o Four amino acids are shown. COO Macmillan Learnin COO COO COO CH2 -NH3 H3N- H H -NH3 H3N- -H CH CH2 CH3 H3C OH SH CH2 cysteine S CH3 threonine methionine alanine Identify the amino acids drawn in the L configuration. ☐ ☐ ☐ ☐ methionine alanine threonine ☐ cysteine

What special role does the amino acid cysteine have in the peptides vasopressin and oxytocin?

22-44 How can a protein act as a buffer?

22-42 (a) How many atoms of the peptide bond lie in the same plane? (b) Which atoms are they?

Using both three- and one-letter codes for amino acids, write the structures of all possible peptides containing the following amino acids: (a) Val, Ser, Leu (b) Ser, Leu2, Pro

22-48 How many amino acid residues in the A chain of insulin are the same in insulin from humans, cattle (bovine), hogs, and sheep?

16*32 Many tumors of the breast are correlated with estrogen levels in the body. Drugs that interfere with estrogen binding have antitumor activity and may even help prevent tumor occurrence. A widely used antiestrogen drug is tamoxifen. kJ1 Name the functional groups in tamoxifen. Classify the amino group in tamoxifen as primary, secondary, or tertiary. How many stereoisomers are possible for tamoxifen? (d, Would you expect tamoxifen to be soluble or insoluble in water? In blood?

22-89 What kind of noncovalent interaction occurs between the following amino acids? (a) Valine and isoleucine (b) Glutamic acid and lysine (c) Tyrosine and threonine (d) Alanine and alanine

Hemoglobin has pI=6.8. Does hemoglobin have a net negative charge or net positive charge at pH=5.3? At pH=7.3?

22-65 (a) What is the difference in the quaternary structure between fetal hemoglobin and adult hemoglobin? (b) Which can carry more oxygen? (c) What would the oxygen saturation curve of fetal hemoglobin look like compared to that of myoglobin and regular adult hemoglobin?