Urea Cycle Flashcards
Amino acids are used to:
* Produce glucose or lipids
* Produce ???
* Provide carbon skeletons
* Produce proteins
energy
Eating signals the secretion of gastrin → lowers or increases stomach pH (more acidic).
lowers
Low pH in stomach triggers proteolytic activation of pepsinogen → pepsin (breaks down proteins) Peptides/amino acids pass through the ???. Pancreatic zymogens are secreted into the intestine for further digestion of peptides
small intestine
Acute pancreatitis: obstruction of pancreatic secretions = proteolytic activation of zymogens within the
pancreas which attack ??? when they have no other proteins/peptides to digest = pain and cellular damage/inflammation.
pancreatic tissue
Enteropeptidase is secreted
from the ??? in response to proteins entering the stomach to begin the cascade of events that turn zymogens into active enzymes
small intestine
Pancreas can synthesise and
secrete Trypsin inhibitor. Inhibition of trypsin is a key regulatory step in preventing over-activation OR under-activation of zymogens?
over activation
amino acids and di-/tripeptides are absorbed into intestinal cells by specific transporters. ??? associated with the intestinal epithelium further digest proteins. Free amino acids are then released into the blood for use by other tissues.
Peptidases
first step of amino acid degradation is ??? whereby an amino group is removed
transamination
Glutamate, ???, alanine and aspartate are central in nitrogen metabolism as they are all readily converted into TCA cycle INTERMEDIATES
glutamine
Gln and Ala are important in the transport of amino groups from ??? tissues and skeletal muscle to the liver
extrahepatic tissues
Aspartate or alanine provides the second amino group in the urea
cycle?
Aspartate
Excess NH4+ in tissues is added
to glutamate to form glutamine which enables ammonia to be safely transported in the ??? to the liver where NH4+ is released and enters the urea cycle
bloodstream
Vigorously working muscles operate nearly ??? and rely on glycolysis for energy = pyruvate –> If pyruvate not eliminated lactic acid will build up
Pyruvate can be converted to alanine for transport into the liver. This alanine in liver can enter the urea cycle and the ??? pathway
anaerobically
gluoconeognesis pathway
In ammonotelic organisms, ammonium (NH4+) can be excreted as ???
ammonia
In ureotelic organisms, ammonium (NH4+) is converted to ??? for excretion
urea
In uicotelic organisms, ammonium (NH4+) is converted to ??? for excretion
uric acid
TRUE or FALSE: Animals that excrete nitrogenous wastes as ammonia need access to lots of water as they release ammonia across whole body
surface or through gills
TRUE
The liver of mammals and most
adult amphibians converts ammonia to the less toxic urea. Circulatory systems carry urea to the kidneys where it is excreted Conversion of ammonia to urea is energetically EXPENSIVE or INEXPENSIVE; excretion of urea requires less water than ammonia
EXPENSIVE
Insects, land snails, many reptiles and birds, mainly excrete uric acid.
Uric acid is relatively NONTOXIC or TOXIC and does not dissolve readily in water. It can be secreted as a paste with little water loss. Uric acid is more energetically expensive to
produce than urea
nontoxic
Step 1 leading to urea cycle: NH4+ arrives in liver mitochondria as ???
Free NH4+ is released from glutamate. NOTE: Other amino group enters urea cycle as aspartate
glutamate
step 2 leading to urea cycle: Carbamoyl phosphate synthetase I (CPS1) Converts free NH4+ and HCO3- to ???
carbamoyl phosphate
TRUE or FALSE CPS1 is allosterically activated by N-acetylglutamate
TRUE
Step 1 of UREA Cycle: In mitochondrial matrix, Ornithine combines with NH4+ (from carbamoyl phosphate) to form ???
citrulline
Step 2 of UREA cycle: In cytoplasm, Citrulline + ??? combine to form arginininosuccinate and then arginine = Release of fumarate, which enters TCA cycle
aspartate
Step 3 of UREA cycle: Arginase catalyses the hydrolysis of arginine to urea and ??? (which continues in the urea cycle)
ornithine
hyperammonemia is a defect in the urea cycle where the urea cycle enzymes or intermediates (?) are defective = elevated NH4+ levels =nervous system malfunction and possible death
Enzymes
Liver damage caused by excessive alcohol consumption can be fatal, in part because the liver is unable to synthesize ??? and consequently NH4+ appears in the blood
urea
TRUE or FALSE: in the catabolism of AAs, the carbon skeleton of the 20 amino acids are converted into one of only 7 molecules
TRUE
Most AAs don’t directly enter TCA cycle, instead, many are first converted to ???
e.g. phenylalanine is converted to
tyrosine before entry into the TCA cycle (as fumarate)
other amino
acids
Phenylketonuria (PKU) is caused by a defect in phenylalanine degradation from a genetic defect in ??? = buildup of phenylalanine and phenylpyruvate
phenylalanine hydroxylase
Phenylketonuria impairs ??? development leading to intellectual deficits and premature death if untreated
neurological
phenylketonuria is controlled by limiting ??? intake of phenylalanine (including artificial sweeteners) and dietary non-phenylalanine protein supplementation
dietary
Protein within muscle can be degraded to AAs during times of long-term fasting. AAs are secreted from muscle for production of ??? and ??? in the liver
glucose and ketones
Glucose derived primarily from glycogen stores in liver via glycogenolysis. Maintaining adequate BGL is essential. When glycogen stores are depleted
(dieting), maintaining BGL requires gluconeogenesis. No intake of food, so muscle protein must be CATABOLISED or ANABOLISED (?) for glucose production = muscle loss rather than loss of fat reserves
CATABOLISED
Potential heath risks of Atkins diet:
* ??? (low glucose in blood) causing neural effects
* Ketoacidosis causing acidification of blood
* High serum lipids causing heart disease
* Increased ammonia causing liver damage
Hypoglycemia
Atkins diet: Metabolism is similar to fasting but with following result:
* Decreased or increased glucose?
* Increased ketones (secreted in
breath + urine = net calorie loss)
* Increased serum lipids
* Increased NH4+
decreased glucose