AP Biology : Understanding Protein Functions

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #26 : Proteins

Which of the following factors has an effect on the rate at which enzymes catalyze a reaction?

Possible Answers:

All of these factors have an effect on the rate at which enzymes catalyze a reaction

pH of environment

Concentration of substrate and enzyme

Temperature of environment

Correct answer:

All of these factors have an effect on the rate at which enzymes catalyze a reaction

Explanation:

The temperature and pH of the environment, as well as the concentration of the substrate and enzyme, all affect the rate at which an enzyme catalyzes a reaction. As a result, enzymes have optimal conditions in which they can work at peak efficiency.

Example Question #27 : Proteins

Which of the following macromolecules has a subcategory that acts to speed up biological reactions in the body?

Possible Answers:

Nucleotides

Proteins

Carbohydrates

Lipids

Correct answer:

Proteins

Explanation:

Proteins commonly act to facilitate reactions that would otherwise not take place. By lowering activation energy, proteins often serve as catalysts. A protein catalyst in a biological reaction is known as an enzyme. All enzymes are proteins.

Example Question #1 : Understanding Protein Functions

GLUT1 is a type of protein used to facilitate the transport of glucose across the plasma membrane. What protein classification accurately describes GLUT1?

Possible Answers:

Enzyme

Peripheral protein

Integral protein

Extrinsic protein

Correct answer:

Integral protein

Explanation:

GLUT1 is a protein that allows glucose to pass into a cell through the membrane. Glucose is a large polar molecule, meaning that it will require a protein in order to diffuse across the membrane. GLUT1 must span the entire length of the plasma membrane in order to provide a "passage" for glucose to diffuse. As a result, GLUT1 is classified as an integral protein, or a protein that fully transverses the membrane.

Peripheral, or extrinsic proteins, are situated on the surfaces of membranes, and do not span across the bilayer. Enzymes catalyze biological reactions; GLUT1 is a transport protein, and does not catalyze any reactions.

Example Question #29 : Proteins

Which of the following is not a common function of proteins?

Possible Answers:

Transport molecules across the plasma membrane

Catalyze chemical reactions

Encode information

Cell motility

Correct answer:

Encode information

Explanation:

While some proteins (such as histones) can pass down information from generation to generation, typically DNA is the macromolecule associated with encoding information.

Proteins commonly catalyze reactions. When these reactions occur in a biological organism, the proteins are considered enzymes. Proteins can also be embedded in cellular membranes, acting as channels or receptors to allow molecular transport. One protein, tubulin, is used to build cilia and flagella (as well as microtubules) that are essential to cell motility.

Example Question #2 : Understanding Protein Functions

Which of the following biological molecules is most similar to proteins?

Possible Answers:

Triglycerides (fats)

Enzymes

DNA

RNA

Carbohydrates

Correct answer:

Enzymes

Explanation:

Proteins are organic molecules made of amino acids that are capable of interfacing with certain substrates and facilitating cellular activities. Enzymes are a sub-group of proteins that are used to speed up reactions within the body. Enzymatic proteins are essential to many biological and cellular processes, such as cellular respiration, transcription, and DNA replication.

Example Question #3 : Understanding Protein Functions

Amylase facilitates the breakdown of glycosidic bonds in carbohydrates. Which functional group will not be present in a molecule of amylase?

Possible Answers:

Correct answer:

Explanation:

You should immediately realize that amylase is an enzyme because it ends in "-ase". Remember that enzymes are proteins; therefore they are made up of amino acids. All amino acids contain a carboxylic acid (-COOH), an amine (-NH2), and a hydrogen (-H) attached to the central carbon. Phosphate groups (-PO3) are more commonly found in lipids and nucleic acids, not in proteins. No amino acids contain phosphate groups, though phosphates can be added to certain amino acids to activate certain proteins and enzymes (phosphorylation).

Example Question #4 : Understanding Protein Functions

Consider the reaction:

This reaction is catalyzed by an enzyme called carbonic anhydrase. Which of the following will result from increasing the concentration of carbonic anhydrase?

Possible Answers:

It will cause reaction to go slower

It will decrease the equilibrium constant

It will have no effect on the equilibrium constant

It will increase the equilibrium constant

Correct answer:

It will have no effect on the equilibrium constant

Explanation:

Enzymes are catalysts that help a reaction proceed faster. Increasing the concentration of carbonic anhydrase will not cause the reaction to go slower. Recall that catalysts (in this case carbonic anhydrase) do not alter the equilibrium of a reaction. They simply speed up the process so that equilibrium can be achieved more quickly. Increasing or decreasing the equilibrium constant means that there is a change in the equilibrium state of the reaction.

The equilibrium constant can only be affected by temperature changes or pressure changes, if there is a gas involved in the reaction. Catalysts affect the rate constant, which is dependent on activation energy. By decreasing activation energy, catalysts can increase the rate constant and allow a reaction to proceed faster.

Example Question #3 : Understanding Protein Functions

In non-physiological reactions an increase in temperature will increase the reaction rate; however, in physiological reactions there is an optimum temperature at which an enzyme operates. Increasing the temperature beyond this will not increase enzyme activity or reaction rate. What explains this phenomenon?

Possible Answers:

Heat will shift the equilibrium to the left, favoring the reactant side

High temperatures will change the shape and functionality of proteins

Increasing the temperature will increase the activation energy

Increasing the temperature will decrease the activation energy

Correct answer:

High temperatures will change the shape and functionality of proteins

Explanation:

There is an optimum temperature at which an enzyme is most effective. Decreasing or increasing the temperature from the optimum will lead to denaturation of proteins, which will affect their functionality. Most protein structure is dependent on non-covalent intermolecular forces, such as hydrogen bonding and hydrophobic interactions. Heat can disrupt these forces, causing the protein to lose its structure, which leads to a loss of functionality.

You can eliminate the answer choices about activation energy because changing temperature will have no effect on the activation energy. Adding heat could shift the equilibrium to the right or left, depending on whether the reaction is exothermic or endothermic.

Example Question #6 : Understanding Protein Functions

Which of the following is true regarding competitive and noncompetitive inhibition?

   I. Both can be overcome by increasing the substrate concentration

   II. Competitive inhibition induces changes to the active site

   III. Noncompetitive inhibition has no effect on the enzyme affinity for substrates

Possible Answers:

II and III

II only

III only

I only

Correct answer:

III only

Explanation:

Statement I is false because increasing the substrate concentration will only help overcome competitive inhibition. Noncompetitive inhibition can only be overcome if the inhibitor is removed from the enzyme.

Statement II is also false because competitive inhibitors do not change the active site. They bind to the active site and prevent substrates from binding. Noncompetitive inhibitors bind elsewhere on the enzyme and alter the shape of the active site, thereby preventing substrate binding.

Statement III is true because noncompetitive inhibition does not affect the enzyme affinity for substrates. The enzyme still has the same affinity, but the substrates can’t bind because of the altered active site.

Example Question #4 : Understanding Protein Functions

Which of the following describes enzymes?

Possible Answers:

Anabolic proteins

Anabolic lipids

Degradative nucleic acids

Catalytic proteins

Correct answer:

Catalytic proteins

Explanation:

Enzymes are catalysts that function to increase the rate of a reaction. All enzymes are proteins and they are never consumed in a reaction. Another form of biological catalyst is ribozymes, which are made of protein and RNA, but are not classified as enzymes.

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