Chapter 6
Learning Objectives
1. What charges do the amino and carboxylic acid groups have at a physiologic pH in any amino
acid? What is the D/L configuration of amino acids
 The amino group is protonated and carries a positive charge, and the carboxylic acid has
donated its proton to become negatively charged. Except for glycine, all amino acids are D-.
2.
How do you measure bilirubin?
 For total bilirubin, use caffeine-benzoate to separate the hydrophobic bilirubin from
glucuronate; next react it with a diazotized sulfonic acid, which generates a blue color
correlated to serum content. For the conjugated bilirubin value only, do not use caffeinebenzoate. Unconjugated can be calculated using conjugated and total bilirubin.
3. What is the hydropathic index? Which AAs have the highest values? In which AA groups are
hydropathic indices low?
 The hydropathic index is larger when an AA’s side group is more hydrophobic. Alanine,
leucine, valine, isoleucine, phenyalanine, and cysteine are positive. Polar groupings of AA’s,
that is: uncharged (polar), chraged acidic, and charged basic are in general the most
hydrophilic.
4. Towards which AA’s peptide bond does chymotrypsin have the highest activity?
 Chymotrypsin targets bulky uncharged AAs, such as those of the aromatic AAs (phe, tyr, trp)
 Think of chyme, the perhaps fatty mass of food, which would contain hydrophobic AAs.
5.
Which AAs can form hydrogen bonds using their hydroxyl-containing R groups?
 Serine, threonine, & tyrosine
6. What causes cystinuria? Symptoms?
 A mutation which alters the renal tubule transport protein that reabsorbs cystine, arginine,
and lysine (other two are polar+basic). Cystine is less soluble, and so is the first to precipitate
as calculi.
7. What is an isozyme? What AA could act as a conservative replacement for aspartate in an
enzyme?
 An isozyme is a sort of isoform (a different form of a molecule with conserved function).
Isozymes have a different AA sequence from their “parent,” but have the same function
 Another charged, acidic amino acid. There is only one that fits the bill: glutamate
8. What’s special about creatine kinase? What form would be elevated post heart attack?
 Creatine kinase is an enzyme that leaks from damaged (hypoxic) cell membranes. The MB
form is commonly elevated after a heart attack
9. How are oligosaccharides bound to proteins? What is their role?
 Oligosaccharides are bound to proteins by either N- or O-glycosidic linkages. N-linked
oligosaccharides are formed using asparagiNe, and protect the cell from proteolysis or
immune attack; while O-glycosidic links are the common way to attach oligosaccharides to
serine’s, threonine’s, or tyrosine’s -OH group
10. What class of enzyme are cholera A-B toxin, pertussis toxin, and diptheria toxin? Fxn?
 These are three bacterial toxins that are ADP-ribosyl transferases. They hydrolyze the Nglycosidic bond of NAD+ and transfer the ADP-ribose portion elsewhere.
11. Why does hydroxyurea work as a treatment for Sickle Cell?
 Hydroxyurea increases the production of HbF, which cannot participate in sickling.
12. What’s lispro? Why is it absorbed more quickly?
 Lipsro is a fast-acting insulin analog. It is absorbed more quickly because lispro molecules
can’t bind zinc to form a hexamer (this is the normal arrangement of insulin when it is
secreted by the pancreas).