L5 Energy Flashcards
What is metabolism?
Metabolism comprises all chemical reactions in a cell
What two types of reactions can metabolism be divided into?
Anabolic and catabolic reactions
What are anabolic reactions? (2)
- Anabolic reactions link simple molecules together
- They are energy storing reactions; they require energy
What are examples of anabolic reactions (3)
- DNA replication
- protein synthesis
- making of starch
What are catabolic reactions (2)
- They break down complex molecules into simpler ones
- They release energy
What is an example of a catabolic reaction?
digestion of food
What is the def of energy?
energy is defined as the potential capacity to do work w
What drives energy conversions?
The tendency of energy to become evenly distributed or dispersed over time (2nd law of thermodynamics)
What is the first law of thermodynamics?
Energy is neither created nor destroyed
What is the second law of thermodynamics
Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so
→ energy moves from high energy area to low energy area
What are examples of the second law of thermodynamics? (3)
- a hot cup of coffee will cool down, but never warm up on its own
- a balloon will lose air, but never gain it on its own
- a swimmer can dive into the water but is never thrown out of the water by concerted movement of water molecules
What happens to entropy (disorder) as energy follows the second law of thermodynamics?
Disorder increases
What is ΔG
Free energy
How can cells release free energy? (2)
- with a chemical reaction creating disorder (entropy aka ΔS)
- with a chemical reaction releasing heat (enthalpy aka ΔH)
What is the equation that expresses the change in free energy
ΔG = ΔH - TΔS
What does it mean when ΔG is negative?
- Energy is released/dispersed
- The reaction is favorable, it can happen spontaneously
What does it mean when ΔG is positive?
Energy is required for the reaction to happen
REACTION 1:
Heat is released (neg ΔH) and disorder increases (pos TΔS)
What does this mean for free energy?
- This reaction is always spontaneous (exergonic) because ΔG is always negative
- (-)ΔH - TΔS = (-)ΔG
REACTION 2:
Heat is released (neg ΔH) and disorder decreases (neg TΔS)
What does this mean for free energy?
- ΔG is only negative under a certain temperature, so the rx is only spontaneous under that T
- (-)ΔH - (-)TΔS = -ΔH +TΔS
- An example of this reaction is in protein folding: this process can only occur below a certain temperature
REACTION 3:
Heat is used (pos ΔH) and disorder increases (pos TΔS)
What does this mean for free energy?
- (+)ΔH - (-)TΔS
- The reaction is spontaneous above a certain temperature
- An example of this is dissolving NaCl in water
REACTION 4:
Heat is used (pos ΔH) and disorder decreases (neg TΔS)
What does this mean for free energy?
- never spontaneous (endergonic)
- (+)ΔH - (-)TΔS = (+) ΔG
- this applies to most anabolic reactions
How can anabolic reactions occur? (reactions with a positive ΔG
They can ONLY occur when they are coupled to a exergonic reaction to make the overall ΔG negative
What happens when you increase the amount of reactants in a reversible reaction?
You speed up the forward reaction
What happens when you increase the amount of products in a reversible reaction?
You speed up the reverse reaction
What happens when you leave a reversible reaction alone?
It will proceed to the point of chemical equilibrium, where no more net changes take place
What happens to the speed of the forward and reverse reactions when there is chemical equilibrium?
They proceed at the same rate from one another
What happens to ΔG at the point of chemical equilibrium?
ΔG = 0
What is ATP?
ATP is Adenosine triphosphate
It is a molecule; an organic compound
What do cells use ATP for?
To capture, transfer and store energy
How is ATP used to allow for endergonic reactions?
Some of the free energy released by exergonic reactions is capture in ATP, which then can drive endergonic reactions
What type of reaction is ATP hydrolysis (endergonic or exergonic)
Exeregonic
What can ATP hydrolysis be used for?
It can be used to drive endergonic reactions such as making a polymer
What is the reaction of ATP hydrolysis?
ATP + H2O → ADP + Pi + free energy
(Pi = phosphate ion)
Why is ATP hydrolysis so exergonic?
Because the resulting ADP from this reaction is constantly removed either by reforming ATP or by hydrolysis to AMP
Can you know the rate of a reaction knowing that ΔG is negative?
No you cannot predict the rate of the reaction
At what rate do most exergonic reactions occur? (slow or fast)
Most occur at an immeasurable slow rate
What do exerfonix reactions need to get started?
They need a bit of activation energy to get started, to put the molecules into a transition state favorable to the reaction
What is a catalyst?
A catalyst is any substance that speeds up a chemical reaction without itself being used up
Can catalysts speed up all types of reactions?
No, catalysts can only speed up spontaneous reactions (reactions where ΔG is negative)
Can catalysts change the value of ΔG?
No
What are most biological catalysts?
Most biological catalysts are proteins called enzymes
What can biological catalysts (enzymes) also be called?
Sometimes they are called RNAs that have folded into a 3D structure, especially within the ribosome.
How do enzymes work?
Enzymes work by lowering the activation energy
Why are enzymes crucial in our body?
- Because at 37 degrees, most spontaneous reactions do not proceed since the energy barrier cant be overcome.
- So, since enzymes can lower the activation energy, they are important to our bodies
What happens when reactants (called substrate) binds to the active site of the enzyme?
The enzyme often undergoes a small conformational change (a shape change) which brings the substrates into a transition state
What happens when the products leave the enzyme site?
The enzyme reverts to its og shape
What does the enzyme do that induces the transition state? (3)
- It can bind the substrates in the correct orientation
- It can expose the reactants to altered charge environments that promote catalysis
- It can induce a strain on the substrate that facilitates breaking of a covalent bond
What are cofactors?
Cofactors are small organic molecules or ions that are not amino acids and are associate more or less tightly with the enzyme
What are cofactors used for
Certain enzymes need cofactors in order to function
When is an enzyme saturated?
When all active sites are occupied
What happens if the substrate concentration increases when an enzyme is already saturated?
Nothing : A further increase in substrate concentration will no longer increase the rate of product formation
What is the maximum speed of a reaction called?
The turnover rate
What determines the turnover rate?
The speed of the reaction when the enzyme is saturated
How much can the turnover rate vary?
It can vary from 1 molec/sec to 40 million molec/sec
What is enzyme regulation?
The control of the rate of a reaction catalyzed by an enzyme by a regulatory molecule
What are the 2 types of enzyme regulation?
Competitive inhibition and allosteric regulation
What is competitive inhibition?
A regulatory molecule binds to the enzyme’s active site and because of this the substrates cannot bind anymore
What is allosteric regulation?
A regulatory binds to a different site on the enzyme which changes the shape of the enzyme’s active site. The substrates can no longer bind to the active site.
Which is more efficient: competitive inhibition or allosteric regulation? and why?
- Allosteric inhibition is much more efficient because less inhibitor molecules are required.
- You need more competitor molecules than substrate molecules for effective competitive inhibition, but you only need more allosteric regulators than enzymes, because nothing else binds at the allosteric site.
