Lectures 12-15: Glucose metabolism Flashcards
energy containing nutrients broken down by catabolism which are then excreted
bond energy transferred
via cofactors fueling anabolic reactions which take simple precursor molecules and make them into macromolecules
metabolism
sum of all chemical reactions in the cell
primarily energy producing - catabolism
primary use energy to build complex structures - anabolism or biosynthesis
everything broken down into acetyl coline - converging
cyclic concentration goes up and down i.e. krebs cycle
diverging - anabolic reactions - complex molecules built up i
Entropy (disorder) in a closed system increases
increase entropy in order to gain a more stable state
to maintain cellular organisation must be able to extract useable energy from surroundings and release useless energy
when the equilibrium constant is 1 = no net energy
when equilibrium constant is
+1 = negative
1 = 0
-1= positive delta G
hydrolysis
spontaneous
highly favourable
isomerization
same chemical formula at the beginning and end of the reaction
smaller free energy changes
between enantiomers delta g i 0
complete oxidation of reduced compounds
strongly favourable
how chemo-trophs obtain energy
reduced fuel with oxygen is stepwise and controlled
delta change depends on
the standard change in free energy
actual concentration of products and reactants
spin states
reduced fuels are in singlet spin state = all electrons are paired in electron pairs
molecular oxygen is in the triplet spin state = 2 oxygens are unpaired
direct electron transfer from a singlet reduces species to a triplet oxidising species is quantum mechanicaly forbidden
direct oxidation = combustion of biomolecules doesn’t occur readily
NAD, FAD and transition metal ions act as cofactors to catalyse consecutive single electron transfers needed for oxygen utilisation = need to funnel electrons in single or double pairs away from the singlet state so they can react with the triplet state
group transfer reactions
proton - ph
methyl
acyl 2C- biosynthesis of fatty acids
glycosyl more than @C- attachment of sugars
phophoryl ATP- activate metabolites = signal transduction
ATP
phosphoryl transfer
donor of the phosphate in biosynthesis of phosphate esters
hydrolysis of ATP is highly favourable under standard conditions
better charge separation in products
better solvation of products - hydroxyl group adding in
resonance stabilisation - drives ATP hydrolysis
ADP is more stable
cellular ATP is high above the equilibrium conc. = potent source of chemical energy
NAD and NADP redox cofactors
pyridine nucelotides
can dissociate from enzymes after the reaction
oxidation = hydride ion = 2 protons + 2 electrons from an alcohol transferred to NAD+ = NADH = reduced form
electron later injected into electron transport chain to make a proton gradient
FAD
shuttles single electron transfers
permits the fate of oxygen as an ultimate electron acceptor
co factors are tightly bound to proteins
fate of glucose
- stored as glucogen starch or sucrose
- synthesis of structural polymers = extracellular matrix and cell wall polysaccharides
- make nucleotides - ribose bisphosphate
4 oxidation via glycolysis = pyruvate
important of glucose
goodfuel - high bond energy = delta g
can be stored as glycogen
versatile biochemical precursor -carbon skeleton can be rebuilt into many different amino acids + nucleotide bases
survive on glucose only - human brain
glucose entry
glucose transporter in membrane = saturable
glucose kept a 2 millimolar in bloodstream
flows down concentration gradient into cell
glycolysis
sugar splitting
make ATP and NADH = more ATP in electron transport chain
6C = 2* 3C pyruvates
5 priming + 5 pay off reactions
3 regulated control enzymes
gluconeogenesis
make glucose for export to brain and muscle
pyruvate back to glucose but not exact reverse of glycolysis
3 regulated control enzymes
glycolysis
1. the preparatory phase
phosphorylation of glucose using hexokinase = glucose 6 phosphate
1st priming reaction = ATP invested
Phosphohexose isomerase
phosphokinase
1 - second priming reaction
aldolase cleaves 6C into 23C phosphates = glycerldehyde 3phosphate + dihydroxyacetone phosphate
payoff phase
ATP + NADH out
inorganic phosphate+ NAD = 2NADH
substrate level phosphorylation 2ADP - 2ATP
second atp forming
glycolysis
glucose + 2 NAD = + 2ADP + 2 phosphates = 2 pyruvates
2 NADH
2H+ + 2 ATP
used 1 glucose invest 2 atps and 2 NADs
made
2 pyruvates
4 ATPs = net gain of 2
2 NADH reoxidised in ETC to make ATP
3 stages of regulation
stages w a large negative delta G are the best to regulate
