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MICB 3301 Lecture > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Extremophiles

A

Microbes that can grow in extreme environments

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2
Q

Solutes that decrease the availability of water to microbes (decrease water activity (aw))

A

Salts, sugars

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3
Q

Hypotonic Environment

A

Low extracellular solute concentration (water wants to move in)

Ex. Freshwater lakes, streams

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4
Q

Isotonic Environment

A

Same solute concentration in and out of cell, used to observe protoplasts (cell walls degraded with lysozyme)

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5
Q

Hypertonic Environment

A

High extracellular solute concentration (water wants to move out), low (aw)

Ex. Dead Sea, Great Salt Lake, Peanut Butter

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6
Q

Halophiles

A

Require high salt concentrations to grow

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7
Q

Osmotolerant

A

Grow over a wide range of (aw)
Ex. Staphylococcus (salt-tolerant commensal of human skin)

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8
Q

Mannitol Salt Agar

A

Medium used to select for Staphylococcus growth
* Pathogenic S. aureus ferments the agar
* S. epidermidis does not

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9
Q

Xerophile

A

Prefer low (aw), dry conditions

Ex. Cronobacter (infant formula shortage cause)

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10
Q

Compatible Solutes

A

How microbes survive in highly concentrated environments

Ex. KCl, choline, some amino acids

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11
Q

Nutrients

A

Substances used in biosynthesis and energy release, required for growth

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12
Q

95% of microbial cell dry weight is made up of a few ingredients:

A

Macronutrients and micronutrients

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13
Q

Macronutrients

A

a.k.a. Macroelements, required in large amounts

Ex. C, O, H, P, N, S, Fe

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14
Q

Micronutrients

A

a.k.a. Trace Elements, required in small amounts

Ex. Cobalt, copper, zinc, manganese

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15
Q

Nitrogen Fixation

A

Reduce N2 to ammonia (NH3)

Carried out by:
* Rhizobium - commensal with plants
* Azotobacter - free living in the soil

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16
Q

Microbial nitrogen sources

A

Microbes can use ammonia (NH3) or nitrate (NO3), a few can use atmospheric nitrogen gas (N2)

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17
Q

In order to sustain exponential growth, food must enter cell:

A
  • At high rates
  • Across membranes
  • In a selective fashion (non-toxic)
  • Often against concentration gradient
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18
Q

Passive Transport

A

Moves material from high to low concentration
* No energy
* Passive Diffusion: Only small molecules and certain gases
* Facilitated Diffusion: Uses membrane carrier proteins (provides selectivity), ex. aquaporins

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19
Q

Carrier Saturation Effect

A

Only a finite number of transport proteins, once all are saturated the rate of transport plateaus

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20
Q

Active Transport

A

Moves nutrients against the gradient
* Requires energy (from ATP or PMF)
* Either Primary or Secondary

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21
Q

ABC Transporters

A

ATP-Binding Cassette (ABC)
* Found in all domains of life
* Solute-binding protein engages with nutrient in the periplasmic space
* Conformational change in transporter leads to nutrient transferred across the channel (requires ATP)

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22
Q

Uptake ABC

A

Moves nutrients into the cell

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23
Q

Export ABC (“Multi-drug efflux pumps”)

A

Move substances out of the cell
* In bacteria, mechanism of antibiotic resistance
* In animal cells, mechanism of chemotherapy resistance

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24
Q

Secondary Active Transport

A

Uses potential energy of ion gradients
Ex. Lac Permease membrane protein
* Uniporter, Antiporter, Symporter mechanisms

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25
Q

Group Translocation

A

Method of active transport, chemically alters the nutrient
* Energy from phosphoenolpyruvate (key intermediate in glycolysis) attaches P to sugars

Ex. Phosphotransferase system in bacteria

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26
Q

Iron Uptake Problem

A

All microbes require iron (Fe), however there is little available outside of insoluble ferric form (Fe3+)

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27
Q

Iron Uptake Solution

A

Microbes release siderophores to acqurie Fe
* Low molecular-weight compounds
* Unique to each microbe
* Siderophore-Fe complex then transported into cell using ABC transport system

Ex. Enterobactin in E. coli

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28
Q

Metabolism

A

All chemical reactions within a cell, comprised of catabolism and anabolism
* Requires enzymes and ATP

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29
Q

Catabolism

A

Breakdown of complex molecules into smaller ones with the release of energy

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30
Q

Anabolism

A

Utilize products of catabolism (ATP and reducing power (NADPH)) to form new cell components and structures

