Cell envelopes

Question 1

What is the envolope and cytoskeleton

Answer 1

• most species of bateria and achea have a cell wall (structural support) and a cell envelope containing at least one structural supporting layer
• The cell envelope = call wall + any associated layers
• few prokaryotes such as mycoplasmas (mollictures) have a cell membrane with no outer layers (no envelope either)
• cytoskeleton = complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including bacteria and archaea. It extends from the cell nucleus to the cell membrane

Question 2

what is the gram stain based off of

Answer 2

• composition and structure of cell walls
• there are bacteria that do not stain with gram stain
• peptidoglycan is typically what peoplea re talking about when thtey say cell wall

Question 3

Morphological diversity in bacterial cells: What are tenericutes / Mollicutes

Answer 3

• have DNA genome / nucleoid, ribosomes, cytoplasm and cytoplasmic membrane
• do NOT have: cell wall, exist as polymorphic blobs

* known as naked or soft skin bacteria

* the mollicute Cytoplasmic Membrane is strengthened by addition of unique lipoproteins, glycolipids and glycoproteins

ex: genus Mycoplasma, Mycoplasma pneumoniae, and M. genitalium

Question 4

pros and cons of mollicute

Answer 4

Pros:

• Small, compact & can squeeze through small spaces
• Does not require a lot of energy to survive
• Opted for metabolic& structural simplicity
• Small size genomes
• Are among the smallest of bacteria

Cons:

• Difficult to maintain an independent lifestyle – are often parasites of eukaryote cells (nutrients, ‘protection’)
• nutreints and protections from other cells, too simple to sustain themselves
• Fastidious in culture –need very special media to sustain
• Amorphous in shape; Shape-less blobs!

Question 5

Cell walls on bacteria

Answer 5

• composed of peptidoglycan/murein: Polymer of 2 sugars (N-acetyl glucosamine (G/NAG) and N-acetyl-muramic acid (M/NAM)) and amino acids (attached to NAM)

*memorize the sugar names

• forms a rigid porous sac (murein succulus) surrounding the cytoplasmic membrane
• protective, confers shape and helps to withstand turgor pressure (osmotic pressure arising from cytoplasm and against the CM)

Question 6

what contains the peptido glycan layer

Answer 6

• gram positive and grma negative
• achaea do not have this type of peptidoglycan, they have a pseudopeptidoglycan layer
• the sugars that form it are different but in terms of function and structure it is the same

Question 7

How is peptifoglycan unqiue to bacteria

Answer 7

• enzymes responsible for the biosynthesis of peptidoglycan are excellent targets for antibiotics
• ex: penicillin inhibits transpeptidase that crosslinks the peptides (link the glycan NAM-NAG chains)
• Vancomycin prevents cross rbidge formation by binding to terminal amino acids (D-ala-D-ala dipeptide)
• PG is a virulence factor - fragments of PG induce fever and inflamation during infection
• lysozime: enzyme in mucus secretion, tears and saliva that diests the bond between the sugars, breaks up the glycan chain. its part of out immune system

Question 8

describe the basic gram positive cell

Answer 8

components: Nucleoid (DNA), ribosomes, cytoplasm, cytoplasmic/plasma membrane, thick! (multiple layers) 20-80nm cell wall of peptidoglycan

Question 9

what is streptococcus aureus

Answer 9

• gram positive cell, cocci shape

Question 10

pros and cons of gram-psotive cell wall

Answer 10

Pros: strong, thick murein succulus, lipoteichoic acids and teichoic acids thread through it adding strength, protect against osmotic lysis, impart shpae to cell

*lipoteichoic acids and teichoic acids: long polysccaride chains unique to gram positive, extend away from surface of cell

Cons: must be protected from Lysozyme (will digest bond between 2 sugars on glycan)

Question 11

examples of cell shapes of gram positive bacteris

Answer 11

• Bacillus cereus: rad/bacillus shape
• Staphylococcus aurenus: round cells that form clusters
• Steptococcus pyogenes: round cells that form chains

*ake sure you know names to give examples of gram pos bacteria

Question 12

what are mycobacteria

Answer 12

• taxonomically classified as gram positive but diff cell walls
• strain gram variable bc of structure of cell wall
• stain them suing ziehl-Nielsen acid fast stain
• Mycobacteria have very complex, thick and hydrophobic cell envelopes
• thich peptidoglycan, thick arabinogalactan layer, outer membrane contains unusual membrane lipids, mycolic acids, and thick capsule of lipids and glycolipids
• very thick cell wall

*bolded ones rae components unique to mycobacerial, memorize those

Question 13

what components are unqiue to the mycobacterial cell wall

Answer 13

-Thick Arabinogalactan* layer and mycolic acids

Question 14

what are mycobacteria resistant to?

