Chapter 6: Energy Flow in the Life of a Cell
substrate
the atoms or molecules that are the reactants for an enzyme-catalyzed chemical reaction
adenosine diphosphate (ADP)
A molecule composed of the sugar ribose, the base adenine, and two phosphate groups; a component of ATP.
electron carrier
A molecule that can reversibly gain or lose electrons. Electron carriers generally accept high-energy electrons produced during an exergonic reaction and donate the electrons to acceptor molecules that use the energy to drive endergonic reactions.
enzyme
A protein that acts as a biological catalyst to speed up a chemical reaction
closed system
A system in which no matter is allowed to enter or leave
What is activation energy? How do catalysts affect activation energy? How do catalysts affect the reaction rate?
Activation energy is the initial input of energy required to start a chemical reaction. Catalysts reduce activation energy required which in turn causes the reaction to occur at a much faster rate
reactant
An atom or molecule that is used up in a chemical reaction to form a product.
Explain why organisms do not violate the 2nd law of thermodynamics. What is the ultimate energy source for most forms of life on earth?
Because earth is not a closed or isolated system but instead receives a constant influx of energy from the sun, which is captured by organisms and used to maintain organized complexity. The sun releases heat and undergoes a continuous increase in entropy.
Compare the mechanisms of competitive and noncompetitive inhibition of enzymes.
Competitive: a substance that is not the enzymes normal substrate binds to the active site, competing with the substrate for the active site. Noncompetitive: a molecule binds to the noncompetitive inhibitor site on the enzyme that is distinct from the active site. As a result the enzymes 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 3D 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 the enzyme it contains by turning genes on or off 2) a cell may synthesize an enzyme in an inactive form that is only activated when necessary and 3) a cell can temporarily activate or inhibit enzymes through allosteric regulation
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 ATP. Heat is released in small amounts too. Activation energy: body heat, which is adequate because enzymes greatly reduce the need for activation energy. 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 both end products are CO2 and H2O. Activation energy: heat of the match overcomes the need for it
feedback inhibition
In enzyme-mediated chemical reactions, the condition in which the product of a reaction inhibits one or more of the enzymes involved in synthesizing the product.
Define metabolism, and explain how reactions can be coupled to one another.
Metabolism is the sum total of all the 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
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: energy that is stored (chemical bonds, elastic energy of a stretched spring, or gravitational energy of water behind a dam or of a coaster at the top of a roller coaster) Kinetic energy: the energy of movement (radiant energy- waves of light or X-ray, heat energy- motion of molecules, or any motion of larger objects such as plummeting coaster car or marathon runners). Kinetic energy can become potential by moving an object up a high (gravitational). Potential can be converted to kinetic when an object falls or when ATP is used in muscle contraction. Heat is always released when energy is converted from one form to another.
law of conservation of energy
The principle of physics that states that within any isolated system, energy can neither be created nor destroyed, but can be converted from one form to another; also called the first law of thermodynamics
denature
To disrupt the secondary and/or tertiary structure of a protein while leaving its amino acid sequence intact. Denatured proteins can no longer perform their biological functions.
Which is not an example of exergonic reaction? a. photosynthesis b. a nuclear reaction in the sun c. ATP---> ADP+Pi d. glucose breakdown
a
enzymes a. increase 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
chemical energy
a form of potential energy that is stored in molecules and may be released during chemical reactions
entropy
a measure of the amount of randomness and disorder in a system
adenosine triphosphate (ATP)
a molecule composed of the sugar ribose, the base adenine, and three phosphate groups; the major energy carrier in cells. The last two phosphate groups are attached by "high-energy" bonds.
coupled reaction
a pair of reactions, one exergonic and one endergonic, that are linked together such that the energy produced by the exergonic reaction provides the energy needed to drive the endergonic reaction
chemical reaction
a process that forms and breaks chemical bonds that hold atoms together in molecules
metabolic pathway
a sequence of chemical reactions within a cell in which the products of one reaction are the reactants for the next reaction
The abbreviation ATP stands for __________. The molecule is synthesized by cells from ________ and ________. The synthesis requires an input of ___________, which is temporarily stored in ATP.
adenosine triphosphate; adenosine diphosphate, phosphate; energy
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
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
According the 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, potential
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
work
energy transferred to an object, usually causing the object to move
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 types of reaction allows the formation of complex biological molecules from simpler molecules?
exergonic, endergonic; exergonic, endergonic
energy-carrier molecule
high-energy molecules that are synthesized at the site of an exergonic reaction, where they capture one or two energized electrons and hydrogen ions. They include nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2)
activation energy
in a chemical reaction, the energy needed to force the electron shells of reactants together, prior to the formation of products
Some poisons and drugs act by _________ enzymes. When a drug is similar to the enzymes substrate, it acts as a _________ inhibitor.
inhibiting; competitive
According to the second law of thermodynamics, when energy changes forms some is always converted into ________ useful forms. This tendency is called _________.
less, entropy
exergonic
pertaining to a chemical reaction that releases energy (either as heat or in the form of increased entropy); a "downhill" reaction
endergonic
pertaining to a chemical reaction that requires an input of energy to proceed; an "uphill" reaction
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 ________ that binds specific biological molecules.
protein; catalysts, activation energy; active site
potential energy
stored energy including chemical energy (stored in molecules), elastic energy, or gravitational energy
catalyst
substance that speeds up a chemical reaction without itself being permanently changed in the process; a catalyst lowers the activation energy of a reaction
energy
the capacity to do work
kinetic energy
the energy of movement; includes light, heat, mechanical movement and electricity
second law of thermodynamics
the principle of physics that states that any change in an isolated system causes the quantity of concentrated, useful energy to decrease and the amount of randomness and disorder (entropy) to increase
noncompetitive inhibition
the process by which an inhibitory molecule binds to a site on an 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 involving its normal substrate.
allosteric regulation
the process by which enzyme action is enhanced or inhibited by small organic molecules that act as regulators by binding to the enzyme at a regulatory site distinct from the active site, and altering the shape and/or function of the active site.
competitive inhibition
the process by which two or more molecules that are somewhat similar in structure compete for the active site of an enzyme
active site
the region of an enzyme molecule that binds substrates and performs the catalytic function of the enzyme
metabolism
the sum of all the chemical reactions that occur within a single cell or within all the cells of a multicellular organism
first law of thermodynamics
The principle of physics that states that within any isolated system, energy can neither be created nor destroyed, but can be converted from one form to another; also called the law of conservation of energy
product
an atom or molecule that is formed from reactants in a chemical reaction
