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Physiology of Microbes > Bacterial membranes, transport and secretion L5 > Flashcards

Bacterial membranes, transport and secretion L5 Flashcards

1
Q

what are the functions of the cell membrane

A

transport
energy production
interaction with environment

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2
Q

what is the transport function in cell membrane

A

controls what comes into and goes out of cell

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3
Q

what is the energy production function in cell membrane

A

bacteria have no intracellular organisms, no mitochondria, cell membrane involved in electron transport so all in cytoplasmic membrane

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4
Q

what is the interaction with environment functions of cell membrane

A
  • acts as a receptor
  • receives signals from both inside and outside the cell (e.g. MCP – chemotactic proteins)
  • lots of receptor molecules in membrane – transfer information throughout cell
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5
Q

what is the amphipathic character

A

Common feature of molecules that spontaneously associate to form a lipid bilayer is an amphipathic character

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6
Q

how are lipids amphipathic

A
  • hydrophilic region (polar or charged) that can interact with aqueous solvent
  • hydrophobic region (two acyl groups or planar multi-ring systems) that can segregate from aqueous solvent
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7
Q

what contains sterols in their membrane

A

eukaryotes and Mycoplasma (cell wall free bacteria) do

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8
Q

what are the membrane proteins

A

Peripheral membrane proteins

Integral membrane proteins

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9
Q

what are the peripheral membrane proteins

A
  • bound to bilayer surface
  • can extend from either surface
  • roles in anchoring, sensing, transport
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10
Q

what are the integral membrane proteins

A
  • amphipathic, if was all hydrophilic would forced out of membrane, wouldn’t be able to stay – need a specialized structure, integral membrane proteins must be amphipathic
  • roles in transport and synthesis
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11
Q

what is the name for all the proteins embedded in the membrane

A

fluid mosaic model

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12
Q

what is the cytoplasmic membrane barrier like

A

Gram-negative and Gram-positive bacteria:
Hydrophobic - good barrier to charged/hydrophilic molecules
Non-polar molecules pass through freely
Small uncharged polar molecules also pass though free

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13
Q

what generates NADH in electron transport

A

Energy from catabolism generates reduced NADH

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14
Q

where are electrons delivered to in electron transport

A

delivered to cytochromes

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15
Q

where are protons delivered to in electron transport

A

H+ pumped out of cell (into periplasm/pseudoperiplasm)

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16
Q

what is the effect of proton movement in electron transport

A

Generates a proton gradient across membrane since charge molecules cannot freely diffuse back into cell

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17
Q

what is catabolism

A

getting food molecules taken up by cell, fed into TCA cycle, energy generation from that, produce NADH

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18
Q

what happens when proton and electron fed into electron transport chain

A

H+ ions pumped out of cell, generates proton motive force as now have a gradient across membrane as charged molecules can’t get back in
some H+ ions can come back into cell through ATPsynthase, create ATP

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19
Q

where does electron transport occur in eukaryotes

A

mitochondria

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20
Q

where does electron transport occur in prokaryotes

A

e.g. bacterial cell this occurs in cytoplasm, in bacteria can be powered directly by H+ ions, don’t need ATP

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21
Q

what is the proton gradient used for

A

power other cellular processes

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22
Q

what is the gram-negative cells outer membrane barrier like compared to cytoplasmic membrane

A

unlike cytoplasmic membrane, outer membrane allows passage of some polar molecules to get to cytoplasm

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23
Q

what is the porins in the gram-negative outer membrane function

A

porins provide, water filled channels for the movement of small hydrophilic molecules

Other porins are highly specific with binding site for one or more molecules e.g. LamB binds maltose

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24
Q

what is a porin

A

porins are proteins, don’t allow passage of large molecules e.g. enzymes and other proteins

