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MB 414 > Cell Structure and Function > Flashcards

Cell Structure and Function Flashcards

1
Q

MreB

A
  • the skeleton that gives the bacterium its shape in bacilli

- as MreB polymerizes cell elongates

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2
Q

Peptidoglycan

A
  • repeating units of B-1,4-N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM).
  • crosslinked through the NAM subunits by peptide bridges consisting of L and D amino acids and the unusual lysine derivative diaminopimelic acid (DAP)
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3
Q

Recognize structure of DAP

A
  • 2 amino groups then -COOH on the end
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4
Q

Cross-linkage of gram positive cells

A

cross-linked to a much greater extend that gram negative cell walls, which give the gram negative cell wall more flexibility but less strength.

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5
Q

Cell wall components are made

A
  • all cell wall components are made in the cytoplasm and must be transported outside (Gram +) or into the periplasm (Gram -) to be assembled.
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6
Q

Peptidoglycan synthesis in cytoplasm

A
  • the carbohydrate subunits all start as NAG
  • all the NAG is coupled to undecaprenyl-phosphate (UDP) (helps the sugar subunits cross the membrane)
  • 1/2 is converted to UDP-NAM
  • Amino acids are added sequentially to NAM to make UDP-NAM-aa (due to carboxylic acid)
  • UDP-NAG and UDP-NAM-aa then cross the cytoplasmic membrane
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7
Q

recognize structure of UDP

A
  • phosphate on the end
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8
Q

Peptidoglycan synthesis outside of the cytoplasm

A
  • The sugar (NAG, NAM) subunits are polymerized via transglycosidation reactions
  • The peptides are cross-linked via transpeptidases.
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9
Q

Further modifications in Gram positive cells

A
  • addition of teichoic acid and lipotechoic acid.
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10
Q

techoic acid

A
  • inserted vertically into the cell wall
  • serves to strengthen the gram + cell wall by crosslinking the layers of peptidoglycan together via covalent bonds to NAM
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11
Q

liptechoic acid

A
  • has a hydrophobic tail that inserts into the cell membrane

- attaches the cell wall to the lipid bilayer via a lipid anchor into the membrane

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12
Q

Cytoplasmic membrane

A
  • permeability barrier. No solutes can pass through without going through specific transport proteins
  • integral membrane proteins act as transporters to allow things in and out
  • bacterial membranes are composed of a phospholipid bilayer - made up of hydrophobic lipid molecules (facing each other) with hydrophilic head groups (facing the water).
  • the membrane is self-associated and not covalently bound together, so it is flexible yet resilient.
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13
Q

cytoplasmic gradient

A
  • H+ on outside - gradient to bring substrates in

- relies heavily on this gradient to power processes and move the cell.

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14
Q

Outer membrane

A
  • not as restrictive a barrier as cytoplasmic membrane

- many low molecular weight compounds are allowed free access through protein channels called porins

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15
Q

Lipopolysaccharide

A
  • covered with carbohydrate
  • O-specific - different for different strains - endotoxin
  • innate immune recognizes this LPS
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16
Q

Nucleoid

A
  • the region of the cell in which the chromosome is located that is not bound by a membrane.
  • Most bacterial chromosomes are circular but must be greatly compacted in order to fit within the nucleoid space.
17
Q

Locomotion

A
  • used for finding nutrients, avoiding toxins, and colonizing favorable ecological niches
  • bacteria use flagella to swim through aqueous solution
  • to move on solid surface, bacteria can glide, swarm, and twitch.
18
Q

Myxococcus

A
  • not flagellum-related, slime-related, “caterpillar”-membrane cycling
  • it is genetically determined, PMF driven, and MreB dependent.
  • motors are localized to focal adhesions on one side of gliding cells.
19
Q

Twitching motility

A
  • mediated by pili or fimbrae
  • used by bacteria to move over solid or semi-solid media
  • twitching cells hyperpilated, and thought that the movement is mediated by the extension and retraction of pili.
20
Q

Flagella structure

A
  • contains a motor and a large extracellular filament
  • filament and motor and connected via a transmission that crosses the periplasm and outer membrane and terminates in the hook.
  • the hook makes it such that when the motor turns the filament turns in a sweeping motion that propels the bacterium like a boat propeller.
  • the motor is powered by the PMF set up by the ETC
  • the direction of the motor can change depending if a phosphate is added or not.
21
Q

Spirochetes and spirilum

A
  • use flagella to move but their flagella are not extracellular.
  • they have a series of amphitrichous flagella that are contained with the periplasm and wrapped around the cell.
  • when the flagella turn, the spirochete will twist and “corkscrew” through a viscous media.
22
Q

Why move in this way?

A
  • adopted based on their environment
  • many are pathogens and live in viscous environments and must constantly evade host detection.
  • corkscrew motion very efficient in moving the cell through very viscous environment such as mucus
  • lacking a prominent external structure helps them to have fewer antigenic features.
23
Q

Gliding

A
  • Myxococcus move through gliding.

- do not use pili or flagella.

24
Q

Chemotaxis

A
  • bacteria move toward attractants (food) and away from toxins.
  • in orer to do they have a sensors clustered in their membranes that are constantly sensing the presence of chemicals in their environment.
  • not big enough tot sense a chemical gradient, so they must be on the move to detect it.
  • sample the chemical, move, and sample again. If the concentration of an attract goes up, they keep going, if it goes down, they change direction.
25
Q

Molecular basis for chemotaxis

A
  • the cell has chemoreceptors in its membrane that detects chemo-attractants and toxins called methyl accepting chemotaxis proteins (MCPs)
  • MCPs pass the signal (phosphate) to a sensor kinase protein called CheA with the help of a signal transducing domain.
26
Q

CheA

A

transfers phosphate to CheY

27
Q

CheY-P

A

binds the motor and causes it to turn counterclockwise, or run

28
Q

When CheY not phosphorylated

A

it will not bind the motor, and the motor will turn clockwise. and tumble

29
Q

Default mode for E. Coli

A
  • tumble

- will only run when it senses a chemical attractant.

30
Q

Adaptation

A
  • make sure the bacterium continues up the gradient, it must “reset” the baseline of how much attractant it is encountering constantly.
  • cell will only continue to “run” if it is encountering increasing amounts of attractant
31
Q

CheR

A
  • regulates how much of the substrate it takes to excite to the MCP.
  • methyl-transferase that will methylate the MCP and cause them to be less sensitive to the chemical.
  • # methyl groups determines how sensitive it is
32
Q

CheB

A
  • methylesterase

- resets the baseline

MB 414 (26 decks)

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