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