Transcript Metabolism II

Metabolism II
• Nearly all of the energy needed by the human
body is provided by the oxidation of
carbohydrates and lipids. Whereas
carbohydrates provide a readily available source
of energy, lipids function primarily as an energy
reserve.
• It is interesting to compare the relative amounts
of energy provided by various biochemicals in a
typical 154 lb male. The free glucose in the
blood provides only a 40 kcal energy reserve -only enough to maintain body functions for a few
minutes.
• Glycogen remaining stored in the liver and
muscles after an overnight fast, amounts to
about 600 kcal energy. Glycogen reserves can
maintain body functions for about one day
without new inputs of food. Protein (mostly in
muscle) contains a substantial energy reserve of
about 25,000 kcal.
• Finally, lipid reserves containing 100,000 kcal of
energy can maintain human body functions
without food for 30-40 days with sufficient water.
Lipids or fats represent about 24 pounds of the
body weight in a 154 pound male.
Lipid Metabolism
• Lipolysis – breakdown of lipids for entry into TCA
cycle
• Triglycerides are predominant lipid in body used
for energy
• Stored in adipose tissue
• Glycerol backbone &
3 fatty acids
The first step in lipid metabolism is the hydrolysis
of the lipid in the cytoplasm to produce glycerol
and fatty acids.
Glycerol
• Has a 3 carbon backbone that fatty acids attach to
• it is metabolized quite readily into an intermediate in
glycolysis, dihydroxyacetone phosphate, which may be
converted into pyruvic acid
• dihydroxyacetone may also be used in
gluconeogenesis to make glucose-6-phosphate for
glucose to the blood or glycogen depending upon what is
required at that time.
Fatty Acids
• Chain of hydrocarbons
• Can be saturated or unsaturated
• Fatty acids are oxidized to acetyl CoA in
the mitochondria using the fatty acid spiral.
Fatty Acid Spiral
• One turn of the fatty acid spiral produces
ATP from the interaction of the coenzymes
FAD (step 1) and NAD+ (step 3) with the
electron transport chain. Total ATP per turn
of the fatty acid spiral is:
• Step 1 - FAD into e.t.c. = 2 ATP
Step 3 - NAD+ into e.t.c. = 3 ATP
Total ATP per turn of spiral = 5 ATP
• In order to calculate total ATP from the fatty acid
spiral, you must calculate the number of turns
that the spiral makes. Remember that the
number of turns is found by subtracting one from
the number of acetyl CoA produced.
• Example with Palmitic Acid = 16 carbons = 8
acetyl groups
• Number of turns of fatty acid spiral = 8-1 = 7
turns
• ATP from fatty acid spiral = 7 turns and 5 per
turn = 35 ATP. [activation energy = 1 ATP] NET
ATP from Fatty Acid Spiral = 35 - 1 = 34 ATP
Beta Oxidation
• The acetyl CoA produced from the fatty
acid spiral enters the TCA cycle. When
calculating ATP production, you have to
show how many acetyl CoA are produced
from a given fatty acid as this controls how
many "turns" the citric acid cycle makes.
• Used palmitic acid (16 carbons) The fatty
acid spiral ends with the production of 8
acetyl CoA
• 1 ATP, 3 NADH,
& 1 FADH2 = 12
ATP per acetyl
CoA in TCA
cycle
• All NADH &
FADH2 will enter
Electron
Transport
system
Step
ATP
produced
One acetyl CoA per turn
C.A.C.
+12 ATP
8 Acetyl CoA = 8 turns
C.A.C.
8 x 12 = 96
ATP
Fatty Acid Spiral
34 ATP
GRAND TOTAL
130 ATP
• These events occur in liver and muscle. During
sustained exercise the cells of slow twitch
muscle fibers (which possess mitochondria)
utilize ß-oxidation as the major source of ATP.
Protein Metabolism
• Proteins make up the structural tissue for
muscles and tendons, transport oxygen or
hemoglobin, catalyze all biochemical reactions
as enzymes, and regulate reactions as
hormones. Our bodies must be able to
synthesize the many proteins, amino acids, and
other non-protein nitrogen containing
compounds needed for growth, replacement,
and repair. Proteins in excess are used to supply
energy or build reserves of glucose, glycogen, or
lipids.
nitrogen or amino acid pool
• mixture of amino acids available in the cell
derived from dietary sources or the
degradation of protein. Since proteins and
amino acids are not stored in the body,
there is a constant turnover of protein.
Some protein is constantly being
synthesized while other protein is being
degraded
Synthesis of New Amino Acids
• these reactions can also be used to synthesize
amino acids needed or not present in the diet.
An amino acid may be synthesized if there is an
available "root" ketoacid with a synthetic
connection to the final amino acid. Since an
appropriate "root" keto acid does not exist for
eight amino acids, (lys, leu, ile, met, thr, try, val,
phe), they are essential and must be included in
the diet because they cannot be synthesized
• if there are excess proteins in the diet those
amino acids converted into pyruvic acid and
acetyl CoA can be converted into lipids by the
lipogenesis process. If carbohydrates are
lacking in the diet or if glucose cannot get into
the cells (as in diabetes), then those amino acids
converted into pyruvic acid and oxaloacetic
acids can be converted into glucose or
glycogen.
• The hormones cortisone and cortisol from the
adrenal cortex stimulate the synthesis of glucose
from amino acids in the liver and also function as
antagonists to insulin.
oxidative deamination
• Deamination is also an oxidative reaction
that occurs under aerobic conditions in all
tissues but especially the liver. During
oxidative deamination, an amino acid is
converted into the corresponding keto acid
by the removal of the amine functional
group as ammonia and the amine
functional group is replaced by the ketone
group. The ammonia eventually goes into
the urea cycle.