Ch8

Question 1

How many amino acids are there? What are the two types of amino acids? How are they grouped into?

Answer 1

• altogether 20 amino acids
• 11 non-essential (can be synthesised in the body); 9 essential (obtained in diet)
• grouped into 6 families according to where the carbon skeleton is derived

Question 2

Why is there amino acid metabolism? How are the amino acid metabolised and what are their respective functions? When will there be amino acid metabolism?

Answer 2

• excess amino acids cannot be stored so they must be metabolised
• α-amino group
  => for amino acids or nucleotides biosynthesis
  => enter the urea cycle and urea is excreted
• carbon skeleton
  => enter the citric acid cycle –> produce energy or generate intermediates for glucose generation (gluconeogenesis) (eg. OAA)
• only during extreme starvation, cellular proteins will be used as fuel

Question 3

How does carbon skeleton form and what is the use of it? Which two types of amino acids can be used for the production of energy? What will the carbon skeleton be broken down into? What is the special thing about one amino acid?

Answer 3

• removal of α-amino group from a.a. –> carbon skeleton as fuel
• glycogenic a.a (eg. alanine Ala and glycine Gly) –> carbon skeleton: pyruvate, OAA, fumarate, succinyl CoA and α-ketoglutarate –> PEP –> glucose
• ketogenic a.a (eg. Leucine Leu) –> carbon skeleton: acetyl CoA –> ketone bodies (alternative fuel for CNS)
• some a.a. are both glycogenic and ketogenic (eg. Isoleucine Ile)

Question 4

What is transamination? What are the enzymes called and where could they be found?

Answer 4

• removal of α-amino group from a.a. and transfer it to an acceptor of α-amino group which is usually α-ketoglutarate –> formation of glutamate and the corresponding α-keto acid (carbon skeleton)
• enzymes catalysing these reactions are transaminases/ aminotransferases, found predominantly in the liver

Question 5

Why do plasma aminotransferases have diagnostic value? What will increases in all liver diseases?

Answer 5

• aminotransferases are intracellular enzymes which should be in the liver cells normally. If there is an increase in plasma aminotransferases which indicate a damage of liver cells
• both aspartate aminotransferases and alanine aminotransferases increases

Question 6

What will happen to the glutamate? What will happen when the cellular ATP level is low?

Answer 6

• glutamate produced by transamination is oxidatively deaminated by glutamate dehydrogenase to produce ammonia
• when cellular ATP is low, there will be an increased oxidation of amino acid –> increased carbon skeleton –> increased ATP production through the citric acid cycle and oxidative phosphorylation

Question 7

How is ammonia excreted in different kind of animals? What are their respective names?

Answer 7

• aquatic animals (ammonotelic animals) –> excreted ammonia directly into water
• birds, reptiles and insects (uricotelic animals) –> excreted in the form of uric acid
• mammals and amphibians (ureotelic animals) –> converted to urea and then excreted

Question 8

How is urea synthesised and what is the pathway for excretion of urea? What substances provide materials of urea? What is the location of the whole process? What are the processes in the two locations respectively?

Answer 8

• synthesised by the liver by urea cycle –> secreted into the blood –> kidneys –> excreted in urine
• CO2 and NH3 provide carbon and nitrogen respectively in urea
• in mitochondria and cytosol
• mitochondria
  => condensation of CO2 and NH3 to form carbamoyl-P
  => formation of citrulline from carbamoyl-P and ornithine –> citrulline is transported out of the mitochondria to cytosol
• cytosol
  => condensation of citrulline and aspartate to form argininosuccinate
  => cleavage of argininosuccinate into fumarate and arginine
  => cleavage of arginine to form urea and ornithine by arginase
  => ornithine is transported back into the mitochondria

Question 9

What will happen if there is any blockage of enzymes in the urea cycle? What is the potential cause? What will happen if there are excessive ammonia? What are the symptoms found in new born babies?

Answer 9

• accumulation of ammonia in blood –> hyperammonemia
• cause by genetic defect present at birth
• overproduction of glutamate and glutamine –> damage to brain –> depletion of α-ketoglutarate –> decrease ATP production –> mental retardation –> affect growth
• unexplained lethargy, hypotonia, vomiting and seizures

Question 10

What is uric acid and how will it be formed in ureotelic organisms?

Answer 10

• major nitrogenous waste of uricotelic organisms
• formed from the breakdown of purine bases of DNA and RNA

Question 11

What is the reason for gout and what is its treatment?

Answer 11

• high serum level of sodium urate (uric acid) –> deposition in joints and kidneys –> gout (painful arthritis)
• anti-inflammatory drugs or avoid food rich in purine (eg. beer, seafood, red meat or organs)

Question 12

How is heme broken down to? How will it be excreted?

Answer 12

• broken down by heme oxygenase to biliverdin and is converted to bilirubin by biliverdin reductase
• bilirubin will then bind to albumin in the blood and conjugated with glucuronic acid in the liver –> conjugated bilirubin is secreted in the bile and excreted in feces

Question 13

When will jaundice be developed? What is the treatment for the first week of new born?

Answer 13

• if there is a liver disease, build-up of bilirubin in blood –> skin and whites of the eyes become yellow
• phototherapy –> help convert bilirubin into an isomer which is more water-soluble