Breakdown Excretion of NCompounds deamination amino acids TCA

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Breakdown & Excretion of N-Compounds deamination amino acids TCA cycle NH 3 pyrimidines alanine

Breakdown & Excretion of N-Compounds deamination amino acids TCA cycle NH 3 pyrimidines alanine + NH 3 + CO 2 (cytosine, thymidine, uracil) purines uric acid (adenine, guanine) urea allantoin/allantoic acid NH 3 + CO 2

Excretory Products NH 3 (NH 4+) - ammonotelic • diffuses rapidly & used for

Excretory Products NH 3 (NH 4+) - ammonotelic • diffuses rapidly & used for ion exchange • toxic • mainly in aquatic spp. Urea - ureotelic - from purine degradation or synthesized via Krebs ornithine cycle. • less toxic & used as organic osmolyte • highly soluble - requires water for excretion Uric Acid - uricotelic • water conservative - sparingly soluble • crystallizes - excreted as paste

Ammonia-Excreting Animals (Ammonotelic) • Toxic – only small quantities stored in body • Requires

Ammonia-Excreting Animals (Ammonotelic) • Toxic – only small quantities stored in body • Requires considerable water to excrete • Gills typical site for excretion in aquatic animals • Isopods, some land snails, crabs---can excrete NH 3 through volatization into air

Acid-Base Balance Intracellular (and therefore extracellular) p. H must be regulated within narrow limits.

Acid-Base Balance Intracellular (and therefore extracellular) p. H must be regulated within narrow limits. In humans, arterial blood p. H at core temp. = 7. 4 Convulsions and death result from p. H > 7. 7 alkalosis - inc. in blood p. H Coma and death result from p. H < 6. 8 acidosis - dec. in blood p. H

Deleterious effects of changes in p. H results from titration of charges on proteins:

Deleterious effects of changes in p. H results from titration of charges on proteins: + H+ _ _ H+ H+ + _ _ + _ H+ H+ _ + Alters the 2°, 3° and 4° structures of protein

Urea-Excreting Animals (Ureotelic) • More soluble, less toxic than NH 3 • Better deal…get

Urea-Excreting Animals (Ureotelic) • More soluble, less toxic than NH 3 • Better deal…get rid of 2 nitrogen molecules O H 2 N—C—NH 2 • Formed by ornithine-urea cycle

Uric Acid-Secreting Animals (Uricotelic) • Major nitrogenous end-product in most terrestrial arthropods, reptiles, birds

Uric Acid-Secreting Animals (Uricotelic) • Major nitrogenous end-product in most terrestrial arthropods, reptiles, birds • Advantage – 4 nitrogen molecules, but requires energy to synthesize • Advantage – does not contribute plasma osmotic pressure

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