in glycolysis hexokinase, fructose 6-phosphate and pyruvate kinase
phosphofructokinase
tetramer
binds fructose 6 phosphate = fructose 1,6 phosphate
allosteric regulation - sigmoidal curve = activity is regulated
high AP = activity of enzyme decreased
low ATP conc =
enzyme more sensitive - reactivity higher
gluconeogenesis
cannot convert fatty acids to sugars
use acetyl CoA as intermediate then pyruvate and back up to glucose 6P
IN: 2 pyruvate 4ATP 2 GTP 2 NADH 2 H= 4 water
out : glucose 4 ADP 2 GDP 6 phosphate 2NAD+
brain n nervous sys only use atp from glucose
when glycogen stores are depleted this is our source of glucose
glycolysis vs gluconeogenesis
both thermodynamically favourable
regulated to prevent futile cycling which is useless to the cell
glycolysis mainly in muscle an brain as require high ATP
gluconeo - occurs in liver site
3 reversible reactions shared in both pathways:
irreversible reaction of glycolysis must be bypasses in gluconeogenesis
glycolysis: hexokinasw phosphofructokinase pyruvate kinase all kinases - changing phosphorylation state of the product
gluconeogenesis PEPcarboxykinase puruvate carboxylase fructose 1 bisphosphotase gluce 6 phosphotasease
g;uconeogenesis is expensive - more energy to make a glucose than burning one
pyruvate fates
yeasts ferment to ethanol
lactate in hypoxic or anaerobic condition
fermentation by lactate dehydrogenase
in contracting muscles
or acetyl-CoA
citric acid cycle
pyruvate 3C to acetate 2C
pyruvate dehydrogenase
citric acid/ krebs cycle catabloic process makes GTP an reduced cofactor to yield ATP but important for Anabolic roles reactions tht take pyruvate into
in matrix of mitochondria
more ATp generation than glycolysis
- acetyl CoA production
pyruvate to acetyl co A oxidative decarboxylation of pyruvate first carbons of glucose are fully oxidised catalysed by the pyruvate dehydrogenase complex found in matrix of mitochondria - requires 5 co enzymes TPP lipllysine prosthetic groups FAD NAD CoA co substrate
outL
NADH + CO2 + Acetyl-CoA
- Acetyl CoA oxidation
3+4 oxidative decarboxylations = 2 NADH *
5 substrate level phosphorylaition ADP = GTP
6 Dehydrogenation = reduced FADH2 electron carrier
7 hydration
8 dehydration rearrangment of hydrogens= NADH
efficient energy storage
- citrate synthase
C_C bond formation - aconitase *2
rehydration = isomerisation via dehydration/rehydration
large positive delta g = unfavourable reaction so equilibrium is pulled to the right hand side
3 isocitrate dehydrogenase *
second oxidative decarboxylation
NADH produced
oxidation of the alcohol to a ketome transfers hydride 2 electrons to NAD
NADP= used as cofactor by cytosolic isozyme
highly thermodynamically favourable irrivrsible regulated by product inhibition and ATP
4 alpha-ketoglutarate dehydrogenase complex *
3rd oxidative decarboxylation
large negative delta g so regulated
5 succinyl-CoA synthetase
succinyl co A had a GDP attached phosphate added to it becomes GTP
succinate produced CoA lost
substrate level phosphorylation
favourable small delta g eq to the right
6 succinate dehydrogenase
succinate goes to active site of succinate dehydrogenase
FAD - FADh2 electrons removed from succinate go into oxidative phosphorylation pathway
delta g is 0 = when fumarate is used eq pulled to the right
7 fumarate
water in the state of a hydroxl ion aded by fumarate making temporary carbanion transition state
8 malate dehydrogenase * malate converted back to
oxaloacetate for citrate synthase
one NADH out
large positive delta g = unfavourable
[oxaloacetate] low pulling reaction forward
for 1 turn of cycle = 3 NADH
+ 1 FADH2
+ 1 GTP later = ATP
why is pyruvate dehydrogenase complex (made up of
pyruvate de hydrogenase E1 + dihydrolipoyl transactylase and dihydrolipoli dehydrogenase E3) efficient
multisubunit
swinging aim
cofactor binding
substrae channelling
intermediates never leave enzyme surface
- short distance between catalytic sites allows channeling of substrate from one catalytic site to another
- channeling minimizes side reactions
3 regulation of activity of one subunit affects the entire complex
you only need to modify one of them to modify all of them
regulated my phosphorylation
citrate synthase -
Allosterically controlled enzyme
rate imiting step
regulated by {oAA] and product inhibition
MM would be sigmoidal
changes conformation once binds oxaloacetate
open conformation = no binding site for acetyl CoA
closed conformation = binding of oxaloacetate creates binding site = induced fit
avoid unnecessary hydrolysis of thioester
regulation of citric acid cycle
