EXAM 3: Chapter 2- Part 2 Flashcards
passive diffusion
Not energy dependent
Molecules move from higher concentration to lower
rate of diffusion depends on concentration gradient
Can be reversible depending on gradient
Examples of molecules that move across membrane by passive diffusion
H2O
O2
CO2
Facilitated diffusion
uses carrier proteins
used for larger and charges molecules
is reversible
gradient can be maintained by transforming the nutrient
happens primarily in Eukaryotes
How is facilitated SIMILAR to passive
movement is not energy dependent
direction of movement is from high to low
size of gradient impacts rate of uptake
How is facilitated DIFFERENT from passive
uses membrane-bound solute-specific carrier molecules
smaller concentration gradient is required for significant uptake (saturation effect)
effectively transports glycerol, sugars, and amino acids
Why is facilitated more prominent in Eukarya?
bacteria and archaea are typically found in nutrient-poor environments
they are mostly using active-transport
Saturation effect
diffusion rate reaches a plateau at higher concentration
the carrier/transporters will become saturated (full)
Example of gradient being maintained by transformation
GLUCOSE
phosphorylate glucose once it enters the cell
glucose will stay high outside because it is not in that form on inside
How does facilitated diffusion works
Carrier protein starts in outward-facing conformation
solute binds
binding causes conformation change- closes to outside and opens to inside
carrier protein is now in inward-facing conformation
releases solutes into the cell
Active transport
energy dependent process
move molecules against gradient
concentrated molecules into cell
involves specific carrier proteins
3 types of active transport
Primary active transport
Secondary active transport
Group translocation
Primary active transport
uses energy produced by ATP hydrolysis to move substances across concentration gradient
ABC transporters
Secondary active transport
couples the potential energy of ion gradients to transport solutes
uses potential energy in ion gradients and turns it into kinetic energy MFS transport
ABC transporters
ATP-Binding Cassette transporters
structure and function is highly conserved across bacteria, archaea, and eukaryotes
Uniport
what does ABC consist of
2 hydropobic membrane spanning transport proteins
2 cytoplasmic ATP binding domains
Uniport
transport 1 molecule at a time
How does ABC work?
Solute binds to solute binding protein
complex interacts with hydrophobic channel subunits
channel undergoes conformational change
ATP hydrolysis in ATP binding subunits provides energy
The channel opens and the solute moves into the cytoplasm
MFS transporters
Major Facilitator Superfamily
uses ion gradients to cotransport substances
Proton moves down its gradient so solute can move againts its gradient
symport and antiport
Symport
two substances both moving in same direction
antiport
two substances moving in opposite directions
symport example
E. coli- transport of lactose using lactose permease
transports lactose and proton simultaneously into cell
antiport example
E. coli- transport of sugars and amino acids
sugars and amino acids into the cell while pumping sodium out
PTS- group translocation
Phosphotransferase system
PEP + sugar (outside)–> pyruvate + sugar-phosphate (inside)
- PEP is high energy bond- when hydrolyzed it gives energy to system
- sugar is modified inside the cell
Also invovled in chemotaxis
Where is PTS found
faculative anaerobes
some obligate anaerobes
Why is PEP not found in aerobes
Uses PEP for respiration
they do not have alternative ways to generate PEP so they do not want to use it elsewhere
How does PEP work
Want to phosphorylate solute so it makes it imposible for it to move back out of cell
E1 is conserved in all PTS organisms
- acts as an intermediate to pass off phosphate from PEP
Phosphate is transferred to incoming sugar by E2
E2 portion gives specificity
- number and arrangement of subunit determens the carb that moves in
Siderophores
molecules with high affinity for ferric iron
Why do microorganisms secrete siderophores
Ferric iron is very insolube so uptake is difficult
siderophores are secreted to aid in uptake
T/F siderophores are secreted all the time
FALSE
only secreted when stores are low
Examples of siderophores
ferrichrome
enterobactin
what happens once siderophores bind iron
whole complex is moved to primary active transport
just iron may be released
How does PM capture energy
embedded electron transport chains help create Proton Motive Force (PMF)
What is PMF used for?
respiration and photosynthesis
derive energy for motion (flagella)
PM and sensory systems
proteins in PM can detect environmental changes
cell uses detected changes to alter gene expresion
maybe bound to integral/peripheral membrane systems
T/F moving materials out of cell requires ATP energy
true
2 ways to move across plasma membrane
Sec system
TAT (twin argine transport)
Sec system
requires energy
Protein has signal at end terminal and SecB binds to protein
SecB keeps protein from folding and brings it to SecYEG complex
SecYEG forms the channel
SecA hydrolyzes ATP
Protein is moved out
signal protein at the end is cleaved and protein folds
TAT
energy comes from potential energy in ion stores
transports folded proteins
Proteins have a 2 arginine end sequence
Which Gram bacteria has an easier time moving things out of cell?
