Bioenergetics

Open system: matter and energy can exchange with surroundings

Closed system: only energy can exchange with surroundings

Isolated system: neither matter nor heat can exchange with surroundings

Heat transfer is energy transfer due to temperature difference.

1 cal = 4.184 J - a dietary Calorie = 1kcal

q=mcΔTq=mc\Delta T

q → heat transferred (J)

c → Specific heat capacity (J g^-1 K^-1)

m → mass of substance (g)

Heat capacity - the relationship between heat and temperature change per unit mass (g) but can also compare between same amounts (moles) of different species.

At a constant pressure in [JK^-1mol^-1]

Work (w) - energy that has been channelled in an organised way to do something useful

Work = force x distance

ΔU=q+w\Delta U=q+w

U → internal energy (J)

q → heat transferred to or from system (J)

w → work transferred to or from system (J)

w=−pΔVw=-p\Delta V

p → work was done at a constant pressure, w is negative

V → change in volume, must be greater than 0

Therefore:

Look at last MCQ for a harder example.

H = U + PV

H → Enthalpy P → Pressure

U → Internal energy V → Volume

A value of a state function depends only on the state of the system, not the path by which that state was reached.

Sum of products - sum of reactants

Bomb calorimeter:

  • Sample ignited in chamber containing oxygen at high pressure

  • Combustion chamber immersed in water in well-insulated outer chamber. Heat from combustion passes to water

  • Relate enthalpy change to increase in temperature of water

Spontaneous: Has a natural tendency to occur

Non spontaneous: Requires work to be done on the system for the change to be brought

ΔS(system)=qT\Delta S\left(system\right)=\frac{q}{T} → q is the heat transferrred to or from the system

the increase in entropy of a substance at any temperature is obtained by measuring the heat added at a temperature T. This must be done in a reversible process → the equation above

ΔS=∑S(products)−∑S(reactan⁡ts)\Delta S=\sum S\left(products\right)-\sum S\left(reac\tan ts\right) for the standard entropy of reaction

ΔS(univ)=ΔS(system)+ΔS(surroundings)\Delta S\left(univ\right)=\Delta S\left(system\right)+\Delta S\left(surroundings\right) > 0 to be possible

ΔS(surroundings)=−ΔHT\Delta S\left(surroundings\right)=-\frac{\Delta H}{T}

ΔG=ΔH−TΔS(system)\Delta G=\Delta H-T\Delta S\left(system\right)

Catabolic - break down complex molecules to simpler ones

Anabolic - synthesise complex molecules from simpler ones

Micelles from because ΔS\Delta S for solvent is highly positive. Breaking of water cages releases water, the entropy of water increases significantly.

Unfolded proteins - free to twist - can adopt large number of conformations. Folded protein more constrained so S (unfolded) should be > S (folded) so S should decrease so why is this spontaneous?

Each hydrophobic side chain reduces the freedom of 2 water molecules. A folded protein has all the hydrophobic groups inside, away from water. Protein interacts with water, folded proteins interact less which makes folding a favourable process.