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Flashcards in Microbiology Deck (110):
1

Peritrichous

Many flagella located randomly all around a cell

2

Endospores

Heat-resistant cells rich in calcium dipicolinate that can germinate into growing cells during adverse conditions

3

Plasma membrane

Inner membrane where the respiratory chain is found and phospholipids, LPS, and capsular polysaccharides are formed

4

Bacterial cell envelope fnxns

Provides structure
Energy production thru electron transport chain
Adhesion to host cells via pili and teichoic acids
Escape from immune recognition via capsule
Metabolic uptake of nutrients

5

Lophotrichous

Many flagella located at one end of a bacterium

6

Peptidoglycan

Pentapeptide bridges that are only found in bacteria consisting of an alternating chain of N-acetlymuramic acid and N-acetylglucosamine connected by a B-1,4 linkage

*Fnxns to interfere w/ phagocytosis, confer shape, and allow uptake of small molecules along with MDP acting as a pyrogen, somnagen, and adjuvant

*B-1,4 linkage digested by lysozyme

7

Sacculus

Tetrapeptide linkage of LDL connected to N-acetylmuramic acid

8

Teichoic Acids

Found on gram + bacteria and act as an anchor onto host cells

LTA terminates in a FA

LTA is capable of activating the coagulation cascade BUT CANNOT cause fever
-unlike LPS

9

LPS

Found on gram - bacteria and consists of:

1. Lipid A (endotoxic activity)
2. Core (structure)
3. O antigen (serological ID)

*Promotes synthesis of IL-1, TNF-a and other cytokines along w/ activating the complement and coagulation cascade

=> DIC

10

Braun lipoprotein

Found in gram - bacteria and acts to covalently anchor the outer membrane to peptidoglycan

11

Omp proteins

Proteins found on the outer membrane of gram - cells that fnxn to stabilize the outer membrane

12

Gram - peptidoglycan

Is covalently attached to each other (no pentapeptide bridges) and is more porous than G+; floats in periplasmic space

13

Periplasmic Space

Contains hydrolytic enzymes including collagenases, hyaluronidase, and beta-lactamases all of which are virulence factors

*Helps gram - bacteria resist lysozyme action

14

Two broad classes of virulence factors

1. Promote colonization and survival in host

2. Exhibit toxicity towards host

15

Biofilms

Dense, multiorganism ayers that adhere a bacteria to a surface

*E.coli cause cystitis in hospitals via catheters

*Staph. epidermitis can infect artificial hearts

16

Adhesins

Proteins that promote the binding of a bacteria to the host cell

*Teichoic acids in gram + bacteria

17

Invasins

Bacterial surface proteins that cause rearrangements in the host cells actin skeleton and manipulate their way into the cell

18

Bacterial Iron Acquisition

(3 Mechanisms)

1. Siderophores chelate iron and bring it inside the cell

2. Transferrin receptors

3. Cytotoxins destroy a cell and retrieve the intracellular Fe3+

19

Bacterial evasion of Destruction

1. Slime layers composed of polysaccharide evades complement

2. Antigenic switching in Salmonella

3. Protein A of S. aureus and Protein G of S. pyogenes bind to Fc portion of Abs rendering them useless

20

AB Toxins

Exotoxins with separate subunits

B- promotes entry into cell

A- kills shit

21

Hemolysins

(Pore Formers)

Lyse cell by permitting rapid H2O entry; often uses cholesterol

OR

Remove phospholipid heads

22

Embden-Meyehof Pathway

Glucose + 2 NAD + 2 ADP + 2 Pi => 2 pyruvate + 2 NADH + 1 FADH2 + 2 ATP

23

TCA

Pyruvate+ 3 NAD + FAD + CoA + GDP + Pi => Acetyl-CoA + 2 CO2 + 3 NADH+ 1 FADH2 + 1 GTP

24

Lactate dehydrogenase action

Pyruvate + NADH => Lactate + NAD

-Regenerates NAD

25

Alcohol Dehydrogenase Action

Pyruvate + CO2 => Acetadelhyde + Ethanol

26

Toxic Byproduct removal (of bacterial metabolism)

