Glycogen Metabolism and Pentose Phosphate Pathway Flashcards
___________ is a glucose polymer (up to 100k molecules of glucose/molecule of glycogen). It is a ______________.
Molecules of __-glucose are linked together by _____________ bonds.
Glycogen; homopolysaccharide
D; O-glycosidic
Glycosidic bond: a bond linking a sugar with another molecule (in glycogen, this other molecule is another glucose). There are O-, N-, and P- glycosidic bond.
The intra chain O-glycosidic bonds are α__–>__
The inter chain O-glycosidic bonds are α__–>__
1; 4
1; 6 (side chain of glycogen)
What are reducing sugars?
Reducing sugars are sugars capable of acting as a reducing agent (give electrons to an oxidizing agent) since they still have a free ALDEHYDE or KETONE group.
A reducing sugar needs to have an HEMIACETAL or HEMIKETAL group.
Match the definitions to their terms;
1) Hemiacetal
2) Hemiketal
3) Anomeric carbon
A) a carbon at the center of an hemiacetal or hemiketal functional group.
B) a carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH). derived from ALDEHYDE (e.g. glucose).
C) a carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH). derived from KETONE (e.g. fructose)
Hemiacetal: a carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH). derived from ALDEHYDE (e.g. glucose).
Hemiketal: a carbon which is part of an ether bond (R-O-R’) but is also attached to an alcohol (OH). derived from KETONE (e.g. fructose)
Anomeric carbon: a carbon at the center of an hemiacetal or hemiketal functional group.
There is one reducing end in a glycogen molecule and all the other ends are non-reducing ends.
Why?
The non-reducing ends are the site of glycogen metabolism (catabolism/anabolism), so the more non-reducing ends there are, the quicker the glycogen is metabolized.
*the branches of glycogen allow for more non-reducing ends.
Why is glucose not simply stored as glucose but rather glycogen?
One molecule of glycogen displays a third of the OSMOTIC PRESSURE when compared to the number of glucose monomers constituting this glycogen molecule.
If the glucose molecules were stocked unchanged in the cell, the cell would be highly osmotic, so WATER WOULD PERMEATE INTO THE CELL, and pumping out the excess water would be too costly in energy, the cells would BURST OPEN.
This allows the cell to keep a NEGATIVE CONCENTRATION GRADIENT OF GLUCOSE between the interior and the exterior of the cell, therefore facilitating glucose entry (tricks the cell into thinking there is no glucose).
Where is glycogen stored in?
1) Liver (public usage)
2) Muscles (private usage)
How is the glycogen used in the liver vs the muscles?
Glycogen in the liver: in case of need, the liver EXPORTS glucose from glycogen breakdown towards other organs (mainly brain)
Glycogen in the muscles: muscles use glycogen during MUSCLE CONTRACTIONS.
Liver contains _____ of stored glycogen in the body (1/8th of liver weight), while muscle contains _____ of stored glycogen (0.8% of muscle weight).
Liver glycogen reserve can be exhausted in less than _____ hours, while muscle glycogen reserve can be exhausted in __ to __ hours of exercise.
1/3; 2/3
24; 1-2
(T/F) Glycogen is stored in the cytoplasm, glycosome and the endoplasmic reticulum.
False!
Glycogen is stored in the MITOCHONDRIA, glycosome (glycogen granuels) and the endoplasmic reticulum.
What is the difference between glycogenesis and glycogenolysis?
Glycogenesis: anabolism of glycogen (synthesis of glycogen to store glucose)
Glycogenolysis: catabolism of glycogen (from diet/endogenous glycogen) into glucose-1-phosphate
Where does glycogen metabolism occur?
1) GUT (postprandial period): digestive catabolism of food glycogen. allows the production of glucose for distribution to glycogen storage areas and organs
2) LIVER (glucostat): glycogen synthesis during postprandial period, glycogen breakdown between meals.
3) MUSCLES: glycogen synthesis when the muscle is at rest, glycogen breakdown when muscles are contracting.
*glycogenesis occurs in the liver + muscles
Glycogen synthesis or degradation depends on:
1) the nutritional state of the organism (right after eating: synthesis, between meals: breakdown)
2) the need for energy
Match the following steps of glycogenesis to their definitions:
1) Reaction 1
2) Reaction 2
3) Reaction 3
4) Reaction 4
5) Reaction 5
6) Reaction 6
A) Glucose-1-phosphate (G1P) is ACTIVATED in UDP-glucose by the UDP-GLUCOSE PYROPHOSPHORYLASE.
