Topic 3 Enzymes (No PEQ) (Complete)

(PQ) Hydrolytic enzymes can function within the cell or can be secreted by the cell, where they are able to catalyze reactions

State the term used to describe an enzyme that function within the cell

(COMES WITH NO ANSWER) The graph shows energy changes in a chemical reaction

What is the activation energy when an enzyme is added?

• 1 + 2

• 2 only

• 3 - 2

• 4

Explain the main difference between the lock and key & the induced fit models of enzyme reaction

• The lock and key hypothesis says that the shape of the active site of the enzyme is exactly complementary to that of the substrate whereas The induce fit hypothesis says that before the substrate enters, the active site is not a perfect fit for the substrate, but becomes so when an enzyme-substrate complex is formed

• The lock and key model suggests that enzyme activity can be inhibited by increasing temperature, while the induced fit model does not depend on temperature changes.

• The induced fit model states that substrates are destroyed in the reaction, whereas the lock and key model suggests substrates are merely altered.

• The lock and key model is only applicable to synthetic reactions, while the induced fit model applies to both synthetic and degradation reactions.

Explain how the shape of an enzyme molecule is relate to its function?

Examiners mark schemes are brief; they contain the key terms that get the marks. Thus, you need to practice writing just the key terms. Say “(Term) & (Term) & (Term) & (Term) & (Term)”.

Freezing temperatures can also completely stop enzyme activity by causing the molecules to undergo ‘cold denaturation’. Enzyme activity is not recovered when temperatures are increased to a normal temperature range

Explain the mode of action of enzymes

• The active site of an enzyme has a specific shape that is complementary to its substrate

  Lock an key model: The substrate fits exactly into the active site.

  Induced fit model: The substrate is NOT an exact fit but the enzyme changes slightly to ensure a perfect fit

  In either model an enzyme- substrate complex is formed

  The enzyme lowers the activation energy by holding the substrate to place strain on bond(s) for bond to break,, or by holding substrates close together for bonds to form

• Enzymes increase the activation energy required for a reaction, making it slower but more controlled.

• Enzymes work by completely changing the structure of the substrate, making it unrecognizable.

• Enzymes function independently of the substrate and do not form any complex.

Figure above is a graph showing how the activity of a-amylase extracted from barley seeds changes as the temperature increases from 10˚C to 66˚C

Explain the effect of temperature on the activity of a-amylase extracted from barley seeds, as shown in the figure above

• The increase in temperature increases the kinetic energy of the substrate and the enzyme

• This increases the rate of successful collisions between enzyme and substrate, more enzyme-substrate complex form

• At temperature higher than optimum the enzyme begins to denature, it loses its shape. The shape of active site changes and enzyme activity decreases

• Enzymes are not affected by changes in temperature.

• Decreasing the temperature always increases the enzyme activity.

Why do extreme changes in pH or temperature of an environment alter enzyme actvity?

Extreme changes in an enzyme’s optimal PH or temperature alter enzyme activity because:

• Disrupts the hydrogen and ionic bonds between the R groups holding the tertiary structure together

• If the 3D shape of the enzyme is affected, the active site changes as well; therefore, substrate may not fit into active site

• Increases the overall energy of the enzyme, leading to faster reactions

• Causes the enzyme to produce more substrates

• Enhances the solubility of the enzyme in water

(COMES WITH NO ANSWER) Which words from the table correctly complete the paragraph about enzymes?

When the pH of an environment is decreased below an enzyme’s optimum pH, …(1)… bonds between adjacent …(2)… groups, holding the …(3)… structure, are disrupted.

• A (No answer chosen)

• B

• C

• D

(COMES WITH NO ANSWER) The graph shows how the concentration of components 1, 2, 3 and 4, of an enzyme-catalyzed reaction changes with time

Which row identifies the components of this reacton?

• A (no answer chosen)

• B

• C

• D

Describe what happens to a protein when is denatured by heat

• Heat breaks hydrogen bonds between the R Groups of the polypeptide chains of a protein. This damages the tertiary structure of the protein

• Heat causes proteins to fold into more complex structures, enhancing their functionality

• Heat stabilizes the protein structure by forming new covalent bonds

• Heat has no effect on the protein structure; it only affects the surrounding water molecules