Microbiology Lecture 3 (Part 3)

In prokaryotes, DNA is often packed in the center to form a dense mass called the:

nucleoid

In prokaryotes, DNA unpacks locally to make:

RNA

In prokaryotes, ribosomes attach to single mRNA molecules to make a:

polyribosome (coupling transcription and translation).

Prokaryotic cells have a ____ ________, which is seen in all cells universally. Similar to plant cells, prokaryotic cells have a ____ ____.

cell membrane; cell wall

Most bacteria are grouped as Gram-positive or Gram-negative depending on what?

the structure of their cell envelope

Gram-positive bacteria have a thick cell wall, composed of what?

peptidoglycan (murein), decorated with teichoic and lipoteichoic acids

Gram-negative bacteria have a thin cell wall and outer membrane. The outer leaflet of the outer membrane is composed of what?

lipopolysaccharide (LPS)

Bacteria are defined as Gram-positive or Gram-negative based on

the Gram stain

Before officially inventing the Gram stain, the inventor of the Gram stain was searching for a method that would:

allow visualization of cocci in tissue sections of lungs of those who had died of pneumonia

Gram's method used _______ ______ as the primary stain, an ______ solution as a mordant, followed by _______ as a decolorizer.

Crystal Violet; iodine; ethanol

What are the five functions of the cell wall?

1) provide structural support
2) maintain cell shape
3) protects against osmotic stress
4) filters out toxins
5) anchors molecules that change the chemistry of the cell's outer surface

The inner cell membrane of modern bacteria is a:

phospholipid bilayer

Phospholipids are amphipathic molecules, meaning that they have both hydrophilic and hydrophobic parts. What are the hydrophilic and hydrophobic part(s) of a phospholipid?

a polar (charged) glycerophosphate head, which is hydrophilic
two nonpolar fatty acid tails, which are hydrophobic

Fatty acid chains make the bacterial lipid bilayer:

flexible

Phospholipids act as a:

partial permeability barrier.

Proteins make up a large part of the cell membrane. What are four functions that proteins confer to the cell membrane?

1) respiration and photosynthesis
2) nutrient uptake
3) appendages
4) signaling

The bacterial cell wall protects the membrane's integrity against what three things?

1) detergents
2) host-derived amphipathic peptides
3) osmotic pressure

Peptidoglycan is a complex polymer of sugars with amino acid side chains. The glycan chains are made of alternating units of:

NAG and NAM.

NAG and NAM are connected by:

β(1, 4) glycosidic bonds

Amino acid side chains of different glycans are crosslinked to make:

a 3D network.

Gram-positive bacteria have a thick cell wall made up of peptidoglycan. This thick, polar barrier limits the passage of:

Hint: polar barrier

hydrophobic compounds.

What are the distinctive molecules that differentiate Gram-positive and Gram-negative bacteria?

lysine (L-Lys) in Gram-positive bacteria
DAP (diaminopimelic acid) in Gram negative bacteria

Gram-positive bacteria have how many lipid bilayers?

one

Gram-negative bacteria have how many lipid bilayers?

two

Gram-positive bacteria cell walls also contain techoic acids, which are linked to either:

peptidoglycan, or the cell membrane.

What are the two functions of techoic acids in Gram-positive bacteria?

1) give rigidity to the cell wall and change chemistry of its external face
2) promote adherence of bacteria to specific surfaces

What is a wall techoic acid (WTA)?

techoic acids that are covalently linked to peptidoglycan

What is a lipid techoic acid (LTA)?

techoic acids that are anchored to the cell membrane

Wall techoic acids (WTA) are covalently linked to a peptidoglycan via a linker

usually consisting of disaccharide and a glycerol phosphate unit.

Lipid techoic acids (LTA) are anchored to the cell membrane via a linker:

of glycolipid and a glycerol phosphate.

Gram-negative bacteria protect their cell (inner) membrane with a thin layer of:

peptidoglycan, and an outer membrane

The outer membrane of gram-negative bacteria is chemically distinct from all other biological membranes, and is especially resistant to:

harmful chemicals.

The lipopolysaccharide (LPS) outer leaflet consists of what three parts?

1) Lipid A
2) Core polysaccharide
3) O-antigen

What is Lipid A?

a short chain of fatty acids that is attached to a disaccharide

Is Lipid A amphipathic or amphiphilic?

amphipathic

The unusual structure of Lipid A is easily recognized by the immune system and induces:

toxic shock (which is why LPS is known as an endotoxin).

What are the two unusual sugars in a core polysaccharide?

1) keto-deoxyoctanoic acid
2) heptose

What are two characteristics of O-antigens?

1) variable and specific to organism
2) highly immunogenic

O-antigens have a long carbohydrate chain of how many sugars?

40

What is the function of O-antigens?

make polar barrier excluding hydrophobic compounds, useful for bile salts and antibiotic resistance.

The lipopolysaccharide (LPS) outer membrane (OM) reduces permeability, which causes what two things?

1) reduction of nutrient uptake
2) slow growth

The outer membrane (OM) of Gram-negative bacteria are decorated with protein channels called:

porins

Porins permit diffusion of what kinds of compounds? What are three examples of them?

hydrophilic; sugars, amino acids, ions

How do porins allow hydrophilic compounds through the lipopolysaccharide (LPS) outer membrane (OM)?

The pores are large enough to permit the entry of molecules (even molecules as large as trisaccharides!).

Special transporters are needed to transport larger compounds, such as:

vitamins, larger polysaccharides, and metals.

What is one major reason why it is important to understand differences in bacterial cell structure?

To know how best to kill them or inhibit them when they cause infection!

What are antibiotics?

the molecules we use to fight bacterial infection

The susceptibility to many antibiotics can be predicted by knowing:

cell structure of the bacteria.

Which type of bacteria has a greater susceptibility to certain antibiotics: Gram-positive bacteria or Gram-negative bacteria?

Gram-positive bacteria

What is vancomycin?

a glycopeptide that can't pass through the outer membrane porins of Gram-negative bacteria, so it is only active against Gram-positive bacteria

What are polymixins?

antibiotics that specifically bind to lipopolysaccharides (LPS), so they are only active against Gram-negative bacteria

What is the aqueous space between the inner and outer membrane of Gram-negative bacteria (due to the architecture of its cell envelope)?

periplasm

Periplasm is the home of many essential processes, contains a peptidoglycan cell well, as well as what kind of enzymes?

degradative enzymes (break down molecules to pass across the inner membrane)

What two proteins are contained within periplasm?

1) proteins that form tight binds to nutrients
2) proteins that inactive antibiotics

Mycobacterium tuberculosis and its relatives developed another way to protect their cell membranes via:

acid-fast cell envelopes.

Cell walls contain large amounts of waxes called:

mycocolic acids.

What are mycolic acids?

long, branched, complexed fatty acids

The mycolic acid bilayer is thick and attached to the cell well via:

complex sugar layers.

The mycolic acid bilayer is impervious to harsh chemicals including:

harsh disinfectants and strong acids.

How does the waxy armor of mycolic acids affect nutrient uptake and growth rate?

It severely reduces both processes.