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MBIO 1010 > Bacteria and Archaea Cell Walls > Flashcards

Bacteria and Archaea Cell Walls Flashcards

Lecture 5-15

1
Q

What are the characteristic(s) of a cell wall?

A 
Outside the cell membrane 
Rigid 
-Helps determine cell shape
-made of polysaccharides 
Not a major permeability barrier
Porous to most small molecules
Protects the cell from osmotic changes
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2
Q

What are the function(s) of the cell wall?

A 
Cell wall prevents cell expansion 
-protects against osmotic lysis  
Protects against toxic substances 
-large hydrophobic molecules  
--ex) detergents, antibiotics 
Pathogenicity 
-Helps evade host immune system 
-Helps bacterium stick to surfaces  
Partly responsible for cell shape
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3
Q

What does peptidoglycan do when it comes to classifying bacteria?

A 
It splits them into two groups: 
Gram Positive 
-has peptidoglycan
Gram Negative
-has little to no peptidoglycan
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4
Q

Gram+ bacteria have one layer of peptidoglycan. Gram negative have two layers, one of peptidoglycan and an ___ layer.

A

LPS layer

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5
Q

What is the function of peptidoglycan?

A

To provide a rigid layer that provides strength to the cell wall.

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6
Q

What is peptidoglycan (or glycan tetrapeptide) made of?

A 
It is a polysaccharide that is composed of:
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
Amino Acids 
-Lysine
Diaminopimelic acid (DAP)
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7
Q

True or False: Peptidoglycan is cross-linked the same in both gram+ and gram- bacteria.

A

False: Peptidoglycan is cross-linked differently in both gram+ and gram- bacteria.

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8
Q

How many different peptidoglycan structures have been identified, and how do they vary?

A

More than 100 different structures have been identified, with variation in their cross-links and/or interbridges.

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9
Q

True or False: In the peptidoglycan of gram- bacteria, no interbridge is present.

A

True

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10
Q

In Staphylococcus aureus (gram positive), what is their interbridges made up of?

A

5 glycine residues.

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11
Q

True or False: Gram+ cell walls contain up to 50% peptidoglycan.

A

False: Gram+ cell walls contain up to 90% peptidoglycan.

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12
Q

In Gram+ cell walls it is common to have what acidic substance embedded in the cell wall? What is it?

A

Teichoic acids- an acidic polymer containing residues of the phosphates of glycerol and adonitol.

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13
Q

What is Lipoteichoic acid?

A

Teichoic acids covalently bound to membrane lipids.

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14
Q

In the backbone of peptidoglycan, what bonds are the NAM and NAG connected by?

A

Glycosidic bonds

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15
Q

In peptidoglycan what are the cross-links formed by?

A

Peptides

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16
Q

What about the peptidoglycan stand shape allows 3-dimensional cross-linking?

A

The fact that the strand is a helical shape.

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17
Q

What are two different prokaryotes that lack cell walls? Give a description of both.

A

Mycoplasmas:
-Group of pathogenic bacteria
-Have sterols in cytoplasmic membrane -> adds strength and rigidity to membrane
Thermoplasma
Species of Archaea
Contain lipoglycans in membrane that have strengthening effect

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18
Q

Which kind of cell wall contains a LPS out membrane, also known as the lipopolysaccharide layer?

A

Gram- bacteria

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19
Q

True or False: In gram- bacteria the cell wall is about 10% peptidoglycan.

A

True

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20
Q

What does the LPS layer consist of? What does it replace in the outer-half of the outer membrane?

A

The LPS layer consists of core polysaccharides and O-polysaccharides. The LPS replaces most of the phospholipids in the outer-half of the outer membrane.

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21
Q

What is the toxic component of the LPS layer?

A

Endotoxin (Lipid A)

22
Q

What is the space between the plasma and outer membrane in gram- bacteria? What are its characteristics?

A

The periplasm layer- a 15 nm wide layer with a gel-like consistency that houses many proteins.

23
Q

What is the name of the channels used for movement of hydrophilic low-molecular-weight substances?

A

Porins

24
Q

True or False: Crystal violet (or CV-I complex) is a soluble stain that forms in the cell during a gram stain.

A

False: Crystal violet (or CV-I complex) is an insoluble stain.

25
Q

What is used to extract the CV-I complex from the bacteria? Which cell wall is the CV-I complex extracted from?