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31
Q

Adenosine Triphosphate (ATP)

A

The main energy currency of cells due to the high free energy change of removing a phosphate, composed of:
* Adenosine: Comprised of nitrogenous base Adenine and 5C Ribose sugar
* 3 Phosphate groups

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32
Q

Aerobic/Anaerobic respiration both produce ATP by ___

A

oxidative phosphorylation

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33
Q

Fermentation

A

ATP by substrate level phosphorylation only

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34
Q

Photosynthesis

A

ATP by photophosphorylation

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35
Q

Energy-Generating Systems

A
  • Aerobic respiration
  • Anaerobic respiration
  • Fermentation
  • Photosynthesis
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36
Q

Redox Reactions

A

Used in metabolic processes to form ATP
* Electrons move from donor to acceptor
* Often involves transfer of H+ proton (ex. NAD+ becomes NADH)
* OIL-RIG!

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37
Q

Malate Dehydrogenase

A

An enzyme found in the Citric Acid cycle, utilized to oxidize malate to form oxaloacetate intermediate and reduce NAD+ to NADH

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38
Q

Rhodoferax metabolins

A

Psychrophilic, obligate anaerobe, oxidizes acetate, reduces iron

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39
Q

Ribozymes

A

Catalytic RNA molecules

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40
Q

Metabolic enzymes act on ___, convert to products, lower ___

A

substrates, activation energy

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41
Q

Reduction Potential (E0)

A

Equilibrium constant for redox reactions, represented by a ladder
* More negative E0 = better donor
* More positive E0 = better acceptor
* Greater difference in coupled pair releases more energy

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42
Q

Electron carriers for redox reactions divided into two groups (locational):

A
  1. Freely Diffusable in cytoplasm (ex. NAD+ and NADPNAD+), reduced forms (NADH and NADPH) are “reducing power” of the cell
  2. Membrane-bound (ex. flavoproteins, cytochromes, quinones)
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43
Q

Microbes transfer energy by moving electrons from:

A

Reduced food molecules (glucose), diffusable carriers in cytoplasm, membrane-bound carriers, O2, metals, or oxidized forms of N and S

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44
Q

Autotrophs

A

“Primary producers”
* CO2 as C source (plants, many microbes)
* Synthesize organic compounds used by heterotrophs

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45
Q

Heterotrophs

A
  • Reduce preformed organic compounds as C source (animals, many microbes)
  • Convert large amounts of C to CO2
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46
Q

Energy Sources

A

Phototrophs: Sunlight

Chemotrophs: Oxidize inorganic chemical compounds for energy

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47
Q

Electron Sources

A

Lithotrophs: Inorganic molecules as electron donors

Organotrophs: Use organic molecules as electron donors

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48
Q

Aerobic Respiration

A

Catabolic process that can break down an organic energy source to CO2:
1. Glycolysis
2. Citric Acid Cycle
3. ETC with Oxygen as final electron acceptor (produces a lot of ATP)

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49
Q

Breakdown of glucose to pyruvate in bacteria

A

3 Pathways:
1. Embden-Meyerhof (Glycolysis)
2. Pentose Phosphate
3. Entner-Doudoroff

All occur in the bacterial cytoplasm

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50
Q

Glycolysis

A
  • 6C Stage: Glucose phosphorylated twice (requires ATP), generating fructose 1,6-bisphosphate
  • 3C Stage: Fructose 1,6-bisphosphate split into 2 glyceraldehyde 3-P then converted to pyruvate

Oxidizes NADH, substrate-level phosphorylation (net yield 2 ATP, 2 NADH, 2 pyruvate)

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51
Q

Glycolysis NADH and ATP generating steps

A

Reaction 1: Glyceraldehyde-3-phosphate oxidized and phosphorylated (generates high-energy P bond, reduces NAD+ to NADH), forming 1,3-bisphosphoglycerate (G3P dehydrogenase), 3GP kinase

Reaction 2: Phosphorylation of ADP by high energy metabolic substrate, generates ATP by substrate-level phosphorylation (catalyzed by pyruvate kinase)

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52
Q

Pentose Phosphate Pathway

A
  • Starts by converting Glucose-6-P to Ribulose-5-P (pentose)
  • Generates many sugars for biosynthesis
  • Yields 6 NADPH (reducing power for biosynthesis) and 1 ATP
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53
Q

Entner-Doudoroff Pathways

A
  • Combines reactions of glycolysis and pentose phosphate
  • Net 1 ATP, 1 NADH, and 1 NADPH
  • Important for growth of Escherichia coli in intestine
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54
Q

