Microbiology Chapter 3B

Front 1

What is the structure and major components of the Gram negative cell wall?

Back 1

-consist of a thin layer of peptidoglycan surrounded by an outer membrane
-outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS)
-no teichoic acids

Front 2

Braun’s lipoproteins

Back 2

connect outer membrane to peptidoglycan

Front 3

Adhesion sites

Back 3

-sites of direct contact (possibly true membrane fusions) between plasma membrane and outer membrane
-substances may move directly into cell through adhesion sites

Front 4

Lipopolysaccharides (LPSs)

Back 4

consist of three parts:
(1) lipid A (similar structure in all LPS)
(2) core polysaccharide (genus-specific)
(3) O side chain
(O antigen)
(O-antigenic region)
(O-polysaccharide)
LPSs are species-specific structure

Front 5

Importance of LPS

Back 5

(1)protection from host defenses
(2) contributes to negative charge on cell surface
(3) help stabilize outer membrane structure
(4) can act as an endotoxin

Front 6

O antigen

Back 6

Protection from host defenses

Front 7

Core polysaccharide

Back 7

Contributes to negative charge on cell surface

Front 8

Lipid A

Back 8

helps stabilize outer membrane structure and can act as an endotoxin

Front 9

Other characteristics of outer membrane

Back 9

More permeable than plasma membrane due to presence of porin proteins and transporter proteins

Front 10

Mechanisms of gram staining

Back 10

-thought to involve constriction of the thick peptidoglycan layer of gram-positive cells
--constriction prevents loss of crystal violet during decolorization step
-thinner peptidoglycan layer of gram-negative bacteria does not prevent loss of crystal violet

Front 11

Osmosis

Back 11

Movement of water across selectively permeable membrane from dilute solutions to more concentrated solutions

Front 12

Hypotonic solutions

Back 12

[solute]outside < [solute]inside

Front 13

Osmotic lysis

Back 13

-can occur when cells are in hypotonic solution
-movement of water into cell causes swelling and lysis due to osmotic pressure
(cell wall protects against osmotic lysis)

Basis of lysozyme and penicillin action

Front 14

Plasmolysis

Back 14

Occurs when cells are in hypertonic solutions. Water moves out of cell causing cytoplasm to shrivel and pull away from cell wall.

Front 15

Hypertonic solution

Back 15

[solute]outside > [solute]inside

Front 16

Protoplast

Back 16

Cell completely lacking cell wall

Front 17

Spheroplast

Back 17

Cell with some cell wall remaining

Front 18

Archael cell wall

Back 18

-lack peptidoglycan (can be composed of proteins, lycoproteins, or polysaccharides)
-some contain pseudomurein

Front 19

Structure of pseudomurein

Back 19

-has L-amino acids instead of D-amino acids (characteristic of bacteria) in its cross-links

Front 20

Major protein secretion systems in procaryotes

Back 20

(1) sec-dependent pathway
(2) type I (ABC) protein secretion pathway
(3) type II pathway
(4) type III protein secretion pathway

Front 21

Overview of bacterial protein secretion

Back 21

-Gram +/- have different problems secreting proteins based on the differences between the structure of walls
-major pathway of transporting proteins across the membrane is the Sec-dependent pathway

Front 22

Sec-dependent pathway

Back 22

*called general secretion pathway
*translocates proteins from cytoplasm across or into plasma membrane
*secreted proteins synthesized as pre-proteins having amino-terminal signal peptides
*translocon transfers protein & removes signal peptide
* translocates pre-protein through plasma membrane. when pre-proteins emerges from plasma membrane a signal peptidase removes the signal peptide

Front 23

Chaperone protein

Back 23

keep pre-proteins unfolded

Front 24

Protein secretion in gram negative bacteria

Back 24

-Type II and V pathways transport proteins across the outer membrane
-Types I and III pathways are sec-independent
-type IV pathway usually function independently of the sec pathway

Front 25

Type II Protein Secretion Pathway

Back 25

Transports proteins from periplasm across outer membrane

Front 26

Type I Protein Secretion Pathway

Back 26

Also called ABC protein secretion pathway. Transports proteins from cytoplasm across both plasma membrane and outer membrane. Translocation driven by both ATP hydrolysis and proton motive force.

