IMED1003 - Bioenergetics (L2)

1st Law of Thermodynamics

- Two fundemental laws govern thermodynamics

1st Law of Thermodynamics:

- Energy cannot be created or destroyed. Energy can be transferred and transformed

2nd Law of Thermodynamics

- Disorder (entropy) in universe is increasing

- Energy transformations proceed spontaneously (convert matter from more ordered and less stable to less ordered and more stable)

- Spontaneous changes that do not require outside energy increase entropy (disorder)

- For a process to occur without energy input, it must increase the entropy of the system

- basically if you just continue normally your room becomes messy. it takes energy to bring order to the room

Second Law of Thermodynamics More details

- during energy transfer or transformation, some energy is unusable, often lost as heat

- Heat = measure of random motion of molecules.

- cells convert organised forms of energy to heat

- According to the second law of thermodynamics: every energy transfer or transformation increases entropy (disorder) of the universe

Life Requires a Lack of Entropy

- Less energy needed for disorder, then for ordered systems

- Living systems: Increase entropy of the universe, use energy to maintain order, have free energy to do work in cellular conditions

- Organisms live at the expense of "free energy"

- think about how proteins, made of many amino acids (disordered pieces) make one single protein (one ordered molecule)

Energy - Summary

- Energy: the ability to do work or cause change

- Kinetic: Motion

- Potential: stored

- Chemical: atoms/molecules

Summary of Laws of Thermodynamics:

1. Energy can be transferred and transformed, but it can't be created or destroyed

2. Every energy transfer or transformation increases the entropy of the universe

Anabolic Pathway of Metabolic Pathway

- anabolism: build complex molecules from simpler ones - consumes energy

Catabolic Pathway of Metabolic Pathway

- catabolism: break complex molecules into simpler ones, releases energy

Potential Energy

- stored energy (includes chemical energy in molecules)

Kinetic Energy

- currently causing change (involves some type of motion)

Gibbs' Free Energy

- in cells, molecules have certain amount of free energy (G)

- Gibbs' free energy (G) - energy contained in molecule's chemical bonds (when Temp and Press Constant)

- the free energy associated with a reaction = energy available for doing work

- Chemical reactions - change in free energy (change in G) (Delta G)

- Delta G can be positive or negative

- In test tube, some reactions release heat (exothermic), others absorb heat (endothermic)

- not all this energy available for chemical reactions - some transferred as heat, as entropy increases

Free Energy

Delta G = Delta H minus (T * delta S)

- equation describes change in free energy when accounting for transfer of heat (enthalpy, H) and change in disorder (entropy, S) of the system (T = temperature)

- Enthalpy: measure of energy in thermodynamic system. We'll simply call it heat content, even though this isn't strictly accurate

- Entropy: amount of disorder. In the context of energy exchange, entropy = energy unavailable for use

More on Free Energy

- the potential energy at the top is higher for the ball, so as it rolls down it loses potential energy hence delta H is negative

- Diffusion of gas increases disorganisation of particles hence entropy is greater then 0

- Explosion massively increases temperature

Exergonic Reaction

- reaction releases free energy

- delta G is negative

- we go from substrate with high level of energy in bonds to products with low level of energy in bonds with dissipation of heat

Endergonic Reaction

- reaction requires energy input

- delta G is positive

- substrate goes from low energy to high energy (energy added)

Delta G examples

- #1 has a Delta G of less then 0 (when ball rolls down slide T increase (friction))

- #2 has Delta G of less then 0 (since entropy increases)

- #3 has T increase so Delta G is less then 0

Exergonic Reactions More Info

- substrates have more free energy then products

- net release of energy and or increase of entropy

- occur spontaneously (without net input of energy)

- Delta G is negative

Endergonic Reactions

- Substrates have less free energy then products

- Net input of energy and or decrease in entropy

- do not occur spontaneously

- Delta G is positive

Energetics of Reactions

- when molecules (substrates) are altered to form new molecules (products), the energy change is given by:

- Delta G = G product - G substrates

DIAGRAM ON SLIDE 16

- ATP = principal molecule providing energy for endergonic cellular reactions

- e.g ATP --> ADP + Pi

Energy Transfer in Cells

- endergonic: use energy

- exergonic: release energy

- Exergonic Reactions can be coupled to endergonic reactions

- ATP Synthesis from ADP + Pi requires energy

- Pi is inorganic phosphate

- basically ATP synthesis from ADP and Pi has delta G positive

- ATP hydrolysis has delta G negative

ATP and Phosphates

- Pi is inorganic phosphate

- PPi is pyrophosphate

we have phosphoanhydride bonds

- each ATP molecule can release energy when Pi is removed

Energy and Us (NO LEARNING OUTCOME)

- chemical energy goes in (carbohydrates, fats, others)

- Chemical waste goes out (carbon dioxide, water)

- Heat goes out

- ATP is the body's energy currency

- Metabolism

ATP levels and usage

- estimated to be around 100g of ATP in healthy adults, some estimates up to 250g, not that much

- We use around 70kg ATP/day. So we have to generate ATP, recycle and reuse the core components

- Cells need 1-10mM ATP to function

- cells have a pool of ATP interconverted to ADP and AMP (and again, again, again and so on)

Energy Change

- a way to describe the energy status of a cell

- value can range from 0 (all AMP) to 1 (all ATP) in cell

- important in regulating some key metabolic enzymes

- we say 1 when ATP is predominant

- we say 0 when AMP is predominant