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Biosci 3313: Microbiology > Exam 4 > Flashcards

Exam 4 Flashcards

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1
Q

What do repressors do?

A

Block RNA polymerase from binding. Bind a DNA sequence called an operator, when bound, expression is off

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2
Q

Where is the operator located?

A

Overlapping or downstream of promoter

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3
Q

Differentiate between inducible and repressible promoters (different terminology from operon)

A

Promoters controlled by repressors can be inducible (adding signal molecule results in expression) or repressible (adding signal molecule results in repression -> as seen with app/co repressors)

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4
Q

What do activators do?

A

Help RNA polymerase bind to DNA. Bind upstream of promoter, when bound, expression is on

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5
Q

Differentiate between cis-regulatory elements and trans regulatory elements

A

CREs are regions of noncoding DNA which regulate transcription of neighboring genes.
TRES are genes that regulate the expression of distant genes

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6
Q

How is the Lac operon controlled by glucose

A

low glucose causes adenylyl cyclase to make cAMP, which binds to the CAP/CRP protein to activate the operon

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7
Q

How is the Lac operon controlled by lactose

A

lactose is converted to allolactose that inactivates the Lac repressor (LacI)

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8
Q

Describe how biosynthesis of tryptophan is affected by the presence of tryptophan

A

Tryptophan binds to and activates a repressor which binds to an operator and prevents synthesis

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9
Q

What is attenuation in regards to the trp operon?

A

Attenuation is a way to finely tune regulation by controlling when the mRNA from the trp gene is processed intro protein

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10
Q

In the attenuation of the trp operon, what happens when levels of trp are low and more needs to be synthesized?

A

When levels of trp are low, the ribosome translating the mRNA gets stuck at a pair of trp codons, allowing regions 2 and 3 to pair with each other and RNA P to continue synthesizing the mRNA

anti-termination signal

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11
Q

In the attenuation of the trp operon, what happens when levels of trp high and none is needed?

A

When levels of trp are high, the ribosome continues past the region with the trp codons, blocking region 2 and causing regions 3 and 4 to pair with each other and RNA P to stop making the mRNA.

termination signal

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12
Q

What does quorum sensing allow?

A

Quorom sensing allows cells to respond to cell density by producing their own regulatory signal

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13
Q

What does bioluminescence require?

A

Oxygen, the luciferase enzyme, and lots of ATP

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14
Q

What are autoinducers?

A

Chemical signal molecules produced by quorum sensing bacteria. Increase in concentration as a function of cell density. The detection of a minimum threshold of autoinducers leads to an alteration in gene expression.

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15
Q

What are the usual autoinducers in the case of gram-negative (bioluminescene)? Gram-positive?

A

Gram-negative- AHLs (acyl-homoserine lactones)

Gram-positive- peptides

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16
Q

Describe how Quorum sensing works for bioluminescence.

A

The bacteria sends out AHLs to its environment. If it receives some back, it produces light and more AHL. LuxR is an activator that binds to AHL and DNA allowing RNA polymerase to synthesize Luxl (which produces more AHL) and genes necessary for light production.

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17
Q

Describe a two-component regulatory system. What does it allow and what does it consist of?

A

A basic stimulus-response coupling mechanism that allows organisms to sense and respond to changes in many different environmental conditions. Consists of an external sensor protein and an internal response regulator protein.

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18
Q

How does a two-component regulatory system work?

A

The signal interacts with the sensor and causes a conformational change. The sensor phosphorylates the regulator protein and converts regulator to active form.

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19
Q

Describe how the location of a regulator binding on a gene affects its role.

A

If a regulator binds upstream of a gene it is an activator, if it binds downstream it is a repressor. Can have different roles for different genes.

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20
Q

Describe flagella. What are the two types?

A

Flagella are rigid and can only rotate clockwise or rotate counterclockwise. They can be either polar (single flagella) or peritrichous (many flagella).

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21
Q

Describe how a polar flagella works when rotated counterclockwise vs clockwise.

A

The flagella is straight (straight line) when rotated counterclockwise allowing the bacterium to move forward

The flagella is distorted (wiggly line) when rotated clockwise leading to random tumbling

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22
Q

Describe how a peritrichous flagella works when rotated counterclockwise vs clockwise.

A

Form a polar bundle when rotated counterclockwise leading to forward movement

Point in all directions when rotated clockwise leading to random tumbling

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23
Q

Describe how flagella work when in the context of an attractant or a repellant

A

Attractant

  • External sensors relay signals through methylation cascade into proteins that control the direction of rotation by phosphorylation
  • –Still have to tumble to sense conditions, extend counterclockwise run if conditions are improving

Repellant
-Tumble more frequently until they find a direction where the levels of repellant are lowering

24
Q

Describe Mutualism

A

benefits both

25
Q

Describe Syntrophy

A

chemical relationship, metabolic interaction

26
Q

Describe Commensalism

A

one benefits, other is unaffected (most of human microbiome)

27
Q

Describe Parasitism

A

one benefits, one is harmed

28
Q

Describe Antagonism

A

one is harmed, other is unaffected

29
Q

Describe Competition

A

both are harmed

30
Q

What are the potential benefits of symbiosis?

A

Protection, access to new habitats, recognition aids, nutrition

31
Q

What are ruminants?

