Lecture 4 - Protein and Amino Acids

Question 1

functions of proteins

Answer 1

• provides structure to all cells in the human body (i.e. cell membrane, cytoplasm)
• muscle, skin and hair are all composed of protein, when diet is deficient, these structures break down
• many proteins are enzymes that increase the rate of metabolic reactions

Question 2

how many different amino acids are found in proteins

Answer 2

• up to 20 different amino acids are found in protein

Question 3

What contains the largest proportion of protein in a human body? What is the most abundant

Answer 3

muscles contain around 40% of all protein
- the most abundant proteins in muscle are contractile proteins actin and myosin

Question 4

what are the most abundant amino acids in muscle?

Answer 4

the three branched chain amino acids (BCAAs)
- leucine
- valine
- isoleucine

Question 5

what are some other roles of AAs, besides just being the building blocks for protein

Answer 5

• some AAs are also precursors and regulators of the synthesis of important etabolic mediator and compounds with a regulatory biological activity (e.g. neurotransmitters, hormones, DNA, RNA)

Question 6

explain protein turnover

Answer 6

it is the simultaneous synthesis and degredations of protein in the body
- AAs are constantly made into proteins (protein synthesis) and broken down (protein degredation) into AAs
- generally, the proteins that have a regulatory function (such as enzymes) or act as signals (hormones) have a relatively rapid rate of turnover (mins, hours, secs)
- the structural proteins such as collagen have a relatively slow turnover

Question 7

explain proteins role as fuel for exercise

Answer 7

• protein has been estimated to only contribute up to 15% of energy expenditure in resting conditions
• during exercise, this relative contribution decreases to about 5% because of an increasing importance of carbs and fats as fuels
• during very prolonged exercise, when carb availibility becomes limited, AA oxidation (mostly BCAAS) may increase somewhat, but the contribution of protein to tottal energy expenditure increases to a ma of about 10%

Question 8

how can resistance exercise impact the rates of protein synthesis and degradation?

Answer 8

• in the hours after exercise, protein synthesis and breakdown are increased
• during exercise protein synthesis is also increased, but more than the breakdown only after feeding on a source of AAs
• without sufficient dietary AAs (protein) intake, net muscle gain will not occur
• both starvation and immobilization result in atrophy and weakness

Question 9

how does resistance training affect muscle protein synthesis

Answer 9

• RE alone results in a long lasting elevation in muscle protein synthesis for at least 48hrs and muscle protein breakdown for 24hrs
• Res.Ex essentially primes the muscle to be more responsive in terms of an increase muscle protein synthesis response to aminoacidemia following ingestion of a protein-containing meal

Question 10

Protein recommendations for non athletes, nonathletes, and strength and endurance athletes

Answer 10

Nonathletes
- 0.8g of protein per kg of BW per day
Athletes
- 1.2 to 2.0 g/kg of BW
Strength athletes
- 1.6-1.7 g/kg of BW per day
Endurance
- 1.2 - 1.8 g/kg/BW/day
- endurance exercise does not increase the rate of BCAA oxidation to any major degree

Question 11

list the factors that affect muscle tissue protein accretion following resistance exercise

Answer 11

• amount of protein ingested
• timing of protein ingestion
• type of protein ingested
• leucine content of protein ingested
• coingestion of carbohydates

Question 12

when is the best time to consume protein

Answer 12

• it used to not matter as long as you ate them an hour before or an hour after
• the new literature is saying that is optimal to ingest protein immediately after a bout of resistance exercise

Question 13

which proteins stimulate whole body protein synthesis suppresses protein breakdown

Answer 13

• whey protein stimulates whole body protein synthesis synthesis
• casein suppresses whole body protein breakdown

Question 14

how do we determine protein quality

Answer 14

1. calculating the propotion of nitrogen retained (the greater proportion of N retained, the greater the protein utilization, and therefore better protein quality)
2. comparing the protein agains egg protein (albumin) which is known to have a near perfect distribution of essential amino acids

Question 15

why is the leucine content of protein important

Answer 15

• leucine acts as a signalling molecule to stimulate translation-initiation pathways, resulting in increased rates of protein synthesis, LEUCINE IS THE ONLY AA THAT DOES THIS
  -leucine stimulates the mechanistic target of rapamycin complex-1 (mTORC1) a key signalling protein that triggers a rise in muscle protein synthesis