Physiology 31
Chapter 4 – Cellular Metabolism
I. Overview
A. Energy in Biological Systems
B. Chemical Reactions
C. Enzymes
D. Metabolism
E. ATP Production
F. Synthetic Pathways
II. Energy in Biological Systems
A. ________ is the capacity to do work.
B. Energy may be in the form of chemical, mechanical, or _________ work
1. ________ work allows cells to grow, reproduce, and store energy
2. ____________ work is used for movement (e.g., muscle contraction)
3. ____________ work enables cells to move particles through cell membranes
C. Two basic types of _________ are potential and kinetic
1. ___________ energy is stored energy (e.g., in chemical bonds)
2. ___________ energy is the energy of motion (e.g., molecules moving through cell
membranes)
D. The laws of _______________ govern the transfer of energy within a system
1. Energy can be _________ from one form to another, but the total energy in a closed
system (i.e., the universe) does not change
2. One form of energy cannot be ___________ converted to another form – there is always
a loss of ______ energy
3. Natural spontaneous processes move from a state of order to disorder – this is called
__________
4. To maintain intracellular order, cells must have a constant input of __________
III. Chemical Reactions
A. Chemical reactions allow cells to transfer the __________ energy of chemical bonds into
_________ energy for growth, maintenance, reproduction, and movement
B. A chemical _________ represents the course of a chemical reaction Example: CH3CH2OH
+ O2  CH3COOH + H2O
(Ethanol + Oxygen  Acetic acid + Water)
1. ____________ are substances that enter into a reaction
2. ____________ are substances produced by the reaction
3. ____________ chemical equations have the same number of each type of _______ on
both sides of the equation
4. The speed of a reaction is called the reaction _______, which is its change in
____________ over time, often measured in M/sec
C. Energy transfer in reactions occurs as ________ are broken, and/or formed
1. Energy stored in the chemical bonds of a molecule, and available to do work is called
the ______ _________ of the molecule
2. ________ molecules generally have more bonds, thus more free energy
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D. _____________ energy is the initial amount of energy needed to bring reactants into
position to react with each other
E. ____________ Reactions
1. Reactants start at a higher energy level than the __________.
2. Often the breakdown (___________) of larger molecules (e.g., breakdown of
glycogen to glucose)
3. Reaction occurs ______________ (needs little energy input)
4. Results in the release of ________.
F. ____________ Reactions
1. End products are at a higher energy level than __________.
2. Often the build-up (____________) of larger molecules (e.g.: glycogen synthesis
from glucose).
3. Requires a greater input of ________ for the reaction to occur.
G. ____________ Reactions
1. Energy released by exergonic reactions are used to drive ____________ reactions.
2. Exergonic break down of _____ is often coupled to endergonic cell reactions
requiring energy.
H. Classes of ____________ include decomposition, synthesis, or exchange reactions
1. In decomposition (___________) reactions a large molecule is broken down into 2 or
more smaller ones (C  A +B), often via the addition of _______ (e.g., starch to
glucose)
2. In __________ _________ reactions, 2 or more small molecules join to form a larger
one (A + B  C), with the loss of water (e.g., amino acids to proteins)
3. In __________ reactions, 2 molecules exchange atoms or groups of atoms (AB + CD
 AC + BD)
(e.g., NaHCO3 + HCl  NaCl + H2CO3)
I. Reversible & Irreversible Reactions
1. ___________ reactions can go in either directions under different conditions, and are
represented by 2-headed arrows:
CO2 + H2O  H2CO3  HCO3- + H+
a. Reversible reactions follow the law of _____ ______, they move from the side with
more reactants to the side with less reactants
b. Reversible reactions normally exist in a state of ____________, in which the ratio of
products to reactants is relatively stable
2. __________ reactions proceed in only one direction because they have a high ________
energy requirement to reverse the reaction
3. Most physiological reactions are ____________ because they are aided by
____________
J. Oxidation-Reduction Reactions
1. _____________ = loss of electrons (or hydrogen); atoms that have lost electrons have
less energy.
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2.
_____________ = gain of electrons (or hydrogen); atoms that have gained electrons
have more energy.
