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Flashcards in Amino Acid Metabolism Deck (30):

What is it important to remember about the half lives of individual proteins?

All enzymes and proteins turnover at different rates, e.g adult collagen is relatively inert and has a half life of 300 days, but lipoprotein lipase has a half life of only 1 hour.


What are essential amino acids?

Amino acids that can't be synthesised by the body by transamination, so have to be obtained from the diet in order to maintain the nitrogen balance in the body.


What are non-essential amino acids?

Amino acids that can be synthesised in the body from common metabolic intermediates by transamination.


What are semi-essential amino acids?

Amino acids that are synthesised in the body by transamination from essential amino acid precursors, so are essential in the diet to stop essential amino acids being used up. They become essential under conditions of metabolic stress.


What do you call amino acids without the amino group?

Carbon skeletons.


What is deamination?

Transferring the amino group to form glutamate by transamination, then glutamate being oxidised (oxidative transamination by glutamate dehydrogenase) to produce ammonia which is excreted as urea.


What is the co-factor for transaminase enzymes?

Vitamin B6.


How does transamination work?

Amine group of amino acid is transferred to transaminase enzyme. Transaminase enzyme transfers amine group onto alpha keto-acid (e.g pyruvate) to produce corresponding amino acid. Remnants of original amino acid are alpha keto-acid (carbon skeleton).


Name the three main transaminase enzymes in the liver.

Alanine aminotransaminase (ALT).
Aspartate aminotransferase (AST).
Glutamate aminotransferase.
ALT and AST are used in liver biochemistry tests, as damage to hepatocytes causes them to leak out into the blood.


What does hypoalbuminaemia show?

Advanced chronic liver disease, or severe acute liver damage.


What do increases in blood alkaline phosphatase (ALP) show?

Increased synthesis by bile cannaliculi, usually due to cholestasis. (Gamma glutamyl transpeptidase [GGT] also raised in cholestasis).


What can happen to the carbon skeletons of the amino acids?

Glucogenic: converted to pyruvate, then glucose and can be oxidised or stored as glycogen.
Ketogenic: converted to acetyl coA, then oxidised, or converted to fatty acids and stored as TGA, or converted to the ketone bodies acetoacetate and butyrate (used to fuel CNS during starvation).


Where is the concentration of ammonia high?

In the liver, because it is produced by oxidative deamination of glutamate, and in hepatic portal venous blood because it is produced by bacteria in the colon from urea and recycled.


How is urea formed?

2 ammonia + carbon dioxide ==> urea
One ammonia comes from glutamate by glutamate dehydrogenase, the other from aspartate.
The urea cycle only happens in hepatocytes.


What happens to urea?

It diffuses into the gut lumen, is hydrolysed by bacteria to produce ammonia which is transported back to the liver via the portal vein to produce amino acids. It is also excreted in urine.


How is the glucose level in the blood regulated?

There is coarse autoregulation by the liver (an isolated liver could maintain the correct level of glucose by glycogenolysis and glycolysis without any nervous or hormonal stimulation).
Superimposed on that there is hormonal control by insulin and glucagon.
Superimposed on that there is stimulation by adrenaline (which can cause immediate glycogenolysis in the liver, and slower glycogenolysis in muscles).


What does insulin stimulate?

Increased glucose transport into cells, increased storage as glycogen, increased protein synthesis and lipogenesis. Decreases glycogenolysis, ketogenesis, lipolysis.


What does glucagon stimulate?

Increased glycogenolysis, gluconeogenesis, and ketogenesis in hepatocytes.


Why is there a big cost of protein in repair of trauma?

A lot of protein is lost so has to be replaced.


Why does the guy use up a lot of protein itself?

To produce enterocytes, enzymes, mucus.


What are the two types of amino acids?

Ketogenic - converted to acetyl coA
Glucogenic - converted to glucose


What do you call amino acids without the amino group?

Carbon skeleton


What happens in the "fed" stage where there is high insulin?

Proteins hydrolysed to amino acids in duodenum and jejunum.
Amino acids transported to the liver in the portal vein.
Liver carries out protein synthesis, and stores excess glucogenic amino acids as glycogen, and ketogenic amino acids as triacylglycerol.
Liver also transports amino acids to extra hepatic tissues like the muscles for protein synthesis.


What happens in the "fasting" stage where there is high glucagon?

White adipose tissue releases fatty acids which are oxidised in the liver to ketones.
Muscles release amino acids to the liver, which the liver converts to pyruvate and acetyl coA.


What are four uses of amino acids that are not in excess?

Growth and repair of cells, plasma proteins, hormones, enzymes.


What are three uses of amino acids that are in excess?

Deamination (glutamate donates amino group to urea cycle in liver)


What is an alpha keto-acid?

What is formed when an amino acid is deaminated, or what recipes the amino group in transamination to form an amino acid.


In the first stage of deamination, which enzyme transfers the amino group to produce glutamate and an alpha-keto acid?

Glutamate aminotransferase


Which reaction is catalysed by glutamate dehydrogenase?

Oxidative transamination - the deamination of glutamate to produce ammonia (to combine with carbon dioxide to produce urea) and alpha-ketoglutamate.


What does autoregulation by the liver mean?

An isolated liver can autoregulate the glucose concentration in the fluid flowing through it, by changing the rates of glycogenolysis and glycogenesis.
This coarse autoregulation is superimposed by hormonal and nervous stimulation.