Thermodynamics and Enzymes Flashcards
Define thermodynamics.
Biological systems exists within the universe,
therefore Biological systems obey thermodynamic law
What is the first law of thermodynamics?
“Energy cannot be created or destroyed, but only transformed from one kind of energy to another”
What is the second law of thermodynamics?
“The entropy of an isolated system never decreases”
Define energy
commonly defined as the capacity to do work or transfer heat
Define work
energy used to cause an object with mass to move
Define heat
energy used to cause the temperature of an object to increase
Define kinetic energy
The energy of motion
Define potential energy
an object may possess potential energy by virtue of its position relative to other objects
Energy is put into a…
…system - which causes reactions to take place
Everything outside of the system is the…
…surroundings
In chemical reactions, the reactants and products are the…
…system
…the container and everything beyond it are the…
…surroundings
Energy can be transformed from…
…potential energy to kinetic energy.
Energy can also be transferred back and forth between…
…a system and its surroundings
Any energy that is lost by the system must be…
…gained by the surroundings and vice
versa
What letter represents internal energy?
U
What is internal energy?
Internal energy of a system is the sum of all the kinetic and potential energies of all of its components
What does the delta symbol represent?
Change in
What do we hope to know in regards to U (internal energy)?
change in U (Delta U) that accompanies a change in the system
Equation for change in U (delta U)?
Change in U (delta U) = U final - U initial
When delta U is positive…
…U final is greater than U initial
indicating that the system has
gained energy from the surroundings
When delta U is negative…
…U final is less than U initial
indicating that the system has lost
energy to the surroundings
Gaining energy from surroundings is an …
…endothermic process.
Losing energy to the surroundings is an…
…exothermic process.
When energy is released into the surroundings we get a …
…negative change in internal energy (delta U)
When energy is taken from the surroundings, we get a…
positive change in internal energy (delta U)
Define endothermic
a process in which the system absorbs heat from the surroundings
Define exothermic
a process in which the system loses heat to the surroundings
What is enthalpy a measure of?
a measure of energy available from a
reaction is used
What letter represents enthalpy?
H (in italics)
What about enthalpy is measured?
Changes in enthalpy are measured (ΔH)
H = ?
changes in HEAT CONTENT of a system during the course of a reaction
Enthalpy (H) accounts for…
…the heat flow in processes occurring at constant pressure
the change in enthalpy (DH) equals the…
…heat
gained or lost at constant pressure by the system
DH = positive heat has been…
…gained by the system from the surroundings i.e.
endothermic
DH = negative heat has been…
…n lost by the system to the surroundings i.e. exothermic
The enthalpy for a chemical reaction is…
DH = Hproducts - Hreactants
What is Hess’s Law?
if a reaction is carried out in a series of steps, DH for the overall
reaction will equal the sum of the enthalpy changes for the individual steps
The magnitude of the enthalpy change depends upon the…
…conditions of temperature, pressure and state (solid, liquid, gas) of the reactants and products.
1 bar =
1 bar = sea level
The standard enthalpy of formation is the…
… change in enthalpy for the reaction that forms one mole of the compound from its elements, with all substances in their standard states at 250 C.
What is entropy?
a state function just like internal energy (U) it measures the tendency to
dispersal – the greater the dispersal, the greater the entropy.
s the change in entropy (DS) depends only in the…
…final and initial states of the
system, not the path taken
DS = Sfinal - Sinitial
Molecules can undergo…
…three kinds of motion
What three types of motion can molecules undergo?
- Translational motion
- Vibrational motion
- Rotational motion
Define translational motion
entire molecule moves within constraints of the container
Define vibrational motion
atoms of the molecule move
periodically toward and away from one another
Define Rotational motion
the entire molecule spins.
These different forms of motion are ways in which…
… a molecule can store energy:
motional energy
What is Boltzmann equation?
S = k In W
W = number of possible microstates exist in a system
k = Boltzmann constant
What does the Boltzmann equation do?
represents the connection between the number of microstates and entropy
What does increased dispersion result in?
Increase dispersion –> increased microstates –> increased +ve entropy.
any change in the system that leads
to an increase in the number of microstates leads to…
…a positive value for entropy
When does decreased dispersion occur?
In spontaneous reactions that have a negative entropy because they are highly exothermic reactions.
Endothermic process (where DH is
positive) are always spontaneous if
there is an …
…increase in entropy (dispersion)
The spontaneity of a reaction depends upon both the…
…enthalpy and the entropy of
a system.
Gibbs Free Energy (G) relates…
…enthalpy (H) and entropy (S)
WHat is Gibbs free energy equation?
G = H - TS
H = enthalpy
T = temperatue (K)
S = entropy
the change in free energy (DG) can be expressed as…
DG = DH – TDS
The value of DG will tell us if a…
… reaction will occur or not
If DG is negative (<0),
the reaction is spontaneous
If DG =0,
the reaction is at equilibrium
If DG is positive (>0)…
the reaction is non-spontaneous
Reactions in the biology rarely occur…
…spontaneously.
Why do reactions in biology rarely ever occur spontaneously?
Because energy is required to start the reaction.
Where is activation energy located?
Reactants line to peak of the graph
WHat represents activation energy?
Ea
What is Ea?
represents the energy required to
‘stretch & deform’ bonds in the
reactants making them venerable to
attack
Where is change in g (delta G) located?
Reactants to products
before
the reactants can be transformed into products …
…sufficient amount of energy must be
supplied
changes in temperature will effect…
…the movement of molecules within the system.
