Enzymes

Chapter 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)

Laws of Thermodynamics• 1st: Energy cannot be created or destroyed

only changed to different forms.• 2nd: Energy conversions always produce heat

so they are never 100 % efficient • Spontaneous chemical reactions head toward

increasing disorder (entropy)

• 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.

• Competitive inhibitors – bind to the active site and stops the enzyme from binding

• Noncompetitive inhibitors – bind to an allosteric site and change the shape of the active site.

• Many inhibitors are used as poisons or drugs.• Use this as a review: http://ats.doit.wisc.edu/biology/cb/td/t4_a1.htm