LecTop4: Bacterial Cell: Struct & Funct Flashcards Preview

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Flashcards in LecTop4: Bacterial Cell: Struct & Funct Deck (26)
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1
Q

What are the two major differences between Gram+ and Gram- cells?

  • Are Acid fast bacteria more similar to Gram+ or Gram- bacteria?
  • How are mycoplasma different?
A
  1. Gram- bacteria have an outer membrane
  2. Gram+ bacteria have a thicker peptidoglycan layer than Gram- bacteria
    - Acid-fast are more similar to Gram+ b/c no outer membrane (remember enclosing membrane is an artificial slide creation)
    - Mycoplasmas are smaller, lack a peptidoglycan cell wall, and can use exogenous sterols in their membrane (Remember: cause pneumonia and contaminate, ideally sterile env’ts).
2
Q

What are the three components of Peptidoglycan cells walls of bacteria? Briefly describe each.

A
  1. Glycan Backbones - Consists of Repeating disaccharide units of N-acetyl-glucosamine & -muramic acid linked by B(1-4) bonds.
  2. Tetrapeptide side chain - aa chains, consisting of four aas. The third aa must be able to form 3 peptide bonds and the aa in position four is always D-alanine
  3. Amino Acid Cross Bridge: Links tetrapeptide side chains, via peptide bonds between aas 3 & 4, on DIFFERENT glycan backbones.
3
Q

What is the 3-D shape of glycan backbones of the peptidoglycan?

A

They form rings circling the cell in all possible directions and planes. Think a random ball of yarn or rubber band ball.

4
Q

Which glycan backbone sugar, glucosamine or muramic acid, do the tetrapeptide side chains always connect to?

A

Muramic acid

5
Q

Cross bridges are formed between the #3 and 4 aas of the tetrapeptide side chains via peptide bonds, what type of bond is this? Ionic, covalent, etc…?

A

Peptide bonds are covalent bonds = strong

6
Q

What is special about D,L-diaminopimelic acid (DAP)?

A

It is the special amino acid ONLY found in position #3 in bacterial peptidoglycan tetrapeptide side chains.
-It has 2 amino groups (hence, ‘diamino-‘) AND 2 carboxyl groups allowing it to form 3 peptide bonds (normal aas can only form 2).

7
Q

What is the big difference in composition of Gram+ and Gram- bacterial peptidoglycan?

A
  • Gram+ peptidoglycan is cross-linked at every possible position (every tetrapeptide chain is crosslinked), creating a very rigid structure.
  • Gram- bacteria has far fewer cross links.
8
Q

What’s a descriptive analogy for peptidoglycan that explains its rigidity and porosity?

A

A chain link fence. Peptidoglycan is a stiff, porous structure, therefore it provides stability w/o necessarily providing much in the way of filtration.

9
Q

Why is peptidoglycan so important to bacteria?

A

Peptidoglycan cell walls allow bacteria to survive in variable turgor (osmotic) pressure conditions.

  • Won’t lyse in a hypotonic solution (cytolysis)
  • Won’t shrivel in a hypertonic solution (plasmolysis)
10
Q

What are three cell shapes that instill evolutionary advantages to the bacteria?

A
  • optimum motility = medium length rods
  • Helical shape = highly viscous environment
  • Very large, small or awkwardly shaped = avoid being eaten
11
Q

What determines bacterial shape?

A

Peptidoglycan cell wall determines cell shape.
Shape of wall determined by how deposited, this is determined by the intracellular matrix (tubulin and actin like protein fibers control this).

12
Q

What is the enzyme found in human secretions, including saliva, that specifically attacks bacterial peptidoglycan? Product?

A

Lysozyme. Cuts Glycan backbone at B(1-4) bonds resulting in a product of two cross-linked disaccharides.

13
Q

What are amphiphilic bacterial polymers?

A

They are usually amphiphilic polymers of glucose that are embedded in bacterial membranes. Often have antigenic properties.

