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MICRB 106 - Exam 3 > Microbial Genetics > Flashcards

Microbial Genetics Flashcards

1
Q

What is the central dogma of molecular genetics?

A

DNA is transcribed into RNA, which is translated into RNA, which is translated to form a polypeptide

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2
Q

What is the exception to the central dogma of molecular genetics?

A

Reverse transcription

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3
Q

Describe transcription

A

Synthesis of DNA into RNA

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4
Q

Describe translation

A

Synthesis of mRNA into proteins

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5
Q

RNA polymerase links RNA nucleotides that are ______ to genetic sequences in DNA

A

Complementary

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6
Q

RNA polymerase binds to specific ______ to initiate transcription

A

Promoters

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7
Q

In bacteria, a polypeptide subunit of RNA polymerase called the ______ is necessary for recognition of a specific promoter

A

Sigma factor

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8
Q

Triphosphate ribonucleotides align ______ of their complements

A

Opposite

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9
Q

How, and in what orientation or direction, do all RNA polymerases synthesize or ‘write’ RNA?

A

5’ to 3’ direction

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10
Q

Like DNA polymerase, RNA polymerase links nucleotides ONLY to the ______ end of the growing molecule

A

3’

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11
Q

What are the 2 types of termination processes in bacteria?

A
  • Self-termination
  • Rho-dependent termination
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12
Q

When does self-termination occur?

A

When RNA polymerase transcribes a terminator sequence of DNA

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13
Q

Describe the regions present in self-termination (2)

A
  • One region is symmetrical in guanine and cytosine
  • One region is rich in adenine bases
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14
Q

RNA polymerase slows down during transcription of the ______ portion of the terminator

A

GC-rich

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15
Q

What is the role of the hairpin loop structure?

A

Puts tension on the union of RNA polymerase and DNA

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16
Q

What specific roles does rho protein play in rho-dependent termination? (2)

A
  • Unzips the DNA / RNA hybrid
  • Binds to a specific RNA sequence
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17
Q

In terms of a ‘unit of code’, how many nucleotides are necessary to encode at least 20 different amino acids?

A

4

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18
Q

If a single nucleotide encoded an amino acid, there could only be ______ different amino acids (insufficient)

A

4

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19
Q

If a pair of nucleotides encoded an amino acid, there could only be ______ different amino acids (insufficient)

A

16

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20
Q

If a triplet of nucleotides encoded amino acid, there could be ______ different amino acids (insufficient)

A

64

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21
Q

What is a codon?

A

mRNA molecule containing sequential nucleotides

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22
Q

How many sequential nucleotides are in a codon?

A

3

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23
Q

Explain why the genetic code is said to be ‘degenerate’

A

There are more codons than amino acids

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24
Q

Of the 64 possible codons, what is the start codon?

A

AUG

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25
Q

What amino acid is encoded by the start codon?

A

Methionine

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26
Q

Of the 64 possible codons, what are the stop codons? (3)

A
  • UAA
  • UAG
  • UGA
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27
Q

What role does mRNA play in translation?

A

Carries genetic information from a chromosome to a ribosome

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28
Q

In prokaryotes, an mRNA molecule contains sequences of nucleotides that are recognized by what types of ribosomes? (3)

A
  • Start codon
  • Sequential codons
  • Stop codon
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29
Q

What role does tRNA play in translation?

A

Transfers amino acids to a ribosome

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30
Q

A tRNA molecule has ______ ribonucleotides

A

75

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31
Q

A tRNA molecule curves back on itself to form ______

A

3 main hairpin loops

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32
Q

A tRNA molecule is held in place by ______ between complementary nucleotides

A

Hydrogen bonding

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33
Q

A tRNA molecule has ______ in its bottom loop

A

An anticodon triplet

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34
Q

A tRNA molecule has ______ at its 3’ end

A

An amino acid acceptor

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35
Q

Anticodons code for amino acid ______

A

Polarities

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36
Q

Acceptor stems code for amino acid ______

A

Sizes

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37
Q

What are the molecular components of a ribosome? (2)

A
  • rRNA
  • Polypeptides
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38
Q

Differentiate between 70S and 80S ribosomes in the context of prokaryotes vs. eukaryotes

A
  • Prokaryotic cells have 70S ribosomes
  • Eukaryotic cells have 80S ribosomes
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39
Q

70S ribosomes are composed of ______ subunits

A

50S and 30S

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40
Q

80S ribosomes are composed of ______ subunits

A

60S and 40S

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41
Q

Structural differences between prokaryotic and eukaryotic ribosomes in the context of antimicrobial drugs play a crucial role in ______

A

Efficacy and safety

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42
Q

What is the role of the A site?

A

Accommodates tRNA bound to an amino acid

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43
Q

What is the role of the P site?

A

Holds tRNA and the growing polypeptide

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44
Q

What is the role of the E site?