3. In _______ reactions, one or more molecules give up electrons (become ___________)
and one or more molecules gain the electrons (become __________)
4. ________ is often the oxidizing agent (hence the term oxidation)
IV. Enzymes
A. ___________ are protein catalysts that speed up reaction rates without themselves being
changed by the reaction
1. In enzymatic reactions, the reactants are called __________
2. Enzyme names are often formed by adding “___” to its substrate (e.g.: lipase) or by the
action it performs (e.g.: phosphatase)
3. Every chemical reaction in a cell requires a _________ enzyme.
4. Enzymes lower the energy of _________ so chemical reactions can take place with
less ______ in a cell
a. Enzymes bind to their ____________ and bring them into the best ___________
for reacting with each other
b. This allows enzymatic reactions to have much __________ reaction rates than
nonenzymatic reactions
5. Enzymes form an __________-________ complex
a. A substrate attaches to a specific enzyme at its _____ _____ (Lock & Key Model
vs. Induced Fit Model).
b. Enzymes help to split substrates (____________) or to join substrates together
(__________) to form product(s).
c. ___________(s) detach from the enzyme, which returns to its original shape, ready
for another substrate.
6. The presence or absence of specific _________ determines what reactions take place in
a given cell.
B. Some enzymes must be __________
1. _____________ (zymogens) are initially produced in an inactive form (e.g.:
pepsinogen )
2. Later they are _________ to become active enzymes (e.g.: pepsin)
C. Some enzymes require Cofactors or Coenzymes
1. ____________ - nonprotein inorganic molecule or ion required by some enzymes to
function (e.g.: magnesium, potassium, calcium ions).
2. ____________ - nonprotein organic molecules that bind to enzymes and serve as
carriers for chemical groups or electrons (e.g.: NAD+, FADH, and CoA).
3. _____________ such as niacin, riboflavin and pantothenic acid are used to make
coenzymes such as NAD+, FADH, and CoA.
D. Factors that affect enzyme _________ _____ include temperature, pH, concentration of
substrate and/or enzyme
1. _____________
a. As temperature increases to an _________ point, the reaction rate increases (in
humans, optimal temp. is 98.6oF).
b. Beyond the optimal point, the rate levels off, then decreases sharply as the enzyme
is ___________ (inactivated)
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2. _____ (acidity or basicity)
a. Each enzyme has an __________ pH, which helps it maintain its functional shape.
b. Change in pH alters bonding of amino acid “___” groups and results in a shape
change (____________) that inactivates the enzyme.
3. Substrate & Active Enzyme Concentration
a. Greater _________ concentration = more chances to bind with enzyme _________
sites = faster reaction rates.
b. Greater active ________ concentration = more active sites for ___________ to bind
with = faster reaction rates.
E. Chemical Modulators alter enzyme activity
1. ___________ - a molecule that binds to an enzyme and alters its catalytic ability.
2. Modulators include competitive inhibitors, ___________ and covalent modulators
a. Competitive ____________ - molecule with shape similar to that of a substrate
competes for the enzyme’s active site.
b. __________ modulator - binds to an enzyme’s allosteric site (not the active site)
and alters the ______ site shape, which can
1) ___________ enzyme-substrate binding OR
2) ___________ enzyme-substrate binding
c. _____________ modulator – atom or functional group (e.g.: __________) that
covalently binds to an enzyme and activates or deactivates it.
1) __________ enzymes and ATP phosphorylate enzymes
2) ________________ dephosphorylate enzymes
V. Metabolism
A. ___________ refers to all of the chemical reactions in an organism. Two types of
metabolism are
1. ___________ – the break down of large molecules to smaller ones. Catabolic reactions
are ___________ (they release energy)
2. __________ – the build up of large molecules from smaller ones. Anabolic reactions
are ____________ (they require energy input)
3. Energy released from or stored in chemical bonds is usually measured in kilocalories
(____)
a. A kilocalorie (__________) is the amount of _______ required to raise the temp. of
one liter of water by 1° Celcius.
b. Energy released from catabolic reactions is often stored in the bonds of ____
molecules, or in high energy electrons in _____ and FADH2
c. Energy provided for anabolic reactions is often provided by breaking the bonds of
____ molecules, or transferring electrons from NADH and ________
B. Metabolic ___________ - organized series of chemical reactions.
1. Begins with a reactant and ends with a __________.
2. Reactants are called __________ in enzymatic reactions
3. Involves many small ________.
4. Proceeds in an ___________ step-by-step manner.
A → B → C → D → E → F →G
E1
E2
E3 E4
E5
E6
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(A-F are substrates, B-G are products, E1, E2…are enzymes)
5. One pathway may lead to other pathways if they have _______ in __________.
6. Allows for easier capture & use of ______ because it is released in _______
increments.
