KINE305 Chapter 8: Protein and Amino Acids

How many different amino acids are found in proteins?

20 different amino acids
muscle contains all the naturally occurring amino acids, making it nutritionally valuable

What are the most abundant amino acids in muscle?

the three-branched amino acids (BCAAs), namely leucine, valine, and isoleucine, which make up 20% of the total amino acids found in muscle protein

What is the importance of leucine?

activates mTOR when dropped on muscle, which is a central focus of driving protein synthesis and cell growth

What are amino acid transporters?

membrane-bound proteins that recognize specific amino acid shapes and chemical properties

divided into sodium-dependent and sodium-independent carriers

Why is the protein turnover rate so great?

proteins are constantly broken down to amino acids, which can then be recycled for new protein synthesis or used to synthesize other amino acids

What must occur before amino acids can be oxidized?

the amino group must be removed either through transamination or oxidative deamination

How is ammonia that is removed from the amino acids disposed?

they are converted to urea in the liver which is then transported to the kidneys where it is incorporated into urine and eventually excreted

What occurs after the removal of the amino group of an amino acid?

the remaining carbon skeleton can enter the TCA cycle to be oxidized to CO2 either by being converted to acetyl-CoA or as a oxaloacetate

What is the largest reserve of amino acids?

skeletal muscle

What is protein turnover?

the simultaneous synthesis and degradation of protein in the body
proteins that have a regulatory function (enzymes, hormones) have a rapid turnover rate
structural proteins (collagen, actin, myosin) have a slow turnover rate

What is Protein/Nitrogen Balance?

the overall synthesis and degradation of proteins are equal to each other; the amount of nitrogen consumed in the diet equals the amount of nitrogen excreted in urine, feces, and sweat

What is the recommended protein intake for strength athletes?

1.6-1.7g/kg bw/day, about twice the value for the general population

What is the recommended protein intake for endurance athletes?

1.2-1.8g/kg bw/day, although it mat be higher in extreme situations

What should be taken into consideration regarding recommended protein intakes?

data came from untrained individuals which could have led to higher levels of protein turnover/optimization

relative to body weight (not lean mass) and not adjusted to training levels

How many grams of protein is effective for muscle growth/optimization?

1.4g/bw

When is protein used as a fuel for exercise?

during very prolonged exercise when carb availability becomes limited, amino acid oxidation may increase somewhat, but the contribution of protein to TEE decreases to a max of 10%

How much does protein contribute to energy expenditure?

15% in resting conditions, and decreases to about 5% during exercise

What is the protein need for games players?

1.2-1.4g/kg bw/day

What is the effect of resistance exercise on rates of protein synthesis and degradation?

in the hours after exercise, both protein synthesis and breakdown are increased

protein synthesis is increased more than breakdown but will exceed degradation only after feeding a source of amino acids

without sufficient dietary amino acid intake, net muscle protein gain will not occur

What factors affect muscle tissue protein accretion following resistance exercise?

1. timing of protein ingestion

2. type of protein ingested

3. amount of protein ingested

4. co-ingestion of carbohydrate

Why should carbs be eaten with protein?

it is more effective in stimulating muscle protein synthesis due to an insulin-mediated increase in amino acid uptake

important only is the protein amount is <20g, if sufficient protein is ingested, adding carbs has no effect

When is it most advantageous to ingest protein?

in the postexercise period, immediately after a bout of resistance exercise

What is the best type of protein to ingest?

rapidly digested and absorbed proteins like whey and soy induce a rise in muscle protein synthesis

whey stimulates whole-body protein synthesis, and casein suppresses whole-body protein breakdown

ingestion of casein, soy, and whey increase muscle protein synthesis is beneficial at rest and following resistance exercise

What is unique about leucine?

is is the only amino acid that acts as a signaling molecule to stimulate translation-initiation pathways, resulting in increased rates of protein synthesis

therefore, it is better to ingest proteins with high leucine content

What is muscle gain in response to resistance exercise influenced by?

the training load and the amount, timing, and type of protein ingested in the following 24-48 hours

When does optimal adaptation to training occur?

when meals containing 0.4g protein/kg bw/meal are consumed shortly after training and at regular intervals throughout the day, totaling 1.6-1.7g/kg bw/day

What is recommended to optimize protein synthesis?

ingesting high-quality protein (20-25g or 0.4g/kg bw) with 8-10g of essential AAs and at least 3 g of leucine at regular (3-4hr) intervals

What type of proteins are most effective at generating increases in protein synthesis?

proteins that are rapidly digested and absorbed with a high leucine content (ex. whey)

What are ways to maximize hypertrophy?

1. engage in regular training bouts of high-load resistance training

2. lifting heavier loads over longer durations stimulates greater improvements in muscular strength

3. lift to point of contraction failure

4. maintain energy balance

5. consider postexercise period as time for rehydration, refueling, repair, and remodeling

How can protein intake maximize hypertrophy?

1. timing of ingestion

2. ingestion in the postexercise period in sufficient doses and up to 3 other meals throughout the day for 1.4-1.6g/kg bw

3. ingesting a larger dose of protein before bedtime

What types of protein can be used to maximize hypertrophy?

1. postexercise - rapidly digested, high-quality proteins with a high leucine content (whey, skim milk, eggs)

2. throughout the day - lean high-quality protein containing all the essential AAs in equal proportions

3. protein from predominantly animal sources

Which athletes are at risk of insufficient protein intake?

female runners, male wrestlers, boxers, and other athletes in weight-category sports;

ski jumpers, male and female gymnasts, and female dancers have protein intakes well below the RDA

vegetarian athletes

What is the use of arginine?

infused intravenously in large quantities can have anabolic properties in patients but oral ingestion does not result in increased secretion of human GH and insulin

What health risks might come with high-protein intakes?

kidney damage, increased blood lipoprotein levels, and dehydration