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Microbial Physiology > Lecture 3 - Exam 1 > Flashcards

Lecture 3 - Exam 1 Flashcards

1
Q

Where is the periplasm?

A

Between the inner membrane and outer membrane of gram negative bacteria.

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2
Q

What is the periplasm?

A

An aqueous compartment containing peptidoglycan and many other components vital to cell survival.

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3
Q

The periplasm is considered a cellular compartment with specialized activities. What are they?

A

Redox reactions, osmotic regulation, solute transport, protein secretion, and hydrolytic activities (phosphatases and nucleases).

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4
Q

Why is the periplasm only in G- bacteria?

A

Only in G- because G- have outer membrane and G+ does not.

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5
Q

Components of the periplasm include:

A

Oligosaccharides, solute-binding proteins, cytochrome C, hydrolytic enzymes, detoxifying enzymes for cell protection, peptidoglycan, and TonB protein.

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6
Q

What are oligosaccharides?

A

They are involved in osmotic regulation. The amounts of oligosaccharides in the periplasm decrease when cells are grown in media with high osmolarity.
Decrease of oligosaccharides when osmolarity increases. This occurs to decrease turgor pressure and amount of solutes coming into the cell.

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7
Q

What are solute-binding proteins?

A

Assist in transport of sugars, amino acids and other solutes.

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8
Q

What is Cytochrome C?

A

Involved in redox reactions and energy transductions (respiration/photosynthesis)

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9
Q

What are hydrolytic enzymes?

A

Degrade nutrients into smaller molecules that can be transport across the cell membrane via specific transporters (proteases and nucleases).

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10
Q

What is the TonB protein?

A

An energy transducer that uses PMF to import iron siderophores or vitamins.
-These solutes are brought into the periplasm against a large concentration gradient.
-TonB couples electrochemical energy (PMF) in the cell membrane to the uptake of certain solutes through the outer membrane into the cytoplasm.

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11
Q

What are Siderophores?

A

Iron bonding machines that bacteria send out into the environment to scavenger iron… in pathogens, iron is the limiting nutrient for bacteria growth survival.

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12
Q

The proliferative capability of many invasive pathogens is limited by…?

A

The bioavailability of iron.
-Pathogens have developed strategies (siderophores) to obtain iron form their host organisms.
-in turn, host defense strategies have evolved to sequester iron from invasive pathogens.

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13
Q

What do TonB transporters do?

A

In gram negative bacteria. Are outer membrane proteins that transport the iron-siderophore complex back into the cell.

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14
Q

The Ton system is specific to what?

A

Gram-negative bacteria and allows for the transfer of energy from the inner membrane (via Ton complex) to receptors found within the outer membrane.

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15
Q

What is the Ton complex?

A

A unique inner membrane complex that is powered by proton motor force (PMF) at the inner membrane.
-The complex consists of three integral membrane proteins: TonB, ExbB, and ExbD.

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16
Q

Discuss ExbB and ExbD proteins.

A

ExbB and ExbD associate to form the proton translocation part of the motor. They help generate PMF and the energy derived from PMF travels through the elongated TonB subunit in the periplasm that physically interacts with TonB-dependent transporters (TBDTs) at the outer membrane. This interaction then opens a gate through the TBDT receptor to allow the entry of the bound nutrient into the periplasm.

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17
Q

G- bacteria have how many cell membranes? What are they?

A

They have two.
1. Outer membrane
2. Cytoplasmic membrane
Between the two membrane lies the periplasm.

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18
Q

Describe the Outer membrane of G- bacterial cell.

A

The outer membrane consists of an inner leaflet of phospholipids and an outer layer of LPS.
Remember:
LPS is amphipathic, so the hydrophobic lipid A portion of LPS is anchored in the phospholipid layer of the outer membrane.
Also, contains porins which form small, nonspecific hydrophilic channels (nonspecific flow… important for turgor pressure) through the outer membrane.
Porins allow diffusion of low molecular weight solutes, such as sugars and ions.
Lipoproteins extend from the phospholipid inner leaflet and bind covalently to PG (anchors the outer membrane to the PG and keeps the outer membrane attached to the cell surface.
Some cell surface receptors are also located in the outer membrane.

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19
Q

Describe the cytoplasmic membrane of G- cells.

A

The cytoplasmic membrane is a phospholipid bilayer containing integral and peripheral proteins. It is said to be the fluid mosaic structure because of the extensive lateral mobility of many proteins and phospholipids… proteins and lipids diffuse laterally.
However, certain protein aggregates remain as aggregates where the proteins interact to catalyze sequential reactions.

