EnzymesChapter 5

(first half only)

1. Types of Energy

Energy – the capacity to perform work Its types:

› Kinetic energy› Potential energy

A form of kinetic energy is heat. A form of potential energy is chemical

energy (energy of molecules)

Chemical reactions can store or release chemical energy.

If a reaction is endergonic – energy is taken in by the reactants to form the products (like dehydration synthesis or photosynthesis)

If a reaction is exergonic – energy is released by the reactants to form the products (like cellular respiration)

Frequently, exergonic reactions fuel endergonic reactions – energy coupling

2. ATP (adenosine triphosphate) ATP: A modified nucleotide molecule

that powers all cellular work directly. Its structure: adenine, ribose and three

phosphates are combined by dehydration synthesis

ATP molecules release phosphate groups to various other molecules. These molecules take in the phosphate by phosphorylation and get excess energy to perform various processes.

When ATP releases a phosphate + energy it produces ADP (adenosine diphosphate)

ADP can turn back to ATP by taking in a phosphate and energy by phosphorylation

http://www.biologyinmotion.com/atp/index.html http://student.ccbcmd.edu/biotutorials/energy/atpan.html

The energy from ATP can be used for the following processes:› Chemical work (forming products from

reactants)› Mechanical work (contracting muscle)› Transport work (moving substances into or

out of the cell)

3. Enzymes Enzymes are proteins that act as biological

catalysts in living organisms. They speed up chemical reactions by

lowering the activation energy of the reaction.

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf

Enzymes have a specific section called the active site that is able to bind with the reactants (substrates) of a chemical reaction

Once the substrates bind to the active site, the active site changes shape and pulls the reactants together. As a result, the reaction occurs faster and more efficiently.

The model that describes that enzymes change shape when bind with the substrate is called the induced fit model

Animations: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

http://www.lpscience.fatcow.com/jwanamaker/animations/Enzyme%20activity.html

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf

Three important special characteristics of enzymes:› They are specific› They are efficient› They are sensitive

Many enzyme do not function without an additional group attached to them. This additional group is called a cofactor.

Some substances can stop enzymes from functioning by attaching themselves to the active site of the enzyme. These are called inhibitors.

Many inhibitors are used as poisons or drugs.