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25
what is homotrimeric
type of porin structure | three copies of same protein, forming a complex, each with a hole in middle
26
what is barrel structure like
type of porin structure | side view, is hydrophobic – all around outside interacts with lipids, keeps it buried in membrane
27
what is the structure like when all the loop bits are hydrophilic
interact with molecules that are being taken up or the water/cytoplasm phase in general
28
what are the porin structures
Homotrimeric Barrel structure All loop bits are hydrophilic
29
how do large polar molecules and ions pass through cytoplasmic membrane barrier
don't pass across cytoplasmic membrane freely; need specific transporters
30
how is the production of transport proteins regulated
in response to presence of substrates, can’t fill fluid membrane with every transport protein - only make transport proteins they need in response to the presence of those substrates
31
uniporter
one molecule moves in one direction (can also be outside to in) causes cell dissipation
32
symporter
two molecules move in one direction
33
antiporter
two molecules move in opposite direction
34
what is important in maintaining charge gradient across membrane
antiporter and symporter
35
how is maltose taken up in gram negative | what does this allow
Outer membrane porin protein | allows selective transport of maltose
36
what happens to maltose once taken up
In periplasm, need to get across inner membrane to be taken up by cell Sugar picked up by specific transport protein – MalE can bind to maltose, will pick it up and transport it across cell to outer face of inner membrane
37
how does maltose affect ATP in uptake
During process ATP used to bring in sugars that will generate more energy
38
how does maltose uptake affect proteins
Complex of proteins will form a particular transport complex – waiting to react with MalE, delivers sugar and get uptake into cell, so maltose inside
39
what occurs in group translocation
Transported compound is chemically modified during the transport process
40
what happens in glucose transport system
During uptake sugar becomes phosphorylated, also first step required for glucose (to be fed into TCA cycle and for energy generation) metabolism, so uptake is energetically ‘neutral’
41
what is involved the phosphotransferase system
5 proteins some of which are cytoplasmic others are membrane protein
42
what happens in glucose translocation
glucose is targeted to PTS Enzyme 1 gets phosphate from PEP PEP comes from TCA cycle Phosphate is then transferred to Glucose via HPr and EII HPr = Histidine Protein/Heat stable protein Enzyme Complex 2 = 2 proteins (EIIA and EIIB)
43
what is the porin in the outer membrane like for group translocation
Porin in outer membrane to allow sugars through membrane | In this case is not a selective recognition system, is an open pore allow molecules through
44
what happens when glucose is moved into the periplasm
interact with complex in membrane Glucose delivered in activate state, is energised from inside – enzyme complex 1, HPr, enzyme complex 2 (made of two parts A and B) and transport system in membrane – enzyme complex 2 part C
45
what does the PEP do, and what does it use
PEP transport phosphate group to enzyme complex 1, transported via HPr to enzyme complex 2
46
what happens when phosphate transported to enzyme complex 2
now providing phosphate on enzyme complex 2 B, glucose reacts with enzyme complex 2 C, phosphate transformed onto glucose = glucose-6-phosphate accumulates inside cell
47
how does glucose translocation affect the cell
energetics: if have glucose on outside and move it inside, chemical gradient changes – more glucose on inside, harder to get glucose into cell as up concentration gradient BUT as soon as become glucose-6-phosphate no longer contributes to gradient as a different molecule – so more glucose on outside than in
48
why are protein transport systems important
transport of proteins outwards across cell envelope, important as relates to pathogens making protein toxins, will make toxin
49
what does the type I (ABC) transporter require
System requires three specific proteins, signal comes in causes a change in transport system, ATP binds causes conformational change of protein, creates channel, opens pore lets protein be translocated ATP hydrolysis to energise all these functions
50
what does the ATP binding cassette protein do in the typeI (ABC) transporter
- provides energy for translocation | - recognises a C-terminal sequence, so cassette knows it’s going to transport out the right proteins
51
what does the inner membrane protein do in the type I (ABC) transporter
- membrane fusion protein (MFP), create a pore, let proteins cross inner and outer membrane in one movement - provides substrate selection and “gate” for pore to control transport process, stops things leaking out of cell. Gate is triggered when the C-terminal signal is delivered into inner membrane proteins
52
what does the outer membrane protein do in the type I (ABC) transporter
allows protein to cross outer membrane and leave cell
53
what is an example of a type I system
Virulence factor secreted by a type I system - E. coli
54
what happens in the haemolysin type I system
Phospholipase enzyme – target the lipid in RBC, cause them to break open, release nutrients from inside RBC, so bacteria get nutrients
55
what is the test to see if something is haemolytic
lysis of RBC incorporated into agar, as make dish, let molten agar cool down mix with blood and add to petri dish then set, when do streaks, can see around single colonies are clear zones as phospholipase secreted by cell, get into agar, causes lysis zones
56
what are type II transporters
Most common and well-studied transport system, known as the General Secretory System Made up of General Secretory Proteins (GSPs)
57
what do type II transporters require
two systems
58
what are the two steps that occur in type II transporters
1. Inner membrane Sec transport system | 2. Outer membrane transport system
59
what does the inner membrane system recognise
Inner membrane Sec complex recognises specific N-terminal sequences in proteins destined for secretion = Leader or Signal sequence as N-terminal at start
60
what does the protein in the sec system do
Protein delivered to Sec complex by SecB, free in cytoplasm, first going to recognition event, pick proteins with N-terminal tag, deliver to inner membrane Sec complex, this transport is energised by ATP
61
what is the function of SecB and what does this lead to
SecB delivers protein that will be secreted to the complex, as it goes through N-terminal tag is snipped off by the protease – cleavage event, so protein that ends up in periplasm is now shortened, now picked up, must be delivered to specific outer membrane system
62
what interacts with the proteins in the sec complexes
Various different outer membrane systems that interact with all proteins that come through Sec complexes
63
how is maltose taken up in gram positive bacteria
don’t need outer membrane part of system sugars can diffuse down to surface of cytoplasmic membrane still picked up by proteins in pseduoperiplasm

Physiology of Microbes (21 decks)

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