Lecture 27: Metabolism 1 Flashcards
Tuesday 19th November
What is metabolism?
All the chemical reactions that take place in side the body
What is anabolism?
building up molecules
What is catabolism?
breaking down molecules
What does thermodynamics tell us?
Thermodynamics tells us which reactions are spontaneous or not and, how much energy is required/released when a reaction occurs
What does the first law of thermodynamics state?
- That the total energy of a system and its surroundings are constant
- Energy can not be created or destroyed
- Energy is converted
- i.e Light to covalent bonds
- i.e Chemical bond to movement
Define energy
Energy is the capacity something has to carry out change
Is it true that energy is transferred between a system and its surroundings?
Yes
What is the energy of a system equal to?
ΔEsystem = E2 – E1
Energy of system after process - energy of system before process
What is the energy of a system equal to in terms of heat and work?
ΔEsystem = Q + W
Energy lost as heat + work carried out
Is it true that change in energy is approximately the same as change in enthalpy for a biochemical reaction?
Yes
Is enthalpy a preferred term to energy ?
Yes
What is the equation for enthalpy?
ΔH = ΔE + pΔV
(Change in energy) + (pressure X change in volume)
In biological systems, how is pressure change and volume change like?
Pressure does not change(remains at 1 atm) and volume change is small (which is why energy change and enthalpy change are pretty much the same)
Define exothermic reactions
Enthalpy is released by the system and ΔH<0
Define exothermic reactions
Enthalpy is taken up by the system and ΔH>0
Which equation relates to the first law of thermodynamics?
ΔH = ΔE + pΔV
Give some examples of enthalpy in reactions
- Transfer of heat/energy to the egg
causes a change in the structure of the proteins. Heat leads to change in noncovalent bonding. (endothermic) - Vaporisation of water requires energy
Taking this energy from your body keeps you cool (endothermic) - Heat is released from the chemical reaction
of turning wood into CO2 (exothermic)
What is entropy?
A measure of the disorder of a system
Tendancy of energy to spread out
Describe the second law of thermodynamics
- Tells us whether a reaction will happen or not
- Energy is always increasing in an isolated system
- (if entropy of system AND surroundings is not increasing, then reaction won’t happen)
What is the Gibbs free energy equation?
ΔG = ΔH – TΔS
ΔG:
Change in free energy
ΔH:
change in enthalpy
ΔS:
change in entropy
T:
Temperature in Kelvin
What is Gibbs free energy?
The amount of energy available to do work
What does a negative ΔG mean?
That the change in a system provides energy to do work. Chemical reactions that provide such energy are spontaneous
What does a positive ΔG mean?
That the system takes up free energy from the surroundings. These reactions are not spontaneous
What factors contribute to a negative ΔG ?
Enthalpy and entropy
If ΔH is negative and ΔS is positive, what will ΔG be?
Negative
Can the entropy of a system decrease if the system is not isolated?
Yes
When is a reaction exergonic?
When ΔG is negative , the reaction proceeds spontaneously, and there is a lot of free energy released.
When is a reaction endergonic?
When ΔG is positive, and the reaction is unfavourable or not spontaneous
Does ΔG depend on the reaction pathway?
No, just on the start and end point of a reaction
What does it mean if ΔG = 0?
- No free energy change takes place
- The system is at dynamic equilibrium
(however, living organisms will never achieve overall equilibrium)
ΔG is negative for diamonds turning into graphite. However, we don’t just see diamonds randomly turning into graphite!! Can you explain this phenomenen?
The reaction can happen, but the conversion rate is very slow. ΔG only tells us if a reaction will happen or not, not how quickly (rate) the reaction will occur.
Is it true that most metabolic reactions are too slow to be physiologically relevant without enzymes?
Yes i.e. most metabolic reactions despite being feasible, need enzymes to speed up the rate
How do we regulate metabolism?
- We don’t regulate by whether or not a reaction will take place, as this is controlled by thermodynamics.
- Instead we regulate the activity of enzymes, which control reaction rates.
How can we control/regulate enzymes?
- By regulating transcription and translation. Very easy method. Regulates how much enzyme is made. Slow,energy consuming, costly.
- Allosteric regulation. For example, in glycolysis. This makes enzyme more or less active. Quick and reversible.
- Phosphorylation of enzymes, switching phosphates on and off.
E.g phosphorylation of glucose
- Glucose + ATP → glucose-6-phosphate and ADP
- ΔG under physiological conditions ~ -30kJ/mol {very negative, spontaneous, but not quick]
- But, reaction only happens at significant rate, if there is hexokinase to catalyse it
- Allosterically regulate hexokinase to control this reacion ( glycolysis) (regulators will turn hexokinase on and off)
-
is enzyme regulation key to regulating metabolism?
Yes
