6

Life’s Mainspring:An Intoduction to Energy

I. What Is Energy? (Section 6.2)A. Definition of energy—capacity to do work

(movement against an opposing force). Energy is a tricky subject because it can be measured but not seen.

B. Two main forms:

1. Potential energy—stored (chemical) energy like a rock on a hill or a lump of coal.

2.Kinetic energy—energy in motion like a rolling rock or heat from a burning lump of coal.

Stores energy in your liver and muscles

Gives you energy when broken down in respiration

II. The Energy Currency Molecule: ATP (Section 6.4) ATP is the energy carrier of the cell

ATP is made up of adenosine and 3 phosphates.

The outer two phosphates can be broken off to release energy.

The outer two phosphates can be added to store energy.

Energy Reactions

• Exergonic reactions release energy: – When ATP loses a phosphate, energy is

released.

• Endergonic reactions store energy

•When ATP is formed from ADP or AMP, energy is stored in the chemical bonds

IV. The Energy Currency Molecule: ATP (Section 6.4)B. How ATP is used to perform cellular work, like

transport:

1. Want to move calcium ions up their concentration gradient into a muscle cell.

(active transport – remember?)

ATP splits into ADP and phosphate, a downhill reaction that releases energy.

The energy is used to transfer phosphate onto a protein, causing shape change that drives calcium across the membrane.

III. Enzymes

A. Characteristics (Section 6.5)

1.Exergonic reactions like splitting sugar may not happen very quickly, so in living organisms the reactions are hastened by enzymes.

2.Many different enzymes may be needed to accomplish one task, like manufacturing breast milk. Series of steps and the enzymes that hasten them are called metabolic pathways: Figure 6.6 animation

3.Substrate—substance being worked on by each specific enzyme. (Interactive Activity 3)

1. Enzymes speed up reactions by lowering the amount of energy needed to get chemical reactions going (activation energy): Figure 6.7

2. Enzymes are catalysts (retain their original chemical composition while bringing about a change in a specific substrate).

A + B + Enzyme Enzyme-substrate C + Enzyme

complex

3. Almost all enzymes are proteins.

Substrate Product

Importance of shape in enzyme function (active site = place that binds substrate, and often coenzymes play a role in this process): Figure 6.8, animation

C. Regulating Enzyme Activity (Section 6.7) What factors influence the amount of product?

1.Amount of substrate available

2.Molecules similar to substrate can bind and block binding of real substrate. An example is the nerve gas Sarin, recently used in a germ warfare attack in a Japanese subway. It binds to the enzyme cholinesterase that breaks down the neurotransmitter acetyl-choline so that it can be recycled and reused for more nerve cell communication. (Interactive Activity 5 & 6)

3. Allosteric regulation, when a compound prevents the substrate from binding the active site by binding another region on the enzyme.

The End