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20
Q

What structure is the most functionally complex of the cell structures?

A

The cytoplasmic membrane.

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21
Q

What are some of the physiological activity responsibilities of the cytoplasmic membrane?

A

Solute transport, electron transport, atp synthesis, lipid biosynthesis, protein secretion, secretion and uptake of intracellular signals, responses to environmental signals.

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22
Q

What are the major functions of the cytoplasmic membrane?

A
  1. Retains contents of cytoplasm
  2. Selective barrier : acts as a permeability barrier to almost all water-soluble molecules
    - most solutes either diffuse or are carried across the cytoplasmic membrane
  3. Energy generation (respiration)
    -Electron transport chain (embedded in the cytoplasmic membrane)
    -carrier proteins and quinones in the CM
    -ATP synthase to generate PMF
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23
Q

Describe the structure of a phospholipid:

A

Two fatty acids (R1 &R2) ester-linked to 2 hydroxyl groups of phosphoglycerides.

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24
Q

What are ester linkages?

A

O - - C - O - C (- - meaning double bond)

25
Q

What are ether linkages?

A

C-O-C

26
Q

Archaea have what kind of linked lipids in their cell membrane?

A

Ether linked lipids

27
Q

Phospholipids are ______ charged due to ______.

A

Negatively charged due to phosphate group.

28
Q

Phospholipids are polar? Nonpolar?

A

Amphipathic, actually. Meaning one side is polar (ionized P end) and the other is non-polar (fatty acid end).
Hydrophobic tails contain fatty acid.
Hydrophilic head contains phosphate and its attached group (X).

29
Q

What determines the type of phospholipid?

A

The group (X) that is attached to the phosphate group of the hydrophilic head of the phospholipid.

30
Q

Phospholipids naturally aggregate with _________ toward each other and with _________ interacting with H2O, proteins etc.

A

Hydrophobic tails ; polar heads

31
Q

What are integral proteins?

A

Embedded in the phospholipid layer - bound to the fatty acids of phospholipids via hydrophobic bonding.

32
Q

What are peripheral proteins?

A

Attached to the membrane surface via ionic interactions.

33
Q

How can you determine what kind of proteins are in the bacterial cell membrane?

A

You can do a salt wash to determine this. If the proteins are removed by the salt solutions then it is a peripheral protein. If it is not removed, then an integral protein.
You can also use a detergent to break the bonds of integral proteins, and that is how you can remove them.

34
Q

What is an aquaporin protein?

A

A water channel that enhances the rapid equilibrium of water across the cell membrane.

35
Q

What represses aquaporin synthesis? What does this help with?

A

Growth in high osmolarity. This helps protect cells from hypo-osmotic stress in the event of a rapid decrease in osmolarity of the environment.
-While E. coli mutants that lack the aquaporin gene are viable, these mutant colonies are smaller than the wild-type.

36
Q

What are Mechanosensitive channels?

A

Bacteria adjust internal osmotic pressure so that is higher than external osmotic pressure -> keeps water flowing into the cell via osmosis.
Maintains high internal turgor pressure that is required for growth. Internal osmotic pressure is kept high by accumulating solutes such as K+, glutamine and other solutes.

37
Q

Mechanosensitive channels open when?

A

Mechanosensitive channels open under hypo-osmotic shock and let internal solutes out of the cell, thereby lowering internal osmotic pressure.
Hypo-osmotic shock is when there is a sudden decrease in external osmotic pressure, this can put the cell in danger -> rapid influx of water. Aquaporins regulate this water influx and mechanosensitive channels regulate solutes and all this helps balance turgor pressure.

38
Q

Turgor pressure keeps the bacterial ______ by pushing up against cell wall.

A

Shape

39
Q

Archaeal cell membranes are _____ linked ________.

A

Archaeal cell membranes are ether linked isoprenols o glycerol phosphate.

40
Q

What kind of linkage is more stable to hydrolytic cleavage and more stable in acidic and thermophilic environments?

A

Ether linkages

41
Q

In Archaeal Cell Membranes: if the isoprenoid alcohol is linked to one glycerol, then..?

A

A monoglycerol diether is formed and the membrane is a bilayer.

42
Q

In Archaeal Cell Membranes: if the isoprenoid is linked to two glycerols, then…?

A

A diglycerol tetraether is formed. These have a polar head at both ends and the membrane is a monolayer. This is the only known example of a membrane having no midplane region!

