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Cell Physiology:
Metabolism
Biology 201
Organism S&F
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
these reactions
Production Efficiency by Individual
Only 1/6 (~15%) of the
leaf’s energy is used to
build the caterpillar’s body.
The energy in the feces
is left in the environment.
and is used by
decomposers.
The part used as cellular
respiration is to maintain
life or is lost as heat.
Only this fraction can be passed
on in the food chain.
Trophic Efficiency
~90% loss of energy
per trophic level
Metabolic Rate
–total rate of energy use in an organism
• Basal MR –MR of a fasting endotherm at
rest
• Standard MR –MR of a fasting ectotherm
at rest at a specific temperature
Energy Budgets
Use of energy by organisms
differ based on body size and
survival strategies
• Total energy consumed by an animal
BMR/g
BMR
Metabolic Rate vs. Animal Size
increases with body size, but when rate
per gram is plotted against body mass a
reciprocal function is seen
•
animal the
higher the MR
per gram of
body mass, yet
the overall
energy
consumption is
greater in the
larger animal
Each class
(reptiles, birds,
mammals, etc)
of organism
follows this
pattern, but on
separate curves
(BMR/g)
• The smaller the
•Unicellular organisms,
endotherms, and
ectotherms, all have a
metabolic rate related to
body mass at a slope of
about 0.75.
RQ
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
•
•
•
•
•
•
•
•
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)
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
• 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
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)
Central Dogma
Protein
Synthesis
Overview
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
• 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 glucose, 2 pyruvates will be processed.
Kreb Cycle
Kreb Cycle
• 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)
• 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 intermembranal space
ATP synthase
complex
• H+ are pushed through
•
the channel due to their
electro-chemical 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
Food
Processing
Protein Metabolism
• Proteins  Amino Acids
• Amino Acids
– 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
In mammals
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
((12 * 4)+15; -1 initial
ATP used; -5 because
last two carbons do not
generate extra coenzymes)
(17x-6) = # of ATP produced
x = # of C pairs in the FA