Cell Envolope Flashcards
What are aquaporins?
Protein channels for water
How do small nonpolar solutes pass through membrane?
simple diffusion
How do polar solutes and ions pass through membrane?
gated channels (facilitated diffusion)
How do large molecules pass through membrane?
large complex transporters
The inside of channels are lined with ______ groups
polar
Water flow results in ______ across the membrane
osmosis
What happens when you place a cell in a hypotonic environment?
Water moves into the cell (lysis)
What happens when you place a cell in a hypertonic environment?
Water moves out of the cell (plasmolysis)
How does cell prevent water from leaving?
Cell imports osmoprotectants,
What are a motive gradients a result of?
both a charge and concentration difference
What is proton motive force?
electrochemical gradient from protons being transported to the extracellular during electron transport system
What is another source of PMF?
bacteriorhodopsin (uses light energy)
What is H+ used for as it reenters the cell
a. to power flagella motor
b. to transport
c. to make ATP (ATP synthase)
Symport vs antiport
Symport: molecules head in the same direction
Antiport: one brought in while other brought out
Describe the cell wall of gram positive bacteria
thick peptidoglycan
Describe the cell wall of gram negative bacteria
thin peptidoglycan and a secondary membrane (outer membrane) called lipopolysaccharide (LPS)
Describe mycobacteria cell wall
thin peptidoglycan but thick layer of waxy mycolic acid
What bacteria don’t have cell walls?
Mycoplasma and spiroplasma
Describe archaea cells walls
they have cell walls. Some are made of protein, others pseudoPG, and others from chondroitin
What are the base units of peptidoglycan?
N-Acetylglucosamine (NAG)
N-Acetylmuramic acid (NAM)
Where are NAG and NAM synthesized?
cytoplasm
What are PBPs?
penicillin binding proteins, they synthesize peptidoglycan using NAG and NAM
What are the two classes of PBP?
Class A: does transglycocylation (links NAG and NAM horizontally)
Class B: does transpeptidase (crosslinks peptide chains on NAM together from different layers)
What bridge is unique to gram-positive?
pentaglycine bridge (joins peptide chains on NAM units)
What is the periplasm?
space between cytoplasm (inner) membrane and outer membrane
What two common antibiotics are used and what do they do?
Penecillin (prevents pentaglycine bridge)
Vancomycin (prevents transglycosylation)
What are the issue with antiobiotics?
only works when bacteria are actively growing and dividing
What else can be used to weaken bacteria cell walls?
lysozyme (hydrolyzes beta-1,4 bond)
What can be found in the cell wall of gram-positive bacteria?
teichoic acid (only in cell wall)
lipoteichoic acid (links cytoplasmic membrane and cell wall)
What can be found in the outer membrane of gram-negative bacteria?
porins (channels)
lipoprotein (has LPS)
Why do we care about LPS?
LPS is also known as endotoxin. When bacteria lyse, LPS is released, it is a potent stimulator of inflammation. So when giving antibiotics, you don’t want to give it all at once.
Describe the LPS structure
O antigen
Core polysaccharide
Disaccharide diphosphate
4 fatty acids
What does LPS do for transport?
It can surround materials, bud off, and transport to another bacteria
What does mycobacterium resemble more - gram (+) or (-)
gram negative because peptidoglycan is loosely organized
What is mycolic acid?
Long chain hydrocarbons that look like a wax (nonpolar) that are found in mycobacterium.
Pros and Cons of mycobacterium
Can prevent phagocytosis by white blood cells
Really slow to grow
Why do mycoplasma have no cell wall?
they are very small. also makes it unaffected by antibiotics
