biochem glycolysis Flashcards
a series of 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate.
Glycolysis:
- During glycolysis, there is net conversion of
2ADP to 2ATP
phosphorylation of α-D-glucose.
- reaction 1
isomerization of glucose 6-phosphate to fructose 6-phosphate
- reaction 2:
- This isomerization is most easily seen by considering the open-chain forms of each monosaccharide; it is one keto-enol tautomerism followed by another
glycolysis- Rexn 2
cleavage of fructose 1,6-bisphosphate to two triose phosphates
- reaction 4
: phosphorylation of fructose 6- phosphate.
reaction 3
: isomerization of triose phosphates
- reaction 5
- reaction 5 is Catalyzed by
phosphotriose isomerase
- Reaction in reaction 5 involves two successive
keto-enol tautomerizations.
oxidation of the -CHO group of D- glyceraldehyde 3-phosphate.
- Reaction 6
- The product contains a phosphate ester and a high- energy mixed carboxylic-phosphoric anhydride.
- Reaction 6
transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP.
- Reaction 7
isomerization of 3-phosphoglycerate to 2-phosphoglycerate
- Reaction 8
phosphate transfer to ADP
- Reaction 10
dehydration of 2-phosphoglycerate
- Reaction 9:
is most commonly metabolized in one of three ways, depending on the type of organism and the presence or absence of O2
- Pyruvate
In vertebrates under anaerobic conditions, the most important pathway for the regeneration of NAD+
reduction of pyruvate to lactate
is a tetrameric isoenzyme consisting of H and M subunits; H4 predominates in heart muscle, M4 in skeletal muscle
- Lactate dehydrogenase (LDH
While reduction to lactate allows glycolysis to continue, it ____ the concentration of _______ and also of _______
increases
lactate
H+ in muscle tissue
- When blood lactate reaches about________, muscle tissue becomes almost completely exhausted.
0.4 mg/100 mL
- Under aerobic conditions, pyruvate undergoes
oxidative decarboxylation.
decarboxylation.
* The carboxylate group is converted to
CO2.
- The remaining two carbons from the decarboxylation are converted to the
- The remaining two carbons are converted to the
- Glycerol enters glycolysis via
dihydroxyacetone phosphate.
are a highly reduced form of carbon.
- Hydrocarbon chains
a series of five enzyme-catalyzed reactions that cleaves carbon atoms two at a time from the carboxyl end of a fatty acid.
- β-Oxidation
the fatty acid is activated by conversion to an acyl CoA; activation is equivalent to the hydrolysis of two high-energy phosphate anhydrides.
- Reaction 1:
oxidation of the α,β carbon-carbon single bond to a carbon-carbon double bond
- Reaction 2:
hydration of the C=C double bond to give a 2° alcohol.
Reaction 3
oxidation of the 2°alcohol to a ketone.
- Reaction 4:
cleavage of the carbon chain by a molecule of CoA-SH.
- Reaction 5
- This cycle of reactions is then repeated on the shortened fatty acyl chain and continues until the entire fatty acid chain is degraded to
acetyl CoA
- β-Oxidation of unsaturated fatty acids proceeds in the same way, with an extra step that
isomerizes the cis double bond to a trans double bond
: acetone, β-hydroxybutyrate, and acetoacetate;
- Ketone bodies
- are formed principally in liver mitochondria
- Ketone bodies
- Formation occurs when the amount of acetyl CoA produced is excessive compared to the amount of oxaloacetate available to react with it and take it into the TCA
- Ketone bodies:
NH2 groups move freely by
transamination
- Pyridoxal phosphate forms an
imine
- Rearrangement of the imine gives an
isomeric imine
- Hydrolysis of the isomeric imine gives an
α-ketoacid and pyridoxamine
- nitrogens to be excreted are collected in
glutamate,
- nitrogens to be excreted are collected in glutamate,
which is oxidized to
α-ketoglutarate and NH +
a cyclic pathway that produces urea from CO2 and NH +.
Urea cycle
- The breakdown of amino acid carbon skeletons follows two pathways
- glucogenic amino acids
- ketogenic amino acids
: those whose carbon skeletons are degraded to pyruvate or oxaloacetate, both of which may then be converted to glucose by gluconeogenesis.
- glucogenic amino acids:
those whose carbon skeletons are degraded to acetyl CoA or acetoacetyl CoA, both of which may then be converted to ketone bodies
- ketogenic amino acids
- When red blood cells are destroyed
- heme is converted to bilirubin.
- bilirubin enters the liver via the bloodstream and is then transferred to the gallbladder where it is stored in the bile and finally excreted in the feces.
