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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
Q

what is homotrimeric

A

type of porin structure

three copies of same protein, forming a complex, each with a hole in middle

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26
Q

what is barrel structure like

A

type of porin structure

side view, is hydrophobic – all around outside interacts with lipids, keeps it buried in membrane

27
Q

what is the structure like when all the loop bits are hydrophilic

A

interact with molecules that are being taken up or the water/cytoplasm phase in general

28
Q

what are the porin structures

A

Homotrimeric
Barrel structure
All loop bits are hydrophilic

29
Q

how do large polar molecules and ions pass through cytoplasmic membrane barrier

A

don’t pass across cytoplasmic membrane freely; need specific transporters

30
Q

how is the production of transport proteins regulated

A

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
Q

uniporter

A

one molecule moves in one direction (can also be outside to in) causes cell dissipation

32
Q

symporter

A

two molecules move in one direction

33
Q

antiporter

A

two molecules move in opposite direction

34
Q

what is important in maintaining charge gradient across membrane

A

antiporter and symporter

35
Q

how is maltose taken up in gram negative

what does this allow

A

Outer membrane porin protein

allows selective transport of maltose

36
Q

what happens to maltose once taken up

A

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
Q

how does maltose affect ATP in uptake

A

During process ATP used to bring in sugars that will generate more energy

38
Q

how does maltose uptake affect proteins

A

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
Q

what occurs in group translocation

A

Transported compound is chemically modified during the transport process

40
Q

what happens in glucose transport system

A

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
Q

what is involved the phosphotransferase system

A

5 proteins some of which are cytoplasmic others are membrane protein

42
Q

what happens in glucose translocation

A

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
Q

what is the porin in the outer membrane like for group translocation

A

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
Q

what happens when glucose is moved into the periplasm

A

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
Q

what does the PEP do, and what does it use

A

PEP transport phosphate group to enzyme complex 1, transported via HPr to enzyme complex 2

46
Q

what happens when phosphate transported to enzyme complex 2

A

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
Q

how does glucose translocation affect the cell

A

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
Q

why are protein transport systems important

A

transport of proteins outwards across cell envelope, important as relates to pathogens making protein toxins, will make toxin

49
Q

what does the type I (ABC) transporter require

A

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
Q

what does the ATP binding cassette protein do in the typeI (ABC) transporter

A
  • provides energy for translocation

- recognises a C-terminal sequence, so cassette knows it’s going to transport out the right proteins

51
Q

what does the inner membrane protein do in the type I (ABC) transporter

A
  • 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
Q

what does the outer membrane protein do in the type I (ABC) transporter

A

allows protein to cross outer membrane and leave cell

53
Q

what is an example of a type I system

A

Virulence factor secreted by a type I system - E. coli

54
Q

what happens in the haemolysin type I system

A

Phospholipase enzyme – target the lipid in RBC, cause them to break open, release nutrients from inside RBC, so bacteria get nutrients

55
Q

what is the test to see if something is haemolytic

A

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
Q

what are type II transporters

A

Most common and well-studied transport system, known as the General Secretory System
Made up of General Secretory Proteins (GSPs)

57
Q

what do type II transporters require

A

two systems

58
Q

what are the two steps that occur in type II transporters

A
  1. Inner membrane Sec transport system

2. Outer membrane transport system

59
Q

what does the inner membrane system recognise

A

Inner membrane Sec complex recognises specific N-terminal sequences in proteins destined for secretion
= Leader or Signal sequence as N-terminal at start

60
Q

what does the protein in the sec system do

A

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
Q

what is the function of SecB and what does this lead to

A

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
Q

what interacts with the proteins in the sec complexes

A

Various different outer membrane systems that interact with all proteins that come through Sec complexes

63
Q

how is maltose taken up in gram positive bacteria

A

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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