Chapter 6 Flashcards
(18 cards)
Which of the following is true?
a. Enzymes increase activation energy requirements.
b. Activation energy is required to initiate exergonic reactions.
c. Heat cannot supply activation energy.
d. Stomach acid inactivates pepsin.
b
Which is not an example of an exergonic reaction?
a. photosynthesis
b. a nuclear reaction in the sun
c. ATP -> ADP + Pi
d. glucose breakdown
a
Which of the following is true?
a. ATP is a long-term energy storage molecule.
b. ATP can carry energy from one cell to another.
c. ADP inhibits glucose breakdown in cells.
d. ATP is produced by exergonic reactions.
d
Coupled reactions
a. are endergonic overall.
b. both synthesize and break down ATP.
c. are catalyzed by the same enzyme.
d. end with reactants that contain more energy than their products.
b
Enzymes
a. increase the rate of a reaction.
b. are active across a wide range of temperature and pH.
c. are not very specific in the substrates they bind.
d. are used up during catalysis.
a
According to the first law of thermodynamics, energy can be neither _________ nor _________. Energy occurs in two major forms: _________ , the energy of movement, and _________ , stored energy
created, destroyed; kinetic and potential
According to the second law of thermodynamics, when energy changes forms some is always converted into ________ useful forms. This tendency is called _______.
less and entropy
Once started, some reactions release energy and are called _________ reactions. Others require a net input of energy and are called _________ reactions. Which type of reaction will continue spontaneously once it starts? _________ . Which type of reaction allows the formation of complex biological molecules from simpler molecules? ________.
exergonic; endergonic; exergonic and endergonic
The abbreviation ATP stands for ________. The molecule is synthesized by cells from _________ and _________. This synthesis requires an input of ________, which is temporarily stored in ATP.
adenosine triphosphate; adenosine diphosphate, phosphate and energy
Enzymes are what type of biological molecule? ________ Enzymes promote reactions in cells by acting as biological ________ that lower the ________. Each enzyme possesses a region called a(n) __________ that binds specific biological molecules.
proteins; catalysts, activation energy and active site
Some poisons and drugs act by _________ enzymes. When a drug is similar to the enzyme’s substrate, it acts as a(n) ________ inhibitor.
inhibiting and competitive
Explain why organisms do not violate the second law of thermodynamics. What is the ultimate energy source for most forms of life on Earth?
Life does not violate the second law of thermodynamics because Earth is not a closed system but instead is receiving a constant influx of energy from the sun, which is captured by organisms and used to maintain their organized complexity. The sun releases heat and undergoes a continuous increase in entropy.
Define potential energy and kinetic energy, and provide two specific examples of each. Explain how one form of energy can be converted into another. Will some energy be lost during this conversion? If so, what form will it take?
Potential energy is energy that is stored, for example, in chemical bonds, in the elastic energy of a stretched spring, or as gravitational energy stored in water behind a dam or a car at the top of a roller coaster. Kinetic energy is the energy of movement, including radiant energy (waves of light or X-rays), heat energy (the motion of molecules), and any motion of larger objects, such as the plummeting roller-coaster car or running marathoners. Kinetic energy can be converted to potential energy (gravitational, for example) by moving an object up a hill. Potential energy can be converted to kinetic energy, as when an object falls or when ATP is used to power muscle contraction. Heat is always released when energy is converted from one form to another.
Define metabolism, and explain how reactions can be coupled to one another.
Metabolism is the sum total of all chemical reactions in a cell. Reactions are coupled so that one reaction releases energy (exergonic) to drive another reaction (endergonic). Energy-carrier molecules, particularly ATP, transfer chemical energy from exergonic to endergonic reactions. In every conversion, some energy is lost as heat.
What is activation energy? How do catalysts affect activation energy? How do catalysts affect the reaction rate?
Activation energy is an initial input of energy required to start a chemical reaction. Catalysts reduce the amount of activation energy required to start a reaction, which results in the reaction proceeding at a much faster rate.
Compare breaking down glucose in a cell to setting it on fire with a match. What is the source of activation energy in each case?
Glucose breakdown in cells occurs in the small, enzyme-catalyzed steps of a metabolic pathway. Energy is released in small increments, and some is stored in chemical bonds such as in ATP. Heat is released in small amounts. When set on fire, glucose releases large quantities of heat energy at a rapid rate, and none is captured in chemical bonds. If the glucose is burned completely, the end products of both the metabolic pathway and fire are the same: carbon dioxide and water. Activation energy in the metabolic pathway is supplied by body heat, which is adequate because enzymes greatly reduce the need for activation energy. The heat of the match flame overcomes the activation energy when sugar is burned.
Compare the mechanisms of competitive and noncompetitive inhibition of enzymes.
In competitive inhibition, a substance that is not the enzyme’s normal substrate binds to the active site of the enzyme, competing with the substrate for the active site. In noncompetitive inhibition, a molecule binds to a noncompetitive inhibitor site on the enzyme that is distinct from the active site. As a result, the enzyme’s active site is distorted, making it less able to catalyze the reaction.
Describe the structure and function of enzymes. How is enzyme activity regulated?
Enzymes are nearly always proteins with complex three-dimensional shapes that bind to specific substrates. Enzymes promote a single reaction involving one or two specific molecules. Enzyme activity is regulated in three ways: (1) A cell may regulate how much of an enzyme it contains by turning genes on or off; (2) a cell may synthesize an enzyme in an inactive form that is activated only when necessary; and (3) a cell can temporarily activate or inhibit enzymes through allosteric regulation.
