Metabolism of parasites Flashcards
Why metabolism has to be done?
-Store energy(ATP) for biological functions
ATP: most general energy carrier/storage unit: but energy can be stored in other things, eg. like kreatin for muscles
-Generate building blocks
-Mediate detoxification (like in river)
All needed to proliferate/grow/invade tissues
Whats the most important reason of doing metabolism? - for parasites
ATP generation! Parasites are very well adapted to niche, they often take t rest directly from the host
eg. Trypanosoma doesnt do any building blocks, blood is all they need
Where can you get the substrates? examples
eg. tsetse fly: trypanosoma carrier snails RBC eg. plasmodium Ascaris: intestine full of worms Depending on environment, metabolism is adjusted
Why study metabolism in parasites?
Fundamental
1) understanding the pathways in general
2) understanding how metabolism is organised: what can you produce from what materials
3) understand eukaryotic evolution
4) understand which organisms have a mitochondrion?
5) study differences btw anaerobes and aerobes
Applied
1) in order to find ways to kill the parasites (drug targets)
2) study bioreactors (H2 production) = hydrogenosomes produce hydrogen, its a organelle of mitochondria origin
Heterotrophes ototrophes
heterotrophes cannot fix carbon, eg. photosynthesis is a way to fix carbon
therefore they take glucose from outside
how do you generate ATP? ways?
1) Substrate level phosp. (SDF)
= direct phosphorylation of ADP provided by another metabolic event, energuy comes from a coupled reaction
2)Oxphos
= ATP generated from oxidation of NADH-FADH carriers
=subsequent transfer of electrons generate proton gradient, used from ATP synthase to generate ATP
=O2 does not need to be the electron acceptor, eg. you can use nitrogen in bacteria (n2) and make NO = still oxphos
OXPHOS? definition
= electron transfer to carriers than final acceptor like O2, redox
=generates ATP by ATP synthase
glycolysis steps? classic one
1) glucose is turned to glucose 6 phosp.
= 1 ATP used to activate glucose
2) G6P - F6P
3) from fructose 6 phosphate to 1,6 phosphate
=1 ATP used to activate glucose
4) glucose is separated to 3C x2 - glyceraldehyde 3 phosphate /dihydroxyacetone phosp.
5) dihydroxiacetone phosp. converted back into g3p
6) 2 times 3C (glyceraldehydes) are turned to 1,3 biposphoglycerate
=2 NADH is generated
7) from 1,3 to 3-phosphoglycerate
=2 ATP generated (1 for each C)
8) 3-p to phosphoenolpyruvate
9) phosphoenolpyruvate to pyruvate
mediated by pyruvate kinase
=2 ATP generated (1 for each C)
Net ATP: 2 ATP - all generated from SDP
2 NADH generated
describe oxidation reduction
oxidation=lose electron
reduction=gain electron
redox examples
eg. Carriers turning NAD to NADH= reduced
oxygen is reduced to water in ETC
glucose is oxidized
role of NAD balance- why should we keep NAD and NADH balanced
NAD is the coenzyme in electron transfer
oxidised form: NAD+, reduced form NADH = gets electron, turns natural
With metabolism redox = H is transferred with electrons
NAD + 2H + 2e = NADH+H
balanced: NAD+ = NADH
The total pool of NAD is constant, backbone cant be produced as fast as glycolysis, so you need to recycle it = glycolysis happens in milliseconds
net glycolysis reaction?
Glucose + 2NAD + 2ADP + 2P = 2 Pyruvate + 2NADH + 2H + 2ATP + 2H2O
waters come from the phosphoenolpyruvate conversion
what would happen if glycolysis ends with pyruvate?
NADH got stuck, also pyruvate can be further oxidized too
Further pyruvate processing (respiration vs fermentation definition)
Respiration: usage of terminal electron acceptor FROM OUTSIDE (eukaryotes usually use oxygen/microbes N2) to store electrons
O2 + 4H + 4e = 2H2O
Fermentation: electron is donated into the acceptors that is generated during the metabolism FROM INSIDE
example: 2H + 2E= H2 - yes hydrogen generated from inside
example: fumarate + 2H + 2e= succinate
pyruvate then acetaldehyde + 2H + 2e = ethanol
pyruvate then lactate
So there’s 3 places to put the electrons: O2/N2 respiration, H2 fermentation, acetaldehyde/fumarate = for fermentation
general oxphos (krebs etc)
Krebs: generates 3 NADH + 1 FADH each 3C (6 NADH + 2 FADH) + 2ATP
ETC: Electron is loaded from NAD and FAD to ETC: generates 2H + 1/2O2= H2O
and ATP with pump
O2 is the electron acceptor
We had 2 NADH from glycolysis + Pyruvate-AcetylCoA conversion = 2 NADH more + 6 NADH + 2 FADH
= loaded on ETC: get 36 ATP in total
ATP synthase generated with proton influx
N2 respiration
N2 = NO then H flux on ATP synthase
What do you do after Krebs/glycolysis with NAD problem?
