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Biochem Exam III
Terms in this set (68)
Glycolysis is the
first stage of glucose metabolism
Breaking down of glucose to ________ in ______ steps
Generic pathway but specific glucose transporters
-GLUT1: RBC, brain, muscle, fat
-GLUT2: liver & pancreatic beta-cells
All sugars in glycolysis have
Each step of glycolysis is catalyzed by
Products of glycolysis
-one molecule of glucose to two pyruvate molecules.
-one 6-carbon --> two 3-carbon
-yields net gain of 2 molecules ATP
Glycolysis has a net conversion of
2ADP to 2ATP
phosphorylation of glucose conversion to 2 molecules of glyceraldehyde-3-phosphate; 2 ATP are used in these reactions.
conversion of glycerlaldehyde-3-phosphate to pyruvate and coupled formation of 4 molecules soy ATP.
Control Points in glycolysis
-hexokinase: inhibited by glucose-6-phosphate
-phosphofructokinase 1 (PFK1)- inhibited by ATP
-pyruvate kinase- inhibited by ATP
-cytosol of all cells
-several hexoses as substrates including glucose, fructose and mannose.
-Km=0.15mM for glucose 1.5mM for fructose.
-inhibited by glucose-6-phosphate
-liver specific enzyme
-glucose only substrate
-important for uptake of glucose after feeding
-glycogen storage in the liver.
activated by ADP and AMP and fructose 2,6-bisphosphate
Pyruvate Kinase (PK) is a ___ enzyme
PK is inhibited by
-ATP (metabolic energy needs)
-Acetyl-CoA (citric acid cycle, from diff compartment)
-Alanine (amino form of pyruvate, protein synthesis)
PK is activated by
(example of feed-forward activation)
PK isoenzymes have ____ diff subunits
-m predominates in muscle
-l in liver
-a in other tissue
Native PK is a
Liver isoenzymes are subject to
-phosphorylation decreases activity
-under hormonal control
Formation in glycolysis
Pyruvate has different _______ depending on whether ______ is available.
No O2 means
-need to re-oxidize the NADH
-do so by reducing pyruvate
If O2 present
-NADH transfer its e- to the oxidative phosphoryltion pathway
-pyruvate is further oxidized to CO2 in the citric acid cycle
Pyruvate to lactate regenerates __________ which is need for _____ to continue
Pyruvate converted to ______ by _______.
Pyruvate to ethanol is used for
yeasts and other micro-organisms.
-which regenerate NAD+ by this two step-pathway
Pyruvate --> Ethanol: two step pathway
(1) decarboxylation of pyruvate to acetaldehyde : requires thiamine pyrophosphate (Vitamin B1)
(2) reduction of acetaldehyde to ethanol: regenerates NAD+
rapid, sustained energy storage
Liver is the main site of
-some in muscle, not much in brain, and kidney.
Synthesis or degradation depending on
-maintain blood [glucose] at 5mM (80mg/dl)
Glycogen is poised for rapid
Glucose can be released as ______ from each _______.
The _____ branches will be shifted to a free ___ end to ______ the number of ends, but allow ______ to continue
breaks down glycogen from the non-reducing end to yield glucose 1-phosphate
glucose 1-phopshate is then converted to glucose 6-phosphate
_____ in glycolysis yields a net _____ since the ____ is formed without _____ hydrolysis
A ______ enzyme transfers ____ branches and ______ the last a(1-->6) linked______.
Glycogen is cleaved by
phosphate to give a-D-glucose-1-phosphate: phosphorolysis
-no ATP is involved in this phosphorylation
*need to deal with branched structure of glycogen
3 fates of G1P
-local generation of energy (glycogen in muscle)
2) G1P-->G6P-->glucose-->release to bloodstream
-generation of energy in other tissues (glycogen in liver)
3)G1P is also the starting point for glycogen synthesis
-BUT pathway for synthesis is NOT the reverse of G1P release from glycogen
Glycogen synthesis from glucose: G1P reacts with
uridine triphosphate (UTP) to give UDPG and pyrophosphate
Glucose from UDP-glucose is added to nonreducing (C4) end of glycogen molecule by
Glycogen phosphorylase has two forms _________. Both forms havev _______ and ________ forms.
-a and b
B-form of glycogen phosphorylase has
inactivators (ATP, G6P) and an allosteric activator (AMP).
A-form of gp has
an allosteric inactivator (glucose)
Allosteric inhibition by:
-overcome by G6P
Activity of glycogen synthase is subject to...
the same type of covalent modifications as glycogen phosphorylase
startle response - fight or flight
dietary sources of glucose are gone
-NO GLYCOGEN LEFT IN LIVER
Glucogenesis is basically the reversal of glycolysis EXCEPT
for three important control points
**at control points different enzymes catalyze the reaction of gluconegenesis
Irreversible steps in glycolysis:
(1) Phosphoenolpyruvate to pyruvate + ATP
(2) Fructose-6-phosphate to fructose-1,6-bisphosphate
(3) glucose to glucose-6-phosphate
Net result of glucogenesis is
reversal of the irreverasable steps in glycolysis BUT by different reactions and using different enzymes.
Oxaloacetate is an ________.
First step of glucogenesis
pyruvate is carboxylated to oxaloacetate.
What does the first step of glucogenesis require
Biotin (CO2 carrier)
Pyruvate carboxylase is subject to
allosteric control; it is activated by acetyl-CoA
What comes after first step of glucogenesis
decarboxylation of oxalacetate is couple with phosphorylation by GTP to give PEP.
Pyruvate to oxalacetate occurs in the
Other than P to O the rest of glucogenesis occurs
in cytosol until very LAST step which is in the ER
Specific transporters in ___________ for ____ and ______.
No transporters for
-converted to aspartate or malate
-specific aspartate and matate transporters in inner mitochondrial membrane
NADH is required for
a pivotal regulartory biomolecule
**allosterically stimulates phosphofructokinase
**allosterically inhibits fructose-1,6-bisphosphatase
Concentration of F2, 6P in a cell depends on the
balance between its synthesis and its breakdown
Synthesis of F2,6P is catalyzed by
Breakdown of F2,6P is catalyzed by
fructose bisphosphatase-2 activity
fructose bisphosphatase-2 activity
Allosteric control of carb metabolism
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