43
Q

Are there fatty acids in archaeal cell membranes?

A

No

44
Q

What is the lipid situation in Archaeal cell membranes?

A

Many different lipids found in archaea: due to different polar head group and different core lipids, with a LOT of cross-linking especially in hyperthermophiles. The variety of lipid structures reflects the need for Archaea to adjust their core functions despite harsh destabilizing environmental conditions.

45
Q

What is the cytoplasm?

A

Portion of the cell enclosed by cell membrane. Thick and viscous due to high solute concentration.

46
Q

What are the things found in the cytoplasm?

A

Nucleic acids: DNA, RNA, nucleic acid precursors
Proteins: structural, enzymes, amino acids, precursors
Metabolites: vitamins, ions
Carbohydrates and derivatives
Fatty acids and derivatives

47
Q

What is the environment of the cytoplasm like?

A

It has a reduced environment.
Provides electrochemical gradient needed for electron flow.

48
Q

Although bacteria do not have membrane enclosed organelles, they have:

A

Highly compartmentalized, some membrane or protein-enclosed compartments
-Intracytoplasmic membranes
-Enzymes of the same pathway working together

49
Q

What is a nucleoid?

A

Genetic information center.
Site of DNA and RNA synthesis and contains tightly supercoiled genome (chromosome). There is supercoiling (negative).

50
Q

What are supercoiled domains?

A

Domains that are required because supercoiling itself is not enough to make the chromosome small enough.

51
Q

Bacteria do not have histones to package their DNA, instead they have what?

A

Bacteria use “histone-like” DNA binding proteins to further compact DNA.
-Binds to DNA with no sequence specificity
-Wraps the DNA , causing it to bend
-Important for nucleoid structure and for regulation of expression of certain genes.

52
Q

What are plasmids?

A

Extrachromosomal DNA that replicate autonomously from chromosome.
Carry useful, but often dispensable genes that are likely necessary for the survival of the organisms in its natural niche.

53
Q

Bacterial cells do not have membrane enclosed compartments, but they do have ____________ membranes that have specialized functions.

A

Intracytoplasmic
-Often connected to cell membrane

54
Q

Examples of intracytoplasmic membranes.

A

Methanotrophs
-Grow on methane as their source of carbon and energy
-The enzymes for methane oxidation are present on intracytoplasmic membrane.
Nitrifying Bacteria
-Bacteria that oxidize ammonia or nitrite as a source of energy.
-Have intracellular membranes where the enzymes necessary for ammonia oxidation, or nitrite oxidation, are located
Photosynthetic bacteria (phototrophs)
-thylakoid membranes in cyanobacteria are highly folded and provide a lot of surface area within cells to harvest energy from sunlight.

55
Q

What are the specialized protein-enclosed compartments?

A

Gas vesicles, carboxysomes, magnetosomes (protein/lipid-enclosed compartment), and granules

56
Q

What are gas vesicles?

A

Specialized protein-enclosed compartment (not membrane-bound). Gas vesicle surrounded by a simple protein coat.
The gas vesicle is hollow and cylindrical.
It is filled with gas in equilibrium with the gases present in the cytoplasm, allows bacteria to maintain their position in the water column in order to maximize photosynthesis.
Cyanobacteria exhibit phototaxis (moving to or away the light) to maintain light environment.

57
Q

What are Carboxysomes?

A

Specialized protein-enclosed compartment (Not membrane bound).
The site of CO2 fixation (the Calvin cycle) in Cyanobacteria and other bacteria.
An icosahedral protein shell encloses enzymes (particularly RuBisCO (most abundant enzyme on the planet)) that are concentrated within the carboxysome structure.

58
Q

What are Magnetosomes?

A

Specialized protein/lipid-enclosed compartment (MEMBRANE BOUND!!!)
Chains of membrane-bound structures found in some aquatic bacteria. The membrane is complex and includes both lipids and proteins. Inside the magnetosomes are strings of iron oxide or other iron compounds.
The magnetosome functions as a navigational structure. It orients the bacteria with the Earth’s magnetic field so that the bacteria can swim in a certain direction …
“Magnetotaxis”

59
Q

What are Granules?

A

Specialized protein-enclosed compartment (Not membrane bound)
Granules exist in different bacteria and can serve as nutrient storage structures, which have a protein coating.
Two examples:
1) A lipid-like compound called Polyhydroxybutyrate
2) Sulfur-oxidizing bacteria

Microbial Physiology (22 decks)

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