What are the functions of protein?
- Muscle growth and repair
- Catalyst
- Transport and structure (e.g. haemoglobin transports oxygen)
- Hormone production (e.g. insulin)
- Cell signalling
- Contractile functions (muscle movement)
- Structural support (e.g. collagen)
- Immune function
What are proteins broken down into?
Amino acids, building blocks of proteins
How does the body use protein for energy?
- Gluconeogenesis – Converts protein into glucose for energy.
- Lipogenesis – In extreme starvation, protein may convert into fatty acids.
- Protein provides 10-15% of the energy needed during prolonged exercise.
How does DNA make new proteins?
- The first step is gene expression
- Involves copying a genes DNA sequence
- They link the complimentary nucleotide to create a new RNA sequence
- The new RNA strand is transported out the nucleus and into the cytoplasm to the ribosome
- The order of these nucleotide bases determines the polypeptide which is produced, and these polypeptides make up a protein
How many amino acids are there?
20
What are the two types of amino acids?
- Essential amino acids (9) – Must come from food.
- Non-essential amino acids (11) – Can be synthesized by the body.
Name 3 types of essential amino acids?
Isoleucine, Leucine, Valine
All are BCAAs
What are Branched-Chain Amino Acids (BCAAs)?
A group of amino acids that:
* Decrease protein breakdown
* Can be used as an energy source
* Regulate glucose metabolism
* Increase protein synthesis
What is the “leucine trigger”?
Leucine, a BCAA, is the most potent stimulator of muscle protein synthesis (MPS) by activating the mTOR pathway
Do athletes need more protein and why?
Yes, due to:
1. Increased oxidation and excretion of amino acids.
2. Higher protein breakdown from exercise.
3. Increased muscle synthesis from training.
What happens if daily protein intake is too low?
The body breaks down muscle protein for fuel, leading to muscle loss
What is Net Protein Balance (NPB)?
The balance between protein synthesis and protein breakdown throughout the day.
* Positive NPB = Muscle growth.
* Negative NPB = Muscle loss.
What are the best ways to stimulate muscle protein synthesis (MPS)?
- Resistance training
- Eating protein regularly
- Consuming enough leucine
How much energy does protein provide?
Protein supplies 10-15% of energy needs but should not be a primary energy source due to muscle breakdown
What happens to excess protein?
If protein intake exceeds needs, excess nitrogen is removed via urine.
Where do amino acids go after being consumed and what happens?
- Protein travels to small intestine and can be broken down into amino acids
- Amino acids also travel to liver where
o Protein synthesis can occur
o Excess amino acids can be converted into glucose and/or fatty acids via metabolic pathways giving energy - Amino acids can travel directly to the muscle, where protein synthesis can occur
How does protein turnover change during endurance sports?
- Endurance exercise is catabolic (breaks down muscle protein).
- Increased BCAA oxidation occurs in long-duration exercise (e.g., cycling, running).
What are the recommended daily protein intakes?
- Non-athletes: 0.8g/kg body mass
- Endurance athletes: 1.2-1.4g/kg body mass
- Strength athletes: 1.4-1.8g/kg body mass
What is the optimal protein intake after exercise?
- 20g for endurance exercise
- 40g for strength training
Method of analysing muscle protein synthesis?
Biopsy
What are the best protein distribution strategies?
- Bolus (2x 40g every 6 hours)
- Intermediate (4x 20g every 3 hours) best
- Pulse (8x 10g every 1.5 hours)
What are the different types of protein?
- Whey – Fast digestion, high in BCAAs, best for muscle protein synthesis.
- Casein – Slow digestion, prevents muscle breakdown.
- Soy – Less effective at stimulating MPS than whey.
What are the three key factors for protein intake?
- Timing – Every 3 hours.
- Type – Meat, dairy, legumes, soy, etc.
- Total – 1.4-2.2g/kg body mass daily
Does protein intake change in a calorie deficit?
Yes, higher protein intake is needed to preserve muscle during weight loss
