Chapter 3: Chemistry of Amino Acids, Proteins, Hemoglobin

Chapter 3: Chemistry of Amino Acids, Proteins, Hemoglobin

1. General Overview of Proteins:

• Proteins are found in all animal and plant cells.

• They are the second most abundant organic substance after lipids.

• They account for about 60% of the dry weight of the cell.

• They are structural components, not specific to each cell type.

2. Which of the following is NOT a characteristic of naturally occurring amino acids?

• B. They usually exist in the form of optical D-isomers.

3. Characteristics of Amino Acids:

• Proline differs from other amino acids in that its NH2 group is not attached to the C?.

• Glycine always exists in the L-Glycine form.

• In addition to the 20 amino acids, there are some other amino acids that do not participate in the structure of protein but play an important role in the metabolism of amino acids and proteins.

• D. All of the above are correct.

4. Which of the following amino acids does not have an optical isomer?

• B. Gly.

5. The group of non-polar, hydrophobic amino acids does NOT include:

• E. Ser.

6. The group of aromatic amino acids includes:

• D. Pro.

7. Which of the following amino acids has an -OH group in its R group?

• D. Ser.

8. Which of the following amino acids has an -SH group in its R group?

• E. Cys.

9. Which of the following amino acids does NOT belong to the group with a positively charged R group?

• B. Leu.

10. His belongs to which of the following groups?

• D. R base, positively charged (+).

11. Which amino acid belongs to the group with a negatively charged R group?

• E. Asp.

12. Leu belongs to which type of aa?

• A. Non-polar, hydrophobic R group.

13. Which amino acid does NOT belong to the group with a polar, non-charged R group?

• D. Ile.

14. Properties of Amino Acids:

• In a medium with a pH greater than pHi, they are positively charged.

• At pHi, they can be positively or negatively charged.

• C. Their solubility is similar to that of monosaccharides.

• They cannot be titrated to find the isoelectric point.

15. The methods used to analyze amino acids, EXCEPT:

• E. Based on vaporization.

16. Amino acid analysis:

• All amino acids have a titration curve like that of Glycine.

• The pK1 value ranges from 1.8 to 3.4.

• The pK2 value ranges from 8.8 to 11.0.

• D. Amino acids with ionizable R groups have the simplest titration curves.

17. Light absorption properties of amino acids, EXCEPT:

• D. Tyr and Trp absorb maximally at near 240nm.

18. Regarding peptides, which statement is NOT correct?

• A. Numbering starts from the end with the ?-carboxyl group, the other end is the n-terminal.

19. Peptides are strongly hydrolyzed when:

• D. All 3 statements are correct.

20. Regarding biologically active peptides:

• C. Substance P has twice as many amino acids as methionine-encephalin.

21. Regarding Proteins:

• A. They are composed of 50 or more amino acids.

• Glucagon is a typical pure protein.

• Albumin is a pure protein, while globulin and histone are mixed proteins.

• Enzyme proteins are often more fibrous than globular.

22. Which of the following is a mixed protein?

• C. Casein.

23. Regarding protein structure levels:

• Insulin is a typical secondary structure with -S-Sb bonds.

• All 4 levels of structure can be studied using X-ray diffraction.

• The ?-helix in the secondary structure is stabilized by hydrogen bonds between two parallel chains.

• D. Tertiary structure involves both folding and twisting, and contains the following bonds: -S-S-, ionic, hydrophobic.

• Hb, along with myosin and trypsin, are examples of tertiary structures.

24. Which of the following factors does NOT cause protein denaturation at low temperatures?

• E. Neutral salts.

25. Regarding the properties of proteins:

• In water, proteins exist in a colloidal form, and they are difficult to dissolve in dilute salt solutions due to the oppositely charged protein particles.

• When proteins are denatured, most of the peptide bonds are broken, except in the case of reversible denaturation.

• C. In reversible denaturation, both viscosity and solubility are altered.

