6.4 &6.5 BIO 151

Where does a substrate bind on an enzyme in order for a chemical reaction to take place?

active site

What is the optimal pH range for most human enzymes?

6 to 8

The optimum ph of most enzymes is 6 to _____.

8

Which of the following best describes an allosteric inhibitor?

A molecule that binds to a site other than the active site of an enzyme and inhibits the enzyme's function.

What is noncompetitive inhibition?

A molecule that binds to an allosteric site and prevents the proper functioning of an enzyme.

What is a substrate?

A reactant molecule that binds to the active site of an enzyme.

The _____ site is a specific region of an enzyme to which non-competitive inhibitors bind in order to regulate enzyme activity.

Allosteric

___ enzymes are enzymes that can exist in either an active or inactive conformation.

Allosteric

A molecule that binds to a site on the enzyme other than the active site and inhibits the enzyme's activity is called a(n)_______ inhibitor.

Allosteric, non-competitive, or noncompetitive

Select the ways in which multienzyme complexes improve catalytic efficiency.

Because products fo not leave the complex, there are no unwanted side reactions. All of the reactions inside the complex can be controlled as one unit. The product of one reaction can be delivered to the next enzyme more easily.

Which of the following are included in metabolism?

Both the synthesis and breakdown of organic molecules

Select reasons why metabolic pathways are regulated.

By regulating metabolic pathways, cells waste less energy. Regulation allows cels to operate efficiently. By regulation metabolic pathways, cells conserve raw materials.

(catabolic or anabolic?) Cells harvest energy during _____ reactions and expend during _______ reactions.

Catabolic Anabolic

Select the statements that correctly describe differences between anabolic and catabolic reactions.

Catabolic reactions release energy, whole anabolic reaction need energy input. In catabolic reactions large molecules are broken down, while in anabolic reactions large molecules are made from smaller ones.

Which of the following is true about the regulation of enzyme activity in cells?

Cells can regulate the activity of enzymes by inhibiting or activating them.

In many oxidation-reduction reactions, electrons pass in pairs from the active site of the enzyme to a(n)_____ that serves as an electron acceptor, which can then release the electrons to the substrates of another reaction.

Coenzyme

What organic molecule can accept electrons from the active site of one enzyme and then transfer to another enzyme where the electrons are released to a substrate in a different reaction.

Coenzymes

_____ are small, chemical components, usually inorganic ions, such as Zn^2+, Cu^2+, and Mn^2+, that are often found in the active cell participating directly in catalyst.

Cofactors

Inhibitors that bond to the active site of an enzyme preventing the binding of substrates are...

Competitive inhibitors

What are competitive inhibitors?

Competitive inhibitors bind to the active site of an enzyme and prevent substrates from binding.

Increasing the temperature outside, the optimal range of an enzyme can lead to _____ of the enzyme, altering the enzyme's structure and function.

Denaturation, unfolding, or denaturing

Select the statements that accurately describe cellular enzyme.

Different enzymes can come together to form complexes. Not all cellular enzymes are located in the cytoplasm. Some cellular enzymes are found inside of cellular organelles.

When a reactant binds to the active site of an enzyme, a(n) ___-____ complex forms.

Enzyme Substrate

Pepsin is an enzyme found in the stomach that functions best at an acidic pH. Why does pepsin not function well at a pH of 7.

Enzymes are sensitive to pH and function best across a narrow range of pH.

Most enzymes in the human body work best at neutral pH. Select the reasons why changing the pH of the fluid in which a human enzyme is dissolved (for example to a pH of 3) will affect the enzyme's ability to function.

Enzymes cannot maintain their 3-D shape at extreme pHs, such as a pH of 3. The balance between positively and negatively charged amino acids in the enzyme is shifted.

Select the characteristic of enzymes.

Enzymes lower the activation energy required for new bonds to form in a chemical reaction. Enzyme may be used more than once in a cell. Enzymes are not changed or consumed in reactions.

______ are proteins or RNA molecules that act as catalyst to speed up reactions in living organisms.

Enzymes or Enzyme catalyst

T or F: All the enzymes that a cell has are found in the cells' cytoplasm.

False

T or F: Biochemical pathways evolved quickly over time.

False

Changes in pH affect an enzyme because the interaction of charged amino acid residues in the enzymes are affected by...

Hydrogen ion concentrations

Select the true statement about the effect of temperature on an uncatalyzed chemical reaction.