A

Alcohol (or ethanol) is used to extract the complex. It is extracted from gram- cell walls, but not gram+ cell walls.

26
Q

We know that crystal violet stains the gram+ cell wall during a gram stain. How does the thick layer of peptidoglycan in the gram+ bacteria contribute to this?

A

The thick layer of peptidoglycan becomes dehydrated during the addition of alcohol, making the porins close and therefore trapping the crystal violet in the cell wall.

27
Q

In gram- bacteria, the alcohol penetrates the outer membrane, and the crystal violet is extracted from the cell. The gram- bacteria then appears invisible until the addition of what stain?

A

Safarin

28
Q

True or False: Like some bacteria, archaeal cell walls also include peptidoglycan and an outer membrane.

A

False: Archaeal cell walls contain no peptidoglycan and no outer membrane.

29
Q

What do archaeal cell walls contain instead of peptidoglycan? What does it consist of?

A

Archaeal cell walls contain pseudomurein. It is a polysaccharide similar to peptidoglycan that consists of:
N-acetylglucosamine
N-acetyltalosaminuronic acid

30
Q

What is an example of an archaea that contains pseudomurein? Do all archaeal cell walls contain pseudomurein?

A

An example would be certain methanogenic archaea. Not all archaea cell walls contain pseudomurein.

31
Q

What is the most common cell wall type among archaea? What does it consist of?

A

The S-layer cell wall type- it consists of protein or glycoprotein.

32
Q

What kind of structure does an archaeal S-layer have?

A

It has a paracrystalline structure for strength and protection.

33
Q

True or False: All archaea have an S-layer and other additional cell wall components.

A

False: Some archaea have only a S-layer, but most have additional cell wall compenents.

34
Q

Because of their lack of peptidoglycan, what are archaea resistant to?

A

Penicillin and lysozyme.

35
Q

Most archaea contain some type of cell wall- what is its function?

A

To prevent osmotic lysis and provide cell structure.

36
Q

What is cytoplasm? What does it contain?

A

Material bound by the plasma membrane that contains ribosomes and other organelles.

37
Q

What is protoplast? What does it contain?

A

The plasma membrane and everything within. It contains:
Macromolecules – amino acids, nucleotides, etc Soluble proteins
DNA and RNA (nucleoid)

38
Q

What kind of cells have protoplast?

A

Living plant or bacterial cell whose cell wall has been removed.

39
Q

Proteins have many functions- what are some examples?

A

Enzymes – Catalyze chemical reactions

Transport proteins – Move other molecules across membranes

40
Q

Polypeptides make up what?

A

Proteins

41
Q

What is the function of structural proteins?

A

To help determine the shape of the cell and assist in cell division.

42
Q

What is the definition of a polypeptide?

A

A long polymer of amino acids joined by peptide bonds.

43
Q

What region contains the genome in a cell?

A

The nucleoid

44
Q

What are the characteristics of a typical bacterial genome?

A

Single circular double stranded (ds) DNA chromosome May have one or more plasmids

  • Smaller circular dsDNA
  • Self-replicating
  • Carry non-essential genes
  • Selective advantage
  • Ex) Genes for antibiotic resistance `
45
Q

What carries genetic info of all living cells and is a polymer of deoxyribonucleotide?

A

DNA

46
Q

Where is the site of protein synthesis?

A

The ribosome

47
Q

What kind of ribosome do bacteria have? What are the two parts that make this ribosome?

A 
Bacteria contain 70S ribosomes. They contain: 
30S subunit (Small subunit) 
-Protein 
-16S rRNA 
50S subunit (large subunit)
-Protein 
-23S and 5S rRNA
48
Q

Why is the 70S ribosome made up of two parts?

A

The reason there are two part is because the 30S subunit (the smaller one) binds to the larger subunit with the mRNA pattern, and the 50S subunit (the larger one) binds to the smaller subunit and the tRNA pattern.

49
Q

True or False: cytoplasmic ribosomes, which make cytoplasmic proteins, float free.

A

True

50
Q

True or False: plasma membrane associated ribosomes, which make membrane proteins which can be exported from the cell, float free.

A

False: Plasma membrane ribosomes attaches itself to the plasma membrane, and tags itself for a protein.

MBIO 1010 (14 decks)

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