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【多选题】
How are the glycogen degradative and synthetic pathways coordinated and regulated?A.
Fasting cells can mobilize glucose that has been stored in the form of glycogen, a branched polymer of glucose . This large polysaccharide is stored as small granules in the cytoplasm of many animal cells, but mainly in liver and muscle cells . The synthesis and degradation of glycogen occur by separate metabolic pathways, which can be rapidly and coordinately regulated to suit an organism’s needs.
B.
When more ATP is needed than can be generated from food-derived molecules available in the bloodstream, cells break down glycogen in a reaction that is catalyzed by the enzyme glycogen phosphorylase. This enzyme produces glucose 1-phosphate, which is then converted to the glucose 6-phosphate that feeds into the glycolytic pathway.
C.
Like glycolysis and gluconeogenesis, the glycogen degradative and synthetic pathways are coordinated by feedback regulation. In this case, enzymes in each pathway are allosterically regulated by glucose 6-phosphate, but in opposite directions: in the synthetic pathway, glycogen synthetase is activated by glucose 6-phosphate, whereas glycogen phosphorylase, which breaks down glycogen, is inhibited by glucose 6-phosphate, as well as by ATP.
D.
This regulation helps to prevent glycogen breakdown when ATP is plentiful and to favor glycogen synthesis when the glucose 6-phosphate concentration is high. The balance between glycogen synthesis and breakdown is further regulated by intracellular signaling pathways that are controlled by the hormones insulin, epinephrine, and glucagon.
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【单选题】To attract more customers, some large stores ______.
A.
employ a company specializing in the use of smells
B.
provide free coffee for them
C.
filter purified air through air-conditioning
D.
decorate themselves with fresh flowers
【简答题】用万用表电阻档检测电容,看到的现象是( )。
【简答题】Some young employees of the firm have to find ways of some money _______ (as an additional job or source of income).
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