Lec 15 - Regulation of Protein Function Flashcards
how do we regulate enzyme activity in the short term ?
alter substrate and product conc
change enzyme confirmation via :
Allosteric regulation
Covalent modification
Proteolytic cleavage
how do we regulate enzyme activity in the long term ?
Up or Down regulation in protein synthesis
change protein degregation rate
how do substrate and product concentrations alter enzyme activity
substrate concentration - less substrate lower enzyme activity
Product inhibition - more product accumulation will inhibit the forward reaction
eg - glucose 6 p inhibits hexokinase activity
how does allosteric regulation alter enzyme activity
allosteric ezymes show a sigmoidial curve between rate and conc
T state - low affinity
R state - high affinty
allosteric binding causes a confrontational change
think haemoglobin
allosteric activators increase proportion of enzyme in R state
allosteric inhibitors increase the proportion of enzyme in the T state
back to gylcolysis notes : phosphofructokinase (PFK) - allosterically regulated
activated by low energy AMP, fructose 2,6 biphosphate
inhibited by high energy ATP citrate and H+
how does covalent modification affect enzyme activity ?
what are some exapmles
Phosphorylation via protein kinases
transfer terminal phosphate from ATP to OH on ser,thr,tyr (amnio acids)
protein phosophotases - catalyse dephosphorylation
ie reverse reaction
phosphorylation adds a bulky negative charge
the created phosphoryl group can make H bonds
this changes protein confirmation
this allows for amplification effects - singal orders of magnitude larger within seconds (extra)
we can alter rate of de/phosphorylation
explain the reciprocal regulation of glycogen breakdown and synthesis
the presence of glycogen will activate glycogen breakdown enzymes
and at the same time turn of the glycogen synthase enzyme
how does proteolytic cleavage affect enzyme activity ?
proteolytic cleavage can activate enzymes
this is good in digestive enzymes - synthesised as zymogens (inactive) in the pancreas and stomach - activated later once into the digestive tract - as we dont wanna dissolve our own cells !! extra : pepsinogen — acitvate —- pepsin
blood clotting is mediated by a proteolytic cleavage cascade
apoptosis works via proteolytic enzymes being activated
explain zymogen activation by proteolytic cleavage
activation of most digestive emzymes are controlled by trypsinogen to trypsin
once activated trypsin can cut many pro-enzymes into their active forms
lipase, elastase, chymotrypsin, carboxy peptidase
pancreatic trypsin inhibitor can bind tightly at active site to inhibit trypsin activity
what are the two ways to regulate enzymes long term ?
Change the rate of protein synthesis - enzyme are made less or more by up/down regulation
change the rate of protein degredation - ubiquitin-proteasome pathway
outline the blood clotting coascade and its use of proteolytic enzymes
there are 13 clotting factors that form a cascade processes
we have an intrinsic pathway - damaged endothelial lining of blood cell promotes binding of factor XII
and an extrinsic pathway - trauma releases tissue factor III
both these paths activate factor X (10)
factor X activates prothrombin to thrombin
leads to production of fibrin and formation of the fibirin clot
it is an amplification cascade - allows for formation of a clot from very small amounts of initial factor
lead to one pro enzyme being activated to an enzyme which converts a pro enzyme to an enzyme ect
thrombin / fibrinogen presence activates earlier parts of the intrinsic pathway - positive feedback
what us the structure change from prothrombin to thrombin
serine protease - active enzyme area
Gla (g-carboxyglutamate) resides domains target it to appropriate site for activatin - brings together clotting factors -
COO- groups on gla find Ca2+ which is present at the break
two kringle domains help keep prothrombin in the inacitve form - these are cut off to activate it
this flash card is not that important
how does thrombin help form the clot
fibrinogen - crab protein
Alpha and beta negative regions prevent aggregation
thrombin cuts of negative alpha and beta regions
fibrinogen now can ploymerize - forms the clot
cross linking - amide bonds - help stabilise the clot
thrombin acitvates another clotting factor to do this
what causes haemophillia
-defect in factor 7
treat with recombinant factor 7
how do we stop the clotting process
localisation of prothrombin - clotting factors are diluted by blood flow, disposed of in the liver
digestion by proteases
regulating the clotting process by specific inhibitors such as antithrombin inhibiting thrombin
how can we break down the clot ?
fibrinolysis - uses proteolytic acitvation
plasminogen (inactive) is acitvated to plasmin
plasmin breaks down fibrin into fibrin fragments