Superoxide Dismutase: 2 O2- + 2 H+ => O2 + H2O2

=> Catalase: 2 H2O2 => 2 H2O + O2

OR

Peroxidase: NADH+ H + H2O2 => NAD + 2 H2O

27

Strict Aerobes

Cant make ATP via fermentation

Includes Bacilli, mycobacteria

28

Strict Anaerobes

Lack SOD, Catalase, and Peroxidase

Includes Clostridia

29

Aerotolerant Anaerobes

Lack SOD but use Mn2+ as a radical scavenger

30

Facultative anaerobes

SOD and Catalase produced in presence of O2; can also use fermentation

31

Microaerophilic Organisms

Require low O2 but lack catalase

Includes Camplyobacter

32

General Secretory System (GSS)

Located in cytoplasmic membrane of bacteria and acts to transport materials outside of the cell

*Type III system acts as a molecular syringe and is found in Yersinia and Pseudomonas

33

Glycerol Transport into bacteria

Is transported via facilitated diffusion and then phosphorylated to trap it in the cell

34

Group Translocation (PTS)

Sugar Phosphtransferase System transfer phosphate groups from PEP in the glycolytic cycle to use the energy to bring sugars into the cell

*Also allows the molecule to bypass some steps of glycolysis

35

Pathogenicity Islands

Clusters of genes encoding proteins involved in pathogenesis; same island can be present in different species due to the action of transposons

36

Quinolones

Block the negative supercoiling of bacterial DNA blocking replication and cell growth

37

Growth Rate Equation

b= a X 2^(t/g)

a= # of initial cells; t= total growth time; g= average growth time

38

DNA-dependent RNA Polymerase

Contains:

Sigma subunit- regulates initiation site specificity to holoenzyme @ -10 & -35 positions of the promoter

Rho factor- assists in the termination of genes

39

Consensus sequence

The most frequently found sequence in a bacteria; the more similar the sequence, the better the promoter

40

Rifampin

Binds to the B-subunit of RNAP and inhibits formation of the first phosphodiester bond

*Treats mycobacteria and gram + bacteria

41

Streptolydigin

Binds to the B-subunit of RNAP and blocks elongation

42

Actinomycin D

Binds to double-stranded DNA and blocks movement of RNAP

*Too toxic for clinical use

43

Translation beginning in bacteria

AUG= N-formlymethionine

44

Shine-Dalgarno Sequence

Ribosome binding site that controls the rate of translation initiation

45

Transpeptidation

Transfer of a free amino group to a charged tRNA molecule mediated by peptidyl transferase in the 50s subunit of the ribosome

46

Streptomycin

Blocks the assembly of the 70S complex

47

Tetracyclines

Blocks binding of charged tRNAs to the A site

48

Chloramphenicol

Binds peptidyltransferase and blocks its action

49

Erythromycin

Blocks the translocation step of translation

50

Coupling

The process of transcription and translation occurring almost simultaneously; can only occur in prokaryotes because???

51

Regulon

Structural genes that participate in a single pathway are scattered at different sites in the genome but contain similar controlling elements

52

Polycistronic

One continuous mRNA spans over several structural genes and can be translated into several different proteins because ribosomes can bind to internal Shine-Dalgarno sequences

53

lacI

repressor protein

54

lacY

encodes a permease which permits the uptake of lactose into the cell

55

lacA

encodes a transacetylase that will detoxify lactose metabolites

56

P-IIIglc

Activates AC under low glucose conditions to create cAMP and induce transcription of lacZYA

57

Two component regulators

Used by Bordetella pertussis, BvgS acts as a membrane sensor and phosphorylates BvgA to initiate transcription modifications

58

3 forms of bacterial mutations

1. UV Radiation

2. Spontaneous mutations

3. Chemical mutations

59

UV Radiation

Causes the formation of 5.6 cyclobutane or 6-4 photoproducts

60

Base analogs

A form of chemical mutation where 2-AP is formed instead of A and binds w/ Cytosine OR 5-bromouracil is formed instead of T and binds w/ Guanine

