amino acid and protein metabolism

What happens to amino acids after they’ve been digested and absorbed into the blood

Why is protein needed in the diet

Do we have a “storage” form of protein reserves in the body that can be broken down and used when needed

What is the amino acid pool

What is protein turnover

the continous breakdown and resynthesis of body protein to amino acids 

Is protein turnover the same for each protein

protein turnobver is the make and removal oft he protein 
no its variabel depending on the protein and their half life

most proteins are a few days
 collagen is years
hormones and dgestive enzymes have half life of minutes

How often does skeletal muscle degrade protein into amino acids

continously

What increases the rate of protein breakdown in muscle

• starvation 

• hormones ( e.g cortisol) 

What happens to foreign “exogenous” proteins

- they're taken into vesicles by endocytosis, or autophagocytosis

- vesicle fuses with lysosomes

- proteolytic enzymes degrade proteins into amino acids

What happens to most cellular proteins when they become recognised as old or damaged

They're removed by the ubiquitin  (you be quiting) breakdown system which gives a mixture of the 20 amino acids

Why is high protein intake in a well-fed individual wasteful

Because surplus amino acids are rapidly catabolised and the nitrogen is excreted as urea in the urine

What happens to amino acids after theyve been digested and absorbed into the blood

• form body protein s

• produce creatine,purine,pyramdine

• excess amino acid stored and glucose or ketone bodies in liver

What are the 2 ways the NH₂ group is removed from amino acids

happens in the liver 


1. trasamination: the amino group is removed from the amino acid and trasnfered to another keto acid making glutamate which can then go through oxidative deamination

2.oxidative deamination: the nh2  of glutamate is removed making nh3 which can go to ornithine cycle 

What are the roles of the liver in nitrogen metabolism

1. removal of aa, glucose & fats from portal blood supply

2. absorbed aa used for synthesis of cellular proteins

3.  synthesis of plasma proteins

4. synthesis of haem, purines & pyrimidines for DNA & RNA

5. degradation of excess amino acids by transdeamination

6.  conversion of NH3 to urea for excretion (ornithine cycle)

What is the only organ which can convert amino groups of amino acids to urea

liver

What are the important amino acids involved in inter-organ nitrogen transport

Alanine
Glutamate
Glutamine
Aspartate

Why is glutamine important for ammonia transport

• its a safe carrier of ammonia in the blood 

• ammonia is toxic to the brain

• it can carry 2  ammonia equivalents  to the liver fro urea formation

What are the 2 possible outcomes for the carbon skeleton after deamination

-depending on whether it was a glucogenic or ketogenic amino acid theoutvome is different 

1. Glucogenic amino acids

• Can be converted into glucose via gluconeogenesis.

• Their carbon skeletons are degraded into pyruvate or TCA cycle intermediates

    2. ketogenic amino acids

• Can be converted into acetyl-CoA  which can form ketone bodies

Urea / ornithine cycle steps

1. Ammonia + CO₂ + ATP → carbamoyl phosphate

2. Carbamoyl phosphate + ornithine → citrulline

3. Citrulline + aspartate → argininosuccinate

4. Argininosuccinate → arginine + fumarate

5. Arginine → urea + ornithine (ornithine recycled)

What are the end products of nitrogen metabolism

 - urea from protein breakdown

- creatinine from creatine phosphate breakdown

- uric acid from DNA & RNA breakdown

- ammonia (NH4+) from control of body pH

What are the waste products from the metabolism of creatine, purines & pyrimidines

Creatinine and uric acid

Nitrogen balance

Intake(protein synthesis) = excretion(protein degredation) → neutral


Intake > excretion → positive 
- happens in: preganancy, normal growth in children

What is the difference between plants & microorganisms and humans synthesising amino acids

• plants and microorganisms can synthesis all 20 amino acids 

• human can only sysnthesis 10 amino acids and need diet for the other 10

Hyperammonaemia

• when you have excessive ammonia 

• this happens when theres not enough conversion of NH3,ammonia into urea

• happens in people with liver failure or people with genetic defects thatreduce the catalytic actviity of enzymes in the urea cycle 

Summary of protein breakdown

1. proteins eaten are broken down to amino acids by enzymes 

2. the amino acids can either be absorbed to the blood to make new proteins or be broken down for energy 

3. in the liver deamination of the amino acid removing the NH3 leaving the carbon skeleton, or transamination where the amino group is mobed to anohter molecule making glutramate 

4. the NH3 is toxic s converted to urea with urea cycle then sent to kidney and excreted 

5. the carbon skeleton has 2 possibel outcomes: 1, if it was glucogenic amino acid it will change into gluocse or ATp. 2, if it was a ketogenic amino aid it changes to fatty acidsd or ketone bodies

6. in fed state the amino acids are used to make proteins when starving the proteins are broken down to glcose or ketones for energy