Proteins

Question 1

What is the free amino acid pool

Answer 1

The amino acids in circulation and extracellular fluids

Question 2

What is the free amino acid protein composed of

Answer 2

Amino acids from food, amino acids degraded in tissues and amino acids metabolised in the liver

Question 3

Why does the amino acid pool exist

Answer 3

We do not store proteins so instead have a constant amino acid flux to be taken up into tissue and oxidised in muscle

Question 4

Where does protein digestion occur

Answer 4

Stomach, duodenum and small intestine

Question 5

What are endopeptidases

Answer 5

Enzymes that work in the centre of the molecule to produce smaller polypeptides

Question 6

What are example endopeptidases

Answer 6

Pepsin, Trypsin and chymotrypsin

Question 7

What are exopeptidases

Answer 7

Enzymes that work on the carboxylic or amine ends of the polypeptide to produce amino acids, dipeptides or tripeptides

Question 8

How are amino acids and small peptides absorbed into the enterocyte (intestinal absorptive cells)

Answer 8

Specific carrier proteins for different amino acids dependent on R group, with an indirect energy requirement linked to symport of Na+ (amino acids) or H+ (peptide) symport back out of enterocyte

Question 9

How are amino acids and peptides absorbed into the blood from the enterocyte

Answer 9

Intercellular peptidases hydrolyse some of absorbed peptides into amino acids and shorter peptides which are transported into the blood by basolateral transport down a concentration gradient via transport proteins (passive)

Question 10

What are non-essential amino acids

Answer 10

Dispensable amino acids that can be synthesised in animals so do not need to be consumed in diet

Question 11

How many non-essential amino acids are there

Answer 11

5

Question 12

Name the 5 non-essential amino acids

Answer 12

Alanine, Asparagine, aspartate, glutamate, serine

Question 13

What are essential amino acids

Answer 13

Indispensable amino acids that cannot by synthesised in animals so must be consumed in the diet

Question 14

How many essential amino acids are there

Answer 14

9

Question 15

What are the 9 essential amino acids

Answer 15

Methionine, tryptophan, threonine, histidine, isoleucine, leucine, lysine, valine, phenylalanine

Question 16

Which essential amino acid triggers protein synthesis

Answer 16

Leucine

Question 17

What are conditionally essential amino acids

Answer 17

Amino acids derived through metabolism of other amino acids so may be needed in the diet if these pre-cursors are not available

Question 18

How many conditionally essential amino acids are there

Answer 18

6

Question 19

Name the conditionally essential amino acids

Answer 19

Cysteine, tyrosine, arginine, proline, glycine, glutamine

Question 20

What does protein quality determine

Answer 20

How large offspring will grow and maintainance of adult health

Question 21

What 3 factors influence protein quality

Answer 21

Storage, digestibility and amino acid composition

Question 22

What is digestibility a measure of

Answer 22

The amount of AA absorbed from a given protein intake

Question 23

What is digestibility dependent on

Answer 23

Protein source and other foods eaten with

Question 24

Does animal or plant protein have a higher digestibility

Answer 24

Animal

Question 25

What is ‘high quality protein’

Answer 25

Protein that contains all essential AA in relatively the same proportions and amounts required by humans

Question 26

What 5 ways is protein quality assessed

Answer 26

• chemical score
• biological value
• net protein utilisation
• protein digestibility-corrected amino acid scores (PDCAAS)
• Digestible indispensable amino acid score (DIAAS)

Question 27

What is the chemical score of protein quality

Answer 27

The amino acid score based on essential amino acid content

Question 28

How is the chemical score calculated

Answer 28

By comparison of a test protein and a high quality, complete (whole-egg) protein
Calculated by the ratio of a gram of a limiting amino acid in a test diet to the same amount of corresponding amino acid in a reference diet (egg or milk) multiplied by 100

Question 29

What is the biological value

Answer 29

The measure of protein absorbed that becomes incorporated into the proteins of an organism (storage and loss of nitrogen measured)

Question 30

What is the net protein utilisation

Answer 30

Percentage of protein eaten that is retained in the body

Question 31

What is the difference between biological value and net protein utilisation

Answer 31

Biological value is calculated from nitrogen absorbed while net protein is from nitrogen ingested

Question 32

How is net protein utilisation calculated

Answer 32

Retained nitrogen/ nitrogen intake x 100

Question 33

What is PDCAAS

Answer 33

A type of chemical score out 1 which is derived from the ratio of a limiting amino acid in a test protein to same AA in a reference amino acid and corrected for true faecal digestibility

Question 34

Why is there a recommendation to combine different plant proteins

Answer 34

Often limited in some essential AA and combination is greater than protein quality of individual components

Question 35

How many kcal/g is in protein

Answer 35

4kcal/g

Question 36

What factors do protein requirements depend on

Answer 36

Age, gender, pregnancy, lactation, health status, stress

Question 37

What is the RDA for protein for adults

Answer 37

0.75g/kg per day