Chapter 8.1 Notes

Period 4 11/17/16

Chapter 8.1 Notes EQ: What Physical Principles Underlie ​Biological Energy​ Transformations?

What is the difference between potential energy and kinetic energy?

Between anabolism and catabolism?

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What are laws of thermodynamics?

How do they relate to biology?

-Metabolic reactions and catalysts are essential to the biochemical transformation of energy by living things. In biochemistry, it is more useful to consider energy as the capacity for change.

There are two basic types of energy and of metabolism -Energy comes in many forms: chemical, electrical, heat, light, and mechanical.

But all forms of energy can be considered as 1 of 2 basic types: ​ • ​Potential energy is the energy of state or position—that is, stored energy. Can be stored in many forms: in chemical (Figure 8.1) b​ onds, as a concentration gradient, or even as an electric charge imbalance • ​Kinetic energy is the energy of movement—that is, the type of energy that does work, that makes things change.

-Chemical reactions continuously occur in the body to provide energy and the totality of these reactions is called ​metabolism​.

• ​Anabolic reactions (anabolism) link simple molecules to form more complex molecules.

Anabolic reactions require an input of energy and capture it in the chemical bonds that are formed.

• ​Catabolic reactions (catabolism) break down complex molecules into simpler ones and release the energy stored in chemical bonds.

-Catabolic & anabolic reactions are often linked.

-The laws of thermodynamics (“energy”; dynamics, “change”) were derived from studies of the fundamental physical properties of energy, and the ways it interacts with matter.

The first law of thermodynamics: Energy is neither created nor destroyed -​The first law of thermodynamics states that in any conversion of energy, it is neither created nor destroyed. Another way of saying this is: in any conversion of energy, the total energy before and after the conversion is the same. (​Figure 8.2) The second law of thermodynamics: Disorder tends to increase -​Although energy cannot be created or destroyed, the second law of thermodynamics states that when energy is converted from one form to another, some of that energy becomes unavailable for doing work.

-It takes energy to impose order on a system. Unless energy is applied to a system, it will be randomly arranged or disordered.

-NOT ALL ENERGY CAN BE USED In any system, the total energy includes the usable energy that can do work and the unusable energy that is lost to disorder:

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total energy = usable energy + unusable energy In biological ​ systems, the total energy is called ​enthalpy (​H )​. The usable energy that can do work is called ​free energy (​G)​. Cells require free energy in order for chemical reactions to allow growth, cell division, and maintenance. ​ The unusable energy is represented by ​entropy (​S) ​ multiplied by absolute temperature (​T).

-DISORDER TENDS TO INCREASE -Chemical changes, physical changes, and biological processes all tend to increase entropy, and this tendency gives direction to these processes. It explains why some reactions proceed in one direction rather than another.

-The construction of complexity also generates disorder.

What is the • In the human body, metabolism creates far more disorder (more energy is lost to entropy) difference between than the amount of order (total energy; enthalpy) stored in 1 kg of flesh. endergonic and -Life requires a constant input of energy to maintain order. exergonic reactions ​Chemical reactions release or consume energy and what is the -​Since anabolic reactions link simple molecules to form more complex molecules, they tend to importance of ΔG? increase complexity (order) in the cell.

• ​Catabolic reactions may break down an ordered reactant into smaller, more randomly distributed ​ products. Reactions that release free energy (–Δ​G) are called ​exergonic​ reactions.

For example: complex molecules → free energy + small molecules • ​Anabolic reactions may make a single product (a highly ordered substance) out of many smaller reactants (less ordered). Reactions that require or consume ​ ​(Figure 8.3) free energy (+Δ​G) are called ​endergonic ​reactions.

For example: free energy + small molecules → complex molecules -At some concentration of A & B, the forward & reverse reactions take place at the same rate, which ​chemical equilibrium.

Chemical equilibrium and free energy are related -All reactions have a specific equilibrium point, meaning that eventually every reaction’s rate of its forward reaction will equal its rate of the reverse reaction.

-Chemical equilibrium DOES NOT mean that the proportion of reactants to products are 1:1.

-The further​ toward completion the point of equilibrium lies, the more free energy (Δ​G) is released.

-A large, positive Δ​G for a reaction means that it proceeds hardly at all to the right (A → B).

-A Δ​G value near zero is characteristic of a readily reversible reaction: reactants and products have almost the same free energies.

Summary:

Two laws of thermodynamics govern energy transformations in biological systems. The first law of thermodynamics is that energy is neither created nor destroyed. The second law of thermodynamics is that disorder tends to increase in chemical reactions. The totality of reactions involving energy transformations is called metabolism. A biochemical reaction can release or consume energy, and it may not run to completion, but instead end up at a point of equilibrium.

RECAP QUESTIONS: 1. What is the difference between potential energy and kinetic energy? Between anabolism and

catabolism?

Kinetic energy is energy possessed by a body by virtue of its movement.

Potential energy is the energy possessed by a body by virtue of its position or state. While kinetic energy of an object is relative to the state of other objects in its environment, potential energy is completely independent of its environment.

Anabolism is the buildup of complex organic molecules from simpler ones, reactions are called anabolic or biosynthetic. They involve dehydration synthesis (release water) and are endergonic.

Catabolism is the breakdown of complex organic molecules into simpler ones. Reactions are called catabolic or degradative reactions, they are usually hydrolytic reaction and are exergonic.

2. ​What are laws of thermodynamics? How do they relate to biology?

The laws of thermodynamics are important unifying principles of biology. These principles govern the chemical processes (metabolism) in all biological organisms.

The First Law of Thermodynamics, also know as the law of conservation of energy, states that energy can neither be created nor destroyed. It may change from one form to another, but the energy in a closed system remains constant.

The Second Law of Thermodynamics states that when energy is transferred, there will be less energy available at the end of the transfer process than at the beginning. Due to entropy, which is the measure of disorder in a closed system, all of the available energy will not be useful to the organism.

Entropy increases as energy is transferred.

Energy enters living systems as chemical energy (either food derived from other organisms or compounds formed by high energy processes such as geothermal energy) or light energy via photosynthesis. This energy is used to maintain the cellular environment (homeostasis), growth and replication. Although breaking down compounds yields energy, some is lost as heat, and more energy is lost as heat building the compounds up.