Microbiology - Bacterial Structure, Function, Growth

Question 1

Bacteria do not have:

Answer 1

a nuclear membrane, mitochondria, lysosomes, ERs

Question 2

Bacterial cell wall:

Answer 2

rigid cell wall external to the cytoplasmic membrane that contains PEPTIDOGLYCAN. Gram+ and Gram- bacteria have different cell wall structures and react differenclty to the gram staining procedure. (+)=Blue, (-)=Red. The rigidity of the cell wall is essential for resisting osmotic lysis (-=5atmospheres, and +=20)

Question 3

Bacterial shapes.

Answer 3

Coccus, Bacillus/Rod, Spirillum, vibrio (curved), spirochete

Question 4

cytoskeletal elements:

FtsZ, MreB, CreS

Answer 4

FtsZ= tubulin like
MreB- Actin Like
CreS = Intermediate filament like. contributes to curvature

Question 5

Peptidoglycan layer

Answer 5

Forms a rigid mesh that surrounds the cytoplasmic membrane. Peptidoglycan consists of a polymer with repeating units of 2 hexose sugars (N-acetylglucosamine and N-acetlymuramic acid (MurNAC).

Question 6

N-acetlymuramic acid (MurNAC). residues

Answer 6

Linked to tetrapeptide chains that contain amino acids found only in bacterial cell wells. Tetrapeptides are cross-linked from one chain (via DAP in gram-negative bacteria or L-lys in gram-positive bacteria) to D-ala on another chain, and cross-linking in gram-positive bacteria occurs via an intervening peptide such as pentaglycine.

Question 7

Cross-linking in peptidoglycan chains

Answer 7

Greater in gram-positive bacteria than in gram-negative bacteria.

Question 8

Gram-Negative bacteria

Answer 8

have a thin, sparsely cross-linked peptidoglycan layer and other major components that are located exterior to the peptidoglycan.

Question 9

Gram-Negative bacteria

Answer 9

have a thick, extensively cross-linked peptidoglycan layer that also contains teichoic acids.

Question 10

outer membrane (OM) of gram-negative bacteria

Answer 10

a lipid bilayer that contains lipopolysaccharide (LPS), lipoproteins (which are linked covalently to the peptidoglycan), and porins (which form transmembrane channels permitting diffusion across the membrane of hydrophilic molecules <600 MW), other membrane proteins, and phospholipids. The OM is a barrier to entry of some antibiotics and also protects the cell against the action of detergents and other toxic compounds.

Question 11

LPS of gram-negative bacteria

Answer 11

is located exclusively in the outer leaflet of the outer membrane, and the inner leaflet consists of phospholipids. LPS contains Lipid A (the toxic component of endotoxin), core polysaccharide, and O side chain oligosaccharides that function as somatic antigens (O antigen)

Question 12

Teichoic acids of gram-positive bacteria

Answer 12

have a repeating polyglycerol-P or polyribitol-P backbone substituted with other molecules (sugars, aminosugars, D-alanine), and they are covalently attached to the peptidoglycan layer

Question 13

Lipoteichoic acids

Answer 13

are attached to the underlying cytoplasmic membrane and help anchor the cell wall to the membrane.

Question 14

Capsules

Answer 14

Loose, gelatinous outer surface layers that usually consist of complex polysaccharides. Capsules often enhance virulence by enabling the encapsulated bacteria to resist phagocytosis. Most capsular polysaccharies are antigenic, and some are used as components of vaccines to prevent specific bacterial infections

Question 15

Flagella

Answer 15

are appendages originating in the cytoplasmic membrane that function as organs of motility. Some bacteria have flagella distributed over their surface
(peritrichous); others may have one or several flagella at one end of the cell (polar). Bacterial chemotaxis (movement toward attractive nutrients or away from toxic substances) involves the control of flagellar rotation (counterclockwise results in swimming; clockwise results in tumbling).

Question 16

Pili

Answer 16

Are long, slender, proteinaceous, antigenic, hair-like structures on the surface of many bacteria. Pili often play a role in bacterial adherence to surfaces and tissues, and antibodies against pili may block adherence and confer

resistance to infection. Sex pili that play a role in bacterial conjugation are found in small numbers on some bacterial cells.

Question 17

Cytoplasmic membrane

Answer 17

is the anatomical and physiological barrier between the inside and outside of the bacterial cell. exhibits selective permeability. It is essentially impermeable to all charged substances, even H+. Only hydrophobic molecules or uncharged molecules no larger than glycerol can diffuse through it. Contains the electron transport system which is the principal source for generating proton motive force during respiration in bacteria

Question 18

Ribosomes

Answer 18

bacterial are 70S vs the 80S seen in eukaroytes

Question 19

nucleoid

Answer 19

The DNA of bacteria is located within a distinct region of the cytoplasm known as the nucleoid or nuclear body. Translation and transcription occur as a coupled process!

Question 20

Plasmids

Answer 20

are extra-chromosomal, self-replicating DNA molecules, much smaller than bacterial chromosomes, and they are usually not essential for bacterial
viability. Plasmids in pathogenic bacteria often encode virulence factors. Plasmids called R factors carry genes that determine resistance to antibiotics in many pathogenic bacteria.