Front 27

Type III Protein Secretion Pathway

Back 27

Secreted virulence factors of gram negative bacteria from cytoplasm, across both plasma membrane and outer membrane, and into host cell

Front 28

Type IV Protein Secretion Pathway

Back 28

Type IV pathways are unique because they secrete proteins and transfer DNA during conjugation

Front 29

Glycocalyx

Back 29

Network of polysaccharides extending from the surface of the cell. A capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx.

Front 30

S-layers

Back 30

Regularly strucutred layers of protein or glycoprotein. Common amond Archaea, where they may be the only structure outside the plasma membrane.

Front 31

Capsules

Back 31

Usually composed of polysaccharides. Well organized and not easily removed from cells.

Front 32

Slime layers

Back 32

Similar to capsules except diffuse, unorganized and easily removed.

Front 33

Function of capsules, slime layers, and S-layers

Back 33

(1) protection from host defenses (phagocytosis)
(2) protection from harsh environmental conditions
(3) attachment to surfaces
(4) source of stored nutrients

Front 34

Constitutive capsule

Back 34

(strep. pneumoniae) always made

Front 35

Inducible capsule

Back 35

(strep. mutans)
-sucrose induces glucosyl transferase
-enzyme transfers glucosyl units from sucrose to form the dextran capsule
-dextran capsule formed only in presence of sucrose

Front 36

Fimbriae

Back 36

-short, thin, hairlike, porteinaceous appendages
-mediate attachment to surfaces
-some required for twitching motility or gliding motility that occurs in some bacteria

Front 37

Sex pili

Back 37

-similar to fimbriae except longer, thicker, and less numerous
-required for mating

Front 38

3 modes of motility in procaryotes

Back 38

(1) flagella
(2) axial filament (spirochetes only)
(3) gliding motility (mechanism not understood)

Front 39

Monotrichous
Polar flagellum
Amphitrichous
Lophotrichouse
Peritrichous

Back 39

-one flagellum
-flagellum at end of cell
-one flagellum at each end of cell
-cluster of flagella at one or both ends
-spread over entire surface of cell

Front 40

Flagellar Ultrastructure

Back 40

(1)filament
(2)basal body
(3)hook

Front 41

Filament

Back 41

-hollow, rigid cylinder
-composed of protein flagellin
-some have sheath around filament

Front 42

Hook

Back 42

-links filament to basal body

Front 43

Basal body

Back 43

-series of rings that drive flagellar motor

Front 44

Flagellar Synthesis

Back 44

-example of self-assembly
-complex process involving many genes and gene products
-new molecules of flagellin are transported through the hollow filament
-growth is from tip, not base

Front 45

Mechanism of flagellar movement

Back 45

Flagellum rotates like a propellar. Counterclockwise rotation causes forward motion (run). Clockwise rotation disrupts run causing a tumble (twiddle).

Front 46

Spirochetes

Back 46

-axial filaments cause flexing and spinning movements
-spirochetes are motile by means of an axial filament

Front 47

Gliding motility

Back 47

-cells coast along solid surfaces
-no visible motility structure has been identified

Front 48

Chemotaxis

Back 48

-movement towards a chemical attractant or away from a chemical repellant
-concentrations or chemoattractants and chemorepellants detected by chemoreceptors on surfaces of cells

Front 49

Bacterial endospore

Back 49

Endospores formed by some bacteria, Bacillus and Clostridium. Dormant. Resistant to numerous environmental conditions.

Front 50

What makes an endospore so resistant?

Back 50

-calcium (complexed with dipicolinic acid)
-acid-soluble, DNA-binding proteins
-dehydrated core
-spore coat
-DNA repair enzymes
-chaperone proteins

Front 51

Sporogenesis

Back 51

Normally commences when growth ceases because of lack of nutrients. Multistage process.

Front 52

Stages in transformation of endospore into vegetative cell

Back 52

*Activation. Prepares spores for germination. Often results from treatments while heating.
*Germination. Spore swelling. Rupture of absorption of spore coat. Loss of resistance. Increased metabolic activity.
*Outgrowth. Emergence of vegetative cell.