Enzymes & E a 3.3

Activation Energy (E a ) even spontaneous reactions require an initial input of energy, called activation energy (E a )

What about thermal E? not a practical source of energy for reactions in living organisms can disrupt or denature proteins is non-specific (would speed up all reactions)

Enzymes and E a

How is E a reduced? enzyme provides proper orientation of substrate(s) provides specific environments such as ionic groups that promote catalysis enzyme puts strain on bonds of substrate(s), making them easier to break

Animation Activation Energy & Enzymes: /animations/content/enzymes/enzymes. htmlhttp:// /animations/content/enzymes/enzymes. html

Food As Fuel 3.4

Redox Reactions electrons are lost from one atom and gained by another atom [see also 1.1, page 17] oxidation is the loss of electrons by an atom/molecule reduction is the gain of electrons by an atom/molecule

Redox Reactions oxidizing agent is the atom/molecule that gains electrons (i.e. is reduced) reducing agent is the atom/molecule that loses electrons (i.e. is oxidized) sometimes entire atoms (with their electrons) are transferred during redox reactions

Redox… redox can occur because of relative loss or gain of electrons CH 4 + 2O 2 --> CO 2 + 2H 2 O –C is oxidized –O is reduced removal of H is also called oxidation; addition of H is also called reduction

Oxidation of Glucose in cellular respiration, glucose is oxidized the combustion (oxidation) of glucose releases a large amount of thermal E in cells, oxidation of glucose occurs in a series of steps (controlled oxidation) to minimize E loss

Energy Carrier: NAD + NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in all living cells it is a derivative of vitamin B 3 (niacin)

Reduction of NAD+

Energy Carrier: FAD FAD (flavin adenine dinucleotide) is a coenzyme involved in respiration it is a derivative of vitamin B 2 (riboflavin)

Reduction of FAD