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Nutrition, metabolic states as related to energy pathways.
I will work through the slide presentation of chapter 25, just
focusing on selected slides and asking how to link back to
earlier supporting information:
slide #14
Protein turns over a certain rate reflected by an outflow
of nitrogen in the urine.
As long as the diet produces an excess of amino acids
in circulation over the daily loss, there is no net loss of
protein, and the excess amino acids can be catabolized.
This creates a minimum daily protein requirement in the
diet prevent loss of bodily protein, amounting to 0.8 to
1.5 g protein per kilogram body weight per day.
Excess amino acids will be used to generate ATP, or
synthesize glucose as discussed in a previous chapter.
There is essentially no significant conversion of amino
acids to fatty acids.
In ketosis, proteins will be degraded as necessary to
gain amino acids to support gluconeogenesis.
Hunt down whether you think the following are true or false:
a) Protein (after digestion to amino acids) is one of three major sources of
dietary calories, along with carbohydrates and fats.
b) You body has a reserve supply of protein to degrade and utulize in
times of starvation that is distinct from your functional proteins.
c) Amino acids are funneled into the TCA cycle for oxidation. In order to
do so, the nitrogen is removed and concentrated into urea for
excretion.
d) During a protracted fast, the liver will use amino acids derived from
body protein to keep up blood glucose levels.
e) All 20 amino acids can be used to synthesize glucose.
http://biochem.uthscsa.edu/hardies-bin/survey.pl
A summary of information about contribution of lipids to daily calorie usage:
1) Fatty acids are broken down to acetyl CoA which is burned in the TCA
cycle.
2) Muscles use fatty acids first, and then augment that with glucose
oxidation, thus sparing glucose for periods of high energy output, and
sparing bodily glucose for cells that are more directly dependent on it.
3) Fatty acids are mobilized from adipocytes and transported by serum
albumin to various cells that can utilize them. Serum albumin can’t pass
the blood brain barrier, so the brain can not directly use fatty acids as an
energy supply.
4) Fatty acids can not be converted to glucose, so when the diet is short of
carbohydrates, this causes a crisis even if there is a plentiful supply of
energy in the fat depot.
5) The liver can convert fatty acids to ketone bodies (a blood borne version
of acetyl CoA). When this happens, you are said to be in ketosis.
Ketone bodies partially replace the requirement for glucose by many
kinds of cells, including cells in the brain
6) Insulin restrains the release of fatty acids from adipocytes, forcing
muscles to rely more heavily on oxidizing glucose for energy.
slide #17
Dietary glucose shortage:
Low blood glucose will be first met by drawing on liver
glycogen, then on liver gluconeogenesis.
Gluconeogenesis will be supported by amino acids,
either from dietary sources or as a result of degrading
tissue proteins.
Insufficient supply of amino acids to support
gluconeogenesis depletes liver oxaloacetate and
causes onset of ketogenesis.
After 48 hours in ketosis, the brain increases its use
of ketone bodies and reduces its reliance on glucose,
thus reducing the degree of muscle wasting
necessary to support ketosis.
True or False?
http://biochem.uthscsa.edu/hardies-bin/survey.pl
a) During starvation, there will cease to be any urea excretion.
b) The reason you need oxaloacetate to oxidize acetyl-CoA is because
oxaloacetate is an allosteric stimulator of citrate synthase at the
beginning of the TCA cycle.
In untreated type I diabetes (caused by failure to make insulin), even
though there is high blood glucose:
c) The adipocytes secrete high levels of fatty acids which are imported to
make acetly-CoA in the liver.
d) The liver is driven into gluconeogenesis.
e) There is excessive production of ketone bodies.
GUT
GUT
GUT
Adipocyte
TAG
Amino acids
slide #24
FED
True or False?
http://biochem.uthscsa.edu/hardies-bin/survey.pl
a) The fed state will feature a surge of insulin secretion.
b) Insulin will favor making glycogen and inhibit breaking down glycogen.
c) Fatty acids move from the intestines to adipocytes carried by serum
albumin.
d) The lipid in the diet that is a major source of calories is triacylglycerol.
Cholesterol in the diet is not useful as a source of calories.
The role of NADPH in all of this is:
a) NADPH is required to support reductive biosynthesis. The
largest demands for reductive biosynthesis are generated by
lipid synthesis and DNA replication.
b) NADPH is a high energy molecule.
c) NADPH is a byproduct of glycolysis.
d) NADPH is interchangeable with NADH.
e) NADPH is synthesized as needed by the pentose phosphate
pathway.
Adipocyte
TAG
slide #25
FASTING
True or False?
http://biochem.uthscsa.edu/hardies-bin/survey.pl
a) In the fasting state liver glycogen is mobilized to support blood
glucose.
b) Muscle glycogen can not be used to support blood glucose levels
because muscle does not have glucose-6-phosphatase.
Adipocyte
TAG
Ketone
bodies
slide #26
KETOSIS
True or False?
http://biochem.uthscsa.edu/hardies-bin/survey.pl
a) Ketosis will set in during starvation.
b) Ketosis will also set in on a diet high in fat and protein but very
low in carbohydrate.
c) On any diet, ketosis will set in during uncontrolled diabetes.