Week 5 (2) - Protein Flashcards
Amino acids (20 AA’s)
- 8 essential: Isoleucine, leucine, lysine, methionine, Phenylalanine, Threonine, Tryptophan, Valine (have to be consumed in the diet)
- 8 oxidised as fuel (can enter aerobic respiration and be used to produce fuel directly): Alanine, asparagine, aspartate, glutamate, isoleucine, leucine, lysine, valine
Structure of AAs
Central carbon atom + 4 side chains
- Hydrogen
- Amino group
- Carboxyl group
- The R can change – it is this R that gives the AA its functional properties in the body
- Transamination can change this R – take the side chain off and insert others on (only in non-essential AAs)
Proteins beyond muscle that are involved in protein turnover:
- hormones
- enzymes
- Collagen
-membrane proteins
Skeletal muscle mass
- In sedentary individuals skeletal muscle mass essentially stable
- Sedentary requirements: ~0.8 g/ kg/ day
- Measured by: nitrogen balance techniques and tracer techniques
The process of AA consumption:
When we consume AA we consume them in intact proteins – a digestion process that occurs that results in single AAs being available in the gut for digestion and absorption into the body’s free AA pool.
- Once in the Free AA pool we see exchange with all the body protein stores
- Protein synthesis in all systems in the body is in a constant rate of flux e.g., proteins in the bone turn over slower than muscle proteins. Muscle proteins turn over slower than the proteins that make up the GI tract, stomach and intestines
- It takes about 50-100 days for all the proteins in the skeletal muscle to entirely turn over – every 3 to 4 months the muscle that was there is no longer the same proteins
- Certain AAs can be infused into the circulation
- Routes of loss: urine, sweat and some oxidation of the proteins in AAs
- Some dietary AAs don’t ever reach the system – the gut is the first barrier they have to pass
what are Di/ tripeptides
Proteins of 2 or 3 AAs that may be able to transit across the GI tract and be available in the blood
Rate of PS and PB in an sednetary indiviudal
Oscillation of synthesis and breakdown that happens in response to protein intake in sedentary individuals
- Synthesis fluctuates much more than breakdown – it is more sensitive
- In a sedentary individual from the age of 18-65 years Net protein balance is essentially consistent. This happens even with varying protein intake, within the same person
- The one way we can modify NPB is resistance exercise (phenotypic adaption to exercise that is specific to body protein pools)
Rate of PS and PB in response to resistance exercise:
- Increase rate of MPS
- There is a net positive balance
- Resistance exercise acts as stimulus to increase synthesis and thereby increase NPB
- Just eating more protein will not allow this to happen – you need a stimulus (exercise)
Muscle protein synthesis measurement:
- Need to measure blood samples and muscle samples to calculate the rate of synthesis and/or breakdown
- Also need to put tracers (stable isotopes of specific AAs that have an extra neutron on it), into the vein to use mass spectrometry to identify where the extra carbon atom has gone (in the muscle, blood albumin, collagen?)
- Infusion of labelled amino acids in combination with blood and muscle sampling to determine protein synthesis
- Need to look at where the amino acid goes to look at the behaviour of the system
Resistance exercise and NPB (Phillips et al 1997):
- Resistance exercise followed by MPS and MPB measures at 3hr, 24hr and 48hr
- Showed that FSR (protein synthesis) was dramatically increased in resistant training naïve individuals, that then comes back down slowly overtime
- In resistance training naïve individuals this increase lasts for at least 48 hours while for well-trained individuals it is more like 24hours
- Breakdown also increases after exercise – this is the basal response of the muscle to this exercise stimulus
- Muscle protein breaks down in response to exercise, but more muscle protein is rebuilt
Why do we breakdown muscle?
Allows the turnover of old, damaged or not optimally functioning protein to be replaced by newer and perhaps more useful proteins. A faster rate of turnover allows the muscle to adapt to the stimulus its being given. It allows the muscle to grow in ways that will help the stimulus (strength exercise)
Protein balance at rest
At rest protein balance in negative. Exercise on its own makes it less negative (but still not positive). Nutrition added to exercise makes it positive – if you don’t exercise, the proteins you eat wont turn into muscle proteins.
Timing of protein intake and MPS (Rasmussen et al 2001):
- Amino acid-carbohydrate mixture given 1h or 3h post-exercise
- No difference in MPS between feeding 1h and 3h post-exercise
- Having protein close to exercise does not change the metabolic biochemical response of the muscle – it does not lead to greater protein synthesis
- The concept of an anabolic window is false
Distribution of protein intake (Areta et al 2013):
- 20g protein every 3hr maximised MPS compared to 10g every 1.5h or 40 g every 6hr
- Most effective feeding strategy = every 3hours with 20g protein
Protein amount and MPS (Witard et al 2014):
- 0g, 10g, 20g or 40g whey protein after unilateral lower-body resistance exercise
- 20g protein maximised muscle protein synthesis post-exercise and at rest
- Both the 20g and 40g dose were greater than the 0g and 10g for both exercise and rest
- In all doses, the exercise leg synthesised more protein than the rested leg – nutrition further stimulates this
