4. A Phospholipid molecule has: A. two hydrophobic tails and one hydrophilic head B. two hydrophilic tails and one hydrophobic head C. one hydrophobic tail and one hydrophilic head D. three fatty acids and one phosphate group E. two phosphate groups and one fatty acid

1. Is there more than one way to fold a protein, given the conflicting demands of the different "R" groups and the protein existing in a watery environment? 2. Explain what an R group is. 3. Compare the backbone of a polypeptide with that of a nucleic acid. 4. Proteins perform critical functions in all of our cells. Without proteins, life wouldn’t exist. Think of some specific proteins and describe what function they perform.  5. Explain the difference between secondary and tertiary protein structures.

1.Which of the following molecules consist of a chain of amino acids? Select all that apply. A. Carbohydrates B. Proteins C. Nucleic acids D. Lipids 2.Isotopes are variations of the same element that differ in their number of…. A. protons B. polymers C. electrons D. neutrons

3. Use the chemical structures shown on the next page to answer the following questions. Some questions may have more than 1 correct answer, so put down all correct answers. Some structures may be used to answer more than 1 question and some may not be used at all. a. Which molecules are amino acids? b. Which molecules are carbohydrates? c. Which molecule is a hydrophobic amino acid? d. Which molecules are lipids? e. Which molecule(s) possess at least one glycosidic linkage? f. Which molecule(s) possess at least one ester linkage? g. Which molecule(s) is a nucleic acid? h. Which molecule(s) is a nucleotide? i. Which molecules are polypeptides? j. Which molecules are steroids?