B) Building side chains (α1–>6) bonds done by AMYLO-(1,4–>1,6)-TRANSGLYCOSYLASE.
C) Extension of the new glycogen molecule by elongation of the branches and formation of new (α1–>4) bonds bu GLYCOGEN SYNTHASE and addition of new side branches by AMYLO-(1,4–>1,6)-TRANSGLYCOSYLASE.
D) Glucose is PHOSPHORYLATED to form Glucose-6-phosphate (G6P) by HEXOKINASE.
E) Synthesis of linear chains (α1–>4); glucose from UDP-glucose is transferred to the nonreducing end of a glycogen primer or a linear chain undergoing elongation done by GLYCOGEN SYNTHASE.
F) Glucose-6-phosphate (G6P) is ISOMERIZED to glucose-1-phosphate (G1P) by PHOSPHOGLUCOMUTASE.
Reaction 1: Glucose is PHOSPHORYLATED to form Glucose-6-phosphate (G6P) by HEXOKINASE.
Reaction 2: Glucose-6-phosphate (G6P) is ISOMERIZED to glucose-1-phosphate (G1P) by PHOSPHOGLUCOMUTASE.
Reaction 3: Glucose-1-phosphate (G1P) is ACTIVATED in UDP-glucose by the UDP-GLUCOSE PYROPHOSPHORYLASE.
Reaction 4: Synthesis of linear chains (α1–>4); glucose from UDP-glucose is transferred to the nonreducing end of a glycogen primer or a linear chain undergoing elongation done by GLYCOGEN SYNTHASE.
Reaction 5: Building side chains (α1–>6) bonds done by AMYLO-(1,4–>1,6)-TRANSGLYCOSYLASE.
Reaction 6: Extension of the new glycogen molecule by elongation of the branches and formation of new (α1–>4) bonds bu GLYCOGEN SYNTHASE and addition of new side branches by AMYLO-(1,4–>1,6)-TRANSGLYCOSYLASE.
Match the following steps of glycogenesis to their definitions:
1) Reaction 1
2) Reaction 2
3) Reaction 3
4) Reaction 4
A) Reversible reaction! Taking the phosphate on C6 and moving it to C1 of G6P!
B) UDP is released. Since UDP-glucose is a high-energy compound, reaction is exergonic and irreversible!
C) There is an investment of ATP; irreversible! Catalyzed by hexokinase I, II, III in the muscles, and by glucokinase in the liver.
D) Reaction is driven by the hydrolysis of the pyrophosphate from the uridine triphosphate (UTP). Irreversible! The activated intermediate, UDP-glucose, used as building blocks in the growing glycogen chain.
Reaction 1: There is an investment of ATP; irreversible! Catalyzed by hexokinase I, II, III in the muscles, and by glucokinase in the liver.
Reaction 2: Reversible reaction! Taking the phosphate on C6 and moving it to C1 of G6P!
Reaction 3: Reaction is driven by the hydrolysis of the pyrophosphate from the uridine triphosphate (UTP). Irreversible! The activated intermediate, UDP-glucose, used as building blocks in the growing glycogen chain.
Reaction 4: UDP is released. Since UDP-glucose is a high-energy compound, reaction is exergonic and irreversible!
In reaction 5 of glycogenesis, after linear chain formation of about ____ molecules of glucose, the last ___/___ glucoses of the _____________ ends are detached and transferred onto a glucose closer to the __________ end, where the formation of an O-glycosidic (α1–>6) bond ties the glucose side branch to the linear branch.
11; 6/7; non-reducing; reducing
How many ATPs are needed to add each new glucose unit onto the glycogen molecule?
When?
Two ATPs!
1) Conversion of glucose into G6P (1 ATP)
2) UTP is used to transform G1P into UDP-glucose. One ATP equivalent is needed to convert UDP into UTP (1 ATP).
*Energy cost is high so glycogen synthesis is done right after a meal so ATP is not an issue! there is tons of glucose floating around used by glycolysis to produce lots of ATPs! ANYTHING COSTLY IS DONE RIGHT AFTER A MEAL.
What is a glycogen primer?
Short chain of glucose residues assembled linked to a small protein named GLYCOGENIN (37 kDa).
