Download Extra Notes on Enzymes (Overview)

Enzymes:
How can we break down a piece of pizza?
It happens through the action of proteins called enzymes. Enzymes help start and run chemical reactions in
living things.
 Example: Enzymes are needed to break down food into smaller molecules that cells can use. Without
enzymes, a Venus flytrap couldn’t break down its food, and neither could you.
Activation energy
 The amount of energy needed to start a chemical reaction
 Once a chemical reaction starts, it can be continued by itself and it will continue at a certain rate
 Often, the activation energy for a chemical reaction comes from an increase in temperature
o After a reaction starts, it may happen very slowly
o The reactants may not interact enough, or they may not be at a high enough concentration, to
quickly form the products of the reaction
o The activation energy and rate of a chemical reaction can be changed by a chemical catalyst.
 Catalyst – a substance that decreases the activation energy needed to start a chemical reaction and, as a
result, also increases the rate of the chemical reaction.
o Normal conditions – reactions require a certain amount of activation energy, and it occurs at a
certain rate
o Catalyst present – less energy is needed and the products form faster.
 Catalysts are not considered to be reactants or products even though they take part in the reaction. The
reason is that catalysts are not changed or used up during a reaction!
Enzymes allow chemical reactions to occur under tightly controlled conditions
 Reactants usually found in low concentrations
 Because reactions must take place quickly, they usually need a catalyst
 Enzymes
o Are catalysts for chemical reactions in living things
o Lower the activation energy and increase the rate of chmical reactions
o Involved in almost every process in organisms
 From breaking down food to building proteins, enzymes are needed
 Example: Amylase is an enzyme in saliva that breaks down starch into simple sugars
 This reaction occurs up to a million times faster with amylase than without it
o Enzymes are proteins
 Long chains of amino acids
 Every enzyme depends on its structure to function properly
o Factors that affect enzyme function and activity
 Temperature and pH
 Enzymes work best in a small temperature range around the organism’s normal
body temperature
 Only at slightly higher temperatures, the bonds inside an enzyme may begin to
break apart and the enzyme’s structure will start to change
o Once the enzyme shape changes, it will lose its ability to function properly
o This is one reason why a very high fever is so dangerous to a person
 A change in pH can also effect the bond in enzymes
o Many enzymes in humans work best at nearly neutral pH that is
maintained within cells of the human body
o Enzyme structure is important
 Because each enzyme shape allows only certain reactants to bind to the enzyme
 Substrate – the specific reactants that an enzyme acts on

Example: Amylase only breaks down starch
 Therefore, starch is the substrate for amylase
 Active sites - Specific places where substrates temporarily bind to
 Lock and Key model
o Like a key fitting into a lock, substrates exactly fit the active sites of
enzymes
o This is why if an enzyme’s structure changes, it may not work at all.
o Lock and Key
 Enzymes bring substrate molecules close together
 Because of the low concentration of reactants in cells, many reactions would be unlikely
to take place without enzymes bringing substrates together
 Next, enzymes decrease the activation energy
 When substrates bind to the enzymes active site, the bonds inside the substrates
become strained
 If bonds are strained or stretched slightly out of position, they become weaker.
 Less activation energy is needed for these slightly weakened bonds to be broken
Critical thinking questions
1. Infer: Some organisms live in very hot or very acidic environments. Would their enzyms function in a
person’s cells? Why or why not?
2. Predict: Suppose that the amino acids that make up an enzyme’s active site are changed. How might this
change affect the enzyme?
3. Connecting concepts: Organisms need to maintain homeostasis, or stable internal conditions. Why is
homeostasis important for the function of enzymes?
Key questions (Aims)
 How does the structure of an enzyme affect its function?
Main ideas:
 A catalyst lowers activation energy
 Enzymes allow chemical reactions to occur under tightly controlled conditions
Acids and Bases:
 Acid – compound that releases a hydrogen ion (H+) when it dissolves in water
o An acid increases the concentration of H+ ions in a solution
 Bases – are compounds that remove H+ ions form solution
o When a base dissolves in water, the solution has a low H+ concentration
 A solutions H+ ion concentration, or acidity, is measured by the pH scale.
 pH scale – measures how acidic a solution is
o pH is usually between 0 and 14
o Solution with a pH of 0 = very acidic, with a high H+ concentration
o Solution with a pH of 14 is very basic, with a low H+ concentration
o Solutions with pH of 7 are neutral – neither acidic or basic
 Humans need to keep their pH within a very narrow range around neutral (pH 7.0).
o Some organisms need different pH ranges
 The azalea plant thrives in acidic (4.5) soil and has a microorganism called Picrophilus
that survives best at an extremely acidic pH of 0.7.
o For all organisms, pH must be tightly controlled
 If your blood (pH between 7.35 and 7.45) has just a small change greater than 7.8 or less than 6.8, for
even a short time, can be deadly.