Enzymes pH Homework Packet

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					              Enzymes & pH
    Homework Packet
   “Enzymes & pH HW #1” (correlates to pages 1-3 of notes)

   “Enzymes & pH HW #2” (correlates to pages 4-7 of notes)

   “Enzymes & pH HW #3" (correlates to pages 7-8 of your notes)

   "Enzymes & pH HW #4 - Enzymes Review" (correlates to pages 1-8 of your notes)

   “Enzymes & pH HW #5” (correlates to pages 8-11 of your notes)
Biology CP                                          Name                               Date       Pd

                           Enzymes & pH HW#1 (see pages 1-3 of your notes)

1. What is a chemical reaction?
A process that changes or transforms one set of chemicals into another.
2. Complete the table about chemicals in a chemical reaction.

                                   Chemicals in a Chemical Reaction

Chemicals             Definition

Reactants             Substances that enter a chemical reaction

Products              Substances that are produced in a chemical reaction

3. The graphs below show the amount of energy present during two chemical reactions. One of the
reactions is an energy-absorbing reaction, the other is an energy-releasing reaction.
     Draw an arrow on each graph to show the energy of activation.

        REACTION "A" (endergonic)                                         REACTION "B" (exergonic)

4. Which of the above reactions would be considered an energy-absorbing (endergonic) reaction?
Why?          Reaction A. The products have higher potential energy than the reactants – showing that
energy was absorbed.

5. Define "activation energy".
The minimum amount of energy needed to “kick start” a reaction
6. Of the two reactions shown, which one is more likely to start spontaneously and why?
Reaction B – net energy is released. The products have less energy than reactants. More stable.

7. In reaction "A", which would have more potential energy - the products or reactants? (circle one)
8. Which reaction - A or B - shows the creation of products that are smaller & simpler than the
reactants? (circle one)
9. Which reaction - A or B - has a higher activation energy? (circle one)
_______10. Regardless of whether an organism makes its own high-energy nutrients or must
obtain them by eating, all organisms must perform the following reaction to release energy for the
a. photosynthesis
b. cellular respiration
c. fermentation

______11. Would the reaction below be considered an energy-absorbing (endergonic) or energy-
releasing (exergonic) reaction?

a. energy-absorbing (endergonic)              b. energy-releasing (exergonic)

______12. Which example below illustrates a "reversible" reaction?
    a.                                                  b.

_____13. When chemical bonds are broken, energy is __?__; when new bonds are formed,
energy is __?__.
a. released; released                                   c. required; required
b. released; required                                   d. required; released
Biology CP                                          Name                              Date   Pd

                        Enzymes & pH HW#2 (see pages 4-7 of your notes)

        Proteins are some of the largest and most complex compounds found in living
organisms. Although 70% of your body is made of water, most of the other 30% is protein. A
cell's DNA or genetic code determines what types of proteins are made by that cell. As a
result, proteins play a large role in determining the structure and function of a cell.

1. Fill in the missing words in the paragraph below.
The words listed below may be used once, more than once, or not at all:

      function             R groups            peptide bonds               homeostasis
      number               types               sequence                    proteins
      amino acids          organic             speed                       identity
      fold                 DNA                 polypeptide                 catalysts

Proteins are one of the four major types of organic _ compounds that we studied in our
biochemistry unit. amino acids _ are the monomers of proteins. When two or more of these
monomers covalently bond together it forms a polymer called a _ polypeptide __. The
covalent bonds which join amino acids are specifically called _ peptide bonds __. When they
are first formed (according to the DNA __ code of a cell), proteins are linear (straight,
unfolded) chains of amino acids. Attractive forces (such as hydrogen bonds) between the
_ R groups _ of the amino acids in the chain cause the chain to _ fold ____ up on itself into
a 3-dimensional globular shape that is unique to each type of protein. Remember, form leads
to function __! Once properly folded, polypeptides become functional         and are properly
called __ proteins ____. Proteins differ in the number ___, _ sequence _, and ___types
____ of the amino acids they contain. A specific group of proteins is called enzymes, which
help to __ speed    ___ up chemical reactions in cells. Enzymes are biological _ catalysts
__ which are critical for the maintenance of _ homeostasis ___ in cells.

2. What do we commonly call the organic catalysts found in cells? ENZYMES

3. Why is a catalyst highly effective in small amounts?            It can be reused
4. Enzymes typically have “-ase” at the
end of their name like “sucrase”. Look at
the picture. Describe what sucrase does to
sucrose.               It helps speed up the
reaction which hydrolyzes sucrose into
glucose and fructose. It probably helps to
de-stabilize the bond.

5. Would the reaction above likely release or absorb energy? Explain your reasoning.
               (exo) Releasing energy – forming simpler, less complex products.

6. How does heat “act” as a catalyst? Why can't cells rely on heat as their main catalyst for
chemical reactions?            Particles move faster when it is hot. They have more kinetic
energy and therefore have more energy to make it over the energy barrier to make products.
Heat is unpredictable, not always available & extremes can denature enzymes.
(Heat speeds up a reaction but it isn’t a catalyst)

7. How does the addition of a catalyst affect the energy of activation of a chemical reaction?

  It lowers the amount of activation energy

8. Using the analogy of a lock and key, explain what the expression “enzymes
    are specific” means..   There is a specific active site to fit a specific substrate. They fit
   together like a lock and key.

