Nitrogen part 2: excretion Flashcards
3 execratory strats
-Ammoniotelism: Excrete nitrogen primarily in the form of ammonia
-Ureotelism: Excrete nitrogen primarily in the form of urea
-Uricotelism: Excrete nitrogen primarily in the form of uric acid or urates (both are considered uricotelic)
Ammonia vs Urea vs Uric Acid (4)
Solubility: Ammonia > Urea > Uric Acid
Toxicity: Ammonia > Urea > uric acid
Amount of water required to excrete: Ammonia > urea > Uric Acid
Amount of energy to produce: Uric acid > Urea > Ammonia
Ammoniotelism requirements (3)
-Because ammonia is highly toxic, a lot of water is needed for dilution
-Ammonia must also be excreted rapidly to avoid accumulation within bodily fluids
-Therefore the vast majority of ammoniotelic animals are aquatic animals (but not aquatic mammals)
How can ammonium (NH4) cross membranes ? (3)
-Diffusion down gradients (pressure or electrochemical)
-By replacing K+ in active transport proteins like the sodium potassium pimp and the cH/K ATPase
-by passing through passive K+ channels because it has a similar size and charge
Ouabain
Ouabain is a poison that inhibits function of the sodium potassium pump and the cH/K ATPase. It can be used by scientists to see if NH3 is passing through membranes without the use of the pump by inhibiting them, but if you have too much of it, the your body will loose its ability to regulate sodium and potassium levels in your cells and you die (hence why its a poison)
Rhesus-like ammonia transporter
Discovered in 2000 by a guy named Marini, members of the Rhesus protein family are very similar to ammonia transporters found in plants and fungi. When an NH4 ion comes near the channel, it looses a proton becoming NH3, allowing it to diffuse through the channel and preventing trapping!
Types of Rhesus-like transporters (3)
RhAG - found in blood cells
RhCG - Found on the apical membrane of ammonia transporting tissue like kidneys and liver
RhBg - same as CG but found on the basolateral membrane
AMT ammonia transporter
-Found in plant roots ,bacteria and invertebrates(not vertebrates)
-responsible for ammonia uptake
-20% homology to Rh-proteins
AMT ammonia transporters mode of transport (3)
-Mode of transport not clear but could be
-Letting the whole NH4 through
-splitting protons in a pore between the 3 cylinders, converting the NH4 into NH3 and letting it diffuse
AMT ammonia transporter structure
It looks like a cylinder, with 2 other cylinders stacked on top like a reverse pyramid
Vesicular ammonia transport
Because NH3 can cross membranes, it can therefore cross a vesicular membrane into a vesicle. So if you have a vesicle with low pH (lots of H+) the NH3 is like YOOOOOOOO Im feeling RAVENOUS for them protons lemme just sneak right in there. It then bonds with the protons, becoming NH4 and can be transported to where the vesicle is going.
Exceptions to Ammonotelism (3)
a few land living animals are ammoniotelic:
-the common woodlouse
-Land Crab
-Blood feeding insects
Metamorphosis and ammonotelism (3)
- There are many benefits to metamorphosis, such as not competing with parents for resources as well as being able to switch ammonia excretion strats
-Dragonflies are ammoniotelic in there larval stage bc they are aquatic, but when they become adults, they transform into uricotelic, as it needs less water to excrete and therefore allowing them to have less weight
-Similarly, bullfrog tadpoles are ammoniotelic but adults are ureotelic as they can no longer use their gills to just directly excrete ammonia into the water.
Ammonia excretion in Aquatic vertebrates
most excretion done in the gills is passive transport but there is also some active transport from Rhesus-like proteins as well. Rhag will transport ammonia to Rhbg, to Rhcg2 which will allow it out. Takeaway from that is that not all amonia excretion in the gills is just passive transport. Same thing happens with freshwater species but there is no RhAG, and it happens in pavement cells not MRC
Why do aquatic animals exhibit active ammonia excretion
-Because ammonia requires a lot of water, which is easy to access in an aquatic environment, its easy for them to dilute and excrete the toxic ammonia. They use active transport to counterbalance ammonia levels when they get too high and their passive transport system isnt enough to handle it.
Advantages of Ureotelism (4)
-less toxic than ammonia
-Does not require such a rapid removal
-Does not require anywhere near as much water as ammonia, and only slightly more than uric acid
-gets rid of 2 nitrogen for every urea molecule
Disadvantages to Ureotelism (2)
-more toxic than uric acid
-Energetically expensive to make, about 4-5 ATP per molecule of urea
Ureosmotic
Uses Urea to balance osmolarity, exhibited in elasmobranchs and most aquatic turtles
Types of animals that are ureotelic (2)
-Mammals
-Adult amphibians
Amphibian Excretion of urea
-Most of their urea is filtered into their nephrons. Their convoluted tubules are poorly permeable for urea, so as water is reabsorbed the urea is concentrated. Because of this the vast majority of urea filtered into the nephron ends up being excreted as urine.
Mammalian excretion of urea (8)
1) urea is produced in the liver and circulates in blood plasma
2). urea is filtered in the kidney
3). 50-70% of urea filtered at the glomerulus is reabsorbed back into the blood
4). Some of the urea contributes to water reabsorption
5). The remainder passes out as urine
6). some the urea that was reabsorbed into the blood diffuses into the colon
7). this urea is utilized by the microflora in the intestine, producing CO2 and Ammonia, which is used for amino acid synthesis
8). the leftover urea returns to the blood once again
Uricotelism advantages (4)
-least toxic of the 3
-Requires the least amount of water
-Can be stored indefinitely as its nontoxic
-Gets rid of 4 nitrogen per every molecule of uric acid
Uricotelism disadvantages
-Very energetically expensive
-Insoluble
What animals are uricotelic (5)
-Animals that live in arid environments (less reliance on water for nitrogen excretion)
-Flying animals (needing to store less water = less weight)
-Land turtles and tortoises
-Snakes and lizards
-Most terrestrial insects
Two ways to make uric acid
- de novo synthesis in the liver (liver will make it)
-Through the purine /pyrimidine nucleotide biosynthetic pathway
Uricotelism in insects (4)
-Used as the primary excretion of nitrogen
1). Uric Acid diffuses from the cells into the haemolymph
2). Its then transported to the midgut/hindgut by the malphigian tubes
3). In the rectum, water is reabsorbed and uric acid comes out of the solution
Other nitrogen excretion strats 4
-Bird eating spiders excrete 90% of their nitrogenous waste as guanine
-Giant dune scorpions excrete 90% of their nitrogenous waste as xanthine
-Nearly all mammals (excluding primates) also excrete Allantoin
-Anglerfish excrete up to 30% of their nitrogenous waste as TMAO
