mitochondria physiology Flashcards
what is function of mitchondria?
they are the site of ATP production
The Krebs cycle occurs here
how is ATP made?
ATP synthase catalyses reaction of ADP+inorganic phosphate
what is the physiological range of ATP?
in cytosol ranges from 1-10mM
How does ATP generates energy ?
ATP is bound to magnesium usually
hydrolysis reaction releases energy as ATP is very negatively charged and there is significant amound of energy stored between phosphate bonds
from which processes can ATP be produced?
around 80% ATP generated from from mitch/Krebs cycle
ATP also generated from glycolysis too
what is the turnover of ATP?
very rapid ~ 1 min in resting cells to 1second in active muscle
why is the turnover of ATP so high?
because of the ANT (adenosine nucleoide translocase) on IMM exchanges 4 ATP out and 3 ADP in
this net negative conc. gradient allows ATP to leave cell quickly
how can we measure mitch function?
oxygen consumption
membrane potential
autofluorescence
what is meant by coupled ATP synthesis
mitochondrial oxygen consumption goes towards generating ATP
what is meant by uncoupled ATP synthesis?
mitochondral oxygen consumption doesn’t generate ATP
instead used for heat generation (as seen in brown fat)
what biological processes is ATP used for
skeletal muscle contraciton
protein synthesis
Na/K ATPase // active transport
why does the kidney have the highest ATP turnover?
needs lots of energy to pump different ions against their conc. grad in the nephron
powers AT processes
what is different about skeletal muscle ATP consumption than that of kidneY?
much more dynamic, not static ATP turnover
demand for energy changes depending on it contracting or not
what is the electrochemical gradient of mitch?
negative 150mV which drives the action of Electron transport chain to generate ATP
how can we investigate ATP synthesis?
use different poisons/chemicals or uncoupler to inhibit different aspects of ATP synthesis
> ETC
> glycolysis
> proton circuit
how do synthetic uncouplers like FCCP and DNP work?
they disrupt proton circuit and collapse the membrane potential
so mitch increases its work to try and restore this = heat generation
> brown fat may posesss natural uncouplers
how can oligomycin be used as a tool to study ATP?
it blocks ATP synthase so prevents any more ATP being made and doesn’t affect the ETC
what is unique about cultured cells (metabolism)
they are all glycolytic and consume far more glucose than the normal cell
what is special about NADH and FAD
they are autofluorecent molecules so testing cells under specific wavelength of light allows investigation of ATP/mitch function
NADH goes up
FAD goes down
what channel does calcium enter the inter-membrane space?
VDAC channel on OMM
actually not that voltage sensitive, more like a large pore
what channel does calcium enter mitch matrix?
MCUniporter on IMM
becomes active when external calcium level is high (above 2microM)
how does calcium act in mitch matrix?
stimulated dehydrogenase involved in Krebs cycle
leads to increase of NADH
enabling ETC to continue and generation of ATP
how does calcium leave mitch?
by the sodium calcium xchanger
NCX
this is driven by sodium gradient
how does the calcium signal influence mitchondrial function
oscialltion of calcium are better at stimulating mitch than a sustained rise
How does the MCU transporter become open?
seems that there is a local rise of mitch calcium from the direct coupling of ER and mitch
this link between IP3R and VDAC provides the extra calcium needed for MCU to open whilst cytosolic calcium remains low
what are homeodynamics?
another form of homeostasis in which the system is stable as an osciallator (in a set dynamic range)
how do oscillations vary?
they can vary in frequency and amplitude and time
Even different cell types exhibit differ oscillations
where can oscillations? happen intracellularly?
calcium oscillation during fertilisation is very large and profound over several hours
or can be quick in PAC cells with cytosolic and ER calcium oscillations
or pulsitile for hormone secretion
what is meant by limit cycle attractor
way that oscillations remain stable and self sustained
circular trajectory so any pertubatons to this system tend towards this closed system thereby maintaining the cycle
can you describe an exampe of a limit cycle attractor?
balance between cytosolic and ER calcium concentrations is a cycle
as one goes up the other other goes down but they feed into each other
how can calcium
oscillations vary?
they can vary in frequency, amplitude and time
how can oscillations be generated?
through positive feedback loops or delayed negative feedback loop
what is the relationship between ER and cytosolic caclium oscillations?
they can be thought of being 180 degrees out of phase with each other
describe a negative feedback loop in calcium signalling pathway
calcium released from ER stores and acts on IP3 kinase
kinase converts ip3 to ip4 preventing any furthur release of calcium from ER
describe a possible feedback loop in calcium signalling pathway
[model 1]
IP3 produced at plasma membranes diffuses across cytosol and activates IP3R to release calcium
the released calcium can influence open probability state of IP3R (weaker negative feedback than positive) to release more calcium
describe a possible feedback loop in calcium signalling pathway
[model 2]
PLC zeta is highly sensitive to calcium so calcium released from ER can stimulate increased activity of PLC zeta
Ip3 is dynamic variable
how do model 1 and model 2 of calcium oscillations differ?
IP3 is either a control variable (model 1) or a dynamic variable (model 2)
how can we distinguish between the 2 models of calcium oscillations?
mathmatical models to simulate calcium oscialltions in different cell types with different agonists
and also use uncaged IP3 to give a ‘‘dose’’ and observe how oscialltion change
what is meant by caged/uncaged IP3?
UV sensitive chemical groups are added to IP3 = caged
when treat cells with UV light these chemical groups fall off leaving IP3 to act on cells (uncaged)
you can experimentally control when IP3 is added to cell
how does IP3 dose affect calcium oscialltion
if model 1 the frequency of amplitude increases as IP3 is a constant
if model 2 then there will be phase shift of oscillations as IP3 is dynamic and interupts the feedback cycle so it needs to reset
what kind of oscillation model occurs during fertilisaiton?
initially model 1 as IP3 is being made at a single point in the cell
as PLC seta diffuses across the egg then model 2 takes over and oscialitons of Ca 2+ and IP3 can synchronise
Describe the structure and function of pancreas
Made up of many islets
Each islet contains many cells 100-1000 depending on animal species
Pancreatic Beta cells secrete insulin into the blood
What is the pattern of insulin secretion?
It is oscillatory in nature
> oxygen consumption/mitch oscialltes in individual beta cells
How can many cells work together as an islet?
There are gap junctions between beta cells allowing coupling of electrical activity
Enables islet to function as a unit
What is the importance of K+ channel in glucose - > insulin secretion pathway?
The potassium channel is sensitive to ATP and will close in response to an increase of ATP production
This leads to membrane delpolarisation and activation of voltage gated L-type calcium channel leading to calcium influx and exocytosis of insulin
Why are sulfonylurease drugs used in diabetic medicine?
Sulfonylurease can bind to K/ATP channel and cause conformational change to closed state.
This wil encourage insulin secretion from pancreatic Beta cell
What is perceval HR? What is it used for?
It’s a fluorescenct probe able to detect the ATP/ADP ratio as it has an ATP-binding site
And becomes more or less fluorescent depending on open or
closed state
