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Lecture 2

Winter Term -Week 2 Lecture Notes

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Queen's University
BIOL 103
Virginia K Walker

Jan 13-19 *i-clicker question* If a polypeptide composed of: leu-thr-val-ile-arg-val was completely digested with an aminopeptidase, the products would be: Leu+thr+thr+val+ile+arg+val *i-clicker question* Cows chew their cud because: It allows microbes to be mixed in their food Absorption • Occurs in small intestine, assisted by villi (contains lacteals and capillaries and microvilli Homework: read about absorption Digestion in Insects • Similar to digestion in vertebrates, but no pepsin because PH is neutral or high • Adaptations: salivary glands and active proteases eliminated with feces Excretion and Ion Transport: • Everything except for undigested food (eliminated as feces) are excreted • After digestion, individual amino acids are absorbed by cells lining the small intestine and then enter the blood • Humans cannot store amino acids in the circulatory system • Liver: refer to slide 5 R deamination enzyme R H2N---C---COOH  C---COOH + H3N + cofactor H2 H O ammonia = nitrogenous waste in aquatic life • Liver (urea cycle) O ll urea o NH3 +CO2 +H2O  H2N ---C---NH2 For shark sin milk beforehand will neutralizes urea, so it won’t taste like urine Saltwater (bony fish) • Hypotonic; danger of dehydrating with water lost across gills, therefore must drink lots of water • Produce large amounts of dilute urine containing very little salts • Specialized gill epithelial cells transport excess salts (Na+ and Cl-) from water into capillaries in gills • Slide 10: y-axis scale is 0-1000 mOsm Human disease: • Liver cirrhosis caused by alcoholism, infectious disease ( ex hepatitis) or fatty liver disease • Damaged liver cannot efficiently carry out urea cycle In birds, reptiles and insects: NH3 + CO2 (no water!) ~ 15 steps uric acid ATP • Uric acid is the nitrogenous waste of birds, since they lay eggs; uric acid is stored in the eggshell and is left behind after hatching • Birds excrete uric acid; found in droppings with digestive waste; important fertilizer Interesting Adaptations: • Lungfish o Switch from producing ammonia to urea when there are high concentrations of urea • Salmon o Saltfresh o In ocean: produce concentrated urine (ammonia) while in fresh water: dilute urine o Gill epithelial cells are able to transport Na+ and Cl- against the concentration gradient o Therefore must adjust to salinity differences by resting in estuaries first • Eels o Fr
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