61

Base modification

Can occur via oxidative deamination which causes C > T mutation

*Important because C is the target in bacterial DNA methylation to distinguish own DNA

62

Alkylation

Mutation caused by mustard gas and causes kinks to be formed in the DNA helix

63

Reactive Oxygen

Most mutagenic lesion is 8-oxo guanine which pairs w/ A instead of C

Formed due to UV radiation

64

Intercalators

Large, flat molecules that slide in b/w base pairs and cause insertions/deletions

*Includes aflatoxin

65

Aflatoxin

Popular intercalator that can be modified by cytochrome P450 to form toxic epoxides

66

Photoreactivation

Absorbance of UV radiation activates photolyase and repairs cyclobutane dimers

67

Nucleotide Excision

1. UvrA and UvrB binds to DNA and scans for damage

2. Uvr-complex detects damage and stops

3. UvrC binds to UvrB and nicks the DNA helix downstream; UvrB nicks it upstream

4. UvrD separates the damaged DNA and removes it

5. DNA Polymerase I and DNA ligase replace the removed DNA

68

SOS Inducible Repair System

1. Cells received heavy UV radiation and activate RecA

2. RecA triggers the cleavage of LexA which is constituently bound to DNA

3. UmuC and UmuD now free to activate DNA Polymerase III and replicate DNA in a really shitty fashion

69

3 Types of Transposons

1. Insertion sequence elements

2. Composite Transposons

3. T2A family

70

Composite Transposons

Has a central region flanked by insertion sequence elements on the left and right; central region is gene for antibiotic resistance

71

TnA transposons

Contains resolution site and resolvase enzyme that mediate the specific recombination of transposons; also has inverted repeats at the ends and a transposase enzyme

*utilize Replicative transposition

*Tn3=ampicillin resistance

72

Replicative Transposition

DNA strand is nicked at one strand and the free ends are reconnected to the target DNA; the transposon is then replicated

*This allows a copy of the transposon to remain in the donor DNA

73

Site-specific recombination

If repeats are in same direction (tandem), recombination will delete the sequence

If repeats are in opposite direction, recombination will invert the sequence in between

74

Phage DNA Replication

1. "+" strand is used as a template to create a "-" strand
-RF is now created

2. Phage II Gene product acts as an endonuclease and nicks the "+" strand

3. Phage begins rolling circle replication and cuts off the product at the end of one rotation

4. Phage coat proteins bind to the pac site to pack the DNA into a new phage

75

Lamda Phage DNA Replication

1. Lambda phage genome is linear-double stranded DNA but when injected into the bacteria, it becomes circular by joining at "cos" sites

2. Circular DNA undergoes theta replication in which replication proceeds in two directions

3. Later switches to rolling circle replication to produce DNA of tandem repeats
*concatemers*

4. Concatemers are cut at the cos site to generate single DNA copy for packaging
*DNA has returned to linear form for packaging

76

T4 Phage DNA Synthesis

T4 exists as linear, double-stranded DNA WITHOUT cos sites

=>Replication begins at multiple origins and eventually forms concatemers via homologous recombination

*Utilizes headfull packaging more likely to contain DNA for genetic exchange with bacterial host

77

Lysogen

Bacterium that harbors a prophage

*Looks like a fried-egg on a growth plate

78

CII

CII is produced until there is an adequate amount when CI and integrase take over; CII promotes the lytic cell cycle

79

CI

Produced when adequate CII has been made; contains a dimerization domain to suppress the fnxn of lytic genes and a DNA binding domain

80

Integrase

Mediates the recombination of phage DNA w/ the host chromosome by attaching at attP and attB

81

Lysogenic Conversion

Bacterium that become superimmune to phage infection due to the prophage genes that have been transmitted to the lysogen

*e.g. cholera toxin

82

Lytic Conversion of prophage

RecA binds to CI and triggers autocleavage

-Derepresses the expression of lytic genes

83

Excisase

Allows the prophage to be excised from the host chromosome and returns the phage DNA to circular DNA form

*Process also utilizes integrase

84

Generalized Transduction

Phages degrade host DNA into small fragments and pack new phage DNA WITH some host DNA; phages then will inject old hosts DNA into new host DNA

85

What makes a phage a transducing phage?

