Metabolism

1
Metabolism
2
catabolism the phase of intermediary metabolism
concerned with the energy-yielding degradation of
nutrient molecules.
Ingested nutrient molecules carbohydrates
proteins fats
The phase of metabolism called catabolism
describes how energy is extracted from nutrient
molecules, how these pathways are regulated in
the cell in order to adjust to changing sources
of nutrient molecules (and/or lack of them), and
how this extracted energy is converted to
adenosine triphosphate (ATP), the universal
carrier (and thus the direct supplier) of energy
for use in other cell functions.
3
The major catabolic pathways glycolysis
(degradation of glucose) b-oxidation
(degradation of fatty acids) nitrogen
metabolism (degradation of amino acids from
protein)
Other important pathways related to catabolism
the anaerobic conversion of pyruvate to
lactate (production of NAD under hypoxic
conditions) glycogenolysis
(the degradation of glycogen)
pentose phosphate pathway (production of
NADPH and pentoses) urea
cycle (elimination of ammonia from the
degradation of amino acids)
4
Anabolic pathways Gluconeogenesis (synthesis of
glucose from non-hexose precursors) Protein
synthesis Nucleic acid biosynthesis Glycogen
synthesis
5
glycolysis
cell membrane
Blood glucose
glucose
hexokinase
glucose-6-phosphate
fructose-6-phosphate
phosphofructokinase-1
fructose-1,6-bisphosphate
(multiple steps)
phosphoenolpyruvate
pyruvate kinase
pyruvate
6
glycogen
glycogenolysis
Pi
glycogen phosphorylase
glucose-1-phosphate
glucose-6-phosphate
glycolysis
Glycogen is a branched polysaccharide entirely
composed of glucose. This is the main storage
form of glucose in vertebrates. Glycogenolysis
is the metabolic process in which this stored
glucose is mobilized (i.e. released from
glycogen) as glucose-1-phosphate, and converted
to glucose-6-phosphate (an intermediate in
glycolysis). From here, the energy in the
nutrient molecule, glucose, is extracted via the
glycolytic pathway with the production of
pyruvate.
7
pyruvate
mitochondrial membrane
pyruvate
HS-CoA
pyruvate dehydrogenase
NAD
NADH
CO2
acetyl-CoA
The reaction catalyzed by pyruvate dehydrogenase
extracts energy from the three-carbon compound
pyruvate by transferring electrons and a proton
to NAD creating NADH. This extraction of energy
is an oxidation process, and one carbon from
pyruvate is oxidized to CO2. The product of the
reaction is a two-carbon fragment attached to
coenzyme A as acetyl-CoA which then enters the
TCA cycle.
8
pyruvate
pyruvate
pyruvate dehydrogenase
mitochondrial membrane
acetyl-CoA
HS-CoA
oxaloacetate
NADH
citrate
malate
TCA Cycle
isocitrate
CO2
NADH
fumarate
FADH2
a-ketoglutarate
CO2
NADH
GTP
succinate
succinyl-CoA
9
What does the TCA cycle (citric acid cycle)
do? It takes a two carbon fragment in the form of
acetyl-CoA and extracts the free energy from
these two carbons, saving most of it in the form
of NADH and FADH2. The two carbons are oxidized
in the process to CO2. One molecule of GTP
(guanidine triphosphate) is also formed. This is
converted to ATP by the enzyme adenylyl kinase.
10
cell membrane
Blood glucose
glucose
Glycolysis
Gluconeogenesis
pyruvate
pyruvate
lactate