Explain why two four-sugar polysaccharides can be different, even if both consist of two glucose monomers and two galactose monomers.
They could differ in 1) location of linkages (e.g., 1,4 or 1,6); 2) types of linkages (e.g., alpha or beta): 3) the sequence of the monomers (e.g., two galactose then two clugose, versus alternating galactose and glucose); and/or 4) whether the four monomers are linked in a line or whether they are branched.
Identify two aspects of the structures of cellulose, chitin, and peptidoglycan that correlate with their function as structural molecules.
1) the beta-1,4-glycosidic linkages in these molecules are difficult to degrade, 2) when individual molecules of these carbohydrates align, bonds form between them and produce tough fibers or sheets.
Describe how the carbohydrates you ate during breakfast today are functioning in your body right now.
Most are probably being broken down into glucose, which in turn is being broken down in reactions that lead to the synthesis of ATP. In short, the carbohydrates are providing you with chemical energy.
What is the difference between a monosaccharide, a disaccharide and a polysaccharide?
The number of monomers in the molecule.
What type of bond allows sugars to polymerize?
What holds cellulse molecules together in bundles large enough to form fibers?
What are the primary functions of carbohydrates in cells?
Energy storage, cell identity, structure, and building blocks for synthesis.
Why is it unlikely that carbohydrates played a large role in the origin of life?
They do not polymerize without the aid of enzymes
What is a "quick and dirty" way to assess how much free energy an organic molecule has?
Compare the number of C-H and C-C bonds vs. C-O bonds it contains.
Explain why the structure of carbohydrates supports their function in signaling the identity of a cell.
Carboydrates are ideal for signaling the identity of the cell because they are so diverse structurally. This diversity enables them to serve as very specific identity tags for cells.
What is the difference between linking glucose molecules with α-1,4-glycosidic linkages versus β-1,4-glycosidic linkages? What are the consequences?
The linkages are located on opposite sides of the plane of the glucose rings ("above" or "below" the plane), and the glucose monomers are linked in the same orientation versus having every other glucose flipped in orientation. the "beta" linkages are much more difficult for enzymes to break, so they resist degredation.
Compare and contrast the structures and functions of starch and glycogen. How are these molecules similar? How are they different?
Starch and glucose both consist of glucose monomers joined by α-1,4-glycosidic linkages, and both function as storage carbohydrates. Starch is composed of unbranched amylose and branched amylopectin, while glycogen is even more highly branched.
Why do the bonds in a carbohydrate store a large amount of chemical energy compared with the chemical energy stored in the bonds of carbon dioxide?
The electrons in the C=O bonds of carbon dioxide molecules are held tightly by the highly electronegative oxygen atoms, so have low potential energy. The electrons in the C-C and C-H bonds of carbohydrates are shared equally and have much higher potential energy.
What aspects of the structure of cellulose and chitin support their function in protecting and stiffening cells and organisms?
They have β-1,4-glycosidic linkages, which are resistant to degradation and put glucose monomers in positions where hydrogen bonds can form between adjacent strands, forming strong fibers.
Both glycogen and cellulose consist of glucose monomers that are linked end to end. How do the structures of these polysaccharides differ? How do their functions differ?
Glycogen has α-1,4-glycosidic linkages with α-1,6-glycosidic linkages at branch points; cellulose has β-1,4-glycosidic linkages and is not branched - instead, it forms hydrogen bonds with adjacent cellulose molecules. Glycogen is an energy-storage molecule; cellulose is a structural polysaccharide.
A weight loss program for humans that enphasized minimal consumption of carbohydrates was popular in some countries in the early 2000s. What was the logic behind the diet?
Carbohydrates are energy-storage molecules, so minimizing their consumption may reduce total energy intake. Lack of available carbohydrate also forces the body to use fats for energy, reducing the amount of fat that is stored.
Galactosemia is a potentially fatal disease that occurs in humans who lack the enzyme that converts galactose to glucose. To treat this disease, physicians exclude the monosaccharide galactose from the diet. Why does the disaccharide lactose also have to be excluded from the diet?
Lactose is made up of glucose and galactose.
Amylase, an enzyme found in human saliva, catalyzes the hydrolysis of the α-1,4-glycosidic linkages in starch. If you hold a salty cracker in your mouth long enough, it will begin to taste sweet, why?
Amylase breaks down the starch in the cracker into glucose monomers, which stimulate the sweet receptors in your tongue.
Lysozyme, an enzyme found in human saliva, tears, and other secretions, catalyzes the hydrolysis of the β-1,4-glycosidic linkages in peptidoglycan. What effect does contact with this enzyme have on bacteria?
When bacteria contact lysozyme, their cell walls, which contain peptidoglycan, begin to degrade, leading to the death of the bacteria.
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