Bacteria Structure and Function (complete)

Question 1

Describe the rigid cell wall of bacteria. What are the functions?

Answer 1

• External to cytoplasmic membrane that contain peptidoglycan
• G(+) and G(-) have different cell wall structures

Functions:

1) Resists osmotic lysis
2) Maintains cell shape

Question 2

Describe the peptidoglycan layer of bacteria

Answer 2

• Forms rigid mesh surrounding cytoplasm
• Consists of polymer of repeating units (GlcNAc and MurNAc)
• these are crosslinked!

Question 3

How does lysozyme interact with bacteria when inside the body?

Answer 3

• Hydrolyzes peptidoglycan by cleaving glycosidic bond between MurNAc and GlcNAc
• contributes to innate immune system

Question 4

Describe the peptidoglycan layer in gram negative bacteria

Answer 4

• THIN!

- Sparsely cross-linked

Question 5

Describe the peptidoglycan layer of gram positive bacteria

Answer 5

• THICK!
• Extensively cross-linked
• Also contains teichoic acids

Question 6

Describe the outer membrane of gram negative bacteria. What are the functions?

Answer 6

• A lipid bilayer
• Contains lipopolysaccharide, lipoproteins, and porins

Functions:

1) Barrier to antibiotics
2) Protects against detergents and toxic compounds

Question 7

Lipoproteins in the outer membrane of gram negative bacteria are covalently linked to what?

Answer 7

Peptidoglycans

Question 8

What is the function of porins in the outer membrane of gram negative bacteria?

Answer 8

• Form transmembrane channels

- Allow diffusion of hydrophilic molecules across membrane

Question 9

Describe the outer membrane of gram positive bacteria

Answer 9

• Have two layers or leaflets
• Outer leaflet: LPS, Lipid A, core polysaccharide, O side chain
• Inner leaflet: phospholipids

Question 10

Describe teichoic acids.

Answer 10

• A repeating polyglycerol-P or polyribitol-P backbone
• Covalently attached to peptidoglycan layer
• Help anchor the cell wall to membrane

Question 11

Describe capsules

Answer 11

• Loose, gelatinous outer surface layers
• Consist of complex polysaccharides
• Enhance virulence b/c it can resist phagocytosis of humans

Question 12

Describe flagella

Answer 12

• Appendages used for motility
• Some bacteria have flagella all over surface (peritrichous)
• some have just one (polar)

Question 13

Describe pili (fimbraie)

Answer 13

• Long, slender, proteinaceous, antigenic hair-like structures
• Play role in adherance to surfaces and tissues
• Abs against pili may block adherance

Also used for bacterial sexy time (aka transfer of chromosomes btwn bacteria)

Question 14

Describe the cytoplasmic membrane

Answer 14

• Barrier between the inside and outside of bacterial cell
• Lipid bilayer made of phoslipids, proteins

Functions:

1) selective permeability
2) e(-) transport system

Question 15

Describe the cytoplasm

Answer 15

• Consists of aqueous solution of proteins and metabolites
• Where metabolic processes occur

Include:

1) Ribosomes
2) Nucleoid

Question 16

Describe ribosomes in bacteria

Answer 16

• Where protein synthesis occurs

- Polyribosomes form when several ribosomes come together to interact with a single mRNA

Question 17

Describe the nucleoid in bacteria

Answer 17

• A specific area of the cytoplasm
• Where DNA is located — tightly packed, coiled
• No nuclear membrane surrounding the nucleoid

Question 18

Describe the bacterial chromosome

Answer 18

• a single, double stranded CIRCULAR DNA molecule

Question 19

Describe plasmids

Answer 19

• Extra-chromosomal, self-replicating DNA molecules
• Not essential for bacterial viability

One type of plasmid called R factors:
- carry genes that determine resistance to antibiotics (Rrrrrr is for Rrrrrresitance!!!)

Question 20

Describe bacteriophages

Answer 20

Viruses that infect bacteria

• inject DNA in bacterial cell
• Viral DNA fuses w/ bacterial DNA
• More viral proteins produced —> more viruses

Question 21

Explain the importance of different cell wall structures in bacteria

Answer 21

Bacterial shape determined by intracellular cytoskeletal elements and rigid cell wall

• Structure determines function

Question 22

Describe a typical bacterial growth curve.

