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MICR 3050 > Microbial Cell Structure and Function > Flashcards

Microbial Cell Structure and Function Flashcards

1
Q

Cocci

A

spheres

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2
Q

Diplococci

A

pairs of spheres

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3
Q

Streptococci

A

chains of spheres

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4
Q

Staphylococci

A

grape-like clusters of spheres

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5
Q

Tetrads

A

4 cocci in a square

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6
Q

Sarcinae

A

cubic configuration of 8 cocci

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7
Q

Bacilli

A

rods

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8
Q

Coccobacilli

A

very short rods

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9
Q

Vibrios

A

resemble rods, comma shaped

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10
Q

Spirilla

A

rigid helices

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11
Q

Spirochetes

A

flexible helices

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12
Q

Filamentous

A
  • mycelium (mat)

- network of long, multicellular filaments

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13
Q

Pleomorphic

A
  • variable in shape
  • may not have cell wall so their shape can depend on what they are against
  • default shape is round
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14
Q

Unique shapes

A

star

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15
Q

Unique arrangements

A

palisades (picket-fence)

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16
Q

What is the size range for eukaryotes?

A

0.8 micrometers-hundreds of mircometers

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17
Q

What is the size range for bacteria/archaea?

A

0.2 micrometers-750 micrometers

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18
Q

What is the size range for viruses?

A

0.01 micrometers-2.3 micrometers

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19
Q

How does surface to volume ratio change with size?

A

smaller organisms have a larger surface to volume ratio

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20
Q

Why is being small an advantage?

A
  • large surface to volume ratio
  • faster binary fission
  • more room for diffusion
  • get nutrients in and wastes out faster
  • get mutations faster which leads to natural selection
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21
Q

What is the cytoplasmic membrane?

A

a thin structure that separates the cytoplasm from the environment

22
Q

What are the major functions of the cytoplasmic membrane?

A
  • permeability barrier
  • site of many proteins: transport systems, bioenergetics, chemotaxis
  • energy conservation: proton motive force
23
Q

What is the cytoplasmic membrane composed of?

A
  • lipid bilayer composed of amphipathic phospholipids (polar heads and nonpolar tails)
  • phospholipids can be saturated or unsaturated depending on the environment
  • have hopanoids to add structural stability
  • have integral and peripheral proteins
24
Q

What are the saturation levels reflected by?

A
  • the environment
  • cold environment: unsaturated (to increase membrane fluidity)
  • warm environment: saturated (to decrease membrane fluidity)
25
Q

What are peripheral proteins?

A
  • loosely connected to the membrane

- comprise 20-30% of the membrane proteins

26
Q

What are integral proteins?

A
  • embedded within the membrane (amphipathic)
  • comprise 70-80% of the membrane proteins
  • carry out important functions: transport, excretion and secretion, energy conservation
27
Q

What is the difference between secretion and excretion?

A
  • secretion is releasing for a purpose

- excretion is getting rid of waste

28
Q

What is the bacterial cell wall?

A
  • rigid structure that lies just outside the plasma membrane
  • contains peptidoglycan (only in domain bacteria)
  • component of most bacterial cells
29
Q

What are the functions of the bacterial cell wall?

A
  • provides shape to the cell (default shape is spherical without the cell wall)
  • protects from osmotic lysis
  • may contribute to pathogenicity (helps it cause disease by attaching to surfaces or keeping toxins or medicines out)
  • protects from toxic substances
30
Q

What does the gram-positive cell wall look like?

A
  • thick layer of peptidoglycan over the plasma membrane

- no outer membrane

31
Q

What does the gram-negative cell wall look like?

A
  • thin layer of peptidoglycan over the plasma membrane

- has an outer membrane

32
Q

What is the structure of peptidoglycan?

A
  • mesh-like polymer
  • two alternating sugars form the backbone:
  • N-acetylglucosamine (NAG)
  • N-acetylmuramic acid (NAM)
  • alternating D- and L- amino acids
33
Q

What kind of linkage connects NAG and NAM?

A

Beta 1,4 bond

34
Q

What is the structure of NAG and NAM?

A
  • NAG has a shorter chain

- NAM has a longer chain with amino acids

35
Q

What breaks the Beta 1,4 bond?

A
  • lysozymes

- works well on gram positive, but not gram negative

36
Q

What does penicillin do to peptidoglycan?

A
  • causes a problem with the linking of amino acids (transpeptidation)
  • if a bacterium is actively growing, it has to elongate and divide and it purposely puts holes in its cell membrane
  • peptidoglycan precursors are put in the cytoplasm
  • precursors are translocated to fill the holes
  • normally, the amino acids would link, but penicillin prevents this
  • then the precursor pieces to fill in the holes fall out, which causes lysing
37
Q

What kind of linkage does E. coli have?

A

direct

38
Q

What kind of linkage does S. aureus have?

A

indirect (has an interbridge)

39
Q

What is the composition of gram-positive cell walls?

A
  • composed primarily of peptidoglycan (90%)
  • may also contain teichoic acids (negatively charged, reason why bacteria have a negative charge)
  • lipetechoic acids
  • some have a layer of proteins on surface of peptidoglycan
40
Q

What do teichoic acids do?

A
  • bind Ca2+ and Mg2+
  • help maintain structure of cell wall
  • protect from harmful substances
  • role in pathogenesis
41
Q

What is the composition of gram-negative cell walls?

A
  • consist of a thin layer of peptidoglycan (10%) surrounded by an outer membrane
  • periplasm (20-40%): contains hydrolytic enzymes, binding proteins, and chemoreceptors)
  • outer membrane is composed of lipids, lipoproteins, and lipopolysaccharide (LPS)
  • porins: channels that hydrophilic molecules can pass through
  • does not have teichoic acids
42
Q

What is LPS?

A
  • made up of lipid A, core polysaccharide, and O-specific polysaccharide (O antigen)
  • lipid embedded in the outer membrane
43
Q

What is the role of LPS?

A
  • contributes to negative charge on cell surface (core polysaccharide)
  • helps stabilize outer membrane structure and can act as an endotoxin (lipid A)
  • may mutate to protect from host defenses (O antigen)
  • may contribute to attachment to surfaces and biofilm formation
  • creates a permeability barrier
44
Q

How does the cell wall protect from cell lysis?

A
  • in hypotonic environments, the solute concentration outside of the cell is lower, so water rushes in
  • the cell wall acts as a barrier to keep the cell from bursting
45
Q

What is plasmolysis?

A
  • happens in hypertonic environments (solute concentration outside the cell is higher)
  • water rushes out of the cell
  • cell shrivels up inside the cell wall
  • hypertonic environments used for food preservation
46
Q

What conditions do bacteria prefer to live in?

A

hypotonic environments

47
Q

What evidence is there of the protective nature of the cell wall?

A
  • lysozyme breaks bond between NAG and NAM in gram positive cells
  • penicillin inhibits peptidoglycan synthesis (in actively growing cells)
  • when cells are treated with either of these, they will lyse if put into a hypotonic solution
48
Q

How do mycoplasma survive without a cell wall?

A
  • don’t have peptidoglycan
  • have hopanoids and sterols (like eukaryotes)
  • plasma membrane is more resistant to osmotic pressure
  • live in isotonic environments without a steep concentration gradient
49
Q

What are gram positive cells without peptidoglycan called?

A

protoplasts

50
Q

What are gram negative cells without peptidoglycan called?

A

spheroplasts

MICR 3050 (18 decks)

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