Life 120 #5

Which complex carbohydrate contains only a-1,4-glycosidic linkages?

Amylose (Amylose is formed from a-1,4-glycosidic linkages of glucose.)

Which statement best summarizes a key difference in the structure of polysaccharides that function in energy storage versus structural support (in that order)?

Built from -glycosidic linkages; form straight chains that bond with adjacent chains.

Which of the following chemical bonds have the lowest free energy?

C-O bonds

Which of the following complex carbohydrates is listed with its correct function?

Cellulose: structural component of plant cell walls (Cellulose is indeed the main structural component of plant cells walls.)

Both carbohydrates and fats are used as fuel in cells, but fats store twice as much energy per gram as carbohydrates. Which statement best explains why?

Fats have more and bonds with high free energy, and fewer bonds with low free energy. (Fats store more chemical energy per gram than do carbohydrates.)

Use the following paragraph to answer the corresponding question. Masatomo Kawakubo et al. reported in Science in August 2004 that the human stomach contains a natural, carbohydrate-based antibiotic that probably protects a large portion of the population from various diseases caused by the bacterium Helicobacter pylori. This bacterium has been linked to peptic ulcers, gastritis, and stomach cancer. This naturally occurring antibiotic is described by Kawakubo as having a terminal 1,4-linked N-acetylglucosamine (NAG), and it acts by inhibiting the biosynthesis of a major component of the cell wall in H. pylori. [Source: M. Kawakubo et al., Science 305 (2004): 1003.] Refer to the paragraph about Kawakubo's group. Kawakubo's group created a glycoprotein with a terminal NAG (i.e., a protein with NAG attached to its end). Their hypothesis is that the terminal NAGand not the protein component-is responsible for the damage to the cell wall in H. pylori. What would be the most appropriate control for testing this hypothesis?

Grow H. pylori in a test tube with glycoprotein that has its terminal NAG removed. (This question includes concepts from Chapter 1. If the instructor has not yet discussed experimental controls, this question would make an excellent introduction to the subject.)

Which of the following statements about monosaccharide structure is true?

Monosaccharides can be classified according to the spatial arrangement of their atoms.

Which polysaccharide contains a modified monosaccharide?

Peptidoglycan (The N-acetylglucosamine and N-acetylmuramic acid units that make up peptidoglycan are composed of modified glucose monomers.)

Bacteria, insects, and plants use carbohydrates to build structures. Which of the following is true of structural carbohydrates?

Structural carbohydrates are long strands of monomers; the strands are chemically linked together to form a network

Carbohydrates that function as structural molecules withstand pulling and pushing forces well. Which structural feature best explains why?

Structural polysaccharides exist as sets of long, parallel strands that are linked to one another. (These structural features result in tough fibers.)

Different types of glycosidic linkage cause glucose polymers to form a helix (e.g., in glycogen) versus a straight chain (e.g., in cellulose). Which statement best explains why?

The geometry of the -1,4-glycosidic linkage results in a flipped orientation of adjacent glucose monomers; the -1,4-glycosidic linkage does not. (The flipped orientation results in a linear polymer, whereas the unflipped orientation results in a helix.)

Where are carbohydrates found in relationship to the cell?

They are found both inside and outside the cell.

The _____ functional group can always be found in a carbohydrate molecule.

carbonyl

You isolate an organic molecule that contains C, H, O, N, and S. This molecule _____.

could be a glycoprotein (can't rule out glycoprotein because both sugars and proteins have C, H and O.)

Which of these best reflects the following relationship: monosaccharide versus polysaccharide?

glucose versus glycogen

Which molecule is not a carbohydrate?

lipid (A lipid is a hydrophobic polymer, not a carbohydrate.)

A glycosidic linkage is a covalent bond that links two _____.

monosaccharides

Which of the following classes of macromolecules always contains a carbohydrate portion?

nucleic acids

Which of the following molecules would you expect to have the most free energy per gram?

one with carbon and hydrogen atoms only

A monosaccharide that has the chemical formula C5 H10 O5 would be characterized as a _____.

pentose

What is the major structural difference between starch and glycogen?

the amount of branching that occurs in the molecule

What is the difference between an aldose sugar and a ketose sugar?

the position of the carbonyl group

True or false? Peptidoglycan is a polysaccharide found only in bacteria.

true

Which of the following linkages would you expect to find at a branch point in glycogen or amylopectin?

α-1,6-glycosidic linkage

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene in humans. A woman whose father suffered from G6PD marries a normal man. (a) What proportion of their sons is expected to be G6PD? (b) If the husband was not normal but was G6PD deficient, would you change your answer in part (a)?

(a) 1/2; (b) no