• The effect of ?-mercaptoethanol on Ribonuclease is an irreversible denaturation.

26. Which of the following is a structural protein?

• A. Collagen.

• F. Elastin

27. Protective proteins include:

• D. All 3 answers above.

28. Methods of studying proteins:

• Protein precipitation using neutral salts of the same concentration.

• B. Ion-exchange chromatography using: Carboxymethyl or Diethylamino.

• The migration rate of proteins or amino acids using resin does not depend on their charge at any pH.

• All ion exchangers carry a negative charge but are placed in different insoluble materials.

29. Hemoglobin:

• It is a pure protein of the fourth level.

• B. Hem synthesis: pyrol*4 porphin +VEMAP porphyrin protoporphyrin + Fe HEM.

• Hem is species-specific.

• 2,3 -DPG increases the affinity of Hb for oxygen.

30. Properties of Hemoglobin:

• 1 Hb can bind a maximum of 4 oxygen molecules.

• The peroxidase activity of Hb is used to detect blood in body fluids in general.

• Hb combines with CO2 to form carboxyhemoglobin.

• D. All are correct.

31. Properties of Hemoglobin:

• The combination of Hb with oxygen is reversible and depends on: H+, 2,3-DPG, CO2, t0.

• When one of the four subunits has bound, it increases the affinity of the remaining subunits for oxygen.

• The affinity of CO for Hb is about 310 times stronger than that of oxygen.

• Methemoglobin can only carry one oxygen molecule.

32. About Myoglobin:

• Mb accounts for about 20% of muscle protein.

• B. It consists of one 153aa polypeptide chain combined with one Hem.

• Mb can only transport half as many oxygen molecules as Hb.

• Unlike Hb, the binding and release of oxygen by Mb does not depend on pH, t0, or ionic strength.

33. Which of the following components determines the difference in Hb between species?

• C. Globin.

34. Which component is NOT present in deoxyhemoglobin?

• E. Fe3+.

35. Substances that can oxidize Hb to MetHb, EXCEPT:

• D. Hydrochloric.

36. Choose the wrong statement:

• D. Higher animals can synthesize D-form amino acids but can only use the L-form.

37. Regarding the increasing hydrophobicity of amino acids:

• A. Pro, Gly, Val, Leu, Ile,

38. Regarding amino acids with aromatic R groups, choose the wrong statement:

• B. UV absorption at 580 nm.

39. Choose the wrong statement about basic amino acids:

• A. Hydrophobicity.

40. Choose the correct statement about amino acids with polar, non-charged R groups:

• A. R is polar, hydrophobic, can form hydrogen bonds.

41. Choose the correct statement about amino acids with polar, non-charged R groups:

• C. Methionine (Met, M) – ?start? amino acid, very hydrophilic, S exists in the form of a thioester bond.

42. Choose the correct statement:

• B. O in the carbonyl group is partially negatively charged.

43. Choose the correct statement:

• D. All are correct.

44. Choose the wrong statement:

• B. Left-handed helices are more common in nature.

45. Choose the wrong statement:

• D. A loop with > 5 aa is called a turning point.

46. Choose the correct statement about beta-sheets:

• D. All are correct.

47. Choose the correct statement about the ?-helix structure:

• D. All are correct.

48. Choose the correct statement:

• E. All are correct.

49. Choose the correct statement:

• D. All are correct.

50. Regarding Hb, choose the wrong statement:

• D. Hb synthesis begins in erythroblasts: 35% in the erythroblast stage.

51. Choose the wrong statement:

• B. The reaction of Hb & oxygen is an oxidation.

52. Choose the wrong statement:

• A. Oxygen transport capacity does not depend on pO2.

53. The normal shape of the b-oxygen dissociation curve does NOT depend on:

• C. O2 in erythrocytes.

54. Rightward shift (easier oxygen dissociation) when:

• D. HbS is low.

55. Leftward shift (difficult oxygen release) when:

• 1. a. 2,3-DPG is low b. HbF c. H+ is low