Cell Physiology:
Metabolism
Biology 211
Anatomy & Physiology 1
Dr. Tony Serino
Metabolism
Refers to all of the reactions that occur
in the cell
 Each reactions requires a specific
enzyme
 Energy may be released or consumed in
the reactions

Energy Flow in Reactions
Metabolic Reactions (R  P)
Most reactions are reversible
 All reactions try to proceed to a
dynamic equilibrium. Therefore, one
way to favor a reaction is to manipulate
the amount of reactants or products
present.

A + B  C + D
Metabolic Pathways
A series of reactions in the body.
 Most are linked with other sets, so that
the products of one reaction become
the reactants of the next.
 Two Kinds:

Degradative (Catabolism)
 Biosynthetic (Anabolism)

Pathway Map of
Cell Metabolism
Note: Kreb Cycle
Enzymes

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Catalyze reactions
Reactants = substrates (S)
S bind to active site on E
S bound non-covalently
3D structure give E specificity
# of bonds formed gives affinity
May use co-factors (co-enzymes)
May bind other chemicals that act
as modulators (change 3D shape
of active site)
Substrate
The enzyme’s 3D shape
allows it to bind to a
specific substrate.
Active
Site
Energy flow in a reaction
Every
reactions
must
overcome an
energy barrier
to begin.
 Energy of
Activation (EA)

Energy Flow with Enzyme Present

Enzymes
increase
reaction
rates by
lowering
the EA
Enzymes Lower EA
Bring reactants into close proximity
 Produce bond strain in substrates

Both of these
characteristics allows
the enzyme to lower
the reaction’s EA
Control of Enzyme Function


Proteins
remain
functional in a
narrow range
of pH and
temp.
Radical
changes in
these values
can cause
proteins to
denature; that
is, change its
3D shape
Enzyme Control
Enzyme activity can
be modified by
changes in both
enzyme and
substrate
concentrations
 Excess substrate
eventually hits a
maximum or
saturation point

Enzyme Control
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Other substances may bind
to the enzyme and modify
its behavior; either as an
activator or inhibitor
If the substance competes
with the substrate for the
active site; it is a
competitive inhibitor
If it binds elsewhere and
changes the enzymes shape
at its active site then it is a
noncompetitive
inhibitor/activator
Enzyme Modulation:
non-competitive inhibition and activation
Binding of a molecule to a site other than the active site may
result in an enzyme conformational change that either turns
the enzyme “on or off”
 If the modulator is bound by non-covalent forces; it is
allosteric modulation (the most common type); if bound
covalently, it is covalent modulation (which is more difficult to
change)

ATP cycle
Utilization of ATP
ATP Synthesis

Two ways to produce ATP
Substrate Phosphorylation
 Oxidative Phosphorylation

Substrate Phosphorylation

An ATPase binds
a substrate that
can be stripped of
a high energy
phosphate to
synthesize ATP
Oxidative Phosphorylation

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High energy electrons are
scavenged from the breakdown
of food molecules and used to
power an electron transport
chain which allows the cell to
synthesize ATP
Uses a series of Redox
reactions to power pumps
Note: the PO4- is an ion of the
environment and contains no
extra energy
Co-enzymes: NADH & FADH2
Oxidized
Reduced
NAD+  NADH
FAD+  FADH2
The co-enzymes pick up high energy electrons and transport them to
where they are needed, such as, the electron transport chain.
Glycolysis
Kreb Cycle
Electron Transport Chain
Glycolysis: Overview
2 PGAL
Transition Reaction: Acetyl-CoA
For one molecule of glu, 2 pyruvates will be processed.
Kreb Cycle
Kreb Cycle
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For one molecule of
glucose, 2 acetyl-CoAs will
be processed, so the Kreb
cycle will make 2 complete
turns
All of the carbon atoms of
the sugar have now been
converted to CO2
After the co-enzymes are
processed, the total
amount of ATP produced
per turn of the wheel will
be 12 ATP
Transition
reaction
Electron Transport Chain
(Respiratory Chain)

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NADH unloads its electrons
at the start of the chain;
yielding the maximum
energy release per electron
pair
FADH2 unloads further down
the line, thereby diminishing
its energy return
Oxygen is the final electron
acceptor, it combines with
hydrogen to form water
Chemiosmosis
Generates a high H+ concentration
in the intermembrane space
ATP synthase
complex


H+ are pushed through the
channel due to their electrochemical gradient
This spins the rotor molecules
which produces the energy
needed to convert ADP to ATP
Cellular Respiration Overview
Aerobic vs. Anaerobic Respiration
Anaerobic Respiration
(fermentation)
Food Processing
Protein Metabolism
Proteins  Amino Acids
 Amino Acids
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Deamination –removes NH forming a keto-acid
Transamination –transfers NH to other keto-acid
Keto-acids can be fed into Kreb Cycle
 Amino group may form ammonia which can be
converted to urea and excreted by kidney

Fat Metabolism
Triglyceride  3 fatty acids + glycerol ( a sugar)
Fat Metabolism
Fatty acids broken down
2 C’s at one time =
Beta-oxidation of fat
 8 C fatty acid would yield
62 ATP molecules

(17x-6) = # of ATP produced
x = # of C pairs in the FA