composed of _____________.

a transposase gene flanked by inverted repeats

109

A region of DNA in which the sequence of nucleotides is identical to an inverted sequence on the complementary strand

inverted repeat

110

3 functions of the enzyme transposase

cuts the DNA so the transposon can leave its current position, cuts the DNA at the new site for a transposon, and covalently links the transposon to the new DNA site.

111

How does replicative transposition differ from cut-and-paste transposition?

Replicative transposition results in multiple copies of the transposon in the DNA; cut-and-paste transposition has only one copy.

112

What is unique about complex transposons?

They have two simple transposons with another DNA sequence between them

113

Why is a complex transposon containing an antibiotic resistance gene more likely to be copied than a simple insertion sequence when the host reproduces?

They confer a survival advantage for the host.