Topic 4 - Prokaryotic Cell Morphology Flashcards
Two componenets to peptidoglycan structure
- Two alternating sugars (N-acetylglucosamine (nag) and N-acetylmuramic acid
- Alternating D and L amino acids
Has a meshlike polymer of identical subunits forming long strands
Peptidoglycan structure
Shape that peptidoglycan has
Helical shape
Peptidoglycan chains are crosslinked by what?
Covelent bonds between the tetrapeptides for strength
Crosslinks are directly between amino acids in the tetrapeptide
Gram negative bacteria
There is often an interbridge of additional amino acids between tetrapeptides
Gram positive bacteria
Peptidyoglycan is only found where?
Bacteria
What happens when peptidoglycan chains are crosslinked by peptides for strength
- Interbridges may form
- Peptidoglycan sacs - interconnected networks
- Various structures occur
Gram positive cells walls are primarily composed of what?
90% of peptidoglycan
What is the second component to cell walls in gram positive cell walls
Teichoic acids (negative charged)
What is the importance of teichoic acids?
- Help maintain cell envelop
- May bind to host cells
- May store PO4; may attract cations
Some gram positive bacteria have layers of what on where?
Proteins on surface peptidoglycan
Last component to gram positive cell walls that attaches wall to membrane
Lipteichoic
Lies between plasma membrane and cell wall and is smaller than that of gram-negative bacteria
Periplasmic space of gram positive bacteria
The periplasmic space of Gram + bacterias has very few what?
Proteins
Enzymes secreted by gram positive bacteria are called _____
Exoenzymes
Aid in degradation of large nutrients
Exoenzymes
Four IMPORTANT characteristics of gram negative cell walls
- More complex than Gram positive
- Consist of a thin layer of peptidoglycan surrounded by an outer membrane
- Outer membrane composed of phospholipids, lipoproteins, and lipopolysaccharide
- No teichoic acids
Peptidoglycan is ______ of cell wall height and in the _____
- 5-10%
- Periplasmic space
How is the periplasmic space different than that of gram positive cells?
- May constitute 20-4-% of cell volume
- Many enzymes present in periplasm
The enzymes that is in the periplasmic space in gram negative cell walls
Hydrolytic enzymes
Transport proteins
Others
In the gram negative cell walls, what is the structure and where do the different components attach?
- Outer membrane lies outside the thin peptidoglycan layer
- Braun’s lipoproteins connect outer membrane to peptidoglycan
- Other adgesion sites reported
What are the three components to Lipopolysaccharide (LPS)
- Lipid A (endotoxin)
- Core polysaccharide
- O side chain (O antigen)
Lipid A is embedded where in the LPS
Outer membrane
Where do the core polysaccharides and O side chains exist on the LPS?
Out from the cell
Six reasons why LPS is important
- Contributes to negative charge on cell surface
- Helps stabilize outer membrane structure
- May contribute to attachment to surfaces and biofilm formation
- Creates a permeability barrier
- Protection from host defenses (O antigen)
- Can act as an endotoxin (lipid A)
What is special about the gram negative outer membrane permability?
- It is more permeable than plasma membrane due to presence of porin proteins and transporter proteins
What do porin proteins do?
Form channels to let small molecules (600-700 daltons) pass
Why does the gram stain reaction happen?
Due to nature of cell wall
What happens in the reaction of gram stains?
- Shrinkage of the pores of peptidoglycan layer of gram positive cells
- Constriction prevents loss of crystal violet during decolorization step
- Thinner peptidoglycan layer and larger pores of gram negative bacteria does not prevent loss of crystal violet
Structures exterior to the cecll wall
- Glycocalyx (Capsule and slime layer)
2. S layer
Polysaccharide rich (glucose or modified glucose subunits) material exterior to cell wall; sometimes has protein component
Glycocalyx
Dense; tightly attached; regular arrangement of polysaccharides; visible to light microscope
Capsule
Diffuse; loosely attached; irregular arrangement of polysaccharides
Slime layer
Functions of the slime layer
Attachment to solid surfaces, anti-dessicant, reserve source of energy, anti-phagocytic for some pathogens, prevents virus attachment
What does the slim layer aid in?
Mobility
Regularly structured layers of protein or glycoprotein that self-assemble
S layer
Where does the S layer go in gram positive and negative bacterias
- Gram negative = adheres to the outer membrane
2. Gram positive = Associated with the peptidoglycan surface
S layer functions
- Protect from ion and pH fluctuations, osmotic stress, enzymes, and predation
- Maintains shape and rigidity
- Promotes adhesion to surfaces
- Protects from host defenses
- Potential use in nanotechnology
What happens to the S layer in nanotechnology?
S layer spontaneously associates
How do prokaryotes differ from eukaryotes?
- Most prokaryotes are smaller than eukaryotes
- Most lack an internal membrane system
- Prokaryotes do not have an internal phospholipid bilayer membranes