How much dietary protein is required per day to offset obligatory loss?
How much protein is recommended per day?
What happens to protein in take in excess of dietary requirement?
Doesn't get stored as protein Used for energy; converted to glucose (gluconeogenesis) or ketone bodies depending on the type of amino acid Stored as GLYCOGEN or FAT
What is the main source of the amino acid pool?
The breakdown of proteins in the tissues
What is the amino acid pool used for?
To build new proteins to replace those broken down
What is the daily turnover of protein in the body?
What is the size of the obligatory loss of protein per day?
20g, must be replaced by dietary protein.
What makes up an amino acid?
a central carbon attached to an H, a carboxyl group, amino group and another group (eg. methyl group CH3)
Summarise what happens to dietary protein in the body
What are the INPUTS in Amino Acid Metabolism?
After deamination, what are some of the outputs of amino acid metabolism?
Ketoacids and NH4+
Pyramidines and Purines
In what ways can N be lost after Amino Acid metabolism?
Hair Nails, Desquamation
What is TRANSAMINATION?
The transfer of the amino group (-NH3+) from an amino acid to a keto acid, which contains a keto (=O) group.
In transamination, the NH3+ group on one molecule is exchanged with the =O group on the other molecule.
The amino acid becomes a keto acid, and the keto acid becomes an amino acid.
By this process, amino acid 1 becomes deaminated and amino acid 2 is generated.
Why is glutamate unique in terms of deamination?
It is the only amino acid that can be deaminated by OXIDATIVE DEAMINATION in humans.
What catalyses the deamination of Glutamate?
What are the products of this reaction?
What cofactor is involved?
What are the main changes that occur?
Ammonium Ion (NH4+)
NH3+ group removed as well as the H attached to the Carbon, and a =O replaces it.
What provide the main deamination route for amino acids?
How may amino acids be deaminated indirectly?
By coupling transamination to oxidative deamination
Oxoglutarate is an intermediate of which cycle?
The TCA (citric acid) cycle or Krebs Cycle
Therefore this provides an entry point for amino acids into energy metabolism
What is transdeamination?
Amino acids are deaminated indirectly by coupling transamination to oxidative deamination.
Fate of about 75% of ingested protein nitrogen
Central role of glutamate
Occurs almost entirely in liver
Where does transdeamination occur?
Almost entirely in the LIVER
Amino acid deamination produces ammonia which is toxic - how is it dealt with to avoid acculuation to toxic levels?
What catalyses this reaction?
Where is this reaction confined to?
It is converted by combination with carbon dioxide to carbamyl phosphate.
Carbamyl Phosphate Synthetase.
The mammalian liver
What is the main function of the urea cycle?
Carbamyl phosphate is converted to urea, which is then excreted by the kidneys
What are the intermediates of the Urea Cycle?
Starts with Carbamyl Phosphate
Aspartate (arginino-succinate synthase)
Fumarate (arginino-succinate lyase)
Ornithine (ornithine-carbamoyl transferase)
Back to Carbamyl Phosphate
What can nitrogen balance equate to?
Nitrogen balance = N-intake - N-loss
What is N-intake?
What is N-loss?
(80-90% as urea)
What occurs when N-intake is greater than N-loss?
Positive N balance
What occurs when N-intake is less than N-loss?
Negative N Balance
Identify situations when N balance is positive?
Growth in childhood
Recovery from illness/injury
(when skeletal muscle is growing)
Identify situiations when N-balance is negative?
Hypermetabolic State (burns, trauma, sepsis)
(when protein containing tissue eg mainly skeletal muslce is shrinking)
What is the clinical relevance of N-balance?
Severe burns, trauma, sepsis (negative N balance)
- elevated levels of cytokines (Interleukin 1-beta, Interleukin-6, Tumor necrosis factor-alpha)
- promote protein breakdown
Protein-energy malnutrition (prolonged negative N balance)
- Adipose tissue energy stores depleted
- Dietary protein used for energy instead of tissue repair/replacement
What is the situation referred to as protein-energy malnutrition?
When no amount of dietary protein will prevent negative nitrogen balance as long as energy intake is inadequate.
What hormonal regulation of protein metabolism takes place?
Stimulates Protein Synthesis
- Growth Hormone
- Insulin in young
- Insulin Like Growth Factor
Inhibits Protein Breakdown
- Insulin Like Growth Factor
- INCREASE extrahepatic protein breakdown
- INCREASE hepatic protein synthesis (inc plasma protein)
How many amino acids occur in humans?
How many of these are non-essential?
How many are essential?
What does a 'non-essential' amino acid mean?
they can be synthesised from other amino acids and are therefore not essential in the diet.
What are the non-essential amino acids?
cysteine (C) (formed from methionine)
tyrosine (Y) (formed from phenylalanine)
What amino acid is formed from methionine?
What amino acid is formed from phenylalanine?
What are the essential amino acids?
(Absence of any one of these leads to malnutrition)
(Volatile Manly Hiccoughs Lead People To Itch Like Trolls)
Discuss the quality of various proteins
Content of essential amino acids
•Animal protein – high quality
•Cereal protein – quality limited by low lysine content
•Legume protein – quality limited by low methionine content
‘incomplete’ proteins complement each other, e.g. eat rice with beans
What does the nutritional value of proteins depend upon?
Its content of essential amino acids. If it is completely deficient in one essential amino acid, it has no nutritional value.
What are 'complete' proteins?
What are 'incomplete' proteins?
Proteins that provide plenty of all of the essential amino acids are ‘complete’ proteins with a high nutritional value.
Proteins that have a low amount of an essential amino acid are ‘incomplete’ and have a lower nutritional value.
What are examples of incomplete proteins?
Cereal proteins and legume proteins are incomplete because they have low levels of an essential amino acid. However, they can complement (‘complete’) each other if eaten together because the limiting amino acid is different for the different types of protein.
What is an indicator of protein metabolism
Dietary protein used for energy at the expense of what?
(when energy intake is low - protein-energy malnutrition)