Citric Acid (TCA) Cycle

A
  • Pyruvate completely oxidized to CO2
  • In cytoplasm of bacteria
  • Generates: CO2, numerous NADH and FADH2, precursors for biosynthesis, GTP
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55
Q

Electron Transport Chains

A
  • Electrons from NADH and FADH2 generated by glycolysis and TCA cycle are transferred through a series of membrane bound electron carriers to a terminal electron acceptor
  • Electrons flow from carriers with more negative E0 to more positive, energy is released to make ATP by oxidative phosphorylation
  • 3 ATP can be generated per NADH using O2 as terminal acceptor
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56
Q

Chemiosmotic Hypothesis

A

Oxidative phosphorylation hypothesis posed by Peter Mitchell
* Energy released during ETC establishes proton gradient and charge difference across the membrane, source of PMF

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57
Q

PMF drives ATP synthesis:

A

Electron flow in ETC causes protons to move outward across membrane, ATP made when they move back in via F1F0 ATP synthase

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58
Q

F0 Subunit

A

Proton channel, ring of C subunits that rotates

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59
Q

F1 Subunit

A

Gamma shaft rotates, conformational changes in sphere of alpha and beta subunits within cell leading to ATP synthesis

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60
Q

Shewanella

A

Gram - bacterium, can transfer electrons extracellularly onto metals (“breathes metal”)

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61
Q

A microbial fuel cell ___

A

Can capture extracellular electrons to generate electricity
* Low O2 conditions (anoxic) promotes formation of electrode biofilm in anode, connected to high O2 cathode (oxic) to generate electricity

Ex. Mudwatts

62
Q

Why does anaerobic respiration produce less ATP than aerobic?

A

Because O2 has the greatest reduction potential (E0) of all electron acceptors

63
Q

Denitirification

A

Uses nitrate (NO3) from nitrogen fixation as terminal electron acceptor, reduced to nitrogen gas (N2)

Ex. Paracoccus denitrificans (facultative anaerobe in soil, depletes soil N, lower crop yield)

Ex. Escherichia coli (facultative anaerobe, nitrate reduced to nitrite (basis for nitrite strip test used to diagnose UTIs))

64
Q

Fermentation

A

Completion of catabolism without the electron transport system and a terminal electron acceptor (process often named after products, ex. lactic, propionic, ethanolic)

  • In cytoplasm
  • Hydrogen from NADH transferred onto pyruvate
  • Generates fermentation products (lactic acid, ethanol), NAD+, ATP (substrate-level phosphorylation)

Also used in clinical identification (ex. S. aureus)

65
Q

Domain: Archaea, Genus: Sulfolobus

A

Lives in volcanic hot springs, thermoacidophile (high acid and heat tolerance), chemolithotroph

  • Oxidizes H2S to H2SO4
  • No cell wall, S layer (protein)
66
Q

Chemolithotrophs

A

Oxidate inorganic sources, transfer electrons to terminal acceptors (usually O2) to generate ATP and PMF via ETC

67
Q

Iron-Oxidizing Bacteria

A

Oxidize iron compounds as electron source using O2 as electron acceptor

  • Generates insoluble ferric hydroxide (toxic)
  • Yield little energy due to iron and O2 having a very small E0 difference

Ex. Acidithiobacillus ferrooxidans

68
Q

Nitrifying Bacteria

A

Oxidation of ammonia to nitrate, carried out by 2 genera together:
Nitrosomonas - ammonia to nitrate
Nitrobacter - nitrite to nitrate

Followed by denitrification

69
Q

Photosynthesis

A

Two parts:
Light Reactions: Light energy is trapped, converted to chemical

Dark Reactions: Chemical energy used to reduce CO2 and synthesize cell material via Calvin Cycle

70
Q

Oxygenic Phototrophs

A

Oxidize H2O for electrons, forms oxygen (eukaryotes and cyanobacteria)

71
Q

Anoxygenic Phototrophs

A

Electrons from other sources (all other bacteria)

72
Q

Chlorophylls

A

Major light-absorbing pigments in eukaryotes and cyanobacteria (utilize thylakoids)

Cyanobacteria are Gram -!