TRUE OR FALSE - if false, correct the statement.
___T__9. Enzymes are reusable.

__F___10. Substrates ENZYMES strain the bonds of enzyme SUBSTRATE molecules,
reducing the amount of energy needed for old bonds to break and new bonds to form.

__F___11. Enzyme-assisted reactions occur much more slowly QUICKLY than they would if
the enzyme were not present.

__F___12. A particular enzyme can catalyze many different types ONE SPECIFIC TYPE of

__T___13. Some enzymes assist with hydrolysis, whereas others assist with dehydration

Use the diagram to answer Questions 14-15.

14.        Label the enzyme, the active site and the products in the diagram above.

15. Write what is happening at each numbered part of the diagram.

      (location #1) enzyme – substrate complex (substrates fit into enzyme)

    (location #2) enzyme has weakened the bonds in the substrates – allows new bonds to form using less
activation energy.

      (location #3) products are released and enzyme is unchanged
Biology CP                       Name                             Date                 Pd

                   Enzymes and pH HW #3 (see pages 7-8 of your notes)

_____1. Which of the following is a factor which can affect enzyme activity?
a. availability (concentration) of enzyme and/or substrate molecules
b. temperature
c. pH
d. regulatory molecules
e. all of these

_____2. Denaturation of an enzyme will usually change its structure, leading to:
a. increased rates of reaction
b. decreased rates of reaction

_____3. Which term or phrase is most related to the term "denaturation"?
a. unfolding      b. refolding        c. breaking apart          d. putting together

_____4. Enzymes tend not to work well at very low temperatures due to:
a. rapid movement of molecules and frequent collisions between substrate & enzyme
b. slow movement of molecules and infrequent collisions between substrate & enzyme
c. denaturation of enzyme molecules

_____5. Enzymes tend not to work well at very high temperatures due to:
a. rapid movement of molecules and frequent collisions between substrate & enzyme
b. slow movement of molecules and infrequent collisions between substrate & enzyme
c. denaturation of enzyme molecules

___F__6. True or False: An enzyme typically works well throughout a wide range of varying
temperature and pH conditions.

7. Define homeostasis.    The maintenance of a constant internal environment.

8. Based upon your knowledge of enzyme action & denaturation, explain why excessively
high temperatures (such as heat stroke or very high fevers) can be dangerous to the human
body.       proteins denature - can lose structure & function (enzymes may not work)

9. What is the name for the region of an enzyme molecule which that binds with a substrate
and is most directly affected by denaturation?
a. inactive site            b. reaction site       c. active site      d. reactive site
Biology                                            Name_________________________
                                                   Date____________ Period________

                Enzymes and pH HW#4 - Enzymes Review (see pages 1-8 of notes)

______1.     Which statement about enzymes is NOT correct?
a. enzymes are polypeptides composed of amino acids
b. an enzyme molecule forms a temporary association with a reactant
c. enzymes are destroyed when they are used and must be synthesized for each reaction
d. enzymes are specific because of their shape and catalyze only certain reactions

______2.      Which of the following enzymes would digest a fat?
           a. sucrase              b. fatase   c. protease d. lipase

_____3. At high temperatures, the rate of enzyme action decreases because the increased heat:
a. changes the pH of the system
b. alters the active site of the enzyme
c. neutralizes the acids and bases in the system
d. increases the concentration of the enzyme

_____4. Enzymes influence chemical reactions in living systems by:
a. providing the substrate required for the reaction to occur
b. affecting the rate at which reactions occur
c. absorbing water released when polymers are formed
d. combining with excess hydrogen to form gaseous wastes

_____5. Which group of organic compounds do enzymes belong to?
a. proteins b. starches c. carbohydrates      d. lipids

_____6. The ‘Lock and key model” attempts to explain the mechanism of:
a. cell wall formation           c. sharing of electrons
b. dehydration synthesis         d. enzyme specificity

_____7. Any substance that is acted upon by an enzyme is called a(n):
a. coenzyme        b. substrate c. vitamin       d. polypeptide

_____8. An enzyme that hydrolyzes protein will not act upon starch. This fact is an indication that
enzymes are:
a. hydrolytic      b. specific   c. catalytic d. synthetic

_____9. Salivary amylase is an enzyme in humans that breaks down starch. The optimum pH for this
reaction is 6.7. The enzyme's effectiveness will NOT be affected by:
a. maintaining the pH of the reaction at 6.7.
b. substrate concentration
c. enzyme concentration
d. decreasing the temperature of the reaction by 15 degrees Celsius.
_____10. A certain enzyme will hydrolyze egg white but not starch. Which statement best explains
this observation?
a. Starch molecules are too large to be hydrolyzed.
b. Enzyme molecules act only on specific substrates.
c. Egg white is composed of monosaccharides.
d. Starch is composed of amino acids.

