Protein

Question 0

In a 70kg person, what would the weight of body protein be?

Answer 0

11kg (16%)

Question 1

What are the functions of protein?

Answer 1

Catalysis (enzymes)
Transport (membrane transporters, haemoglobin)
Movement (actin, myosin)
Structure (collagen, keratin)

Question 2

What are the essential amino acids?

Answer 2

Valine, methionine, phenylalanine, isoleucine, leucine, tryptophan, threonine, lysine, (histidine), (arginine)

Question 3

What is the Kjeldahl method of protein analysis?

Answer 3

Protein heated with concentrated sulphuric acid- C and H oxidised, N reduced. Forms H2O, CO2, NH3. NH3 in solution (ammonium sulphate)- alkaline- distilled, condensed with dilute acid, titrated with sulphuric acid= quantitative measure of N

Question 4

How do we get the value of crude protein and why is this method used?

Answer 4

Value of nitrogen obtained in Kjeldahl method x 6.25

6.25 as body protein is 16% and 6.25 is reciprocal of .16

Question 5

What are the requirements for protein?

Answer 5

RNI- 45g per day (women)

- 55g per day (men)

Question 6

What are the average intakes of protein?

Answer 6

Male- 16% energy intake

Female- 17% energy intake

Question 7

What are the products of amino acid oxidation?

Answer 7

UREA + CO2 + H20 + ATP

Question 8

What is the Atwater factor for protein?

Answer 8

4kcal/g

Question 9

What amino acids are ketogenic?

Answer 9

Leucine

Lysine

Question 10

What amino acids are both glucogenic and ketogenic?

Answer 10

Cysteine
Isoleucine
Methionine
Phenylalanine
Tryptophan
Tyrosine

Question 11

Give two examples of transamination

Answer 11

Glutamate and pyruvate (catalysed by alanine transferase) forming 2-oxoglutarate and alanine

Glutamate and oxaloacetate (catalysed by aspartate transaminase) forming 2-oxoglutarate and aspartate

Question 12

What is protein quality?

Answer 12

A measure of the efficiency with which protein is utilised

Question 13

How is the protein efficiency ratio calculated?

Answer 13

Weight gain/protein intake

i.e. growth/intake

Question 14

What is net protein utilisation and how is it calculated?

Answer 14

The increase in nitrogen retention per unit increase in nitrogen balance

N Retained/N Intake

Final body protein- final body protein (protein free)/intake

Question 15

How is true N digestibility worked out?

Answer 15

Intake - (faeces of normal diet-faeces of protein-free diet)/intake

Question 16

How is the biological value calculated?

Answer 16

Intake- difference in urine- difference in faeces/I-F(normal) - I-F (protein free)
N retained/ N absorbed (I-F)

Question 17

How do you work out the amino acid score?

Answer 17

Mg aa per g test protein/ mg aa per g reference protein

Reference protein is a hypothetical mixture of the 8 essential amino acids

Question 18

How do you work out the chemical score of an amino acid?

Answer 18

Mg aa in 1g test protein/ mg aa in 1g egg protein

Question 19

What is the limiting acid in a protein and where are these found in the diet?

Answer 19

Amino acid present in smallest quantity in relation to requirement. Not always a limiting amino acid- usually in plant protein

Question 20

What is meant by the term mutual supplementation?

Answer 20

Combining dietary products that have different limiting amino acids to produce a meal with no limiting amino acids.
For example beans on toast. Lysine limited in cereals, methionine limited in legumes.

Question 21

What are the common dietary source for protein?

Answer 21

Meat, cereals, dairy