Biology 130l Exam Review

Topics: DNA, Cell, Cell cycle Pages: 13 (2549 words) Published: March 4, 2013
1. Identification of Some Macromolecules
1) What are 2 types of treatment controls, and explain each.

Positive control: gives positive result if experimental conditions were followed correctly Negative control: gives negative result if experimental conditions were followed correctly

2) What are the most abundant elements in living material?

Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur and Phosphorus

3) What are the 4 major biological macromolecules?

Carbohydrates (monosaccharides & polysaccharides), lipids, proteins, & nucleic acids.

4) What is the original colour of iodine, and what colour does it turn in presence of starch and glycogen?

Starch: yellow --> blue-black (amylase in starch reacts with iodine) Glycogen: yellow --> reddish-brown (due to the multi-branched component)

5) How do plants and animals store simple sugar glucose?

In the form of polysaccharides. In plants, starch is the polysaccharide with glucose units linked by glycosidic bonds. Glycogen, in animals, is a larger polymer.

6) How do starch and glycogen differ?

Molecular weight, overall shape and degree of branching in the final polysaccharide structure. Amylose is unbranched and helical, where glucose units are joined by a(1-->4) linkages. Amylopectin has straight, branched sections from a(1-->6) linkages. Glycogen is similar to amylopectin, but more highly branched.

7) What makes sugar a reducing sugar?

The terminal aldehyde group makes it an aldose sugar, which reacts in Benedict's test to make glucose a reducing sugar. Blue solution will develop precipitate ranging from yellow, green, red or brown (positive).

8) What happens when benedict's solution mixes with solution with reducing sugar?

The blue cupric ions (Cu++) in benedict's solution get reduced to Cu+ by the terminal aldehyde group. The amount of Cu2O formed is proportional to the concentration of free aldehyde groups. 4Cu+ + 2OH +2e --> 2Cu2O + 2H+ +2e

9) What gives a false positive reaction?

Presence of other substances that could be oxidized (i.e. ketose sugar --> fructose)

10) What test is done for proteins? And how does the colour change occur?

Biuret test; The peptide bonds in the proteins with Cu++ ions and alkali give a violet peptide complex.

2. Isolation of Some Macromolecules

1) Why should the yeast be grinded with water and sand?

It will rupture the cell walls and cell membrane; the glucan (cellulose) in the cell walls, and glycogen, proteins and NA in cytoplasm will be released.

2) What is TCA used for?

Polysaccharides (starch and glycogen) are soluble in TCA. Proteins and NA aren't, so they'll remain in suspension.

3) What is centrifugation?

Supernatant is liquid above the pellet. The pellet is also precipitate. Controlling the speed and time of a centrifugal run will allow particles of different sizes/properties to be separated from the same suspension. A fractionation technique where centrifugal force sediments suspended particles at the bottom of the tube.

4) What is in the supernatant, and what is in the pellets?

Supernatant: polysaccharides
Pellet: proteins and NA

5) What does NaCl do to the pellets?

Nucleic acids are soluble in strong NaCl, but protein isn't so it will remain in suspension.

6) What will boiling do to the protein? What will centrifugation do?

I will thicken (coagulate) the suspended protein molecules. Centrifugation will pack the proteins into a pellet, and nucleic acids will be the supernatant.

7) Why is ethanol added to supernatant?

NA are insoluble in ethanol, so it will precipitate out of the solution to form a white suspension.

8) After centrifugation, H2SO4 is added to the pellets. Why?

NA are soluble, so it will go into the solution.

9) What will boiling the acid do?

It's a hydrolyzing process, so it will break up NA into component nucleotide subunits, and then eventually into base and sugar and phosphoric acid subunits.

10) What's the...
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