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 1937. Airships now use helium gas because it is nonflammable and therefore a safer lifting gas.

2H2 + O2 → 2H2O + energy

Enzymes & EnergyEnzymes & Energy

• In biological systems, In biological systems, the are 3 general the are 3 general energy paths a energy paths a reaction can take.reaction can take.

•   • 1.1.            ExergonicExergonic

Reaction - One in Reaction - One in which energy is which energy is released (Products released (Products have less chemical have less chemical energy than energy than reactants). This often, reactants). This often, however requires however requires Activation energyActivation energy to to initiate a reaction.initiate a reaction.

Endergonic ReactionEndergonic Reaction

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

Catalyzed Catalyzed ReactionReaction

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

EnzymesEnzymes• EnzymesEnzymes are proteins which cells use to are proteins which cells use to

speed up biological reactions.speed up biological reactions.• They are usually Globular in shape.They are usually Globular in shape.• Often have surface depressions called Often have surface depressions called

active sitesactive sites which allow which allow• SPECIFIC molecules to bind to the SPECIFIC molecules to bind to the

enzyme.enzyme.

• Several models of activitySeveral models of activity

Enzymes AnimationEnzymes Animation

Enzymes.swf

Lock & Key ModelLock & Key Model

• Has static Has static active siteactive site

• Molecules Molecules fit into fit into active site active site where where chemical chemical change change occursoccurs

Lock & Key Model Contd.Lock & Key Model Contd.

Induced Fit ModelInduced 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 Factors effecting enzymes:enzymes:• TemperatureTemperature - Most - Most

human enzymes operate human enzymes operate at 35-40at 35-40OOC. At lower C. At lower temperatures, temperatures, allostericallosteric changes cannot occur. At changes cannot occur. At higher temperatures, higher temperatures, proteins (enzymes) can proteins (enzymes) can be be denatureddenatured..

• pHpH - Charged areas of an - Charged areas of an enzyme can be effected enzyme can be effected by [Hby [H++, OH, OH--], thus ], thus reducing their action in reducing their action in high or low pH.high or low pH.

• Substrate concentrationSubstrate concentration: : As amount of substrate As amount of substrate decreases, the rate of decreases, the rate of enzyme activity will enzyme activity will decrease alsodecrease also

Enzyme Regulation:Enzyme Regulation:

• Enzymes are usually regulated by Enzymes are usually regulated by 3 mechanism3 mechanism – Competitive InhibitionCompetitive Inhibition– Non-competitive InhibitionNon-competitive Inhibition– Allosteric IndibitionAllosteric Indibition

Competitive InhibitionCompetitive Inhibition

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

Non-competitive Non-competitive inhibitioninhibition

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

AllosteryAllostery

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