Chapter 3

*Enzymes Part 2

*Enzyme Function*Enzymes can catalyze rxns to break up a substrate into 2 new

products of combine two substrates into 1 new product*Parts of rxn:*Enzyme*Substrates*Enzyme-substrate complex*Enzyme product complex*Product(s)

*R-groups on enzyme interact with substrates, forming or breaking bonds between/on substrate(s)*Enzymes remain UNCHANGES after product is formed and

leaves active site*Enzyme available to catalyze rxn for another substrate*Rapid process (substrate binding to active site, products

forming and products leaving active site)

*Examples*Catalase*Enzyme that breaks

up hydrogen peroxide H2O2 (toxic) into H2O and O2 gas*rxn happens at rate

of 10 million molecules per second

*Lysozyme*Enzyme that

defends body against bacteria*Saliva, sweat, tears*Breaks down

polysaccharide chains in bacterial cell wall

* Activation Energy of Rxns

*Extra energy required by chemical reactions to convert substrates into products*E required to start making

products*Higher activation energy =

takes longer to make products (increase rate of chemical reaction) *Lower/less activation

energy = less time to start making products (decrease rate of chemical reaction)

*Enzymes in Action

*Enzymes speed up chemical reactions that take place in cells*They DECREASE ACTIVATION ENRGY*The energy needed to

get the reaction started (or energy needed to start making product)

*Heat helps INCREASE rate of chemical reaction by causing molecules to collide with each other more rapidly, thus reaction*Increase heat = increase rate at which

reactants collide with each other, thus increasing the rate at which a product is made*Body temp. 37*C *Warm but not enough heat to make

biochemical rxns in living organisms happen fast enough*If we raise body temp. to much, body’s

proteins denature = not good*How do we speed up rate at which products

are made without increasing temperature?*Use ENZYMES allow reactions to occur quickly

without increasing temperature*Enzymes required*Enzymes DECREASE Activation energy of

Rxns*Enzyme HOLD substrate(s) in place in position to

enable molecules to react

Example:• Benedicts Test for

Reducing Sugar (monosaccharaides and disaccharides)

• Benedicts solution + sugar will not react

• In order to see rxn, we must HEAT up Benedit & sugar solution reaction occurs and we see color change

* Course of Enzyme Catalyzed Reaction

Catalase

*All biological materials contain catalase

*Used to break up the toxic H2O2 (hydrogen peroxide produced by our cells) into oxygen gas and water

*Measure production of oxygen gas

Amylase* Found in saliva* Breaks down starch into maltose* Use iodine to measure

concentration of starch* Iodine is brown* When in contact with starch, turns

dark blue/black* Measure intensity of color for

qualitative results* Measure time to change for

quantitative results

*Important enzymes used in

experimentation

*Measuring Course of Reaction

*Measure rate of formation of product *Catalase releases

oxygen gas*We can measure

the volume of oxygen gas produced (or number of oxygen gas bubble)

*Measure rate of disappearance of substrate*We can test for Starch (iodine solution

test)*Presence of Starch = blue-black color*When AMYLASE is added, it will start

breaking down starch*When starch breaks down = less starch

= less blue-black color*Measure time it takes to blue-black

color to disappear

*Explain*Use scientific

knowledge to explain WHY the relationship is found between your independent and dependent variable

*Describe*Describe results use table (best to

use graph)*How to describe results shown on

graph:*Begin by describing overall trend*Look for changes in gradient on graph

and describe these changes*Quote figures from the graph* Pick specific points of interest, such as

where gradient changes occur* State x and y coordinates

*Do not use phrases that suggest something is occurring over time if time is not one the graph* Phrases to Avoid if time is not on your x-

axis* At first* More quickly* Slower* rapidly

*Rxns begin swiftly (exponentially at first, steep slope)*As soon as enzyme is

mixed with substrate, product begins forming (increase in concentration of product)*As rxn progresses, rate of

product formation slows down (slope will flatten out, horizontal)*Rxn gets slower until it

stops

* Large # of substrate molecules; every enzyme has a substrate molecule in it

* Rate of rxn will depend on # of enzymes available and how fast they work they can turn substrates into products

* As more and more substrates are converted into products, there are fewer substrate molecules available to bind to active site of enzymes

* Enzymes are now “WAITING” for substrate molecules to hit their active sites

* Eventually, there are no more substrate molecules left to attach to enzymes, thus no more products being made, enzymes are empty and the reaction is over

Explaining the Course for an Enzyme Catalyzed Rxn“Describ

e”“Explain”

*Calculating Initial Rate of

Rxn

*Curve steepest at beginning*Initial rate of Rxn = steepest

part of the curve*2 ways to measure to measure

initial rate of reaction:1. Calculate the SLOPE of a

tangent to the curve AS CLOSE TO TIME 0 as possible

2. Read the amount of product produced at the first 30 s (if this is steepest part of graph)

* Sometimes it is hard to measure the rate at which a product is formed * think about mixtures in which the

products and reactants are indistinguishable

* Alternate way to measure rate of reaction: * Measure rate at which SUBSTRATE

disappears from reaction mixture* (measuring rate at which amylase breaks

up starch)1. Mix enzyme and substrate2. Take samples at KNOWN times3. Use indicator that measure intensity

(thus concentration of substrate)4. As concentration of substrate

decreases, color intensity will decrease5. Plot on graph “amount of remaining

substrate vs. time”6. Calculate initial rate of reaction as

before

*To determine gradient at a point on a curved

graph1. Draw a tangent to the curve at that point, making sure it is at least HALF as long as the line of the graph

2. Draw a right angle on the tangent

3. Calculate the gradient using the lengths of the triangle sides x2 and y2:*Gradient = y2

x2

*Factors that Effect Rate of

Enzyme Catalyzed Reaction*Enzyme

Concentration*Substrate

Concentration*Temperature*pH*Inhibitors