enzymes that are reuglated PDH citrate synthase IDH and aKDH = sigmoidal MM curve
activated by substrate availablity
inhibity by product accumulation
NADH and ATP
affect all regulated enzymes in cycle
inhibitor NADH and ATP
activators NAD+ and AMp
regulation of citric acid cycle
enzymes that are regulated PDH citrate synthase IDH and aKDH = sigmoidal MM curve
activated by substrate availability
inhibity by product accumulation
NADH and ATP
affect all regulated enzymes in cycle
inhibitor NADH and ATP
activators NAD+ and AMp
- Electron transfer + oxidative phophorylation
proton motive force built up across inner membrane
=synthesis of atp
protons flow back through from inter membrane space into a matrix of the mitochondria
electrons from reduced cofactors NADH and FADh2are passed to proteins in respiratory chain
oxygen final electron acceptor = water
energy of oxidation by flow of protons own the electrochemical gradient used to phosphorylate ADP = ATP
energy released by electron transport used to transport protons against electrochemical gradient
outer membrane of mitochondria porous permeable to metabolites
inter membrane space similar to cytosol high [proton] =low pH
inner membrane
large surface area due to cristae convolutions
location of ETC complexes
matrix
location of krebs cycle lipid/acid metbaolism
low [h+]
electrons taken from matrix into inter membrane space
protons pumped through by complex 1 and 3 and 4
complex 2 passed though series of electron carriers into inter membrane space and meets oxygen in complex 4
each complex contains multiple redox centers
1. flavin mononucleotiode (FMN) or flavin ADEnine (FAD) initial electron acceptors for complax 1 n 2 carry 2 e by tranferring 1 at a time 2. iron-sulfur cluster carry 1 co ordinated by cysteines in the protein 3 coenzyme ubiquinone carry 2 - proton is added so 2 OH groups added ubiquinol reduced result 2 cytochromes a b or c carry 1 e
1.
NADH dehydrogenase
succinate dehydrogenase
ubiquinon cytochrome c
COMPLEX 1 proton pump
transfer or. 2 electron from NADH to ubiquinone carrier that can carry 2
per NADH 4 protons from matirx (N) into intermembrane space (P)
conenzyme Q picks up 2 protons transported by proton wires
=reduced ubiquinone = only soluble in the membrane
2 electrons from NAD+ passed down and meet protons make QH2
complex 2
succinate dehydrogenase
delta g 0
2 electrons stripped off of succinate
transferred to FADH2 one at a time via iron sulfur centers in ubiquinone
added to protons = QH2
doesn’t transport protons
reduce [proton] in matrix
complex 3
buiquionen:cytochrome C oxidoreductase
shunts electrons from ubiquinol onto cytochrome and cytochrome moves it onto final complex
into inter membrane space
moving electrons
used 3 electrons from QH2 to reduce t molecules of cytochrome c
contains iron sulfur clusters and haem grops
Q cycle causes 4 additional protons transported to IMS
complex 4
cytochrome released into inter membrane space
hydrophiic
bump into complex 4
cytochrome oxidase
4 electrons used to reduce one oxygen molecule to 2 waters
4 protons picked up from matrix in this process
4 additional protons passed from matrix to inter membrane space
electrons injected via a series of coppor centres to produce water
oxygen reduced 1 at time = 2 waters
polar but uncharged diffuse out of cell =maintain hypertonic sate
huge positive change in intermambrane space made up of protons
ATP synthase part of respiratome complex
electron transport sets up a proton motive force
FoF1 ATP synthase has amembrane binding portion in inner membrane
Fo =and head group in matrix
protons flow through and spin inner spindle in head at high speed by protons flowing in and back into matrix to meet OH groups
f1 soluble in matric
making ATP
Fo intergral membrane complex
tramsports protons back to matrix dissipating the proton gradient
energy transferred to F1 to catalyse phosphorylation of ADP
hexamer arranged in 3 alpha beta dimers arranged in 3 conformations open = empty loose = binding to ADP and pi tight = catalyses ATP formation and binds product
proton translocation causes a rotation of the Fo subunit and the central shaft gamma = conformational change by the gamme subunit rotating inside
within all the 3 alpha beta pairs
promotes condensation of ADP into ATP
binding change model
alpha and beta subunits from dimer release and ATP molecule the gamma spindle pushes ATP off
ADP and PI come in to bind and spindle moves to next position
particular position inside head required pushing against the beta conformation
ATP is churned off
ADP + Pi bound state
ATP form
ATP exclusion from binding site
