Protein Metabolism PPT Flashcards
Not stored in the human body, they are constantly broken down into their constituent amino acids and then reused for protein synthesis.
Protein
Excess of this are not stored! but rapidly degraded for the synthesis of glucose (glycolosis) and lipids. Degradation of excess this causes an excess of nitrogen.
Degradation (Catabolism of AA)
Nitrogen excess is transformed into urea (80%) and ammonium (NH4 +) in order to be thrown away in the urine. (Liver and Blood)
Waste
Protein breakdown begins in the _______
stomach
No protein hydrolyzing enzymes are found in _______
saliva
Hydrolysis (10% of peptide bonds) & denaturization by _____ & ____ produce short chain polypeptides in the stomach.
pepsin enzyme & HCl acid
enzymes from pancreatic juices
Trypsin, chymotrypsin, & carboxypeptidase
also an from Pancreatic juices, it is from cells in the small intestine Brush Zone create “free” amino acids.
Aminopeptidase
Chemical digestion: it is produced in the pancreas
Pancreatic juice
2 pancreatic enzymes
Trypsin and Chymotrypsin
The total supply of free amino acids available is called
Amino Acid Pool
3 sources of “free” amino acids
Dietary protein breakdown
Biosynthesis of amino acids in the Liver
Protein turnover
is the breakdown & re-synthesis of body protein:
Old tissues
Damage
Recycling enzymes & hormones
Protein turnover
It’s in the mouth, it has no effect on digestion
Saliva
In the stomach, which denatures protein
HCl
It hydrolyzes peptide bonds
Pepsin
From large polypeptides to
oligopeptides
Amino acids in the small intestine
Trypsin, Chymotrypsin, Carboxypeptidase, Aminopeptidase
Dietary protein entering the stomach effects the release of the hormone _______ by stomach mucosa cells
gastrin
its antiseptic properties kill most bacteria
Hydrochloric acid
its denaturing action “unwinds” globular proteins, making peptide bonds more accessible to digestive enzymes
Hydrochloric acid
its acidity leads to the activation of pepsinogen, which is the inactive form of the digestive enzyme pepsin
Hydrochloric acid
Passage, in small batches, of the stomach’s acidic protein contents into the small intestine stimulates production of the hormone ________, which in turn stimulates pancreatic production of bicarbonate ion, HCO3, whose function is neutralization of gastric hydrochloric acid
secretin
secreted by intestinal mucosal cells, also attacks peptide bonds
Aminopeptidase
Pepsin, trypsin, chymotrypsin, carboxypeptidase, and aminopeptidase are all examples of
proteolytic enzymes
Two steps in degrading amino acids
1) remove α-amino group
2) breakdown & process carbon skeleton
Release of an amino group is also two steps:
1) Transamination
2) Oxidative deamination
Four amino acids of central role of glutamate:
glutamate, aspartate, alanine and glutamine
present in mammalian cells at much higher concentrations than the other 16
glutamate, aspartate, alanine and glutamine
function as excitatory neurotransmitters in the central nervous system, and glutamate is partly responsible for the flavour of food. (It is the mono sodium glutamate listed on processed food labels.)
Glutamate and aspartate
occupies a special position in amino acid breakdown, and most of the nitrogen from dietary protein is ultimately excreted from the body via the glutamate pool.
glutamate
present in higher concentrations in mammalian cells. Have metabolic functions as well as roles in proteins.
Glutamate, aspartate, alanine & glutamine
Escapes in large amounts from dead or dying liver tissue. Measured in blood samples for diagnostic purposes
alanine aminotransferase
Very active enzyme, exists in mitochondrial and cytosolic variants. The detailed iso-enzyme pattern is tissue-specific.
Glutamate: pyruvate transaminase [GPT]
is the principal amino acid released from muscle tissue during starvation. It is an important substrate for hepatic gluconeogenesis
Alanine
required for the proper maintenance of fasting blood glucose concentrations.
Alanine transamination
very active enzyme inside heart cells. Also escapes in large amounts from dead or dying heart tissues & enters bloodstream. Measured in blood for diagnosing myocardial infarction.
aspartate aminotransferase
It exists in mitochondrial and cytosolic variants, and the detailed iso enzyme pattern is tissue-specific. It escapes in large amounts from dead or dying tissues and enters the bloodstream, so it is often measured in blood samples for medical diagnostic purposes. The metabolic importance of this enzyme is that it brings about a free exchange of amino groups between glutamate (which is the most common amino acid) and aspartate which is a second major amino acid pool.
Glutamate: oxaloacetate transaminase [GOT]
_______ and _______ are each required for separate but essential steps in the urea cycle, which is responsible for ammonia detoxication and nitrogen excretion.
Glutamate and aspartate
Most transaminases share a common substrate and product (oxoglutarate and glutamate) with the enzyme __________
glutamate dehydrogenase
has a central role in the overall control of nitrogen metabolism.
Glutamate
The glutamate produced from the transamination step is then deaminated by __________ using the enzyme glutamate dehydrogenase
oxidative deamination
Recycles back to a ketodiacid & releases ammonia
Oxidative Deamination
will reversibly convert glutamate to α-ketoglutarate and α-ketoglutarate to glutamate.
Glutamate dehydrogenase [GluDH]
Deamination reaction uses
NAD+
reverse reaction uses
NADPH
converting glutamate to α-ketoglutarate is an easily shifted equilibrium reaction.
Oxidative deamination
building up favors the synthesis of excessive amounts of glutamate, decreasing the Krebs cycle intermediate α-ketoglutarate.
Ammonium ions
What are the inputs to the urea cycle
NH3, CO2, and aspartic acid and fumaric acid
__________ from the urea cycle enters the Krebs cycle
Fumarate
________ produced from oxaloacetate of the Krebs cycle enters the urea cycle.
Aspartate
takes off amine groups from amino acids and forms glutamate (ionized glutamic acid)
Transamination
Amine groups form ________ when removed in deamination
ammonia
Spiders excrete _______, 5 nitrogen atoms in a small molecule.
guanine
Reptiles & birds excrete ______ – very insoluble purine compound – forms supersaturated solutions.
uric acid
Transamination or Oxidative deamination both produce _________
α-keto acids
Amino acid C skeletons that degrade to form a Krebs cycle intermediate can then be used to make glucose via gluconeogenesis. These are called:
Glucogenic Amino Acids
Amino acid C skeletons that degrade to form acetyl CoA or Acetoacetyl CoA can form fatty acids or ketone bodies. These are called
Ketogenic Amino Acids.
Use glycolysis intermediates:
3-phosphoglycerate & pyruvate
Krebs cycle intermediates:
Oxaloacetate & α-ketoglutarate
Defective phenylalanine hydroxylase – phenylalanine accumulates in body. Phenylalanine is transaminated to phenylpyruvate.
Phenylketonuria (PKU)
Iron atom stored in a protein
ferritin
degraded to bile pigments
Tetrapyrrole
Central methylene bridge of Biliverdin is reduced creating _______.
It is found to be the major antioxidant in blood
Bilirubin
_______ transported to liver. Becomes more water soluble with attachment of glucoronide sugars to propionate side chains
Bilirubin
Intestinal bacteria help change Bilirubin into ______ and _______ for excretion.
Stercobilin and urobilin
Changing color of a bruise shows dominant degradation product of heme: either _____ or _____
biliverdin or bilirubin
when bilirubin accumulates in the blood. Spleen is degrading heme, but liver isn’t removing the product
Jaundice
the Brain uses ______or _______bodies for fuel.
Glucose or Ketone
