Metabolism Flashcards
metabolism:
all chemical processes going on continuously inside the body that allow life and normal functioning (homeostasis)
catabolism:
breakdown of larger molecules
anabolism:
synthesis of larger molecules
what is the reaction of glucose (including metabolism)
C6H12O6 + 6O2 -> 6CO2 + 6H2O (metabolism occurs in the middle, at the arrow)
what is ∆G
change in free energy during a reaction in vivo
exergonic reaction:
free energy is released, ∆G is negative
endergonic:
an input of free energy is needed to drive the reaction, ∆G is positive
what happens when ∆G is 0
a system is at equilibrium and no net change can take place
what is ∆G°’:
change in free energy during a reaction under standard conditions
where does the free energy used in glycolysis come from
the hydrolysis of ATP
the hydrolysis of ATP is
exergonic
enzymes:
- catalysts that speed up chemical reactions
- are not permanently altered during the course of a reaction
- affect only the rates of reactions
- are present in small amounts
- are highly specific for their particular reactants (substrates)
- can be regulated to meet the needs of a cell
enzymes may be conjugated with:
non-protein components (co-factors and co-enzymes)
enzymes are mediators of:
metabolism, responsible for virtually every reaction that occurs in a cell. without enzymes, metabolic reactions would proceed so slowly as to be imperceptible
the active site and the substrate have:
complimentary shapes that allow substrate specificity
the active site:
- region of the enzyme that binds substrate (and cofactor/coenzymes)
- contains the residues that directly participate in the making and breaking of bonds (catalytic groups)
catalyst:
a substance that increases the rate or velocity of a chemical reaction (without itself being changed in the overall process)
how does a catalyst work?
- by lowering the activation energy thereby increasing the fraction of molecules that have enough energy to attain the transition state and makes the reaction go faster
what happens to free energy with a catalyst
nothing, it stays the same. only the rate of the reaction changes
Vmax:
the velocity at saturation (at saturation every enzyme is working at full capacity)
Km:
the Michaelis constant, the substrate concentration at one-half of Vmax
what is the relationship between Km and affinity
the higher the Km, the greater the substrate concentration that is required to reach one half Vmax and the lower the affinity of the enzyme for that substrate. The lower Km = higher affinity
what are other factors that strongly influence enzyme kinetics
pH and temperature
temperature effects of enzymes
enzymes have an optimal temperature where activity peaks. At temperatures lower, activity decreases and at temperatures higher, denaturation occurs
pH effects of enzymes
reaction rates are highest at the optimal pH. enzymes are activated at different pH
Km is the concentration of substrate at which:
half of the enzyme sites are filled and therefore provides a measure of the substrate concentration required for ‘significant’ catalysis to occur
ethanol forms into toxic methanol and ethylene glycol. how do you prevent these toxic metabolic products to form?
alcohol dehydrogenase has a higher affinity for ethanol than it does for methanol or ethylene glycol (lower Km)
an increase in glucose in the bloodstream following a rich carbohydrate meal stimulates the secretion of ____ by the pancreas. ____ binds to:
- insulin, insulin
- insulin receptor which results in a variety of signals transmitted to the cell. among these signals are the recruitment of glucose transport proteins (GLUT4) from the cytosol to the membrane in muscle cells and adipocytes
glycated hemoglobin (GHB):
is used to measure ‘average’ blood glucose concentrations over time
what would you expect to see if blood glucose concentrations are elevated over time?
AGEs
AGEs:
advanced glycation end products. can covalently cross-link to proteins. the more of this that occurs, the higher the potential damage
irreversible inhibitors:
bind tightly to the enzyme (often covalently)
competitive inhibitors:
compete with the substrate for active sites and usually resemble the substrate in structure. a type of reversible inhibitor
noncompetitive inhibitors:
bind to a site different than the substrate and change the conformation of the enzyme inhibiting substrate binding (allosteric inhibitors). a type of reversible inhibitor
allosteric inhibition steps:
without allosteric inhibitor: high affinity form of enzyme. substrate binds to active site, product formation occurs.
with allosteric inhibitor: low affinity form of enzyme. allosteric inhibitor binds to site other than active site, changing conformation of active site. substrate can’t bind or can’t bind well, leading to little or no product formation.
allosteric activation steps:
without allosteric activator: low affinity form of enzyme, allosteric site is empty, substrate does not bind to active site = little or no product formation
with allosteric activator: high affinity form of enzyme, allosteric activator binds to allosteric site, changing conformation of active site allowing substrate to bind, product formation occurs
how is ATP made
one 6 carbon glucose is converted to two 3 carbon molecules of pyruvate at the end of the 10 steps of glycolysis. 2 ATP is used, 4 ATP are generated for a net gain of 2 ATP. 2 NADH are generated
NADH
carries 2 electrons that will be passed onto the electron transport chain and will be transferred to molecular oxygen resulting in formation of ATP
FADH2
carries 2 electrons that will be passed onto the electron transport chain and will be transferred to molecular oxygen resulting in formation of ATP
NADH and pyruvate from glycolysis:
enters the mitochondrial mix
pyruvate is converted to:
acetyl-CoA. these reactions occur on the pyruvate dehydrogenase complex
where are the 3 carbons lost in glycolysis
2 carbons are lost through CO2 during the formation of 2 molecules of pyruvate, 2 molecules are lost during the citric acid cycle (TCA) - which runs twice (totalling 4)
glycolysis also forms:
3 molecules of NADH, one molecule of FADH2, both of which go to the electron transport chain
describe the electron transport chain
- complexes 1,3,4 are proton pumps: protons accumulate in the intermembrane space
- protons flow down through ATP synase
- this turns C subunit, gamma and changes conformation of alpha beta dimers
- leads to ATP synthesis as protons move down their gradient back to the matrix
- ___ protons per pair of electrons that enter complex ___ from ____
- ___ protons per pair of electrons that enter complex ___ from ____
- 10, 1, NADH
- 6, 2, FADH2
protons flow from the inner membrane:
through a channel in the a subunit, then enter the c subunit. this results in a rotation of the c subunit and the gamma subunit which is associated with the c subunit
ATP synthesis occurs as a result of:
the conformational changes of the alpha-beta dimers
there are ___ dimer conformations.
3, at any given time, each of the 3 dimers is in one of them.
in order to synthesize ATP, each dimer goes through:
all 3 conformations
what happens in the 3 conformations of the dimer
- in the loose conformation, substrate enters/is trapped (ADP and inorganic phosphate (Pi)
- in the tight formation, ATP is formed
- in the open conformation, ATP is released
what are the importance of coupled reactions
when a reaction is endergonic (requires energy), it is very unlikely that this reaction will occur. An exergonic reaction such as hydrolysis of ATP that releases a lot of energy can be ‘coupled’ to the endergonic reaction, therefore pushing the reaction along and getting rid of the positive delta G.