C. Cells __________ their metabolic pathways in several ways
1. Control of enzyme __________ and activity
2. Production of allosteric and covalent ___________
3. Use of different __________ to catalyze reversible reactions
4. Isolation of enzymes within intracellular __________
5. Maintenance of an optimum ratio of ATP to _____
D. _____ is the main energy transfer molecule in metabolic reactions
1. ATP = Adenosine Triphosphate, composed of adenine, ribose sugar, and 3 __________
connected by high _______ bonds
2. When energy is required, the phosphate ____ between the 2nd and 3rd phosphate is
broken, yielding ____ + Pi (inorganic phosphate)
3. If more energy is needed, the phosphate bond between the 1st and 2nd phosphate may be
broken, yielding _____ + Pi
4. ADP and AMP can be converted back to _____ via the process of cellular respiration
E. ATP Production occurs during cellular ______________:
C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP + Heat
Enzymes
1. ____________ cellular respiration (fermentation)
a. Does not require _________
b. Occurs in the cell __________
c. Involves _________, in which a 6-carbon ________ molecule is progressively split
into 2 3-carbon __________ molecules
d. The energy liberated as glucose bonds are broken is used to produce a net of ___
ATP and ___ NADH
e. When oxygen is not present, pyruvate is converted to _______ via lactate
dehydrogenase and NADH is restored to ______
2. ___________ cellular respiration requires _______, and includes glycolysis, the citric
acid cycle, and the electron transport chain
a. _____________ occurs as in anaerobic respiration, except
1) Pyruvate is transported into the mitochondrion, and converted to a 2-carbon
__________ molecule, with the loss of ____
2) ________s transport their high energy electrons to the ETC
b. _________________ occurs via enzymes in the mitochondrial _______ in the
following sequence
1) ___________ is joined to a 4-carbon molecule to form a
6-carbon ___________ molecule
2) In a cycle of enzymatic reactions, citric acid is progressively broken back down to
the 4-carbon molecule, with the loss of ______
3) Energy liberated as citric acid bonds are broken is used to generate __-ATP
molecules, ___-NADH, and ___-FADH2
c. __________ _________ chain involves proteins (enzymes and cytochromes) in the
mitochondrial _________
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1) _____ and FADH2 transport their high energy electrons (in H atoms) to proteins in
the ETC
2) __________ are stripped from their H atoms and passed from protein to
_________ along the ETC
3) ________ from the electrons allows ____ ions to be pumped from the matrix into
the intermembrane space
4) At the end of the ETC, ____ ions diffuse back through ATP __________,
providing energy to convert ADP + Pi to ____
5) H+ and their electrons are reunited to join with ________ and form ____
6) About ___-___ ATP are generated in the ETC via ________ ______________
F. Large _________ can also be used in cell respiration to regenerate ____
1. Glycogen can be broken down via glycogenolysis into ________ molecules
2. Lipids can be broken down via lipolysis into glycerol and ______ ________
a. ___________ is fed into glycolysis
b. Fatty acids are broken into ___ ____________ fragments via beta-oxidation and fed
into the citric acid cycle
3. Proteins can be broken down via proteases into ____________, then by peptidases into
_______ acids; the glucogenic A.A.s can be used in cell respiration
G. ____________ pathways
1. ____________ is made from glucose (glycogenesis), primarily in the liver and muscle
cells
2. Glucose can be made from glycerol or glucogenic amino acids (______________) in a
process similar to the reverse of glycolysis
3. Lipids are made from ___________ units linked together by fatty acid synthase in the
smooth ER
4. Protein synthesis is directed by DNA sequences called ________. We will discuss this
more later in the semester during the genetics unit.