3: Coupled Reactions and Metabolic Pathways Flashcards
thermodynamics
set of principles that apply to all physical and biological processes and govern the conditions under which they occur
thermodynamics laws
1st law: the total amount of energy in a system and its surroundings is constant
2nd law: the total entropy (S) (level of disorder) of a system and its surroundings always increases spontaneously
3rd law: the entropy of a system approaches a constant value when its temperature approaches absolute zero
enthalpy (H)
enthalpy refers to the heat storage capacity of a system
enthalpy (H) = energy (E) + constant pressure (P) x volume (V)
exothermic reaction = releases heat
endothermic reaction = absorbs heat
gibbs free energy (G)
gibbs free energy tells us is a process will occur on its own (spontaneously or not)
G = change in H - T x change in S
G < 0 = spontaneous, exergonic, energetically favourable = reactants has more energy than products
G > 0 = non-spontaneous, endergonic, energetically unfavourable = reactants have less energy than products
G = 0 = equilibrium
coupled reactions
an energy input is required if G is greater than 0
ATP reaction has change in G of -30.5 JK per mol
the overall free energy change of a coupled reaction is the sum of both individual reactions
activated carrier molecules
energy released by oxidation is stored by activated carrier molecules so not all energy is lost as heat
this energy can then be used for endergonic reactions
ATP is the most widely used and most important activated carrier molecule
obtaining energy
cells obtain energy through oxidation or organic molecules (food)
metabolism = anabolic and catabolic reactions that occur within a cell enabling us to obtain energy from food
fuel oxidation
oxidation = the loss of electrons from a molecule
reduction = gain of electrons
electrons never lost so if one molecule is oxidised another is reduced
OILRIG
when oxidised, there is a loss of hydrogen as protons follow electrons
NAD
NAD+ and NADP+ are both activated carrier molecules
both can get reduced to NADH or NADPH
NAD = catabolic reactions
NADP =anabolic reactions
glycolysis
glycolysis is the initial step of obtaining energy from sugars
consists of 10 reactions
ATP is hydrolysed (-30.5G) in reactions 1 and 3
glycolysis involves oxidation so NAD is reduced
energy is invested at the start
energy is generated at the end
in step 6 and 7 the oxidation of an aldehyde to a carboxylic acid releases energy, much of which is captured in the activated carriers ATP and NADH
lactate
in aerobic cells glycolysis is the main source of ATP so NAD needs to keep being regenerated
when there is no oxygen to accept electrons, NADH passes the electrons to pyruvate acid to form lactate
pyruvate is reduced producing lactate, which takes away electrons from NADH to produce NAD
if there is no lactate, pyruvate moves into the mitochondria where it is decarboxylated to form acetyl CoA
beta oxidation
oxidation of fats
lipids in the body need to be oxidised to become fatty acids
fatty acids firstly converted to fatty acyl-CoA and transported to the mitochondria
fatty acyl-CoA enters cycle of beta oxidation = series of 4 enzymatic reactions which reduce the number of carbon atoms on the fatty acyl-CoA
each cycle = 2 carbon atoms lost
each cycle = 1 acetyl CoA, 1 NADH, 1 FADH2 produced
cycle continues until fatty acid is completed degraded to acetyl CoA
TCA cycle
results in complete oxidation of the carbon atoms in acetyl CoA
acetyl CoA has two carbons, but is transferred to the 4 carbon oxaloacetate to from 6 carbon tricarboxylic acid (citric acid)
consists of 8 reactions which in turn regenerate oxaloacetate
produced 3 NADH, 1 FADH2, 1 GTP