A

Herbivorous mammals with four-chambered stomachs that eat plant matter (insoluble polysaccharides) with help from microbes.

32
Q

Describe what bacteria do in ruminants. What are the major types?

A

Bacteria provide volatile fatty acids through unfavorable reactions that are powered through the removal of hydrogen gas (converted to methane/CO2)

Bacteria are mostly Firmicutes (G+ fermentation), then Euryarchaeota (methanogens), then Bacteroidetes

33
Q

What is the human gut biome like?

A

Fecal is mostly firmicutes and bacteroidets, then proteobacteria (coliform). E coli is less than 1% (we think it represents more because it is easy to culture and is used as an indicator for fecal matter)
Varies with diet, antibiotics, age, exercise

34
Q

What is the skin microbiome like?

A

Mostly gram positive. Staphylococcus, Micrococcus, Corynebacterium, Propionibacterium. Nutrient sources are the sebaceous and sweat glands, dry areas have much lower densities.

35
Q

What is the Respiratory Tract microbiome like? (excluding mouth)

A

Mouth, throat, trachea, bronchi, lungs.

Mucus membranes form barriers to bacteria; they are antibacterial (let macrophage in) and can slough off to remove bacteria.

The lower respiratory tract (trachea, bronchi, lungs) should not have bacteria, microbes in these sites would be harmful. (Kep tout with barrier defenses: alive, movement of air, mucus, ciliated cells.

36
Q

What is the mouth microbiome like?

A

Mouth: nutrient-rich, stable pH and temperature, colonies can adhere to the tongue/gums/teeth. Dental plaque is a biofilm created when tooth enamel is colonized by bacteria such as streptococcus mutant, S. ssanguis, and the anaerobic actinomycetes.

37
Q

What is the gastrointestinal tract microbiome like?

A

Esophagus, stomach, small intestine, large intestine

Bacteria change throughout the intestinal tract

O2 levels drop.

We don’t want bacteria in our small intestine, because that is where we absorb food. The Duodenum has few bacteria due to stomach acids, bile, pancreatic secretions.

We can’t eat the food that made it to our large intestine, so we let the bacteria break it down. Mostly just remove moisture, population is anaerobes, bacteria that can digest the complex macromolecules left over and we get extra food out of that.

38
Q

How is the gut of a newborn populated with bacteria?

A

Sterile gut of newborn is quickly populated by bacteria from adults and milk
If breast-fed, Bifidobacterium is dominant due to the presence of an amino disaccharide in the milk

39
Q

Define Virulence

A

ability to cause disease and how aggressive that disease may be

40
Q

What type of bacteria are associated with obesity and which with leanness?

A

Obesity is linked to Firmicutes and leanness to Bacteroidetes

41
Q

Describe Virulence factors

A

Allow the organism to obtain nutrients the body does not normally make available

Ex: pathogens make molecules that have a higher affinity for iron that the host’s (free iron is usually very low)

42
Q

Describe endotoxins (characteristics)

A

Causes fever, inflammation

Low lethality, weak immunogenicity

Heat stable

Similar structure for all G-

Lipid A

43
Q

What is the structure of endotoxins?

A

component of the cell membrane of gram negative bacteria, all have a core of lipid A

44
Q

How do endotoxins act?

A

Reacts with proteins in the bloodstream → we overreact → septic shock (low concentrations of endotoxin our reaction is helpful, high concentrations our reaction hurts us) -> fever/inflammation

45
Q

Define cytokines

A

substances secreted by certain cells of the immune system, cell signaling

46
Q

Define pyrogens

A

substances that produce fever when they react with cytokines

47
Q

Describe exotoxins (characteristics)

A

Specific effects based on targeting of receptors

Lethal/strong immunogenicity

Heat labile

Spread throughout the body

Vary widely (each species is different)

Protein

48
Q

Which type of bacteria produce exotoxins?

A

Gram +

49
Q

How are endotoxins/exotoxins produced?

A

endotoxins are released when the cell dies or reproduces

exotoxins are secreted

50
Q

Where do enterotoxins work?

A

gut

51
Q

Where do cytotoxins act?

A

cells

52
Q

Describe AB toxins

A

A subunit is enzyme that produces toxin, B subunit targets cells

Can permanently attach a ADP to an interior enzyme that turns it on or off forever

53
Q

Describe superantigens

A

Toxic shock by overstimulating immune system

Link antigen presenting cells will many different B cells → overproduction of cytokines

54
Q

What can inactivate toxins? What are they called then?

A

All toxins can be inactivated by formalin

Then called toxoid, used in vaccines

55
Q

What is antigenic variation?

A

External proteins such as fimbriae, pipi, and flagella help the bacteria adhere and colonize

Antigenic variation among populations allow the bacteria to evade the immune system

Immune system selects for those that are not recognized

56
Q

What are some human factors that contribute to infectious disease?

A

domestication of animals, travel, overuse of antibiotics/fungals/virals, overcrowding, hygiene + living conditions, technology (legionnaires and air conditioners), moving into new areas (lyme), foods and shipping, mass food production, cultural factors (burial practices → prions)

57
Q

Describe how most pathogens are opportunists

A

take advantage of changes, good bacteria in the wrong place

Biosci 3313: Microbiology (4 decks)

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