Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
31 Cards in this Set
- Front
- Back
Glycogen
|
the animal storage form of branched poly(glucose).
|
|
The process of glycogen breakdown?
|
(glucose)n → glucose-1-phosphate + (glucose)n-1
|
|
The process of glycogen breakdown?
|
(glucose)n → glucose-1-phosphate + (glucose)n-1
|
|
Glycogen synthesis
|
(glucose)n-1 + UDP-glucose → (glucose)n
|
|
Regulation of glycogen breakdown and synthesis is controlled by?
|
2 enzymes, glycogen phosphorylase and glycogen synthase, the activities are activated/inactivated by allosteric regulation and phosphorylation/dephosphorylation
|
|
Glucogen structure
|
-main chain glucose molecs connected by alpha(1→4) glycosidic bonds
-The branches are attatched by alpha(1→6) glycosidic linkages -A glucose on the non-reducung ends is cleaved or attatched 1 by 1 |
|
pathways of Glycogen breakdown
|
In muscle: Glycogen→glucose-6-phosphate(G6P)→glycolosis
In liver: Glycogen→G6P→glucose→ bloodstream→various cells→ glycolysis -This is because the muscle cells mainly consume glucose molecules whereas the liver cells mainly store the glucose molecules |
|
Glycogen breakdown requires what 3 enzymes?
|
-Glycogen phosphorylas, with Pyridoxal phosphate co factor
-Glycogen debranching enzyme -Phosphoglucomutase |
|
Glycogen phosphorylase
|
(glycogen)n+ Pi ↔ (glycogen)n-1 + G1P
-This enzyme releases a glucose unit 1 by 1 until it reaches about 5 units (limit branch) from a branch point - the enzyme has a crevice where 4-5 units of a left handed helical glycogen can fit, but its too narrow to fit a branch point |
|
Enzyme-catalyzed modification/ demodification process yields ? forms of phosphorylase
|
2
Phosphorylase a: E-O-PO (attatched at Ser-14) Phosphorylase b: no phosphate attaachment Both forms are are allosterically activated or inactivated |
|
Allosteric Inhibitors?
Allosteric Activators? |
Inhibitors: ATP,G6P,Glucose
Activators: AMP, [F2,6P] |
|
? is an essential cofactor for phosphorylase
|
Pyridoxal phosphate (PLP)
-PLP covallently bound to phosphorlase via Schiff base to Lys-679 -PLP's phosphate group probably functions as an acid-base catalyst |
|
Glycogen debranching enzyme
|
removes branches so that glycogen phosphorlase can complete reaction
|
|
Phosphoglucomutase
|
-Catalyzes the conversion of G1P to G6P
-G1P produced from the glycogen breakdown must be converted to G6P in order to enter glycolysis or to produce glucose in liver -The Ser of the enzyme is phophorylated |
|
Glycogen Synthesis
|
A. UDP-glucose formation by UDP-glucose pyrophosphorylase
B. Glycogen synthesis by glycogen synthase C. Glycogen Branching |
|
UDP-glucose formation by UDP-glucose pyrophosphorylase
|
-in the glycogen synthesis pathway, at first, the uridine diphosphate (UDP) is attatched to glucose
-This reaction is catalyzed by UDP-glucose pyrophosphorylase |
|
Glycogen synthesis by glycogen synthase
|
1. The glycosidic bond between glucose and UDP in UDP-glucose is hydrolyzed. The cleaved glucose ion takes on the oxonium ion intermediate (1/2 chair conformation), stabilized by the enzyme
2. The glucose unit of UDP-glucose is transferred to the C4-OH group on one of glycogen's non-reducing ends to form an alpha(1-4) glycosidic bond. |
|
Thermodynamics of glycogen synthesis by glycogen synthase
(glucose)n->G1P +(glucose)n-1 |
∆G of glycogen breakdown by glycogen phosphorylase is less than 0, about -5 to -8 kj/mol
|
|
∆G of glycogen synthesis by glycogen synthase
|
about -14 kj/mol
(glucose)n-1+UDP-glucose ->(glucose)n |
|
Both reactions are?
|
spontaneous under the same physiological conditions
- but glycogen synthesis uses one ATP hydrolysis per glucose for energy source |
|
Glycogen Branching
|
about 7 units of the non-reducing end of alpha-amylose chain are removed at alpha(1-4)linkage, and reattatched to the C6 of the other alpha-amylose chain by alpha(1-6)linkage
-the transfer is carried out by amylo-(1,4->1,6)-transglycosylase (branching enzyme) |
|
∆G of hydrolysis of alpha(1->4) glycosidic bond?
|
-15.5 kj/mol
|
|
∆G of hydrolysis of alpha (1->6) glycosidic bond
|
+7.1 kj/mol
|
|
Control of glycogen metabolism
A: Allosteric control of glycogen phosphorylase and glycogen synthase |
Glycogen phosphorylase- has two forms (a and b), and each form is activated allosterically from T-form to R-form
|
|
Phosphorylase b
|
non-phosphorylated enzyme and its R-form is less active
-but it's response is fast because it's activation signal(activators) come from inside the cell. |
|
Phosphorylase a
|
The Ser-14 phosphorylated enzyme and it's R-form is the most active enzyme
-resonse is slow since its activation signals (effectors) come from the outside of the cell |
|
Phosphorylase kinase and phosphoprotein phosphatase
|
Phosphorylates and dephosphorylate the enzyme, this is called covalent modification
-they are enzyme modificator and demodificator respectively Unmodified form (phosphorylase b) is mostly T-form, whereas modifie form (phosphorylase a) is mostly R-form |
|
At high demand for ATP ie low ATP, low G6P, and high AMP?
|
Glycogen phosphorylase is stimulated and glycogen synthase is inhibited, so flux through this pathway favors the glycogen breakdown
|
|
At high ATP and G6P
|
Glycogen synthasis is favored
|
|
what is the most effective activatin process of phosphorylase?
|
Phosphorylation
|
|
Enzyme cascades
|
when one molecule of enzyme can produce a many product through a series of reactions
|