73
Q

Bacteriochlorophylls

A

Major light-absorbing pigments in purple and green bacteria

74
Q

Accessory Pigments

A

Transfer light energy of broader wavelengths to chlorophylls, quench toxic forms of oxygen (photoprotection antioxidants), integrated in photosystems within thylakoids (PSI and PSII)

Ex. Carotenoids, phycobiliproteins

75
Q

Reaction Center Chlorophyll

A

Energy is transferred here after the photosystem absorbs light energy, electrons are excited and passed to the first acceptor in the ETC

76
Q

Light Reactions: Plants and Cyanobacteria

A

Occurs within thylakoid membranes (chlorophyll)
* Oxygenic (in plants and many bacteria), H2O serves as electron donor/acceptor
* Two photosystems
* Cyclic and Noncyclic photophosphorylation

77
Q

Cyclic Photophosphorylation

A

Uses PSI, energy from ETC generates PMF to make ATP via F1F0 ATP synthase

78
Q

Noncyclic Photophosphorylation

A

Uses PS I and II, electrons used to generate NADPH in PSI (which are used in biosynthesis), replenished by splitting water in PSII

79
Q

Z Scheme

A

Energy diagram for electron transfer in the light reactions of photosynthesis (P680 (PSI) and P700 (PSII))

80
Q

Light Reactions: Green and Purple Bacteria

A

Occurs in plasma membrane using bacteriochlorophyll
* Anoxygenic (use H2, H2S, or organic matter as electron donors)
* Only PSI (only cyclic photophosphorylation, generates ATP but no NADPH)

81
Q

Photosynthetic Archaea

A

Utilize rhodopsin pigment protein (also found in retina) instead of chlorophyll

82
Q

Microbial Rhodopsin

A

Pigment protein found in plasma membrane
* 7 Transmembrane helices
* Uses retinal pigment protein to absorb light
* Pumps proton out (light-driven proton pump, rather than ETC)

83
Q

Calvin Cycle

A

Anabolic pathway for fixing CO2 into carbohydrate, occurs in carboxysomes
* Dark reactions of photosynthesis
* Energy demanding (18 ATP to make glucose)
* Occurs in chloroplasts in plants, cytoplasm in bacteria
* Crucial to life: provides organic matter for heterotrophs (use reduced organic molecules as C sources)

84
Q

Many biosynthetic pathways are ____ of catabolic pathways

A

reversals

85
Q

Gluconeogenesis

A

Glucose synthesis (aerobic reversal of glycolysis)
* Animals, plants, fungi (humans use to maintain blood glucose levels)
* Requires ATP and GTP
* Uses 6 enzymes from glycolysis, 4 unique enzymes

86
Q

Griffith’s Transformation Experiments

A

Through testing on mice, Griffith found that DNA of dead pathogenic bacteria (Streptococcus pneumoniae) was taken up by live non-pathogenic cells, which gained pathogenicity via HGT

87
Q

Gene

A

Functional unit of genetic information, made of DNA
* Gene notation: pilA, lacZ
* Protein notation: PilA, LacZ

88
Q

Genome

A

All genetic material within a cell or virus
* Consist of usually one, sometimes more DNA chromosomes in bacteria

89
Q

Many genes in bacteria are organized as ___

A

Operons

90
Q

Operon

A

A cluster of genes controlled from common regulatory elements

91
Q

Repressor Proteins

A

Bind to block transcription of operons

92
Q

Inducer Proteins

A

Molecules that bind to repressors, preventing them from binding to operators, facilitate transcription

93
Q

DNA Structure

A

Made up of nucleotides containing a pentose sugar (deoxyribose), a nitrogenous base (A/T/G/C), and a phosphate group

Each strand is composed of phosphodiester bonds, they bind to each other using H bonds

  • Antiparallel structure of complementary strands, moving 5’ to 3’ in double helix
94
Q

Purines

A

Adenine and Guanine

“pure as silver (Ag)”

95
Q

Pyrimidines

A

Cytosine and Thymine

96
Q

Base pairing rules:

A

A with T (via 2 H bonds)
G with C (via 3 H bonds)

97
Q

5’ GAATTC 3’
3’ CTTAAG 5’

A

Palindrome, restriction enzyme EcoR1 cuts here

98
Q

DNA Size

A

Expressed as base pairs (bp), can be kbp or Mbp

99
Q

Smallest bacterial genome with only 580 kb encoding 480 proteins:

A

Mycoplasma

100
Q

Prokaryotic DNA

A
  • Usually circular, closed supercoiled molecule
  • Bacteria pack DNA into loops or domains, collectively the nucleoid
101
Q

Eukaryotic DNA

A
  • Linear
  • Eukaryotes wrap DNA around histone proteins, collectively called nucleosomes “beads on a string”
  • Genes interrupted by introns

Archaeal chromosomes are circular with histones

102
Q

Semiconservative DNA Replication

A

Strands separate first, each serves as a template strand

103
Q

DNA replication in eukaryotes is ___

A

bidirectional, with multiple origins of replication (ori)

104
Q

DNA replication in prokaryotes is ___

A

bidirectional, with a single ori and two forks moving in opposite directions, ending in termination region (ter)

104
Q

How is the prokaryotic ori selected?