Answer 14

• highly resistant to environmental stress
• dryness, osmitic stress, detergents, most antiseptics, most antibiotics (especially hydrophilic ones), phagocytosis by host efence cells, killing by host immune defenses
  cons: must grow slowly, cell envelope is expensive to synthesize and maintian (takes a lot of nutrients and energy to make that intense cell wall)
  ex: M. tuberculosis

Question 15

desribe the basic gram negative cell

Answer 15

• contains: Nucleoid (DNA), ribosomes, cytoplasm, cytoplasmic/plasma membrane,
• THIN (1-3 sheets) of peptidoglycan, outer membrane (contains Lipopolysaccharides LPS), well defined periplasm

*periplasm = compartment between the CM and outer membrane, contains the thin PG

• periplasmic compartment contains lots of proteins

Question 16

describe the gram-negative cell envelope-

Answer 16

• in addition to the thin peptidoglycan there is a periplasmic component and an outer membrane (bilayer, inside has phospholipids and outer is lipopolysaccharides)
• cell envelope is the outer membrane, its a lipid bilayer (unlike the sytoplasmic membrane)
• the outer leaflet has the G-bacteria unique Lipopolysaccharide

Question 17

what is LPS

Answer 17

• lipopolysaccharide
• unique to gram negative
• all gram neg bacteria have an outer membrane and LPS which is a complex glycolipid with 3 distinct parts/regions
  1. Lipid A endotoxoin, anchors LPS to the outer membrane - toxic when released from lysed cells into tissues/bloodstream (induces a cytokine storm)
  2. Core polysachharide
  3. O-antigen containing repreating units (2-5 sugars joined to eachother) - antibodies made against this unit, diff bacteria will have diff o-antigens so you can use to differentiate *used for serological typing of gram-neg bacteria

Question 18

pros and cons to gram negative cell

Answer 18

Pro

• puter membrane is an excellent selective permeability barrier - able to defend against wide range of toxic molecules
  
  • lipid bilayer so same function as cytoplasmic mebrane but also has proteins for selective transport
• has a built in storage compartment (periplasm) - protects the PG, used for storage, scanenging enzymes, nutrient bidning proteins and detox proteins
• protects against osmotic lysis
• various shapes
• stains prinkish-redish with gram stain

Cons

• toxic if not handled correctly (lipid A component of LPS is an endotoxin
• energetically expensive to build and maintain - usually have larger genomes (need genes for periplasm and OM comp)

Question 19

examples of gram negative bacteria

Answer 19

• escherichia coli: rod shpaed

- Neisseria gonorrhoeae: coccoid-shaped

- Helicobacter pylori and Treponema pallidum (syphilis): helical/spiral shaped

Question 20

bescribe the cytoskeleton of bacteria

Answer 20

• much simpler than that of eukaryotes
• discovered by looking at gene mutations: exp found that gene mutations caused changes in cell shape (bacillus rod to occi, the genes effected were fro proteins that were similar to those in eukaryotes that code for cytoskeleton)

Question 21

what are the different shape determining cytoskeleton patterns?

Answer 21

• FysZ: forms a Z-ring in spherical cells - function: maintains cell diameter
• MreB: forms a coil inside rod-shaped cells - function: MreB together with FtsZ are required for cell shape, growth and division
• CreS crescentin: forms a polymer along the inner side of crescent-shaped bacteria - cell shpae determining (only relevant for bac with crescent shape

Question 22

what is the Surface layer

Answer 22

• an additive external-most protective layer - (someitmes called bacterial exoskeleton/chainmail) 5-25nm thick
• Crystalline layer of thick subunits, protein or glycoprotein
• highly ordered/crystalline - can flex and has pores to allow movement of molecules, protects against osmotic stress, predation

Question 23

applications for S-layer in biotochnology

Answer 23

• biomaterials of the future
• can act as a scaffold or template building inorganic nanocrystal super lattices for molecular electrons
• subunits for self assembly: can act as a scaffold for building synthetic plasma membranes for all kidna of applications

Question 24

what are capsules

Answer 24

• added extra to cell
• sometiems called slime later: available for both G+ and G- models
• consist of a slippery coat of polysaccharides loosely bound to the cell envelope, protective layer

