Week 7 - Protein Flashcards
Roles of protein/amino acids
- proteins provide structure to all cells in the human body
- proteins are enzymes that increase the rate of metabolic reactions
- amino acids have a central role in the metabolism of many organs and tissues
- amino acids are precursors for the synthesis of body proteins
- amino acids are precursors and regulators of the synthesis of neurotransmitters, hormones, DNA and RNA
Essential proteins
those that the body cannot synthesize endogenously and must be consumed through dietary sources (exogenous)
What does whole-body protein balance inform us?
whether an individual is consuming sufficient dietary protein levels required to support human health
How can we determine whole-body protein balance?
measure protein in (consumed + secreted) and protein out (faeces and urine)
What factors contribute to overall protein balance (in)?
1) Protein consumed
2) Protein secreted across different components of the GI system
What are the 3 ways we can measure protein leaving the body?
- Feaces
- Urine (majority)
- Sweat, skin, hair losses
Why is measuring whole-body protein balance not the best method to use?
because it doesn’t tell us about individual protein requirements or the protein status of individual tissues and organs in the body
What has higher rates of protein turnover - Gut or skeletal muscle?
Gut - has very high turnover rates of protein
What is the major site of protein synthesis?
Liver
What is the by-product of the conversion of amino acids in the liver to an energy substrate? How is this excreted from the body?
ammonia
- the liver converts this into urea and this is released into the bloodstream and then metabolized in the kidney and secreted or removed from the body in urine.
What happens to excess amino acids in the liver?
they are released into the bloodstream and used in peripheral tissues such as skeletal muscle.
Amino acids are a source of …. in the body. What % of protein is made up of…?
Nitrogen
16% of protein is nitrogen
How to calculate nitrogen (protein) balance?
1) Determine nitrogen excretion (e.g. urine, feces, sweat) in grams per 24h period.
2) Determine nitrogen intake: protein intake (grams per day) divided by 6.25
3) N balance = Intake minus excretion
What can calculating nitrogen balance estimate?
the protein intake required to maintain protein balance
What is the protein reference nutrient intake (RNI)?
0.75 g/kg/d
80kg body mass = 60g of protein/day
What is the recommended dietary allowance (RDA) for protein?
0.8 g/kg BM
How much protein is in 1g of nitrogen?
6.25 grams
Limitations of nitrogen balance method.
- No information of tissues (only whole body)
- Lacks sensitivity (only gross measures of intake and excretion)
- Zero balance on low intake may reflect accommodation
- Positive balance may not relate to lean body mass
What is the major determinant of muscle mass regulation?
Muscle protein synthesis
- Protein synthesis rates fluctuate a lot more whereas protein breakdown is more robust.
Body nitrogen loss can occur through…
skin, feces, sweat
What happens to amino acids once they are released into circulation and travel to skeletal muscle?
Amino acids in the arterial blood shuttle into muscle to intracellular amino acid pool.
Upon entry into this pool, amino acids can be synthesized into new muscle protein.
This replaces losses from protein that are broken down and released back into circulation to support the protein synthesis needs of other tissues and organs.
4 amino acids
Leucine, isoleucine, methionine, lysine
