Friday, October 24, 2008


Metabolism-the totality of an organism's chemical reactions

Metabolic pathway
- begins with a specific molecule that is altered in to a final product

Catabolic pathway
- releases energy and breaks down complex molecules into simpler compounds
(ex. cellular respiration)

anabolic pathway- absorbs energy to build complicated molecules from simpler ones
(ex. protein synthesis from amino acids)

bioenergetics- the study of how energy flows through living organisms

energy- capacity to cause change; ability to rearrange collection of matter

kinetic energy- relative motion of obejects

potential energy-energy that is not kinetic; energy that matter possess because of its ocation or structure

The study of energy transformations the occur in matter is called thermodynamics, and there are two basic laws of thermodynamics. The first law of thermodynamics (even bioenergetics) states that the energy of the universe is constant and that energy can be transferred and transformed, though it cannot be created or destroyed.

*Also called the Principle of Conservation of Energy

Everything Works continuously! When there is system within a certain surrounding, things come in and out and there are lots of transformations, but nothing gets outside barrier of Universe. So energy is constant, just transformations are different.
Living Cells covert organized energy into heat.

Example: By turning on a fan, you convert mechanical energy to kinetic energy

The second law of thermodynamics states that very energy transfer of transformation increases entropy, or the amount of disorder or randomness, in the Universe.

Another definition to the second law-For any process to occur spontaneously, it must increase the entropy of the universe.

- When you eat a protein or any polysaccharide, it is broken down and energy is released (catabolic)

-You are getting ready play a big game, and you play the sport to release energy (catabolic)
Afterwards, you eat to absorb energy (anabolic)

-An example of entropy is a messy room... it takes energy to clean it up
-Another example, a cheetah eating a gazelle to convert food into chemical energy, to go and catch more prey
*With each input there is an output

-An aside: The energy drinks that rock stars drink contain monosccharides which break down fast in the body. Really you need to eat polysaccharides for some time before a big game. The energy drinks just give you a rush of silly energy and then you pass out.


The free energy change of a reaction tells us whether or not the reaction occurs spontaneously
Unstable systems are rich in free energy, G. They have a tendency to change spontaneously to more stable state, and it is possible to harness this “downhill” change to perform work

Example: A diver has more potential energy (free energy to utilize) right before they dive and that transforms to kinetic energy during dive (heat is released when someone dives).
-Up on the diver platform=positive Delta G which indicates a greater work capacity but instability

Free energy is defined as the part of a system’s energy that us able to perform work when the temperature of a system is uniform. Free energy is depicted as G. The symbol for the total energy of a system is H, and the symbol for entropy is S. The relationship between the change in free energy, change in energy, change in entropy, and temperature is as follows”

Delta G=Delta H – T Delta S
Total-heat= final

In order for a chemical reaction to occur spontaneously (going down), the system must experience either a decrease in H (energy) or an increase in S (entropy)

Keep in mind that nothing, not a car, a washer, a dryer, are 100% efficient because heat is still released

An exergonic reaction is one in which energy is released (Delta G is negative). The greater the decrease in free energy, the greater the amount of work that can be done. The products have less free energy than he reactants
**Exergonic is spontaneous with a negative delta G (potential)


An endergonic reaction is one that requires energy in order to proceed. Endergonic reactions absorb free energy from the surroundings. This reaction is “uphill” which uses energy.
**Endergonic is non-spontaneous with a positive delta G (kinetic)

Review of reactions

Exergonic Reactions

energy released=catabolic
- Delta G (free energy)
H (energy) must decrease
gives up order (TS must increase)
system becomes more stable

Endogonic Reaction
energy absorbed=anabolic
+Delta G (free energy)
non spontaneous
system becomes less stable

ATP Is very important molecule, because it is primary source of enrgy for the cell. Also known as adenosine triphosphate, ATP is made up of the nitrogenous base adenine, bodnded to ribose and a chain of three phosphate groups. When a phosphate group is hydrolyzed, energy is released in an exergonic reaction

Work in the cell is done by the release of a phsphate group from ATP. When ATP tranfers one phosphate group through hydrolysis, it become ADP (adenosine triphosphate).

The ATP cycle in the cell involves the use of energy that’s released from catabolic reaction re-phosphorylate ADP to form ATP. Energy is released when ATP is then dephosphorylates and exergonic reaction to power important cellular processes

Practice questions

1. Which of the following best describes a pathway which absorbs energy to build complicated molecules from simpler ones?

a) anabolic pathway
b) thermodynamic pathway
c) catabolic pathway
d) metabolic pathway

2. Which reaction process with a net release of free energy?

a) endergonic reaction
b) decomposition reaction
c) exergonic reaction
d) hydrolysis reaction

3. In which reaction is there a positive delta G (the quantity of energy required to drive a reaction)?

a) endergonic reaction
b) metabolic reaction
c) exergonic reaction
d) thermal energy reaction

Answers: 1.a, 2.c, 3.a

1 comment:

meghan said...

Thanks Marina! The cartoon was really cute, too! LOL :)