14
Q

What is Lipoteichoic Acid (LTA)? Where is it found?

What are LTA’s two main parts?

A

LTA is an amphyiphilic bacterial polymer found in Gram+ bacteria.

  • It has a glycolipid (hydrophobic, membrane) portion and a Polyglycerophosphate (long, hydrophilic, ECM) portion
    • Note: Polyglycerophosphate portion extends through capsule/glycocalyx region.
15
Q

What is Lipopolysaccharide (LPS)? Where is it found? What are the 3 main parts? What is an alternative name for LPS?

A

LPS or Endotoxin is Amphiphilic bacterial polymer found in outer membrane of Gram- bacteria.

  • 3 parts
    1. Lipid A (toxic): Conserved membrane anchor
    2. Core Polysaccharide: Variable sugar composition
    3. O-antigen: O-polysaccharide, acts as antigen
16
Q

KDO is a sugar in linker-region b/t lipid A and core regions. What is its significance?

A

KDO is an easily cleaved sugar that was cleaved to isolate the lipid A portion of LPS.

  • Acid Labile Region
  • Allowed to isolate and determine that Lipid A is the region of LPS responsible for toxic effects.
17
Q

What purpose do Porins serve in the outer membrane of Gram- bacteria?

A

Because Gram- bacteria have two membranes it is difficult for them to get nutrients into the cell. The porins provide aqueous transport through the outer membrane for hydrophilic substrates.
-there is a size restriction, however, sugar polymers larger than pentosaccharides generally can’t pass through (ex glycogen).

18
Q

Why is the outer layer of gram- bacteria an assymetric bilayer?

A

Because Lipid A displaces most of the phospholipids on the outer membrane.

19
Q

What is mycolic acid?

A

Bacterial surface polymers on Acid-fast bacteria.

  • Causes acid-fast bacteria to have a waxy-like coating = the reason acid-fast bacteria can’t absorb normal dyes.
  • Inhibits absorption of water and water associated compounds. Leads to slow growth; important for development of disease (TB)
20
Q

What is a glycocalyx?
What bacteria express glycocalyx?
What evolutionary advantages does it instill?

A

Glycocalyx or capsule = Variably expressed, Carbohydrate polymers deposited on surface of bacterium (there are some protein types as well).

  • Certain species of both Gram+ and Gram- bacteria express capsules. Also dependent upon growth factors in env’t.
  • Capsules give bacteria antiphagocytic properties, may block lysozymes, and also may be ingested by bacteria in times of nutrient deficiency.
21
Q

What are flagella used for? What filament makes up the major structure?

A

Motility.

Axial Filaments

22
Q

What is the major function of Pili?

What’s another name for Pili?

A

Pili or Fimbriae are generally thought to be adherence appendeges. Also coaggregation, and conjugation (Sex pilus)
-Important in oral cavity

23
Q

Describe flagellum powered movement.

  • What are peritrichous flagella?
  • Describe the axial filaments of spirochetes.
A

Single flagella are rotated in one direction to cause straight forward movement or rotated in the opposite direction to cause scattered backwards movement (Related to chemotaxis!)

  • Peritrichous flagella are groups of flagella
  • The axial filaments of spirochetes attach at both polar ends of the spirochets and assist in the corkscrew type movement of spirochetes.
24
Q

What is E. Coli O157:H7?

A

It is a strain of E. coli that was implicated in contaminating certain meats and vegetables.
-It has the O-antigen 157 and the H-antigen 7

25
Q

We saw that LPS has the O-antigen. What bacterial structures house the H and K antigens?

A
  • H antigen is located on Pili (and flagella?) of Gram+ and Gram- bacteria
  • K antigen is located in the capsule of Gram- bacteria
26
Q

What is arabinogalactan?

A

It is a surface polymer in acid-fast bacteria that inhibits phagolysosomal comonents (similar to mycolic acid).