Gram-positive
Gram-negative secretion
either one step or two step
one step Gram-negative secretion
Doesnt use TAT or Sec
moves protein all the way across the PM then the outer membrane
Types 1 and 3
Two step Gram-Stain secretion
Pick up proteins from Sec/TAT then moves them the rest of the way
Types 2,4 and 5
Functions of cell wall
Maintains shape of bacterium
helps protect from osmotic lysis
helps protect from toxic material
may contribute to pathogenicity
How does cell wall help maintain shape?
organization of peptidoglycan in juction with other things
How does cell wall contribute to pathogenicity
Specifically in Gram-negative pathogenic area within the cell
Peptidoglycan has PAMPs
What are PAMPs?
pathogen-associated molecular pathways
Peptidoglycan structure of cell wall
mesh-like polymer of identical subunits forming long strands
Two alternating sugar
Penta/tetra peptide side chains of D and L amino acids
2 D-ala bonds which are important for cross linking
What are the two alternating sugars in peptidoglycan
N-acetylgulcosamine (NAG)
N-acetylmuramic acid (NAM)
Penta/tetra peptide side chains
ALWAYS attached to NAM
initially penta but after crossing they become tetra
Gram-Negative cross linking
Direct peptide cross link
position at 2 and 3
Gram-positive cross link
indirect cross-link
forms a pentaglycine interbridge
How do D-form of amino acids form?
Only L-from is naturally encoded
Racernaces break bonds in L form to create D-from
Why are D-forms created
Helps protect cell wall against proteases/peptidases
How is peptidoglycan structure of cell wall made?
NAM is synthesized in cytoplasm
NAM is linked to Bactoprenol and NAG is added to NAM
Bacteroprenol flips NAM-NAG into periplasm
disaccharides added to existing chain and cross-linking occurs due to transpeptidase
Bactoprenol flips back into cytoplasm
What is bactoprenol?
a flipase
Effect of lysozyme secretions on cell wall
Targets the b, 1-4 glycosidic bonds and cleaves it leaving the peptidoglycan weak
the cell can then lysis if osmotic gradient changes
Where do lysozyme secretions come from?
naturally secreted in our mucus, tears, sweat, etc.
Effect of lysostaphin
targets and cleaves inter-bridges in certain staphylococcus species only
what is b-lactam
antibiotic
natural product produced by other bacterial
How do b-lactam antibiotics work?
their structure resembles the 2 D-ala
transpeptidase can’t distinguish and binds to b-lactam structure
Forms an irreversible linkage and cross-linking cannot occur
How do bacteria develop b-lactam resistance?
Efflux pumps
mutations in pore proteins- make pores too small so antibiotics cant move in
Beta lactamases
Where are pore proteins located?
outer membrane of Gram-negative bacteria
What do b-lactamases do
High a high affinity for N and O bond in the peptidoglycan backbone
no longer looks like D-ala and transpeptidase will not bind to it
Peptidoglycan is both…
rigid- comes form b-glycosidic bonds (in backbone)
flexible- comes from cross linkages
Two types based on Gram-stain
Gram positive- thick layer of peptidoglycan
Gram-negative
Peptidoglycan structure
lies just outside cell membrane
it is porous
forms helical strands
has a backbone of two alternating sugars connected by b, 1-4 glycosidic bonds
How does penicillin work?
B-lactam antibiotic
How does augmentin work?
works together with amoxicillin
Has clavulanic acid-beta lactam rings but no antibiotic activity
It reacts with b-lactamase so they target it and leave amoxicillin alone
How vacomycin works?
non b-lactam
cell wall inhibitor
sits on 2 D-ala and binds them together
transpeptidase cannot recognize and crosslink will not happen
Example for another antibiotic
One that targets siderophores
Why would you want an antibiotic that targets siderophores?
siderophores are not found in eukaryotic cells
bacteria need iron to live
