bioenergetics Flashcards
what are the laws of bioenergetics
The laws of thermodynamics determine the course of enzyme reactions.
1st law of Thermodynamics: “Energy can be transferred and transformed, but it can neither be created or destroyed”
2nd Law of Thermodynamics: “Every energy transfer or transformation increases the entropy of the Universe”
molecules have energy and so have the capacity to do what
Work:
Muscle movement
Active transport of ions and molecules
Maintaining cells against an osmotic gradient
Synthesis of molecules
Degradation of molecules
Nerve impulses
what is enthalpy H
Enthalpy (H) can be considered as the energy content of a system such as a molecule and is stored in its bonds (kilojoules per mole).
what causes a change in enthalpy
When chemical reactions take place, chemical bonds are formed and are broken. There is therefore likely to be a change in enthalpy
Enthalpy is affected by changes in pressure and concentration but this is minimal in biological systems and can be ignored.
By comparing published values we can predict what about enthalpy
whether a reaction will be endothermic (heat energy taken in from surroundings, DH>0) or exothermic (heat energy released to the environment, DH<0).
why do exo and endo thermic reactions usually need initial energy output
because there is an activation energy barrier to be overcome.
ex: Fireworks: highly exothermic
Molecules absorb the activation energy (from spark), an explosion begins to take place, energy is released in the form of heat, light, and sound.
explain Spontaneity of biological reactions
“Spontaneous” reactions occur without any external input of energy over and above the activation energy.
In general, a reaction is more likely to be feasible if calculations show it to be exothermic rather than endothermic i.e. it is driven by Enthalpy ….but this is not the only factor.
explain entropy , S
Reactions can also be driven by the fact that at the end of the reaction the substances are in a more random state than at the beginning.
This phenomenon is measured by a quantity known as Entropy (S).
nature favours a process that increases what
“nature favours a process that
increases disorder”
explain free energy, G
can be defined for every compound and combines both entropy and enthalpy.
The change in free energy, DG is the overall determinant of whether a given chemical reaction is possible or not.
DG must be negative for the reaction to occur spontaneously i.e. to occur without a NET addition of energy to the system.
describe an exergonic free energy reaction
therefore is spontaneous….but it will still require activation energy, which is later recovered in the course of the reaction.
describe an endergonic free energy reaction
therefore not spontaneous….it will require activation energy, plus a net addition of energy to the system.
what does delta G=
delta H - T delta S
delta G - change in free energy
delta H - change in enthalpy
T - temperature
delta S - change in entropy
It can be easily calculated from published tables and is useful for comparisons.
what is the Standard free energy change delta G
the change in free energy that accompanies the formation of 1 mole of that substance from its component elements, at their standard states (1M).
what does the biological standard free energy change delta G assume
assumes all participants are in the standard state (ie. 1M) except H+ (pH is assumed to be 7.00).
Chemical reactions with a positive DH value can often be made to occur by what
increasing T (in delta G equation) until delta G becomes negative.
Plants and animals cannot so readily increase their temperature to get such reactions to occur, instead they employ what
enzymes (to lower the activation energy barrier) and coupled reactions (to supply the net energy).
for a series of coupled reactions we can add what together
add the free energy changes together
coupled reactions much have a common what
intermediate
what is metabolism
Sum total of all the chemical reactions that take place in a living organism.
describe what metabolic pathways are
Reactions in cells are organised in pathways.
The major metabolic pathways for all life forms are similar.
the study of metabolic reactions in simple life forms help understanding of what
corresponding metabolic reactions in more complex organisms such as humans.
what are some common features of metabolic pathways
Most pathways have (at least) one reaction which has:
large keq ie. is irreversible – ensures pathway operates in one direction only
large, negative DG : pathway is energetically favourable
high energy compounds in metabolic pathways have greater what
greater free energy of hydrolysis than a typical compound.
They are therefore key intermediates in metabolic reactions.