A

DnaA protein binds to distinct sequences within the ori

105
Q

DNA Polymerase

A

Catalyzes DNA synthesis in 5’ to 3’ direction
* Needs: template, dNTPs, and a primer (RNA with 3’ OH group)
* Most bacterial have several, with DNA Pol III being the major replication enzyme

106
Q

DNA Gyrase (topoisomerase)

A

Underwinds DNA, cuts one DNA and passes another through the gap and seals
* Target for Ciprofloxacin (quinolone) antibiotic

107
Q

DNA Helicase

A

Hydrogen bond breakers

108
Q

DNA Polymerase I removes ___

A

RNA primers and fills in

109
Q

DNA primase lays down ___

A

RNA primers

110
Q

Single-Stranded Binding proteins (SSBs)

A

Coat newly separated strands to prevent them from rejoining

111
Q

DNA Ligase forms ___

A

phosphodiester bonds to seal daughter strands

112
Q

Transcription in Bacteria

A
  • DNA to RNA via RNA polymerase
  • Generates 3 RNA types (tRNA, mRNA, and rRNA)
113
Q

RNA Polymerase

A
  • Opens and unwinds DNA without a primer
  • Made up of a core and sigma factors
  • Targeted by antibiotic rifampin
114
Q

Sigma Factors

A

Proteins that direct the core of RNA Polymerase to promoter regions and attach

Ex. o70, oS

115
Q

RNA Structure

A
  • Usually single stranded
  • Ribose instead of deoxyribose
  • Uracil replaces Thymine
116
Q

tRNA (“transfer RNA”)

A

Converts the language of RNA into that of proteins
* Clover leaf shape
* Two functional regions (anticodon - complementary to codon in mRNA, 3’ end - synthetase enzyme attaches an amino acid to it)
* Carries amino acids during protein synthesis (translation) to the ribosome

117
Q

rRNA (“ribosomal RNA”) component of ___

A

ribosomes

118
Q

mRNA (“messenger RNA”) is a template for ___

A

protein synthesis

119
Q

Rho (p) Independent Termination

A
  • DNA sequences
  • Encodes RNA stem loop structure
  • Causes RNA Polymerase to release from DNA
120
Q

Rho (p) Dependent Termination

A
  • DNA sequence
  • Causes RNA Polymerase to slow due to high levels of G-C 3H bonds
  • Protein Rho (p) then binds to RNA, catches up to RNA Polymerase and causes release
121
Q

Bacteria use ____ signal transduction systems to control gene transcription in response to their environments

A

two-component
(also known as Histidine-Kinases)

122
Q

EnvZ/OmpR system senses and controls…

A

EnvZ senses high osmolarity, phosphorylates OmpR response regulator to regulate transcription of structural genes OmpF and OmpC controlling aquaporin formation in E. coli

123
Q

Transcription in Eukarya

A

Occurs in nucleus, uses 3 RNA Polymerases
* Has transcription factors (no sigmas)
* TATA box - promoter element
* RNA splicing to remove introns
* mRNA is modified to add 5’ cap and 3’ poly A tail to stabilize (infleunza virus carries out “cap snatching”)

124
Q

Translation is the synthesis of ____ directed by mRNA sequence, requires ____ and ____

A

polypeptides, ATP, GTP

125
Q

Bacterial Ribosome

A

The site of protein synthesis, “read” mRNA sequence as a code (codons) and match to corresponding amino acids

  • Consists of the E (exit), P (peptidyl), and A (aminoacyl or acceptor) regions

2 subunits: 30S and 50S
* 30S: 21 proteins and 16S rRNA
* 50S: 34 proteins and 23S and 5S rRNA

126
Q

23S rRNA

A

Peptidyl transferase (ribozyme) - catalyzes the formation of peptide bonds between amino acids during translation

127
Q

16S rRNA

A

Aligns mRNA with ribosome, has sequence complementary to Shine-Dalgarno sequence of the mRNA

