A molecule of a branched glucose polymer has 6000 glucose units…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A molecule of a branched glucose polymer has 6000 glucose units. In glycogen a branch starts at about every 10th unit. In amylopectin it starts at about every 25th unit. A molecule with branch points has chain ends that are non-reducing, and one end that is reducing. Find the number of branch points in each polymer, and the number of non-reducing ends in each. Say which polymer can release glucose faster, and why.
Need a reminder? The key ideaShow
A glycosidic link releases one molecule of water, so units in a chain have links. Hydrolysis adds the water back. Sucrose gives equal moles of glucose and fructose. The observed rotation of a mixture is the sum of the contributions of each sugar: .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Branch points are the units divided by the spacing. A branched chain has one more end than it has branches.
Step 1. Glycogen. branch points. Non-reducing ends: .
Step 2. Amylopectin. branch points. Non-reducing ends: .
Step 3. Speed. Enzymes remove glucose from the non-reducing ends, one unit at a time. Glycogen has about ends against , so more enzymes can work at once. Glycogen releases glucose faster.
Answer: 600 and 601 for glycogen, 240 and 241 for amylopectin. Glycogen is faster, because it has more ends.
Check. Closer branches give more branch points and more ends.
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