enzyme quiz

-What is an enzyme?

A macromolecule that acts as a catalyst, a chemical agent that speeds up a reaction without being consumed by it.

-How do enzymes speed up the rate of a reaction?

It lowers the activation energy required to reach the transition state.

Specific ways: Activation site is a template for the substrates to meet in a proper orientation. Enzyme enfolds the substrates and brings them towards transition state form. Active site can provide a microenvironment that is more conducive to a particular reaction than the solution on its own. Active site can directly participate as well, such as by covalently bonding to the substrate.

-Why is shape so important for enzymes? What happens when an enzyme becomes denatured?

The shape of an enzyme (more specifically, its active site) determines which substrate it can bind to. The induced fit that forms enhances this fit between the site and substrate. When denatured, its shape changes and it will no longer function since it cannot fit a substrate.

-What is activation energy?

The "free energy of activation"

The initial investment of energy in a reaction, needed to contort the reactant molecules enough to break the bonds (to set it in transitional form, in which the bonds can break). Represented by E subA.

-What is a substrate?

The reactant an enzyme acts on/binds to

-What is an active site?

The region of an enzyme which binds to the substrate; where the catalysis actually occurs. Formed by only a few on the enzymes amino acids, while the rest make a framework determining the configuration of the site.

• What is the enzyme substrate complex?

The enzyme bound to the substrate(s); while they are joined, the catalysis occurs and the product(s) are made

-How many different types of enzymes can act on one type of substrate? Why?

Only one type of substrate, due to the very specific shapes of both the substrates and the enzymes.

-Know the catalytic cycle of an enzyme.

The substrate enters the active site and is held by the induced fit (enzyme changes shape so active site enfolds substrate).

Substrates are held in the site by weak interactions like hydrogen and ionic bonds.

Substrates are converted to products (process catalyzed by enzymes that make up the active site).

Products are released.

Active site is available for new substrate(s).

-What is the effect of temperature and pH on enzyme activity?

They affect the active shape of an enzyme; denaturation happens if it gets too extremely. This is since proteins (which most enzymes are) are very sensitive to their environments.

-What is the optimal temperature for a typical human enzyme? Why does this temperature allow this enzyme to function?

37 degrees Celcius (for thermophilic (heat tolerant) bacteria, it is 77 degrees Celcius). It allows the greatest number of molecular collisions and fastest conversion of reactions to products without denaturation occuring.

• What is the optimal pH for pepsin? What about trypsin? Why is there a difference?

Pepsin is 2, and trypsin is 8. In general, pH is best at 6-8. The difference is because while pepsin's acidic environment would denature most enzymes, it is adapted to maintain its functional structure in the acidic stomach (as opposed to trypsin in the intestine's alkaline environment, which would denature in the stomach).

-What are enzyme inhibitors?

Chemicals that bond to enzymes and disable them by either binding to the active site or of another part of the enzyme (changing the active site). If done with covalent bonds, usually irreversible, but with weaker ones, reversible.

-Compare and contrast competitive inhibitors and noncompetitive inhibitors.

Competitive bind to the active site (they resemble the substrate) and block substrates from entering. This can be overcome by increasing substrate concentration.

Noncompetitve bind to another part of the enzyme and cause the active site to change shape and become ineffective.

-What is allosteric inhibition?

A protein's function at one active site is affected by a regulatory molecule bound to another site. Inhibition specifically means an activator stabilizes an enzyme to be inactive.

-What is feedback inhibition? How does this work? Why would we not want an enzyme working in a pathway non-stop (unregulated)? Be familiar with the isoleucine pathway example from your text (page 132 figure 6.19)

A mode of metabolic control. A metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway. If we left it unregulated, the cell would waste chemical resources and get an overflow of unnecessary materials.