enzymes: “helper” protein molecules what are enzymes? an enzyme is a biological catalyst that...

Enzymes:

“Helper” Protein molecules

What are enzymes?

• An enzyme is a biological catalyst that makes chemical reactions in cells possible.

Examples synthesis

digestion

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enzyme

enzyme

Chemical reactions of life• Enzymes can help in:– building molecules• synthesis

– breaking down molecules• digestion

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Nothing works without enzymes!• How important are enzymes?– all chemical reactions in living organisms

require enzymes to work• building molecules– synthesis enzymes

• breaking down molecules– digestive enzymes

– enzymes speed up reactions• “catalysts”

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enzyme

enzymeWe can’t live without enzymes!

Enzymes

• A protein catalyst• Enzymes are important

proteins found in living things. An enzyme is a protein that changes the rate of a chemical reaction.

• They speed metabolic reactions.

• Enzymes do not catalyze processes that would not take place on their on. They just make processes take place faster!

Enzymes aren’t used up• Enzymes are not permanently changed or used

up in reactions.– used only temporarily– re-used again for the same reaction with other

molecules– very little enzyme needed to help in many

reactions

enzyme

substrate product

active site

Enzymes are proteins• Each enzyme fits only one specific type of

reaction, but can catalyze many of this particular reaction one after another.– each enzyme needs to be the right shape for the

job– enzymes are named for the reaction

they help• sucrase breaks down sucrose• proteases breakdown proteins• lipases breakdown lipids• DNA polymerase builds DNA

Oh, I get it!They end in -ase

Substrates• Substrate– A molecule that enzymes work on– Substrates undergo chemical changes to form

new substances called products.• Products– what the enzyme helps produce from the

reaction• Active site– part of enzyme

that substrate molecule fits into

It’s shape that matters!• Lock & Key model– shape of protein

allows enzyme & substrate to fit

– specific enzyme for each specific reaction

Activation Energy

• The activation energy of a reaction is the minimum amount of energy needed to start a reaction.

• It is like traveling over a hill because the peak represents the activation energy needed for the reaction.

What affects enzyme action• The rate of a reaction depends in part on the shape of the

enzyme. If the enzyme is large, its concentration is high, which increases reaction rate.

• Correct protein structure– correct order of amino acids– why? enzyme has to be right shape– why? enzyme has to be right shape

• Temperature• pH (acids & bases)– why? enzyme has to be right shape

37°

Temperature

temperature

reac

tio

n r

ate

What’s happening here?!

humanenzymes

Order of amino acids• Wrong order = wrong shape = can’t do its job!

DNA

DNA

chain ofamino acids

chain ofamino acids

foldedprotein

foldedprotein

right shape!

wrong shape!

Temperature• Effect on rates of enzyme activity– Optimum temperature• greatest number of collisions between enzyme

& substrate• human enzymes – 35°- 40°C (body temp = 37°C)

– Raise temperature (boiling)• denature protein = unfold = lose shape

– Lower temperature T°• molecules move slower • fewer collisions between enzyme & substrate

pH • Effect on rates of enzyme activity– changes in pH changes protein shape~ Denatures– most human enzymes = pH 6-8• depends on where in body• pepsin (stomach) = pH 3• trypsin (small intestines) = pH 8

7

pH

pH

reac

tio

n r

ate

20 1 3 4 5 6 8 9 10

stomachpepsin

intestinestrypsin

What’s happening here?!

11 12 13 14

Other important facts about enzymes!

• Enzymes are a type of protein!• Enzymes usually end in the suffix –ase.• Examples:– Carbonic anhydrase: removes carbon dioxide

from the blood before it becomes toxic.– Lipase: speeds up the digestion of fats– RNA polymerase: speeds up protein production

Enzyme Disorders

• PKU: phenylketonuria*Cells fail to make an enzymethat is used to break down phenylalanine.*If phenylalanine builds up in the blood, it can cause death.

• Tay-Sachs:*It is a genetic disease that affects the human brain.*In this disease, cells do not produce an enzyme that breaks down lipids.*Over time, the buildup of lipids in and around the brain cells causes blindness, seizures, and usually death.

For enzymes…What matters?

SHAPE!