Answer 22

• Bacteria are placed in a new environment and growth is measured
• Divided into 3-4 phases (lag, exponential, stationary, death)

y-axis: log bacterial #
x-axis: time

Question 23

Explain the characteristics of lag phase

Answer 23

THINK: Adjustment phase

• Produces new enzymes to new environment!
• Establishes proper intracellular environment for optimal growth in this here new place

Question 24

Explain the characteristics of exponential phase

Answer 24

THINK: growth phase

• rate of increase in cell #/mass is proportional to cell #/mass already present
• constant interval required to double #/mass (GENERATION TIME)

Question 25

Explain the characteristics of stationary phase

Answer 25

THINK: plateau phase - Essential nutrients consumed; toxic metabs accumulate - Growth slows/ceases - Where most bacteria spend their time

Question 26

Explain the characteristics of death phase

Answer 26

THINK: death phase of course - Doesn't always happen, but some bacteria can't withstand stationary phase - there's a decrease in total #/mass - Only seen when bacteria lyse!!! (makes sense, eh?)

Question 27

What are the different classifications for bacteria according to nutrition requirements?

Answer 27

1) Aerobe 2) Anaerobe 3) Indifferent 4) Facultative 5) Microaerophilic

Question 28

Describe aerobe bacteria's nutritional requirements for growth response

Answer 28

GR: aerobic conditions - Requires O2 - Cannot ferment

Question 29

Describe anaerobe bacteria's nutritional requirements for growth response

Answer 29

GR: anaerobic conditions - Killed by O2 - Fermentative metabolism

Question 30

Describe indifferent bacteria's nutritional requirements for growth response

Answer 30

GR: aerobic and anaerobic - Ferments in presence or absence of O2

Question 31

Describe facultative bacteria's nutritional requirements for growth response

Answer 31

GR: aerobic and anaerobic - Respires w/ O2 - Ferments in absence of O2

Question 32

Describe microaerophilic bacteria's nutritional requirements for growth response

Answer 32

GR: anaerobic (primary) and aerobic (small amount of growth) - Grows best at low [O2] - can grow w/o O2

Question 33

Define respiration

Answer 33

- When O2 is used as the final e(-) acceptor in the electron transport/ATP generation process - Anaerobic resp: some bacteria may use inorganic substrates (nitrate, nitrite) as e(-) acceptors (not O2)

Question 34

Define fermentation

Answer 34

- Organic compounds serve as both e(-) donors and acceptors | - No net oxidation/reduction between substrates and products

Question 35

Explain how metabolic "energy currency" is generated

Answer 35

Two types of currency: 1) ATP 2) Electrochemical gradients (proton motive force) - Generated by fermentation/respiration - Bacteria also need "reducing power" (NADPH, NADH)

Question 36

Explain why unique bacterial components are important as potential targets for antimicrobial therapy

Answer 36

- Ensures you kill less of the host | - Selective inhibition of microbial growth at [drug] tolerated by host (aka SELECTIVE TOXICITY)

Question 37

What are the major groups of antibiotics used for human medicine?

Answer 37

1) Cell wall-active antimicrobials 2) Outer/cytoplasmic membrane-active antimicrobials 3) Protein synthesis inhibitors at ribosomal level 4) Nucleic acid synthesis inhibitors 5) Metabolic inhibitory antimicrobials

Question 38

What are the principal targets for cell wall-active antimicrobials?

Answer 38

Peptidoglycan Examples 1) Beta-lactams 2) Vancomycin 3) Cycloserine

Question 39

What are the principal targets for outer/cytoplasmic membrane-active antimicrobials?

Answer 39

- Outer and cytoplasmic membranes (duh) | - Use polymyxins to disrupt the membranes --- they are cationic surfactants

Question 40

What are the principal targets for protein synthesis inhibitors at ribosomal level?

Answer 40

Bacterial ribosomes (b/c they are different from mammalian ribos!!!) Examples: 1) Aminoglycosides 2) Tetracyclines 3) Chloramphenicol 4) Macrolides

Question 41

What are the principal targets for nucleic acid synthesis inhibitors?

Answer 41

Nucleic acid synthesis ... :P Examples: 1) Quinolones 2) Rifampicin

Question 42

What are the principal targets for metabolic inhibitory antimicrobials?

Answer 42

Specific metabolic reactions Examples: 1) Sulfonamides (folic acid formation) 2) Trimethoprim (folic acid metabolism) 3) Isoniazid (lipid synthesis) 4) Metronidazole (anaerobic metabolism)