Protein metabolism Flashcards
Protein digestion begins where?
stomach
- secreted by chief cells
- hydrolyses 46 amino acids from its N-terminus (autocatyltic reaction) to make pepsin
pepsinogen
- secreted by parietal cells in response to food entering the stomach
- denatures proteins
HCl
chyme
acidic mass as it enters the duodenum
chyme stimulates cells of intestinal mucosa to secrete what into the blood?
secretin and cholecystokinin
stimulates release of bile from gall bladder and digestive enzymes from pancreas
cholecystokinin
stimulates acinar cells of pancreas to release HCO3- rich fluid that neutralizes the acidic chyme as it enters the intestines
secretin
- activated by enteropeptidase
- activates the following:
chymotrypsinogen»chymotrysin
proelastase»elastase
procarboxypeptidases»carboxypeptidases
trypsin (made from trypsinogen by action of enteropeptidase, membrane-anchored)
transport systems of amino acids generally use energy provided by what?
sodium electrochemical gradient
- inappropriate response to alpha-gliadin, found in gluten
- loss of villi, appears flat
symptoms: nutrient dieficiency
Celiac Disease
treatment: gluten-free diet
- inflammatory disease of pancreas
- digestive enzymes are being activated inside the pancreas
- causes mild (abdominal pain) to severe (pancreatic necrosis) symptoms
acute pancreatitis
- defect in large neutral acid transport system, unable to get into the epithelial cells
- same transporter in kidney that is responsible for reabsorption
- exhibit malnutrition and presence of neutral amino acids in urine
Hartnup Disease
treatment: niacin
major site of amino acid degradation during fasting
liver
What enzyme catalyzes the reaction glutamate»alpha-ketoglutarate?
glutamate dehydrogenase
- makes NADH from NAD+
- transfer of ammonium ion
- major route for glycine catabolism
- most active in liver
- major contributor to synthesis of glycine
mitochondrial glycine cleavage system
glycine+THF»N5,N10-methylene THF (NADH is made as well)
*fully reversible
How does the body get glycine?
mostly from the diet, other times from mitochondrial glycine cleavage system
- defect in mitochondrial glycine cleavage system
- present soon after birth
symptoms: lethargy, lack of muscle tone and muscle twitching, may progress to apnea and death
Glycine encephalopathy (aka nonketotic hyperGLYcinemia) - reduction in glycine greatly affects muscles because collagen is mostly made up of glycine
What is the relationship between glucose and alanine?
it’s a way for muscles to get rid of ammonium ions
- in the muscle glucose is converted down to alanine, which then leaves and moves to the liver
- in the liver alanine is converted to pyruvate (transferring ammonium ion) then back to glucose (gluconeogenesis), which gets released and absorbed back by muscle
Where is AST found?
liver, cardiac muscle, skeletal muscle, kidney and several other tissues
Where is ALT found?
mostly liver
Elevation of AST in serum is indicative of what?
inconclusive because it’s found in a lot of muscles, but definitely some sort of organ damage because it’s normally really low in serum
Elevation of ALT in serum is indicative of what?
if it’s just ALT, then it’s also inconclusive, it must be both AST and ALT in serum to rule that it is liver damage as both are found in the liver
What amino acid is required to facilitate new tissue growth thus considered as essential during periods of growth and is a cause for pressure ulcers in the elderly population?
arginine
- result in the inability to convert Phe»Tyr
- deficiency in either Phe hydroxylase or DHBtn Redutase
- Phe is instead converted to phenylpyruvate
Symptoms: intellectual disability, recurrent seizures, hypopigmentation, eczematous skin rashes
Phenylketonuria (PKU)
Treatment: Phe-free diet, lifelong monitoring
