ENZYMES

Vocabulary (4 slides are review from last day)

• Metabolism• Anabolic Pathways• Catabolic Pathways• Free Energy• Activation Energy• Catalysts

ENZYMES

• PROTEINS THAT INCREASE METABOLIC REACTION RATES

• STRUCTURE IS IMPORTANT• ACTIVE SITE – THE PART OF THE ENZYME THAT

BINDS THE SUBSTRATE• SUBSTRATE – THE COMPOUND THAT IS BEING

DIGESTED (CONVERTED INTO PRODUCT)

ENZYME SUBSTRATE COMPLEX

• The enzyme substrate complex is formed as an intermediate (it doesn’t last long)

• The enzyme and substrate come together in an ‘induced fit’ model (like a lock and key) on the enzyme’s active site

• The enzyme + substrate makes up the EZ complex without which the reaction could not proceed

Steps to Enzyme Catalysis

Due to kinetic energy (energy of motion), enzymes and substrates will collide

• In a successful collision, the substrates will enter and bind to the enzymes active site forming the enzyme substrate complex

• The substrate is often held in the enzymes active site by weak chemical bonds

Steps continued...

• The enzyme’s active site will then change shape to hold the substrate more snugly in a process called induced fit

• Within the enzyme’s active site, the reactions activation energy is lowered by creating an unstable transition state

• The enzyme creates the transition state by placing stress on the reactant groups in the substrate and arranging the substrate so that a reaction can easily occur between them

The last of the steps!

• Cofactors may assist the enzyme in catalyzing the reaction by accepting or contributing atoms

• Once the reaction is complete, the product is released from the enzymes active site.

• The enzyme resumes its original form and is ready to accept more substrate into its active site.

7 Factors that Affect Enzymes

• Temperature within optimum range• Temperature beyond optimum range• pH above or below optimal• Combining with Heavy Metals• Substrate Concentration until saturation• Enzyme Concentration• Competitive Inhibitors

Temperature

• Enzymes have an optimal temperature range• Human enzymes optimum temperature is

body temperature• As temperature increases toward optimal the

Kinetic Energy increases so the rate of reaction increases

• Once optimal temperature is reached the enzyme function will be at it’s best rate

Temperature beyond Optimal

• High temperatures will denature proteins

• Enzymes are proteins and this denaturing will change its active site’s shape

• The enzyme substrate complex will be more difficult to form and the rate will decrease

pH outside of optimal

• Enzyme pH is also optimized within the body. • Enzymes that work in the mouth (salivary

amylase) works best at a pH of 7• Enzymes that are released in the stomach

work best at a pH of 2• ENZYMES are PROTEINS, acid/base changes

protein SHAPE and therefore change or DESTROY enzyme function

Heavy Metals

• Heavy metals denature proteins (including enzymes) thereby decreasing the rate of the enzyme by changing the shape of its active site

Substrate Concentration

• Low concentrations of substrate will have lower reaction rates

• Increasing the substrate concentration will initially increase the rate

• Once the substrate concentration has reached a certain level however, all of the enzyme active sites will be occupied and there will be no further change in reaction rate

Enzyme Concentration

• At low enzyme concentration the reaction rate is very slow

• Increasing the enzyme concentration will increase the rate of reaction (as long as there is substrate present)

COMPETITIVE INHIBITIORS

• Competitive inhibitors are not substrates, but they have the same shape and can occupy the enzyme’s active site

• This prevents the substrate from binding so the reaction cannot proceed

• Increasing competitive inhibitors presence will decrease the reaction rate

Questions:

1. Explain IN DETAIL, why each of the graphs has the SHAPE it does.

2. Describe TWO ways the rate of an enzyme catalysed reaction could be determined.

• Explain how the following would affect the rate of an enzyme catalyzed reaction. In each case, explain WHY that effect would occur.– Increase in temperature from 35-37C– A competitive inhibitor is added

4. An experiment was carried out to investigate the action of the enzyme catalase. Catalase breaks down hydrogen peroxide (found in liver cells) into oxygen and water. Five test tubes were set up as show in the table below.

• Equal portions of liver homogenate were placed in the five test tubes

• Test tubes were placed in water baths at the temperatures indicated in the table for 5 min

• 10 ml of hydrogen peroxide was added to each tube• the amount of oxygen released was recorded

Tube 1 2 3

Temp C 18 28 38

Ml O2 Produced

4.1 8.8 18

Question #5

– Explain the change in reaction rate in the graph above

– Identify and explain how THREE other factors could DECREASE the reaction rate of this enzyme catalysed reaction

Question #6

• Describe the effect the following will have on the activity of an enzyme that normally functions in the human stomach– A change in temperature from 37 to 34 C– A change in temperature from 37 to 60 C– Addition of lead (a heavy metal)– Addition of a buffer to maintain a pH of 7