L2: Protein and Amino Acid Metabolism Flashcards
(61 cards)
State some major and minor nitrogen containing compounds.
Major: amino acids, proteins, purines & pyrimidines
Minor: creatine phosphate, some hormones (e.g. adrenaline)
How is creatinine formed and at what rate?
Breakdown of creatine and creatine phosphate. Formed at a constant rate dependent on muscle mass (unless muscle is wasting)
How does creatinine provide an estimate of muscle mass?
- Filtered by kidneys
- Creatinine urine excretion over 24 hour period is proportional to muscle mass
Alongside being used as an indicator of muscle mass, state another use of creatinine?
Indicator of renal function.
High plasma concentration and low urine concentration indicates poor kidney function.
State the reference range for creatinine excreted in urine per 24 hour period for:
- men
- women
Men: 14-26mg/kg
Women: 11-20mg/kg
Men tend to have larger muscle mass
How is creatinine phosphate used as a small store of energy in muscles?
Creatine converted into creatine phosphate by enzyme creatine kinase. Reaction converts ATP -> ADP.
Reaction can be reversed to regenerate ATP.
Define nitrogen balance
A measure of nitrogen input - nitrogen output
Define nitrogen equilibrium
Intake of nitrogen = output of nitrogen
Define positive nitrogen balance. When is it normal?
Intake of nitrogen > output of nitrogen
Increase in total body protein; this is the normal state in times of growth, pregnancy or adult recovering from malnutrition
Define negative nitrogen balance. When is it normal?
Intake of nitrogen < output of nitrogen
Net loss of protein. NEVER NORMAL- causes can include trauma, infection or malnutrition
In an average 70kg man, approximately how much nitrogen by mass is in:
- Body proteins
- Amino acid pool
- N-containing compounds
Body proteins= 2kg
Amino acid pool= 16g
N-containing compounds= 60g
Where does the body’s nitrogen come from?
Dietary protein (16g)
State the four compounds in which nitrogen is excreted
Mostly as urea (85%), creatinine, ammonia and uric acid in the urine (some in faeces and sweat)
Define protein turnover
Balance between protein synthesis and protein degradation
What two things happens to excess amino acids?
- Converted into intermediates of carbohydrate and lipid metabolism
- Oxidised to provide energy
THEY ARE NOT STORED
Describe the process of protein turnover
- Amino acids from digested dietary protein and de novo amino acid synthesis enter free amino acid pool
- Amino acids used to synthesis proteins
- Amino acids return to free amino acid pool when proteolysis occurs. 75% reutilised for synthesis the rest metabolised in liver
- Free amino acids metabolised into amino group and carbon skeleton by liver
- Amino group: nitrogen either incorporated into other compounds or excreted as urea
- Carbon skeleton -> glucogenic amino acids or ketogenic amino acids
**Glucogenic amino acids undergo gluconeogenesis
**Ketogenic amino acids from ketone bodies
Both produce energy
Amino acids can be glucogenic, ketogenic or both glucogenic and ketogenic; provide one example of each.
- Glucogenic: Glycine
- Ketogenic: Lysine
- Both glucogenic & ketogenic: Phenylalanine
When does mobilisation of protein reserves occur?
Extreme stress (starvation)
State the effect of insulin and growth hormone on:
- Protein synthesis
- Protein degradation
Protein synthesis: increase
Protein degradation: decrease
State the effect of glucocorticoids on:
- Protein synthesis
- Protein degradation
Protein synthesis: decrease
Protein degradation: increase
If, during a starved state, you wanted proteins to be mobilised what hormone would be released?
Glucocorticoids (E.g. cortisol)
What can occur, regarding proteins, in Cushing’s syndrome and what are the consequences?
Excessive breakdown of protein (due to excess cortisol). This weakens skin structure and leads to striae formation.
State the nine essential amino acids
If learned this huge list may prove truly valuable
Isoleucine Lysine Threonine Histidine Leucine Methionine Phenylalanine Tryptophan Valine
State three conditionally essential amino acids and when they may be required from diet
Arginine, tyrosine and cysteine when there is a high rate of protein synthesis e.g. pregnancy, growth as child
Arginine can be synthesised by body in small quantities
Tyrosine can be synthesised from phenylalanine
Cysteine can be synthesised from methionine
