Download Chapter 7

Metabolism:Transformations &
Interactions
Chapter 7
Prepared by
L.Nicholle Clark MS, NDTR, HC
5/7/2017
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Nutrition in your life
• All energy that sustains human life initially comes
from the sun?
• Photosynthesis- the process plants use to make
simple sugars to capture the Sun’s light energy in
the chemical bonds of the sugars.
• Food provide energy but..
• How does the body obtain energy from food?
• Metabolism= all the actions by which the body
obtains and expends energy from foods
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Chemical Reactions in the Body
• Each body cell conducts its metabolic work all the
time. The type & extent of metabolic activities
vary depending on the type of cell.
• Glucose molecules joined together = glycogen
chains, fatty acids =triglycerides, Amino Acids =
proteins = Anabolism or anabolic reactions the
building up of body compounds (drawn as up
arrows.)
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Chemical Reactions in the Body
• Digestion breaks down the triglycerides in
to their simplest molecules =3 fatty acid 1
glycerol molecule,= catabolic reactionsbreaking down of body compounds, these
reactions release energy(drawn as down
arrows)
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Chemical Reactions in the Body
• Transfer of energy in reactions-ATP-contains 3
phosphate groups the bonds connecting these
groups are “high energy” bonds drawn as wavy
lines.-Phos group make it vulnerable to
hydrolysis-the reaction readily break the highenergy bonds of ATP splitting off one or two phos
group & releasing their energy. These reactions
can occur simultaneously with reaction that use
energy called coupled reactions.
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Chemical Reactions in the Body
• Thus energy capture here (catabolic) is used
to fuel anabolic reactions.
• Metabolic Reactions almost always require
enzymes and their assistants coenzymes.
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Chemical Reactions in the Body
• Coenzymes are organic molecules that
associate closely with most enzymes but are
not proteins themselves. Without its
coenzymes an enzyme cannot function.
• For ex. Some of the B vit. serve as
coenzymes that participate in the energy
metabolism of glucose, glycerol fatty acids
& A Acids.
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Breaking Down Nutrients for
Energy
• Carbohydrates= glucose(other
monosaccharides (provides most of the
body’s energy needs)
• Fats(triglycerides)= glycerol & fatty
acids(provides most of the body’s energy
needs)
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Breaking Down Nutrients for
Energy
• Proteins= amino acids-building blocks of proteins
10-15% of the day’s energy requirements.
• Glucose, glycerol, fatty acids, & amino acids are
the basic units derived from food, but a molecule
of each these compounds is made of still smaller
units- atoms-carbon, nitrogens, oxygens, &
hydrogens. During catabolism, the body separates
these atoms from one another.
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Breaking Down Nutrients for
Energy
• Pyruvate (3carbon structure)- can be use to make
glucose
• Acetyl CoA(2 carbon structure with a coenzyme
CoA attached)- cannot be use to make glucose, but
can readily provide fat.
• The body needs glucose to fuel its activities.
When given only fat which can only supply Acetyl
CoA the body will have to breakdown its own
protein tissue to make glucose.
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Breaking Down Nutrients for
Energy
• If given only protein the body will have to
convert it to glucose.
• Thus the best diet should supply the body
with adequate amts. of Carb, protein & an
some fat.All eventually enter the TCA cycle
and the electron transport chain.
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Breaking Down Nutrients for
Energy
• Glucose-Central role in carbo metabolism.
• Glucose to Pyruvate= Glycolysis (glucose splitting
Fig.7-5) 6 carbon glucose to two 3 carbon to 2
pyruvate molecules. One glucose molecules yields
2 pyruvate molecules. A small energy yield as the
body uses a little energy for this process that
yields only a little more than the body spent
producing the energy.Pyruvate can be converted
again to glucose by the cells in the liver & to some
extent the kidneys.
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Pyruvate’s Options
• Body needs quick energy (sprint)-Pyruvate will
enter the anaerobic (w/o O) pathway by being
converted in to lactate by accepting the H left
from glucose breakdown. The H are carried by the
coenzyme so as the coenzymes are freed they
return to glycolysis to pickup more H. This allows
glucose to provide energy anaerobically for a
while. The process occurs to a limited extent at
rest.
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Pyruvate’s Options
• Body needs energy at a slower pace (bike
ride)- Pyruvate will enter the aerobic (w O)
energy cycle where pyruvate enters the
mitochondria of the cell where the carbon
group (COOH) from the 3-carbon pyruvate
is removed to produce a 2-carbon
compound that bonds with a molecule of
CoA, becoming acetyl CoA.
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Pyruvate’s Options
• The carbon group from pyruvate becomes carbon
dioxide, which is released into the blood and
breath out by the lungs. The process is irreversible
show only as down arrow. More ATP is produced
than with glycolysis.
• Acetyl CoA’s has two main functions 1. used
synthesize fats or 2. to generate ATP. When ATP
is in excess it will produce fat.
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Glycerol & Fatty Acids
• Glycerol to pyruvate- 3 carbon compound
but a different arrangement of H & OH on
the C than pyruvate.
• Fatty acid to Acetyl CoA- during fatty acid
oxidation fatty acid are taken apart 2
carbons at a time in a series of reactions
each fragment splits off and combines with
a molecule of CoA to make acetyl CoA.
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Glycerol & Fatty Acids
• As the fragments break off H and their
electrons are released and carried to the
electron transport chain by coenzymes made
from B Vits. Riboflavin & niacin.
• Fatty Acids cannot be used to synthesize
glucose. Important because red blood cells
& brain & nervous system depend primarily
on glucose as fuel
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Amino Acids
• After deamination (loose N and produces keto
acid & ammonia which can upset the acid-base
balance in excess amt.) catabolized by conversion
to pyruvate,( can provide glucose) conversion to
acetyl CoA ( can provide additional energy or
make body fat but cannot make glucose) or enter
the TCA cycle directly as compounds other than
acetyl CoA (can continue in the cycle and generate
energy and can generate glucose good source of
glucose when carbo are not available.
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Amino Acids
• Through transamination reactions with
many different keto acids the liver cells can
synthesize the nonessential amino acids.
• The liver combines any remaining ammonia
with carbon dioxide to make urea.Urea is
released in the blood to be removed by the
kidneys and excreted in the urea.
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The Final Steps of Catabolism
• All energy-yieldiing nutrients proceed down three
different pathways that lead to the point where
acetyl CoA enters the TCA cycle. These reactions
take place in the mitochondria.
• The TCA-Oxalacetate is the first 4-carbon
compound to enter the TCA cycle. And cannot be
made from fat carbs.are needed from the diet) It
picks up acetyl Coa drops off one carbon (as
carbon dioxide) than another carbon and returns to
pick up another acetyl CoA.
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The Final Steps of Catabolism
• The electron transport chain-energy is captured in
the high-energy bonds of ATP
• Why then does fat yield more kcalories per gram?
• Fat contains many carbon-hydrogen bonds that
can be readily oxidized, it sends numerous
coenzymes with their H and electrons to the
electron transport chain where that energy can be
captured in the bonds of ATP.
• Energy Balance- when energy input is equal to
energy output.
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Feasting–Excess Energy
• When a person eats too much metabolism favors
fat formation. The pathway form dietary fat to
body fat is direct. The pathway from excess
protein and Carbo are not as direct.
• Transition for Feasting to Fasting
• Fasting Inadequate Energy
• Symptoms of starvation- slowing of energy output
and reduction in fat loss.
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Summary
• References
• Whitney, E., Rolfes, S., Understanding
Nutrition., Belmont, CA: ThomsonWadsworth
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