A

Exit site for discharged tRNA

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45
Q

Where does the smaller ribosomal subunit of a prokaryotic initiation complex attach?

A

At the ribosomal-binding site

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46
Q

Where does the smaller initiatory tRNA of a prokaryotic initiation complex attach?

A

At the P site

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47
Q

What does the larger ribosomal subunit of a prokaryotic initiation complex attach to form?

A

A complete initiation complex

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48
Q

What the cyclical process involving the addition of amino acids to a polypeptide chain growing at the P site?

A

Elongation

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49
Q

During the elongation phase, where is the dipeptide attached to the tRNA?

A

At the A site

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50
Q

What specific role do ribosomes play during the elongation phase of translation?

A

Formation of a peptide bond

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51
Q

Where is the peptide bond formed during elongation?

A

Between the newly introduced amino acids and the terminal amino acid of the growing polypeptide

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52
Q

What are ribozymes?

A

RNA enzymes

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53
Q

Translocation uses energy supplied by GTP to …

A

Move the ribosome one codon down the mRNA

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54
Q

What does translocation accomplish?

A

Transfers each tRNA to the adjacent binding site

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55
Q

During translocation, the first tRNA moves from the ______

A

P site to the E site

56
Q

The ribosome releases the empty tRNA from the ______

A

E site

57
Q

How is translation terminated?

A

The ribosome dissociates into its subunits

58
Q

Translation termination does not involve ______

A

tRNA

59
Q

What are translation release factors?

A

Proteins that halt elongation

60
Q

Name the 3 components that make up an operon

A
  • Promoter
  • Operator
  • Series of structural genes
61
Q

Transcription of the structural genes is under the control of a ______

A

Promoter

62
Q

What role does the regulatory gene play in operon regulation?

A

Controls transcription of the structural genes

63
Q

The regulatory gene can bind to ______

A

Operators

64
Q

The regulatory gene is not considered part of the ______

A

Operon

65
Q

The regulatory gene has its own ______

A

Promoter

66
Q

The regulatory gene is transcribed / translated into a ______

A

Regulatory protein

67
Q

Describe inducible operons

A

Can be turned on by a small molecule

68
Q

Describe repressible operons

A

Can be turned off by a small molecule

69
Q

What occurs during the default state of the lac operon of E. coli (absence of lactose / allolactose)?

A

The repressor binds to the lac operator

70
Q

The lac operator is adjacent to the ______

A

lacZ gene

71
Q

In the presence of lactose, the binding of RNA polymerase is …

A

No longer blocked

72
Q

What conditions must first be met before E. coli transcribes its lac operon? (2)

A
  • E. coli breaks it into glucose and galactose
  • β-galactosidase converts lactose into allolactose
73
Q

The lac operon is a ______ operon

A

Negative inducible

74
Q

Why must glucose be absent before lactose is catabolized?

A

Ensures that bacteria only use lactose after all energy is used up

75
Q

β-galactosidase is encoded by the ______ gene

A

lacZ

76
Q

Permease is encoded by the ______ gene

A

lacY

77
Q

What results from a high concentration of glucose compared to cAMP?

A

Low levels of cAMP

78
Q

What results from a low concentration of glucose compared to cAMP?

A

High levels of cAMP

79
Q

What role does CAP play in activating the lac operon of E. coli?

A

The concentration of cAMP is proportional to the level of available glucose

80
Q

Before CAP can bind to DNA, it must form a complex with ______

A

cAMP

81
Q

Describe negative control of the lac operon

A

Prevents the RNA polymerase from transcribing

82
Q

Describe positive control of the lac operon

A

Enhances the binding of RNA polymerase to the promoter

83
Q

Define mutation

A

A permanent change in the nucleotide base sequence

84
Q

Name the 2 types of point mutations

A
  • Base-pair mutations
  • Frameshift mutations
85
Q

What are base-pair mutations?

A

A single nucleotide is substituted for another

86
Q

What are frameshift mutations?

A

Changes that alter the reading frame

87
Q

Explain how single base insertions or deletions generate frameshift mutations

A

Nucleotide triplets are displaced

88
Q

What do frameshift mutations typically result in? (2)

A
  • Nonsense mutations
  • Missense mutations
89
Q

What type of mutation results when the substitution does not change the amino acid sequence because of the redundancy of the genetic code?

A

Silent mutation

90
Q

What type of mutation results from changing an amino acid codon into a stop codon?

A

Nonsense mutation

91
Q

Nonsense mutations result in ______

A

Nonfunctional proteins

92
Q

What type of mutation results from a change in nucleotide sequence resulting in a codon that specifies a different amino acid?

A

Missense mutation

93
Q

What is a gene’s reading frame?

A

Multiples of 3 nucleotides that encode amino acids

94
Q

What are mutagens?

