Nitrogen Metabolism Flashcards
1
Q
Nitrogen Metabolism
A
- Nitrogen enters the body from dietary protein
- Dietary proteins are digested to amino acids
- Nitrogen leaves the body as urea, ammonia and other products derived from amino acid metabolism
2
Q
Amino Acids
A
- Contains C, H, O, N
- amino acids are not stored in the body
- amino acids obtained by diet, de novo synthesis, protein degradation
3
Q
Amino Acid Pool
A
Come from:
- degradation of body proteins
- digestion of dietary protein
- synthesis of amino acids
Go to:
- synthesis of body proteins
- degradation of amino acids
- synthesis of N-containing compounds
4
Q
Digestion of Dietary Proteins
A
- most nitrogen in diet is consumed as protein
- proteins are too large to be absorbed by the intestine
- must be hydrolyzed to yield individual amino acids, di- and tri peptides which can be absorbed
- proteolytic enzymes are produced by the stomach, pancreas and small intestine
5
Q
Where does digestion of proteins begin?
A
The stomach
6
Q
HCl in the stomach
A
- Acts to kill some bacteria (antiseptic)
- Denature proteins - making them more susceptible to hydolyses by proteases
7
Q
Pepsin- acid stable endopeptidase
A
- Secreted as an inactive zymogen- pepsinogen
- Pepsinogen is activated to pepsin by HCl or other previously activated pepsin
- Release peptides and amino acids from protein
8
Q
Protein digestion by pancreatic enzymes
A
- In small intestine, polypeptides are further digested by pancreatic enzymes (trypsin, chymotrypsin, elastase, carboxypeptidase)
- Enzymes secreted as inactive zymogens (trypsinogen, chymotrypsinogen) - prevent digesting own self
- Trypsinogen is activated to trypsin by enteropeptidase (trypsin activates all other proteases)
9
Q
Fate of Digested Proteins
A
- Mixture of free amino acids and short peptides taken up by intestinal cell, majority shipped out to blood to be transported to diff. tissues of body where they will be taken up by diff. tissues
10
Q
Protein Turnover
A
- Most proteins in the body are constantly being turned over (synthesized and degraded, permits removal of abnormal or unneeded proteins)
11
Q
Concentration of protein is controlled one of 2 ways
A
- Synthesis is regulated determining conc. while degradation plays a minor role (need less, make less)
- Synthesis is constant, and amounts of protein are controlled by regulated degradation (degradation is increased/decreased but the input is constant)
12
Q
Rate of Protein Turnover
A
- In healthy adults, total amount of protein is constant
- Rate of protein synthesis is just sufficient to replace protein that is degraded
13
Q
Rate for individual protein turnover varies widely
A
- Regulatory proteins are short lived, half-life of minutes
- Majority of proteins are long-lived, half-life of days to weeks
- Structural proteins such as collagen are stable and have half-lives measured in months to years
14
Q
Catabolism of amino acids involves
A
- The removal of a-amino groups
- Breakdown of the resulting C skeletons
- don’t want to store excess amino acids since N is acidic and hazardous in body
15
Q
Catabolism of C skeletons generates
A
- Oxaloacetate, pyruvate, fumarate, acetyl CoA and succinyl CoA
16
Q
Products of catabolism of C skeletons enter into
A
- Synthesis of glucose or lipids
- Production of energy
17
Q
Glutamate is a collector of ammonia
A
- Amino groups are converted to ammonium by oxidative deamination of glutamate
18
Q
Urea cycle
A
- After transport of ammonia to liver, ammonia is converted to urea via the urea cycle
19
Q
What is urea?
A
The major disposal form of amino groups from amino acids
- once urea is formed in the liver it is transported to kidneys to be excreted in urine
19
Q
Urea Cycle Substrates
A
- CO2 combined with ammonia to form caramoyl phosphate in mitochondrial matrix (starting substrate)
- Eventually release one molecule of urea (restart cycel)
20
Q
Glucogenic amino acids
A
- Amino acids whose catabolism yields pyruvate or intermediate of TCA (oxaloacetate…),
- These intermediates are also substrates of gluconeogenesis
20
Q
Ketogenic amino acids
A
- Catabolism yields acetoacetate or one of its precursors
- These may be converted to ketone bodies but are not substrates for gluconeogenesis
21
Q
Amino Acid metabolic disorders
A
- Disruption of either synthesis or removal of amino acids can lead to disorders
- Newborn screening leads to prevention/mitigation of symptoms
- Treatments tend to be changes in diet (phenylketonuria, maple syrup urine disease, albinism)
21
Q
PKU
A
- Phenylalanine is an essential amino acid that is precursor to tyrosine (used in synthesis of melanin)
- elevated levels of phenylalanine in tissues, blood, urine
- phenylylacetate, phenylacetate and phenylpyruvate are elevated
- phenylpyruvate excreted through urine
- hypopigmentation of skin
- CNS symptoms
- treatment with diet low in phenylalanine
22
Q
Maple Syrup Disease
A
- Deficiency of enzyme branched chain a-keto acid dehydrogenase (enzyme involved in degradation of branched chain amino acids)
- elevated levels of branched-chain amino acids and their a-keto acids in the blood and urine
- severe metabolic acidosis results in maple syrup odor to urine
- treatment; diet low in protein
22
Q
Albinism
A
- Defect in tyrosine metabolism results in deficiency in production of melanin
- Partial or full absence of pigment from skin, hair, eyes