1. Cannot cause complete degradation of host DNA

2. Must have low sequence specificity for packing DNA into its head

86

Specialized Transduction

When the prophase is excised from the host, chromosome recombination may take place b/w phage and bacterial DNA instead of at hybrid attachment sites; host DNA with sequences close to the attachment sites are more likely to be transferred

87

Conjugation

Transfer of DNA to a recipient cell via a plasmid trasmitted by a sex/F pilus

Endonuclease cuts at the Ori-T site and the DNA is rolled into the donor cell

*Meanwhile, both sides of the nick are being replicated

*Strand is cut in the middle of the DNA being transfered

88

F plasmid

Self-transmissable that includes genes for pilus, helicase, and primase

*Must help mobilizable plasmids when necessary

89

F plasmid transfer

1. Endonuclease cuts at oriT sige

2. Helicase unwinds the plasmid DNA

3. Strand w/ nick is transferred via the sex pilus; complementary strands for both the donor and recipient DNA begin to be synthesized

90

Transconjugant

Cell that receives an F plasmid after conjugation

91

Hfr

Bacterial strain containing an integrated F plasmid in the bacterial chromosome (usually exists as an episome)

*Genes closer to the oriT site are more likely to be transferred

92

F' plasmid

"Prime Factor"

Give rise to recombinant strains when homologous recombination b/w IS1 and F plasmid occurs; bacterial DNA is then transferred later

93

R plasmid

Large plasmid associated with multiple antibiotic resistance genes; exists due to transposon-mediated recombination

94

Transformation

Uptake of naked DNA by a bacterial cell; does not require a phage or plasmid

95

Transfection

Process of eukaryotic cells uptaking naked DNA

96

Competence

The ability of a bacteria to uptake naked DNA; appears late in the growth cycle

Can be induced in two ways:

1. Calcium phosphate treatment

2. Electroporation

97

Limitations to Koch's postulates

1. Human susceptibility to disease varies

2. Some bacteria are not as easily cultured as others

3. Late onset of growth

4. Virulence can vary within some species

5. Ethical considerations of postulate 3

6. Polymicrobial diseases

98

Viroids

Organisms that consist of RNA only; delta Hepatitis

99

Metro diploid

Partial diploid state in a bacterium resulting from transfer of some bacterial material

100

Homologous Replication

A single-stranded DNA is generated which invades a DNA duplex and forms a Holiday Junction

=>Homologous recombination b/w genetic material then occurs

101

Insertion Sequence Elements

Transposons containing only the genes necessary for transposition

Bracketed by repeat sequences of the host DNA

102

Resolvase

Enzyme required for the Replicative transposition of TnA transposons

103

Antigenic expression in Salmonella

Hin invertase moves the promoter away from the H2 gene and activates expression of its repressor

=>Expression of H1 Gene

104

What Phages have no Lytic cycle?

Filamentous Phages

105

Cro

A gene whose expression is induced after RecA cleaves CI during radiation damage in a lysogen

=>Inhibits expression of CI causing the lytic cycle to occur

*Excisase and Integrase also now expressed to excise phage DNA from the lysogen

106

Lipofuscin

"Brown Atrophy"

Undigested lipid molecules that appear in dying cells

107

Cardinal sign of coagulation necrosis

Eosinophilic cytoplasm

*Fibrinoid necrosis can also appear this way but more smudgy

108

Shock-sensitive Activve transport mechanism

Sensitive to osmotic shock; cannot transport galactose across with carrier protein in the periplasm

109

Cardiac Hypertrophy

Shows increased ANP; myosin heavy chain is replaced with B-chain which produces slower, more favorable contractions

110

Mitochondrial apoptosis pathway

Inhibited by Bcl; triggered by the loss of survival signals