Lecture 5: Microbial Physiology

Question 1

isotonic

Answer 1

solution has the same solute
concentration on either side

Question 2

hypertonic

Answer 2

external solution has greater solute

Question 3

hypotonic

Answer 3

cell interior is more concentrated

Question 4

in natural settings, cells are in ____ solutions

Answer 4

hypotonic

Question 5

inside us the external fluid is very salty, creates
_____ situation

Answer 5

isotonic

Question 6

Cells without walls will burst when placed in ______
solution

Answer 6

hypotonic

Question 7

Cells with walls (like bacteria, plants) build up ______ pressure inside cell

Answer 7

turgor

Question 8

turgor pressure

Answer 8

pressure in cell due to solute/water differences

Question 9

Osmolarity

Answer 9

The total concentration of dissolved molecules in water

Question 10

diffusion

Answer 10

Solutions tend toward even distribution of solutes

Question 11

osmosis

Answer 11

the flow of water in
response to this concentration difference

Question 12

Cell wall

Answer 12

• peptidoglycan
  Sugar components:
• N-acetyl glucosamine (NAG)
• N-acetyl muramic acid (NAM)
• Peptide cross-link
  through NAMt
• This structure is G- PG
• Penicillin antibiotics work
  on cell wall synthesis

Amino Acids:
- L-alanine
- d-glutamate
- med-diaminopimelic acid
- d-alanine

Question 13

PG cross-linking

Answer 13

Peptide cross-bridge
- Can vary from species to species
- In G- uses D- amino acids (L form used in proteins)
- In G+ uses penta-glycine
- In all cases interactions between peptide chains creates a mesh structure that stabilizes the cell against turgor pressure

Question 14

Different cross-linkers

Answer 14

• S. Aureus murein
• E. coli murein

Question 15

peptidoglycan synthesis

Answer 15

• PG monomer NAG-
  NAM(pentapeptide)
• Carried out of cell on carrier lipoprotein
• Addition to cell wall requires autolysin and
  transpeptidase activity
• Cut and paste new subunits
• made in cytoplasm of the cell

Question 16

Gram negative-murein sacculus (cell wall)

Answer 16

• Thin cell wall only a few layers thick, in between
  two membranes
• uses L-alanine,D-glutamate,
  meso-diaminopimelic acid, D-alanine

Question 17

Gram positive cell wall

Answer 17

• a thick cell wall made up of
  PG, also contains lipoteichoic acid (LTA)
• Gram positive cell wall uses primarily glycine, serine, threonines

Question 18

Lipopolysaccharide (LPS)

Answer 18

has two major components:
- O antigen repeating polysaccharide
- Lipid A (attaches it to OM)
- LPS is an endotoxin
- Lipid A component is the
causative agent of gram
negative septic shock (septicemia)

Question 19

Gram negative OM

Answer 19

 Makes cell negatively charged
 Prevents entry of large molecules (antibiotics)
 Porins control flow of nutrients, ions, chemicals
 Allows for antigenic variation (O157:H7), immune system evasion

Question 20

Gram negative periplasm

Answer 20

• Space in between outer and inner
  membranes
   Bacteria secrete many enzymes into this
  space
   Hydrolysis of many nutrient precursors,
  harmful chemicals may occur here

Question 21

Periplasmic space

Answer 21

 Gram negative only
 A great deal of biochem occurs here
 OM is a prefilter for large molecules
 Porins not very specific
 Periplasmic proteins scavenge nutrients
 PG layer is here
 Many proteins are secreted into the periplasm from cytosol

Question 22

Plasma membrane

Answer 22

• The plasma membrane is the same in all bacteria
   “Fluid Mosaic” model- proteins float freely in a mobile“ phospholipid bilayer
   Some proteins may be attached to the phospholipid head group
   Integral membrane proteins-can only be removed by disruption of the membrane
   This includes transmembrane proteins (pores)

Question 23

Role of the membrane

Answer 23

 Membrane controls flow of molecules in
and out of the cell
 “Semi-permeable”
 Some molecules (water, for example) flow freely through membrane pores
 Other molecules are restricted, by size or charge

Question 24

facilitated diffusion

Answer 24

a pore or channel
may allow the cell to expend energy to control this flow of molecules (doesn’t
work against the gradient, though)

Question 25

active transport

Answer 25

energy is spent moving
molecules against their concentration gradient (a pump)

Question 26

How do cells create gradients?

Answer 26

Cells use gated channels and active transport to create gradients in various
molecules

Question 27

What are gradients used for?

Answer 27

can be used for many
things, including the production of energy
for cell metabolism (chemiosmotic
mechanism)

Question 28

chemiosmotic mechanism

Answer 28

the production of energy
for cell metabolism