MCAT Biology : Enzymes and Enzyme Inhibition

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1611 : Mcat Biological Sciences

Functions of enzymes include all of the following except __________.

Possible Answers:

lessening the time required for a reaction to take place

shifting the equilibrium of a reaction

catalyzing both forward and reverse reactions

shifting substrates into more favorable positions in the active site

decreasing the activation energy of a reaction

Correct answer:

shifting the equilibrium of a reaction

Explanation:

Enzymes are unable to shift the equilibrium of a reaction. This is a commonly confused enzyme concept, but it should be known that, chemically speaking, only adding or removing reactants and/or products can shift the equilibrium of a reaction. Although this concept is mainly seen in chemisty, known as Le Chatelier's principle, this principle is surprisingly helpful and applicable to many fields of science, including biology. All other answer choices are functions of enzymes.

Example Question #12 : Enzymes And Enzyme Inhibition

Which of the following would most greatly increase the activity of an enzyme functioning in the small intestine?

Possible Answers:

Increase the amount of substrate

Decrease the temperature

Decrease the pH

Increase the amount of enzymes

Correct answer:

Increase the amount of substrate

Explanation:

The rate of enzymatic activity can be increased in a few ways. Enzymes have optimal levels of acidity and temperature at which they function best. If this optimal level is exceeded, the enzyme will denature. Enzymes of the small intestine are adjusted to a relatively alkaline environment and will denature in acidic environments. Decreasing the temperature would decrease the rate of catalyzation. By increasing the amount of substrate, the enzyme will function faster. The level at which an enzyme's rate of catalyzation can no longer be made faster by the addition of substrate is referred to as its Vmax.

Example Question #13 : Enzymes And Enzyme Inhibition

Among the most important pH buffer systems in humans is the bicarbonate buffer, which keeps the blood at a remarkably precise 7.42 pH.  The bicarbonate buffer system uses a series of important compounds and enzymes to make the system function.  Figure 1 depicts the key reactions that take place.

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The activity of this buffer system is mainly controlled by the renal and respiratory systems.  The renal system excretes bicarbonate in the urine, while the respiratory system “blows off” carbon dioxide as needed.   By balancing these two systems as needed, blood pH is maintained in such a narrow range.

 

Carbonic anhydrase exhibits typical enzyme kinetics expected of similar enzymes. Which of the following is the quantity described by the value Km?

Possible Answers:

The time it takes to reach half maximum reaction rate under standard conditions

The enzyme concentration necessary to achieve half maximum reaction rate

The substrate concentration necessary to achieve half maximum reaction rate

The half maximum reaction rate with enzyme catalysis

The volume of inhibitor necessary to reduce the catalyzed reaction rate by half

Correct answer:

The substrate concentration necessary to achieve half maximum reaction rate

Explanation:

Reaction rates are generally impacted by the concentration of the reactants in the reaction. The Km is the amount of substrate needed to attain a concentration resulting in half of the maximum rate achievable by an ezyme catalyzed reaction.

The maximum rate will be limited by the number of enzyme moleules available, and will be reached when the enzyme active sites are saturated.

Example Question #14 : Enzymes And Enzyme Inhibition

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells. 

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below.  In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

 

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Cancer cells often invade by breaking through the collagen of a basement membrane of epithelial tissue. Considering the composition of basement membranes, which of the following compounds is most likely to be used by cancer cells for this purpose?

Possible Answers:

Lipase

Peroxidase

Protease

Synthase

Amylase

Correct answer:

Protease

Explanation:

The basement membrane and sub-basement structures are predominately made of protein (connective tissue). To infiltrate this region, a protease would be most appropriate. The remaining choices are all enzymes, but would not be capable of digesting appropriate proteins.

Example Question #15 : Enzymes And Enzyme Inhibition

Which amino acid has a side chain that can form covalent bonds?

Possible Answers:

Leucine

Glycine

Cysteine

Isoleucine

Histidine

Correct answer:

Cysteine

Explanation:

Cysteine has a sulfide (-SH) in its side chain, which can form covalent disulfide bonds. These bonds are often integral in creating protein tertiary structures.

Example Question #16 : Enzymes And Enzyme Inhibition

A supercoiled helix is described by which level of peptide structure?

Possible Answers:

Tertiary

Secondary

Quartenary

Primary

There is not enough information to tell

Correct answer:

Secondary

Explanation:

Secondary peptide structure refers to alpha-helices and beta-sheets, which are formed by hydrogen bonding. A supercoiled helix is due to the secondary structure of a peptide. Primary structure is the sequence of amino acids, tertiary structure is the three-dimensional arrangement of the protein, and quatenary structure arises when more than one peptide subunit interacts.

Example Question #17 : Enzymes And Enzyme Inhibition

Disulfide linkages are connections made between polypeptide chains to increase the cohesion of a protein. These bonds fall into the category of __________.

Possible Answers:

hydrogen bonds

covalent bonds

ionic bonds

metallic bonds

Correct answer:

covalent bonds

Explanation:

Disulfide bonds are covalent attachments created between two sulfur atoms. Cysteine is usually the amino acid that creates these connections.

Example Question #18 : Enzymes And Enzyme Inhibition

Pepsin is an enzyme found within the stomach. As a physiologist you are setting up an experiment to study the properties of pepsin. You place pepsin enzymes into a solution and notice that the pH of the solution is 4. 

Which of the following would you add in order to maximize the enzyme's ability to function normally?

Possible Answers:

Equal portions of HCl and NaOH

Neither HCl, nor NaOH would have an effect on pepsin's ability to operate normally

HCl

NaOH

Correct answer:

HCl

Explanation:

Pepsin is used to break down protein in the stomach by hydrolyzing some peptide bonds. Pepsin can operate best at a pH of 2 (same pH as the stomach). Adding HCl to the solution will bring the solution's pH closer to this optimal pH.

Example Question #19 : Enzymes And Enzyme Inhibition

The functional properties of an enzyme are dependent on the pH of the body as well as temperature. Each protein has specific conditions at which it will function optimally. These conditions can help predict where a protein will be found in the body.

In what area of the cell would you expect to find an enzyme that functions best in acidic conditions?

Possible Answers:

The mitochondria

The plasma membrane

The lysosome

The nucleus

Correct answer:

The lysosome

Explanation:

Lysosomes are responsible for the degradation of macromolecules, and typically have an internal pH of 5. They contain acid hydrolases: enzymes that function optimally in an acidic environment.

Example Question #20 : Enzymes And Enzyme Inhibition

In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:

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In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.

The enzyme PERK is a kinase. Which of the following is not true of all kinases?

Possible Answers:

All kinases modify translation factors

All kinases add phosphate groups

All kinases preserve thermodynamic properties of reactions

All kinases lower activation energies of reactions

All kinases are proteins

Correct answer:

All kinases modify translation factors

Explanation:

Kinases are protein enzymes that add phosphate groups to targets. These targets can be diverse, however, and are not always translation factors.

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