*bind water to form a hydration layer

• difficult to stain so appear as halos around cells
• may exist with S-layers: if so they are found external to the S-layer

functions: protection against immune system (resist phagocytosis, antibodies bound can easily be shed with the capsule), adherence, nutrient reserve and protects from dehydration

ex: Streptococcus and Rhizobium trifolii

Question 25

what are nanotubes

Answer 25

- specialized structure - hollow and extention of cytoplasmic membrane, share nutrients, excahnge genetic material between cells - some bacteria and archaea can form membrane extensions that merge directly with the membranes of neighboring organisms - these nanotubes allow bacteria to directly shpae proteins and mRNA useful under hostile conditions, such as when exposed to anti-biotics

Question 26

what are storage granules

Answer 26

- during optimal conditions bacteria can store excess energy in form of storage granules - are consumed later as needed when nutrient availability is low - usually contain stored glycogen and polyhydroxybutyrate (PHB) - some baccteria store sulfer granules in cytoplasm or outside as vesicles on membranes (found in some sulfer oxidizing bacteria, use sulfur as an electron source)

Question 27

what are thylakoids and carboxysomes

Answer 27

- specialized strucutres **Thylakoids** * only found in gram NEG phototrophs * specialist systems of extensively folded lamellae (sheets) of cytoplasmic membranes * packed with photosynthetic pigments, proteins and electron carriers * maximize photosyntheic capability of the cell (help to cov light to chem energy) * infolding of cytoplasmic membrane, continuous with it **Carboxysomes:** in ALL cyanobacteria and some gram negative AUTOTROPHS (bacteria that fix CO2) * polyhedral shaped bodies packed with the enzyme Rubisco for CO2 fixation

Question 28

what are gas vesicles

Answer 28

- found in **aquatic photosynthetic** bacterial cell variants - also found in some **aquatic heterotrophs** (bacteria that use preformed organic material to build organic matter?) - thin inflatable/deflatable structures lined with an extremely hydrophobic protein - allows the bacteria to square buoyancy to change position in the water

Question 29

what are pilli and fimbriae

Answer 29

- diff between the two mainly just how thick and long it is - sex pilli are long structures that transfer DNA, during conjugation/mating from donor to recipient - pilli can be targets for bacteriophage attachment and infection - pathogens often use pili/fimbriae to **attach/adhere** to host cells and initiate disease, these appendages are a great therapeutic/vaccine strategy to prevent infection \*they are assocaited and attached to cell wall

Question 30

what is rotary flagella

Answer 30

- prokaryotes that are motile gnerally swim by means of a rotary flagella (plural) vs flagellum - present as singular, multiple or in bundles - each flagellum is a RIGID spiral filament composed of protein monomers called Flagellin (present in both G+ and G- bacteria) - multiple flagella rotate together in a bundle like a propeller behind the swimming cell

Question 31

how do flagellum enable motility

Answer 31

- filament is rotated by a motor driven by the proton motor force - flagella work together with chemoreceptors in optimal directions using 'runs' and 'tumbles' - flagella only move in response to **Chemotaxis:** chemotactic motility, driven by sensing a chemical that the bacteria either uses or is toxic (moves towards or awar) \*moving in response to a signal - sensing is done my chemoreceptors

Question 32

Where on the cell is a monotrichous, lophotrichous, amphitricous and peritricheous flagella

Answer 32

monotrichous: only one lophotrichous: a bundle amphitrichous: one ither side Peritrichous: all over cell

Question 33

describe chemotaxis

Answer 33

- movement of a bacterium in response to chemical gradients - attractants cause CCW rotation: flagella bundle together and push cell fwds - repellents (or absence of attractant) case CW rotation: flagellar bundle falls apart, tumble (bacterium briefly stops then changes direction) \* CW or CCW is relative to body of the cell - OVERALL: appears as a 'random walk' alternating between the runs and tumbles - receptors detects attractant conc gradient (sugars, amino acids), movement towards conc gradient means concentration around it is increasing to the run os prolonged (biased random walk) \*causes a net movement of bacteria towards attractants or away from repellents

Question 34

what are Chemoreceptors

Answer 34

- bacteria dont have a brain they have a complex network of signal proteins within the cell - chemoreceptors receive signals and transmit them to the flagellar motor which moves using the proton gradient

Question 35

what is the murein succulus

Answer 35

- cell wall made of peptidoglycan and the NAM and NAG sufars forms a rigid porous sac (murein succulus) surrounding the cytoplasmic membrane