Increased temperature increase the rate of the reaction. Increased temperature increases random molecular movements which increases stress on bonds.

Temperature affects chemical reactions in the following way: increasing the temperature of an uncatalyzed reaction ______ the rate of that reaction.

Increases, raises, speeds up, speeds, accelerates, or hastens

How does the temperature affect the functioning of an enzyme?

Increasing the temperature outside the optimal range for an enzyme can alter the enzyme's structure and impair its function

A substance that binds to an enzyme and decreases its activity is called a(n)....

Inhibitor

Which of the following describes the activity of a particular enzyme?

It can be affected by substances which bind the enzyme and alter its shape.

Which of the following describes the active site of an enzyme?

It is part of the enzyme where the substrate fits.

The stomach enzyme pepsin functions well at very _____ pH.

Low or acidic

Why do enzymes function maximally in a narrow range in temperature?

Lower temperatures prevent the formation of the substrate-enzyme complex while higher temperatures can denature the enzyme.

Which statement best describes metabolism?

Metabolism refers to the sum of all chemical reactions that occur within an organism.

When several enzymes that catalyze different steps of a sequence reaction are associated with another in a noncovalently bonded assembly, they form a(n) _______ complex.

Multienzyme

Select the statements that accurately describe multienzyme complexes.

Multienzyme complexes improve catalytic efficiency. Within the multienzyme complex, products of one reaction can be delivered to the next reaction. Enzyme in multienzyme complexes catalyst a sequence of reactions.

A more efficient way to catalyze a sequence of related biochemical reactions is to combine several proteins into a _____ complex; in this way, the product of each reaction can be delivered to the next enzyme, without being released to diffuse away.

Multienzyme or multi-enzyme

A(n) _______ inhibitor binds to an area outside of the active site of an enzyme and impairs proper functioning of an enzyme.

Noncompetitive, allosteric, non competitive, or non-competitive

In the earliest cells, the first catalyze chemical reactions were probably reactions composed of how many steps?

One

Most human enzyme functions best between 35 and 40 degree Celsius, while the enzymes of bacteria that inhabit hot, sulfur springs have a higher _______ temp.

Optimum or optimal

Which of the following is an accurate description of a coenzyme?

Organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction.

How can the function of an enzyme be affected by the external environment?

Temperature and pH can greatly affect the function of some enzymes by causing denaturation.

What happens if a chemical substance binds to an enzyme and alters its shape?

The enzyme's activity can be increased or decreased

How does feedback regulation regulate enzyme activity?

The final product of a metabolic pathway inactivated the first enzyme in the pathway by binding to its allosteric site.

On the following figure representing how temperatures affects the activity of two different enzymes, which of the two curves (left or right) could represent an enzyme isolated from a microorganism that inhabits a hot spring.

The right curve.

Select the true statements about allosteric enzymes.

They can exist in either active or inactive form. They have an allosteric site which differs from the active site.

Which of the following statements are correct about noncompetitive inhibitors?

They cause the enzyme to change shape. they bind to a site other than the active site of the enzyme. They prevent the substrate from binding to the enzyme.

Select the true statement about enzymes?

They lower the activation energy of a reaction by binding to the substrates

How can some enzymes function well at a very low pH?

They maintain their 3-D shape even at a very low pH.

Select the true statements about allosteric sites on enzymes.

This is where a non-competitive inhibitor would bind. The binding of a substance to the allosteric site can switch an enzyme between its active and inactive configurations.

T or F: Each step of a metabolic pathway is catalyze by a specific enzyme.

True

T or F: Substances can bind to an enzyme and change its shape, affecting its activity.

True

_____ are small organic molecules that temporarily attach to an enzyme and promote a chemical reaction without being changed during the reaction.

coenzymes

What are small chemicals, usually inorganic ions, that temporarily attach to the surface of an enzyme and promote a chemical reaction?

cofactors

_____ inhibitors bind to the active site of an enzyme and prevent the substrate from binding.

competitive

During each step of the metabolic pathway that adds phosphate groups to various sugars, a separate ______ is needed to catalyze the reaction?

enzyme

What is produced by the binding of enzyme and substrate?

enzyme-substrate complex

What are enzymes?

proteins or RNA molecules that act as catalyst

_______, or reactants, are molecules that bind to an enzyme at the active site and are converted to products in chemical reactions.

substrates