How does increased temperature result in a greater rate of reaction?
Increased temperature –> movement increases —> more kinetic energy (translational, vibrational, and rotational energy) –>tendency toward dispersion (more entropy) –> collision frequency increased = increased rate of reaction.
How does decreased temperature result in decreased rate of reaction?
decreased temperature –> movement decreases –> less kinetic energy –> decreased rate of reaction.
As general rule, for each
10oC rise in temperature,…
…the rate of reaction doubles.
This is known as the Q10 phenomenon.
Why does rate of reaction double with each 10 degrees rise?
This is due to the effect that temperature has on the distribution of molecular speeds
As temperature is raised,
the average energy of the
molecules in the system …
…increases
The Arrhenius Equation expresses…
…the relationship between temperature and rate of reaction in terms of number of collisions.
Increasing temperature increases the rate of reaction because there are…
…more
molecules with sufficient energy to overcome the activation energy
Catalysts help increase rate of reaction by…
…by lowering the activation
energy.
Catalysts do not alter the
position of the equilibrium –
but…
…change the rate at which
the equilibrium is attained.
Catalysts provide…
…an alternative route
for the reaction to occur
Catalysts do not…
… get used up in the
reaction
How do enzymes act as catalysts and lower activation energy?
- Enzymes are catalysts and lower activation energy.
- They do this by increasing the entropy in a system.
- Catalysts do not get used up in a reaction and is just a vehicle used to create entropy
Almost all biochemical reactions are controlled by…
…enzymes (biological catalysts)
Catalysts are…
…proteins.
Activity depends on the…
…tertiary and quaternary protein structure (shape of the active
site)
Substrates have a specific…
…size and shape.
a given enzyme
will usually only react with a…
… single of small group of related substrates
Substrates have a shape which is…
…complementary to the active site
The active site has a particular shape which…
…only the substrate can enter.
Describe reactions of enzyme and substrate.
E + S –> ES –> E + P
<–
(possible forward and reverse reactions)
E = enzyme
S = substrate
ES = enzyme-substrate complex
P = products
The rate of an enzyme catalysed reaction increases with…
…increasing substrate concentration until a point where the rate is limited by the concentration of enzyme.
Define the Vmax.
The maximum velocity of an enzymatic reaction when the binding sites are fully saturated with substrate.
What is Vmax measured in?
Vmax is usuaally measured in moles per second
What is Km?
- And the substrate concentration at half Vmax (1/2Vmax)
What is Km measured in?
mM
The rate of an enzyme catalysed reaction increases with…
…increasing substrate affinity.
What is enzyme affinity?
A measure of how tightly the substrate binds to the enzyme.
How does affinity affect Km?
Substrates with a higher affinity have lower values of Km.
The relationship between rate of an enzyme catalysed reaction and substrate concentration is defined by…
…the Michaelis-Menten equation.
What is the Michaelis-Menten equation?
Rate of reaction = Vmax * [S] / Km + [S]
By measuring the rate of reaction using different concentrations of substrate…
…we can determine some important properties of the enzyme.
What important properties of the enzyme can be determined by using different concs of substrate when measuring the rate of reaction?
1) How fast the enzyme can possibly work - Vmax
2) How tightly it binds to the substrate
WHy cant we measure Vmax directly?
Because our data never actually reaches the point of Vmax.
Define competitive inhibition
binding of the inhibitor to the active site of the enzyme prevents substrate binding and vice versa. Here Vmax unchanged however Km changes (affinity is lost)
a non-competitive inhibitor works by…
…Inhibiting allosteric binding site and chnages the chemistry of the active site causing a change in structure, reducing its activity.
- This effects Vmax NOT Km.
an uncompetitive inhibitor works by…
…binds to the enzyme-substrate complex (stabilising it), preventing it from converting into products. Unlike non competitive inhibitors, uncompetitive inhibitors need to the enzyme and substrate to be bound before it can bind.
- Effects Vmax and Km
What factors effect rate of reaction?
- Temperature
- pH
- Inhibitors
what affect does temperature have on enzymes?
enzymes have an optimal temperature. They wont work as effectively at temps above or below this optimum.
what affect does pH have on enzymes?
enzymes have an optimal pH. They wont work as well in pHs above or below its optimum.
In competitive inhibition, the inhibitor…
…competes for active site bindings, reducing enzyme-substrate affinity (Km)
The effect of competitive inhibitors can be overcome by…
…adding more substrate and Vmax can still be reached.
Because the substrate has to compete with the inhibitor, more substrate is needed to achieve the same rate of reactions, therefore Km (enzyme-substrate affinity) increases.
In uncompetitive inhibition, the enzyme binds to…
…allosteric site on
enzyme-substrate complex: complex is
stabilised reducing Vmax and Km
In uncompetitive inhibition, the enzyme is unable to complete the…
…catalytic cycle (turnover), therefore Vmax is lower.
In uncompetitive inhibition, what happens to the ratio of E:ES?
…the ratio or E:ES changes in a way
that it is more favourable for substrate
to bind enzyme = higher affinity and
therefore Km decreases
In non competitive inhibition the enzyme is unable to complete the…
…catalytic cycle (turnover), therefore Vmax is lower
What happens to Km in non competitive inhibition?
the substrate is still able to
bind to the inhibited and uninhibited
enzyme in equal measure, therefore Km
does not alter
In non competitive inhibition…
Inhibitor binds to allosteric site on
enzyme: conformation of active site
is altered, reducing Vmax not Km
