Lecture 27: Metabolism 1

Question 1

What is metabolism?

Answer 1

All the chemical reactions that take place in side the body

Question 2

What is anabolism?

Answer 2

building up molecules

Question 3

What is catabolism?

Answer 3

breaking down molecules

Question 4

What does thermodynamics tell us?

Answer 4

Thermodynamics tells us which reactions are spontaneous or not and how much energy is required/released when a reaction occurs

Question 5

What does the first law of thermodynamics state?

Answer 5

• 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

Question 6

Define energy

Answer 6

Energy is the capacity something has to carry out change

Question 7

Is it true that energy is transferred between a system and its surroundings?

Answer 7

Yes

Question 8

What is the energy of a system equal to?

Answer 8

ΔEsystem = E2 – E1

Energy of system after process - energy of system before process

Question 9

What is the energy of a system equal to in terms of heat and work?

Answer 9

ΔEsystem = Q + W

Energy lost as heat + work carried out

Question 10

Is it true that change in energy is approximately the same as change in enthalpy for a biochemical reaction?

Answer 10

Yes

Question 11

Is enthalpy a preferred term to energy ?

Answer 11

Yes

Question 12

What is the equation for enthalpy?

Answer 12

ΔH = ΔE + pΔV

(Change in energy) + (pressure X change in volume)

Question 13

In biological systems, how is pressure change and volume change like?

Answer 13

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)

Question 14

Define exothermic reactions

Answer 14

Enthalpy is released by the system and ΔH<0

Question 15

Define exothermic reactions

Answer 15

Enthalpy is taken up by the system and ΔH>0

Question 16

Which equation relates to the first law of thermodynamics?

Answer 16

ΔH = ΔE + pΔV

Question 17

Give some examples of enthalpy in reactions

Answer 17

• 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)

Question 18

What is entropy?

Answer 18

A measure of the disorder of a system

Tendancy of energy to spread out

Question 19

Describe the second law of thermodynamics

Answer 19

• 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)

Question 20

What is the Gibbs free energy equation?

Answer 20

ΔG = ΔH – TΔS

Question 21

ΔG:

Answer 21

Change in free energy

Question 22

ΔH:

Answer 22

change in enthalpy

Question 23

ΔS:

Answer 23

change in entropy

Question 24

T:

Answer 24

Temperature in Kelvin

Question 25

What is Gibbs free energy?

Answer 25

The amount of energy available to do work

Question 26

What does a negative ΔG mean?

Answer 26

That the change in a system provides energy to do work. Chemical reactions that provide such energy are spontaneous

Question 27

What does a positive ΔG mean?

Answer 27

That the system takes up free energy from the surroundings. These reactions are not spontaneous

Question 28

What factors contribute to a negative ΔG ?

Answer 28

Enthalpy and entropy

Question 29

If ΔH is negative and ΔS is positive, what will ΔG be?

Answer 29

Negative

Question 30

Can the entropy of a system decrease if the system is not isolated?

Answer 30

Yes

Question 31

When is a reaction exergonic?

Answer 31

When ΔG is negative , the reaction proceeds spontaneously, and there is a lot of free energy released.

Question 32

When is a reaction endergonic?

Answer 32

When ΔG is positive, and the reaction is unfavourable or not spontaneous

Question 33

Does ΔG depend on the reaction pathway?

Answer 33

No, just on the start and end point of a reaction

Question 34

What does it mean if ΔG = 0?

Answer 34

• No free energy change takes place
• The system is at dynamic equilibrium

(however, living organisms will never achieve overall equilibrium)

Question 35

ΔG is negative for diamonds turning into graphite. However, we don’t just see diamonds randomly turning into graphite!! Can you explain this phenomenen?

Answer 35

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.

Question 36

Is it true that most metabolic reactions are too slow to be physiologically relevant without enzymes?

Answer 36

Yes i.e. most metabolic reactions despite being feasible, need enzymes to speed up the rate

Question 37

How do we regulate metabolism?

Answer 37

• 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.

Question 38

How can we control/regulate enzymes?

Answer 38

• 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.

Question 39

E.g phosphorylation of glucose

Answer 39

• 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)

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Question 40

is enzyme regulation key to regulating metabolism?

Answer 40

Yes