1) Put on ETC
2) On glycolysis: reduce pyruvate to lactate or ethanol
Lactate and ethanol is reduced
3) Excrete pyruvate completely - normally not possible but Trypanosoma can do it
hydrogenosomes
malate-pyruvate (ferrodoxin) acetylcoa- acetate
from acetylcoa to acetate, succinate is transferred to succinyl coa = ATP generated w SDF
Hydrogen accepts electrons from ferrodoxin = fermentation!!
Ferredoxin here is free-floating
Once you leave electrons on hydrogen= no ATP= you need to couple it with SDF
Pyruvate oxidised, Ferrodoxin oxidised, Ferrodoxin reduced, Hydrogen reduced
normal mitochondria vs hydrogenosome: similar or different?
Similarities
Both are double membrane-bound organelle
Similar chaperone to fold proteins is used
ETC and hydrogenosome Fd is similar, hydrogenosome one is just floating
Some hydrogenosomes have a genome, like mitochondria
Apparently though: everything they use is so similar =
So hydrogenosomes are mitochondria that is anaerobic
Differences: No ETC in hydrogenosome, there’s just ferrodoxin
O2 is terminal e. acceptor, vs H2 is terminal electron acceptor
ATP synthase/gradient/OXPHOS used = SDF/fermentation used
organelle classification/how to find what your organelle is
1) Does it generate ATP or not
-Doesn’t: mitosome
-Does: continue
2) Uses ONLY O2 as terminal electron acceptor = aerobic mitochondria
Uses other compounds as well = continue
3) Does not produce H2: anaerobic mitochondria
Does produce H2: continue
4) Has ETC: H2 producing mitochondria
Doesn’t have ETC: hydrogenosome
All of them are organelles of mitochondrial origin - too much similarity
Why not everyone is aerobic?
-No O2 around/or need to survive hypoxia for some time due to lifecycle
-There’s enough substrate so no need to be efficient, you can just load the glycose and go SCF/fermentation = faster
-Not much ATP is needed sometimes either, it is enough to get 2 ATP from glycolysis
-Doing all those big pathways also need proteins, and that’s costly
-Also using O2 has the risk of generating ROS: if you put too little O2 you can get superoxides
So oxygen is an opportunity: but often not every opportunity is used
Anaerobic metabolism examples / Warburg Crabtree
Crabtree on yeast: Can go either normal oxphos/or fermentation: puts electron on acetaldehyde = ethanol
Yeast does fermentation when there’s too much sugar = it faster rather than efficient= how beers are made!
Warburg on cancer: Cancer cells use glucose very fast, produce lactate even when there’s O2 = muscle cells normally do it too but they get tired/muscle pain when there’s too much lactate, cannot continue
Why theres mitosomes if they dont produce ATP?
They have other pathways, but metabolism pathways rather moved to the cytosol.
If it was completely useless it would get lost, so it should have a role
True anaerobes definition + how they deal w O2
No need for O2 to survive and multiply
Also cant grow when there’s O2 either: growth inhibited by O2, the enzymes in ATP production, eg. ferrodoxin reductase, does not work = there’s O2: Fd cannot get the electrons instead of O2!!
ex. some bacteria
Since they cnannot live with O2:
they do: 2NADH + 2H + O2 = 2NAD + 2H2O (NADH oxidase-diaphorase enzyme)
So they just load the electrons on O2 directly with no ETC = get their NAD back. They use it as an electron acceptor directly.
No ATP generated
But they are happy that they got rid of O2: still, there’s a ROS risk though
another example. flavodiiron protein
Microaerophiles
Can survive in low O2 (%1-10)
grow a bit faster when there’s low O2, its better than none
Whats important to study in organelles of mitochondria origin?
- main differences in metabolism
- where does reactions occur
- which class they belong to: the organelle
- what are the terminal electron acceptors
How to check the maps of metabolism? / trypanosoma eg.
Check genome.
But careful: often genome will show everything. eg. Trypanosoma genome will show the enzymes generated in every stage, but tsetse fly stage and mammal stage is completely different: tsetse fly stage is huge, mammal stage is much smaller
To differentiate stages: do measurements with labeled glucose: check where it goes, eg. to fermentation or respiration
Fasciola hepatica example:
anaerobic mitochondria example:
-Generates ATP
-no krebs, no ETC
-no O2 around
-no H2 : NADH puts electron on 1 electron acceptor:then electron goes Rhodoquinine: then it drives fumarate to succinate = fermentation!!! = not SDF see electron carried and put on the carrier generated in the metabolism
terminal electron acceptor: propironate
