ICA#2 Summer 2021 KEY posting PDF

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BSC 2010 In-class Assignment #2 KEY

Summer 2021

The average on this I-CA was 90%. Please look over the answers and contact me ASAP if you have questions over content or your ICA grade. A good strategy is to ask yourself WHY the wrong answers are wrong for each item. 1. An amino acid is CLASSIFIED (polar, nonpolar, charged) based on the chemistry of its _____. a) amino group b) carboxyl group c) R group d) H atom e) alpha carbon Be able to group amino acids based solely on their structures, by the RULES found in the I-CA supplement. 2. Based on the specific rules for classifying amino acids, how would you classify this amino acid? a) nonpolar b) polar c) charged d) more than one of the above This is because the side chain contains only C and H, which are joined by nonpolar covalent bonds. 3. Based on the specific rules for classifying amino acids, how would you classify this amino acid? a) nonpolar a) polar b) charged c) more than one of the above This is because the side chain contains an O, which forms two polar covalent bonds with C and with H, leading to partial charges. 4. Based on the specific rules for classifying amino acids, how would you classify this amino acid? a) nonpolar b) polar c) charged d) more than one of the above Some got the prior two questions correct, then missed this one by choosing ‘d’. It’s true that the presence of oxygens in the side chain leads to polar covalent bonds and partial charges. But the side chain also contains a FULL CHARGE. Full charge trumps partial charge, and the amino acid is classified as ‘charged’. Remember that each amino acid is classified into only ONE GROUP, nonpolar, polar (but uncharged), or charged. 5. Which functional groups are present in this polypeptide? a) amino group b) carboxyl group c) hydroxyl group d) sulfhydryl group e) all of the above Be sure you can identify them all! Which one behaves as an acid at cellular pH? Which one a base?

6. The POLYPEPTIDE BACKBONE contains which of the following atoms? a) carbon b) hydrogen c) oxygen d) nitrogen e) all of the above The backbone is shaded in the structural formula on the right above. It includes the repeating pattern of “N—C—C”, but also the H bonded to N and the O bonded to the second C. 7. Which level of structure is held together by COVALENT BONDS (only/always)? a) 1° b) 2° c) 3° d) both b and c e) all of the above These covalent bonds are known as ______________ bonds. 8. Which level of structure is held together by NONCOVALENT BONDS? a) 1° b) 2° c) 3° d) both 2° and 3° e) all of the above Which noncovalent bonds (i.e. weak interactions) specifically hold together each level? (One answer can be found in the next question!) The take-home is that polymers are formed by covalent bonding, while conformation is established through noncovalent bonding (intramolecular weak interactions). Noncovalent bonds also allow two different molecules to interact with each other (intermolecular weak interactions). These are the two reasons weak interactions are essential for biology, which we listed back in Chapter 2 (in the hormone-receptor example)! 9. Which level of structure is held together ONLY by h-bonds? a) 1° b) 2° c) 3° d) more than one of these answers e) none of these answers Which THREE atoms of the polypeptide backbone help to form the h-bond? Circle them on the chain in the earlier question! 10. All proteins are composed of _____. a) atoms b) amino acids c) several polypeptides d) atoms and amino acids e) all of the above Only some proteins have quaternary structure, so ‘several polypeptides’ is not a correct answer....