Cell Structure and Function

Question 1

MreB

Answer 1

• the skeleton that gives the bacterium its shape in bacilli

- as MreB polymerizes cell elongates

Question 2

Peptidoglycan

Answer 2

• 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)

Question 3

Recognize structure of DAP

Answer 3

• 2 amino groups then -COOH on the end

Question 4

Cross-linkage of gram positive cells

Answer 4

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

Question 5

Cell wall components are made

Answer 5

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

Question 6

Peptidoglycan synthesis in cytoplasm

Answer 6

• 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

Question 7

recognize structure of UDP

Answer 7

• phosphate on the end

Question 8

Peptidoglycan synthesis outside of the cytoplasm

Answer 8

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

Question 9

Further modifications in Gram positive cells

Answer 9

• addition of teichoic acid and lipotechoic acid.

Question 10

techoic acid

Answer 10

• 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

Question 11

liptechoic acid

Answer 11

• 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

Question 12

Cytoplasmic membrane

Answer 12

• 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.

Question 13

cytoplasmic gradient

Answer 13

• H+ on outside - gradient to bring substrates in

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

Question 14

Outer membrane

Answer 14

• not as restrictive a barrier as cytoplasmic membrane

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

Question 15

Lipopolysaccharide

Answer 15

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

Question 16

Nucleoid

Answer 16

• 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.

Question 17

Locomotion

Answer 17

• 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.

Question 18

Myxococcus

Answer 18

• 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.

Question 19

Twitching motility

Answer 19

• 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.

Question 20

Flagella structure

Answer 20

• 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.

Question 21

Spirochetes and spirilum

Answer 21

• 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.

Question 22

Why move in this way?

Answer 22

• 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.

Question 23

Gliding

Answer 23

• Myxococcus move through gliding.

- do not use pili or flagella.

Question 24

Chemotaxis

Answer 24

• 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.

Question 25

Molecular basis for chemotaxis

Answer 25

- 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.

Question 26

CheA

Answer 26

transfers phosphate to CheY

Question 27

CheY-P

Answer 27

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

Question 28

When CheY not phosphorylated

Answer 28

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

Question 29

Default mode for E. Coli

Answer 29

- tumble | - will only run when it senses a chemical attractant.

Question 30

Adaptation

Answer 30

- 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

Question 31

CheR

Answer 31

- 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

Question 32

CheB

Answer 32

- methylesterase | - resets the baseline