Week 7 - Protein

Question 1

Roles of protein/amino acids

Answer 1

• 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

Question 2

Essential proteins

Answer 2

those that the body cannot synthesize endogenously and must be consumed through dietary sources (exogenous)

Question 3

What does whole-body protein balance inform us?

Answer 3

whether an individual is consuming sufficient dietary protein levels required to support human health

Question 4

How can we determine whole-body protein balance?

Answer 4

measure protein in (consumed + secreted) and protein out (faeces and urine)

Question 5

What factors contribute to overall protein balance (in)?

Answer 5

1) Protein consumed
2) Protein secreted across different components of the GI system

Question 6

What are the 3 ways we can measure protein leaving the body?

Answer 6

1. Feaces
2. Urine (majority)
3. Sweat, skin, hair losses

Question 7

Why is measuring whole-body protein balance not the best method to use?

Answer 7

because it doesn’t tell us about individual protein requirements or the protein status of individual tissues and organs in the body

Question 8

What has higher rates of protein turnover - Gut or skeletal muscle?

Answer 8

Gut - has very high turnover rates of protein

Question 9

What is the major site of protein synthesis?

Answer 9

Liver

Question 10

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?

Answer 10

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.

Question 11

What happens to excess amino acids in the liver?

Answer 11

they are released into the bloodstream and used in peripheral tissues such as skeletal muscle.

Question 12

Amino acids are a source of …. in the body. What % of protein is made up of…?

Answer 12

Nitrogen
16% of protein is nitrogen

Question 13

How to calculate nitrogen (protein) balance?

Answer 13

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

Question 14

What can calculating nitrogen balance estimate?

Answer 14

the protein intake required to maintain protein balance

Question 15

What is the protein reference nutrient intake (RNI)?

Answer 15

0.75 g/kg/d

80kg body mass = 60g of protein/day

Question 16

What is the recommended dietary allowance (RDA) for protein?

Answer 16

0.8 g/kg BM

Question 17

How much protein is in 1g of nitrogen?

Answer 17

6.25 grams

Question 18

Limitations of nitrogen balance method.

Answer 18

• 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

Question 19

What is the major determinant of muscle mass regulation?

Answer 19

Muscle protein synthesis
- Protein synthesis rates fluctuate a lot more whereas protein breakdown is more robust.

Question 20

Body nitrogen loss can occur through…

Answer 20

skin, feces, sweat

Question 21

What happens to amino acids once they are released into circulation and travel to skeletal muscle?

Answer 21

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.

Question 22

4 amino acids

Answer 22

Leucine, isoleucine, methionine, lysine