_____11. Which environmental condition would most likely have the LEAST effect on the rate of
enzyme-controlled hydrolytic reactions in humans?
a. the pH of the solution
b. the temperature of the solution
c. the amount of enzyme and substrate present
d. the amount of light present

_____12. Gastric Protease and Intestinal Protease are digestive enzymes found in humans. Which
statement best expresses the information represented in the graph shown?

a.   The action of enzymes varies with pH.
b.   A pH of 7 provides the optimum environment for all digestive enzymes.
c.   Gastric protease is active at from pH 0 to 12.
d.   Acids have a pH greater than 7.

_____13. Lipase, maltase and protease are all members of a group of catalysts known as:
a. hormones b. carbohydrates       c. lipids     d. enzymes

_____14. The effect of temperature on the relative rate of action of an enzyme is represented in the
graph below.

The optimum temperature for the action of this enzyme is approximately __?__ degrees Celsius.
a. 15        b. 22         c. 37           d. 50
_____15. Here are some stages of an enzyme-controlled reaction:

The stage at which the enzyme is attached to the substrate and straining the substrate's bonds (called an
enzyme-substrate complex) is represented by diagram __?__. (choose a, b, c or d)

_____16. The diagram below represents three steps in the hydrolysis of a molecule of sucrose.

In this diagram, structure X is most likely:
a. a molecule of oxygen                      c. an organic catalyst
b. the end product                           d. the substrate

______17. Which letter represents an enzyme functioning to hydrolyze molecule "A" in the diagram

a. A           b. B           c. C           d. D           e. E

______18. The fact that amylase in the human small intestine works best at normal body temperature
(37 degrees Celsius) suggests that:
a. amylase is denatured at temperatures below 37 degrees Celsius
b. amylase can function only in the small intestine
c. the lock-and-key model of enzyme action does not apply to amylase
d. the optimum temperature for amylase is 37 degrees Celsius
_____19. Which statement best describes the enzyme represented in the graphs below?

a.   This enzyme works best at a temperature of 35 degrees and a pH of 8.
b.   This enzyme works best at a temperature of 50 degrees and a pH of 12.
c.   Temperature and pH have no influence on the activity of this enzyme.
d.   This enzyme works best at a temperature above 50 degrees and a pH above 12.

_____20. Enzyme “X” works best within the range of 20 – 27 degrees Celsius. At which of the
following temperatures would this enzyme most likely be denatured?
a. 15 degrees        b. 20 degrees       c. 25 degrees         d. 39 degrees

_____21. A student placed groups of 50 seeds in a variety of temperatures ranging from 0 to 50
degrees Celsius. A difference in the rate of germination observed in the groups at different
temperatures was most likely due to the effect of temperature on:
a. acids              b. glycogen             c. enzymes           d. cellulose
Biology CP                          Name                              Date                  Pd

                    Enzymes and pH HW #5 (see pages 8-11 of your notes)

1. Review your chemistry notes. What happens to an ionic compound when it is placed in
water?            The ionic compound dissociates in water. (ionizes)

2. What do we call a compound that releases H+ ions in solution? an acid

3. What ions does HCl dissociate into? H+ and Cl-

4. What is a base?           A substance that increases the hydroxide ion (OH-) concentration

5.   Which of the following is true regarding a neutral compound?
a.   in solution the concentration of H+ ions is the same as the concentration of OH- ions.
b.   it has a pH = 7
c.   pure water is an example
d.   all of these

______6. Which of the following TWO statements are true regarding buffers?
a. Strong acids and strong bases are good buffers.
b. Weak acids and weak bases are good buffers.
c. Buffers cause dramatic pH changes in organisms.
d. Buffers prevent dramatic pH changes in organisms.

______7. What would be the best buffer for a solution with a pH of 12?
a. a strong acid
b. a strong base
c. a weak acid
d. a weak base

______8. A solution with a pH of 8 contains __?__ more H+ ions than a solution with a pH of
a. 1        b. 4          c. 104       d. 10,000

______9. Which solution contains more OH- ions?
a. pH 8.2        b. pH 8.3

10. If we mixed KCl (a common salt) with pure water, do you predict the resulting solution
would have a pH above, equal to, or below 7? Explain.          7 since KCl is a neutral salt – it is
neither acidic nor basic.

11. What does the pH scale measure?              -log [H+]     measure of the H+concentration
12. Label the following solutions as acid, base or neutral.

____A_____pH 1

____B____pH 8.9

____B_____pH 14

____A_____pH 3.2

____N_____pH 7

13. Why is pure water neutral?

    There is an equal number of hydrogen ions (H+) and hydroxide ions (OH-) in solution.

14. On the pH scale below, label the arrows on either side of "Neutral" to indicate which direction is
increasingly acidic and which is increasingly basic.

         -- increasingly acidic                               increasingly basic 

15. Name any two solutions that have more H+ ions than OH– ions.
    Stomach acid and Lemon juice (even normal rainfall) (ANYTHING BELOW PH7)

16. Name any two solutions that have more OH– ions than H+ ions.

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