128
Q

5S rRNA

A

Functions in ribosome stability

129
Q

Codon

A

A nucleotide triplet encoding a specific amino acid or function
* 64 codons
* 61 specify amino acids (“sense”)
* 3 are stop codons (“nonsense”), UAA, UAG, UGA
* AUG is the start codon (codes for Methionine)

130
Q

mRNA code is ____, multiple codons can encode the same amino acid

A

degenerate

131
Q

Translation Phases

A
  1. Initiation
  2. Elongation
  3. Termination
132
Q

Shine-Dalgarno Sequence

A

Ribosomal binding site in bacterial mRNA, located 8 bases upstream of the AUG start codon

133
Q

Translation: Initiation

A
  1. 16S rRNA in the ribosome hybridizes with the Shine-Dalgarno sequence of mRNA, which aligns with the ribosome
  2. tRNA with formylmethionine binds start codon in P site (anticodons matching mRNA sequence)
134
Q

Translation: Initiation

A
  1. 16S rRNA in the ribosome hybridizes with the Shine-Dalgarno sequence of mRNA, which aligns with the ribosome
  2. tRNA with formylmethionine binds start codon in P site (anticodons matching mRNA sequence)
135
Q

Translation: Elongation

A
  1. tRNA binds at A site (requires GTP)
  2. Peptide bond joins amino acids, catalyzed by 23S rRNA ribozyme
  3. Ribosome moves 1 codon along mRNA
  4. Empty tRNA moves from P to E region

Antibiotic tetracycline inhibits binding of tRNA to ribosome complex

136
Q

Translation: Termination

A
  1. Any one of 3 stop codons (UAA, UAG, and UGA), no tRNAs
  2. Release facotrs (RF) cleave, release peptide
137
Q

Mutation

A
  • Occurs in all domains
  • Heritable change in DNA sequence
  • Can generate alleles, give rise to new phenotypes
138
Q

Vertical Gene Transfer (Eukarya)

A
  • Sexual reproduction
  • New combinations of genes when gametes of parents fuse
139
Q

Horizontal Gene Transfer (HGT)

A

Transfer from one independent organism to another via 3 mechanisms:
1. Transduction
2. Conjugation
3. Transformation

140
Q

Transduction

A

Bacterial gene transfer by phages
Two forms:
1. Generalized Transduction
2. Specialized Transduction

141
Q

Phages

A

Viruses that infect bacteria
* Abundant and diverse, impact composition and behavior of microbial communities

Two phage types:
1. Virulent Phages - lytic cycles (cell lysis)
2. Temperate Phages - lysogenic cycles

142
Q

Generalized Transduction

A
  • Occurs during lytic cycle, any part of the bacterial genome can be transferred
  • During viral assembly, pieces of degraded host DNA can be mistakenly packaged into phage
143
Q

Specialized Transduction

A
  • During lysogenic cycle, a specific part of host genome is transferred
  • Prophage incorrectly excises, takes part of genome with it (adjacent to site of integration)
144
Q

Prophage

A

Sequence of viral DNA that integrates into the host cell during the lysogenic cycle

145
Q

Lysogenic Conversion

A
  • Phenotypic change in a host by temperate phages

Ex. Diphtheria and Cholera toxin genes are encoded by prophages (cell without phage DNA are not pathogenic)

146
Q

Phage Therapy

A

Therapeutic use of bacteriophages to treat pathogenic bacterial infections

147
Q

Conjugation

A

DNA transfer by direct cell contact
* Requires sex pili and plasmids
* Major mode of spreading antibiotic resistance genes (R plasmid transfer)

148
Q

Plasmids

A

Double-stranded, circular DNA
* Extrachromosomal (episomes), can be transferred by conjugation
* Carry genes that confer advantages
* Are replicons (have own ori)

Ex. F Factor in E. coli is a well-studied conjugative plasmid (most genes have tra label which are required to transfer itself)

149
Q

Conjugation: F+ x F- Mating

A
  1. Begins with the F+ donor extending pilus to F- recipient
  2. Pilus retracts once connection is made
  3. Plasmid-encoded enzyme nicks one strand of F factor, allowing DNA Pol III to replicate new strand as single strand enters recipient
  4. A new complementary strand is made in the recipient, and in the donor (via Rolling Circle Replication)
150
Q

High Frequency of Recombination (Hfr) Cell

A

Can transfer integrated F factor and prt of chromosome to F- cell, which becomes an F’ cell (not +)

MICB 3301 Lecture (5 decks)

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