A

Physical or chemical agents that cause mutations

95
Q

Describe the origin of pyrimidine dimers

A

UV light causes adjacent pyrimidine bases to bond

96
Q

Describe the consequences of pyrimidine or thymine dimer mutations (3)

A
  • Prevents hydrogen bonding
  • Distorts the sugar phosphate backbone
  • Prevents replication and transcription
97
Q

Nucleotide analogs are structurally similar to ______

A

Normal nucleotides

98
Q

Nucleotide analogs inhibit ______

A

Nucleus polymerases

99
Q

Nucleotide analogs result in ______

A

Mismatched base pairing

100
Q

How does 5’-bromouracil cause point mutations?

A

Replaces thymine resulting in a wrong complement

101
Q

What is an enzyme that is activated by visible light to break pyrimidine dimers?

A

DNA photolyase

102
Q

What role does DNA photolyase play in the repair of pyrimidine dimers?

A

Reverses mutations

103
Q

How does dark repair of pyrimidine dimers differ from light repair?

A

Involves a different repair enzyme that doesn’t require light

104
Q

What roles do DNA polymerase I and DNA ligase play in dark repair?

A

They fix the gap created dark repair enzymes

105
Q

During mismatch repair, old strands are ______

A

Methylated

106
Q

What are homologous sequences?

A

Identical nucleotide sequences

107
Q

Describe vertical gene transfer

A

The passing of genes to the next generation

108
Q

Describe horizontal (lateral) gene transfer

A

Prokaryotes acquire genes from other microbes of the same generation

109
Q

When the recipient cell inserts part of the donor’s DNA into its own chromosome, it becomes a ______

A

Recombinant cell

110
Q

What are the 3 types of horizontal gene transfer?

A
  • Transformation
  • Transduction
  • Conjugation
111
Q

When a recipient cell takes up DNA from the environment, it is called ______

A

Transformation

112
Q

The transfer of DNA from one cell to another via a replicating virus is called ______

A

Transduction

113
Q

______ requires physical contact between cells

A

Conjugation

114
Q

Describe the significance of Frederick Griffith’s experiments with Streptococcus pneumoniae

A

Discovered the process of transformation in 1928

115
Q

What structural feature of Streptococcus pneumoniae conferred virulence in Griffith’s transformation studies?

A

The polysaccharide capsule

116
Q

Describe strain S bacteria (2)

A
  • Smooth colonies
  • Encapsulated cells
117
Q

Describe strain R bacteria (2)

A
  • Rough colonies
  • CANNOT make capsules
118
Q

Describe what happened when Griffith injected heat-killed strain S bacteria into mice

A

The mice lived (no strain S cells were recovered)

119
Q

Describe what happened when Griffith injected both heat-killed strain S and living strain R bacteria into mice

A

The mice died - even though neither strain was harmful when administered alone

120
Q

Streptococcus pneumoniae / strain S cells are ______

A

Virulent

121
Q

Strain R cells are ______

A

Non-virulent

122
Q

What substance was ultimately shown to be responsible for the ‘transformation’ that Griffith had discovered?

A

DNA

123
Q

What role did Avery, McCarty, and MacLeod investigators play in identifying the chemical nature of Griffith’s transforming principle?

A

Showed that the transforming principle was DNA

124
Q

What term is used to describe viruses that only infect bacteria?

A

Bacteriophage

125
Q

Describe the ‘life cycle’ of a lytic bacteriophage (4)

A
  • Injects its genome into the host cell
  • Synthesizes new DNA and proteins
  • The host cell lyses
  • Daughter and transducing phages are released
126
Q

When bacteriophages mistakenly incorporate remaining fragments of bacterial DNA, it is caused by ______

A

Transducing phages

127
Q

What are the bacterial structures that mediate conjugation?

A

Conjugation pili (sex pili)

128
Q

Where are the genes responsible for conjugation located within the cell?

A

F plasmid

129
Q

What are F+ cells?

A

Cells that serve as donors during conjugation

130
Q

F+ cells contain ______

A

F plasmid

131
Q

What are F- cells?

A

Recipient cells that lack F plasmid and conjugation pili

132
Q

In what state is the F plasmid transferred from donor to recipient?

A

Conjugation

133
Q

What happens when the F- recipient synthesizes a complementary strand of F plasmid?

A

Becomes an F+ cell

134
Q

What happens when the donor cell synthesizes a complementary plasmid DNA strand?

A

Remains an F+ cell

135
Q

What are Hfr donors?

A

Cells that can conjugate with an F- cell

136
Q

How is the outcome of conjugation between an F+ donor and an F- recipient different from that of an Hfr donor and an F- recipient?

A

Remains an F- cell

137
Q

Hfr donor cells are considered to be ______

A

Fertile

MICRB 106 - Exam 3 (2 decks)

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