The Hindenberg

The Crash The famous German- built Hindenburg had a length of 245 m (804 ft) and a gas capacity of 190,000,000 liters (6,710,000 cu ft). After making ten transatlantic crossings in regular commercial service in 1936, it was destroyed by fire in 1937 when it was landing at Lakehurst, New Jersey, with 97 passengers and crew; 35 people on board and 1 ground crew member were killed.

Hydrogen Hydrogen gas, because it is lighter than air, floats upward in the atmosphere. People once used it to lift zeppelins and other airships into the sky, allowing trans- Atlantic voyages by air. However, because the gas is so flammable, it contributed to many explosive accidents, including the Hindenberg explosion in Airships now use helium gas because it is nonflammable and therefore a safer lifting gas. 2H 2 + O 2 → 2H 2 O + energy

Enzymes & Energy In biological systems, the are 3 general energy paths a reaction can take. In biological systems, the are 3 general energy paths a reaction can take. 1. Exergonic Reaction - One in which energy is released (Products have less chemical energy than reactants). This often, however requires Activation energy to initiate a reaction. 1. Exergonic Reaction - One in which energy is released (Products have less chemical energy than reactants). This often, however requires Activation energy to initiate a reaction.

Endergonic Reaction Endergonic Reaction - One in which energy must be supplied for the reaction to occur (products have more chemical energy than reactants)

Catalyzed Reaction Catalyzed Reaction. - Usually an exergonic reaction - Which in the presence of a catalyst, is speeded up because the action of the catalyst reduces the amount of activation needed for the reaction to occur.

Enzymes Enzymes are proteins which cells use to speed up biological reactions. Enzymes are proteins which cells use to speed up biological reactions. They are usually Globular in shape. They are usually Globular in shape. Often have surface depressions called active sites which allow Often have surface depressions called active sites which allow SPECIFIC molecules to bind to the enzyme. SPECIFIC molecules to bind to the enzyme. Several models of activity Several models of activity

Enzymes Animation

Lock & Key Model Has static active site Has static active site Molecules fit into active site where chemical change occurs Molecules fit into active site where chemical change occurs

Lock & Key Model Contd.

Induced Fit Model Often these molecules are flexible, and change shape when an appropriate molecule binds to an active site. This is known as an Induced Fit.

Factors effecting enzymes: Temperature - Most human enzymes operate at O C. At lower temperatures, allosteric changes cannot occur. At higher temperatures, proteins (enzymes) can be denatured. Temperature - Most human enzymes operate at O C. At lower temperatures, allosteric changes cannot occur. At higher temperatures, proteins (enzymes) can be denatured. pH - Charged areas of an enzyme can be effected by [H +, OH - ], thus reducing their action in high or low pH. pH - Charged areas of an enzyme can be effected by [H +, OH - ], thus reducing their action in high or low pH. Substrate concentration: As amount of substrate decreases, the rate of enzyme activity will decrease also Substrate concentration: As amount of substrate decreases, the rate of enzyme activity will decrease also

Enzyme Regulation: Enzymes are usually regulated by 3 mechanism Enzymes are usually regulated by 3 mechanism –Competitive Inhibition –Non-competitive Inhibition –Allosteric Indibition

Competitive Inhibition Another substance binds to the active site, preventing the substrate from binding there. Another substance binds to the active site, preventing the substrate from binding there.

Non-competitive inhibition Another substance binds to the enzyme, at a site other than the active site. This blocks the binding of the regular substrates

Allostery An Inhibitor or Activator binds to a separate allosteric site on the enzyme, changing the shape of the enzyme, either Inhibiting or activating it's function. Often the products serve as inhibitors. This is known as Feedback inhibition An Inhibitor or Activator binds to a separate allosteric site on the enzyme, changing the shape of the enzyme, either Inhibiting or activating it's function. Often the products serve as inhibitors. This is known as Feedback inhibition