Question 21

Bacteriophages

Answer 21

are viruses that infect bacteria. The DNA genomes of temperate bacteriophages can integrate into bacterial chromosomes and replicate as part of those chromosome. Temperate bacteriophages often carry genes that encode bacterial toxins, other bacterial virulence factors or resistance to antibiotics

Question 22

Bacterial growth lag phase

Answer 22

An initial lag phase is a period of physiologic adjustment for the starting cells, or inoculum, involving the induction of new enzymes and the establishment of a proper intracellular environment for optimal growth in the new medium.

Question 23

Bacterial growth exponential phase

Answer 23

the rate of increase in cell number/cell mass is proportional to the cell number/cell mass already present. A constant interval of time (ranging from about 20 minutes up to about 1 day) is required for doubling of cell number/cell mass, and this interval is termed the generation time

Question 24

Bacterial growth stationary phase

Answer 24

occurs as essential nutrients are consumed and toxic products of metabolism accumulate. Such non-growing or slow-growing cells may exhibit markedly increased resistance to antibiotics such as penicillin or other

Question 25

Death phase

Answer 25

the number of viable bacteria will decrease over time. If spontaneous cell lysis (autolysis) occurs, the mass of intact bacteria in the culture will also decrease.

Question 26

Bacterial nutrition

Answer 26

This includes factors such as nutrients, pH, temperature, aeration (O2 tension), salt concentration, and osmotic pressure.

Question 27

Heterotrophic bacteria

Answer 27

Bacteria that require an organic carbon source (including most bacterial pathogens)

Question 28

Autotrophic bacteria

Answer 28

bacteria that obtain their carbon exclusively from CO2

Question 29

Aerobe

Answer 29

requires oxygen, cannot ferment.
bacteria that can grow in the presence of oxygen usually produce catalas (or peroxidase) and superoxide dismutase (SOD) that protect them against toxic reactive oxygen species.

Question 30

anaerobe

Answer 30

killed by oxygen, fermentative metabolism

Question 31

indifferent bacterial response

Answer 31

ferments in the presence or absence of O2

Question 32

facultative

Answer 32

respires with )2, ferments in absence of )2

Question 33

energy currency

Answer 33

ATP and electrochemical gradients (the proton motive force). ATP drives many biosynthetic reactions, and electrochemical gradients drive other functions like flagellar rotation and certain substrate transport systems. These two types of potential energy are interconvertible by the membrane ATPase. Bacteria also require reducing power in the form of NADH and NADPH to drive various metabolic interconversions. Heterotrophic bacteria obtain both energy and reducing power by subjecting nutrients to fermentation or respiration.

Question 34

fermentation

Answer 34

organic compounds serve as both electron donors and electron acceptors, and no net oxidation of substrates occurs.

Question 35

respiration

Answer 35

many bacterial species, like the mitochondria of higher organisms, generate ATP through electron transport and use molecular oxygen as the final electron acceptor. In anaerobic respiration, certain bacteria may use inorganic substrates such as nitrate or nitrite as terminal electron acceptors instead of O2.

Question 36

Sporulation

Answer 36

Spores are specialized cells that are produced by certain bacteria, such as Clostridium sp. and Bacillus sp., when the nutritional supply of carbon, nitrogen or phosphorus is limited. During sporulation, these bacteria differentiate to form highly resistant, dehydrated forms (spores) that have no metabolic activity. Spores are adapted for prolonged survival under adverse conditions such as heat, drying, freezing, the presence of toxic chemicals, and radiation.

Question 37

antimicrobial agents

Answer 37

work on the principle of selective toxicity, namely the selective inhibition of microbial growth at drug concentrations tolerated by the host. Many aspects of microbial metabolism are very similar to those of eukaryotic organisms (including humans). However, there are some components of bacteria that are not present in eukaryotes or are sufficiently different from their counterparts in eukaryotes be effective as targets for antimicrobial agents.

Question 38

Cell wall-active antimicrobials

Answer 38

Selective toxicity due to the lack of peptodoglycan in mammalian cells. Examples: B-lactams, Vancomycin, Cycloserine

Question 39

Outer and cytoplasmic membrane-active antimicrobials

Answer 39

Polymyxins are cationic surfactants that disrupt bacterial outer and cytoplasmic membranes They are less active on mammalian cell membrans.

Question 40

Inhibitors of protein synthesis at the ribosomal level

Answer 40

Selective toxicity is due to differences between bacterial and mammalian ribosomes.. Ex) Aminoglycosides, tetracyclines, chloramphenicol, macrolides,and lincomycins

Question 41

Inhibitors of nucleic acid synthesis

Answer 41

Quinolones - inhibit DNA gyrase and topoisomerase and therefor interfere with DNA replication
Rifampicin - Inhibits RNA polymerase and interferes with initiaion of transcription

Question 42

Metabolic inhibitory antimicrobials

Answer 42

ex) sulfonamides, trimethoprim, Isoniazid, Metronidazole.

Question 43

mRNA in bacteria

Answer 43

can be mono or poly for coding of proteins. In human cells mRNA only codes for one protein.

Question 44

Bacteria use multiple secretion systems to:

Answer 44

1) deliver proteins to the cell surface. 2) assemble organelles on the cell surface. 3) export proteins to the extracellular milieu. 4) inject proteins or DNA into other cells