Lecture 4 - Proteins

Question 1

What is EAR?

Answer 1

estimated average requirment - where the intake at which the risk of inadequacy is 50 %

Question 2

What is RDA?

Answer 2

Recommended dietary allowance - intake at which the risk of inadequacy is 2-3%

Question 3

What is AI?

Answer 3

Adequate intake - does not bear a predictable relation to the EAR and RDA. Based on the estimate of nutrient intake in healthy people.

Question 4

What is UL?

Answer 4

Tolerable upper level intake - intake above the UL, higher risk of adverse effects.

Question 5

What is the goal of having protein in the diet?

Answer 5

To replace the amino acids that are degraded in the body.

Question 6

Unlike fats and CHO, there is a …… for protein in the diet

Answer 6

requirement

Question 7

Functions of glycine?

Answer 7

1. ) aminolaevulinic acid, a key intermediate in heme synthesis is made from glycine and succinyl CoA
2. ) Required for detoxification reactions in the liver
3. ) Principal inhibitory transmitter in the brain stem and spinal cord
4. ) Occurs at every 3rd AA residue in collagen (the most abundant protein in the body)

Question 8

Function of tryptophan?

Answer 8

Precursor of the NT serotonin

Question 9

Function of Histidine?

Answer 9

decarboxylated to histamine which is used in an immune response or the physiological function of teh gut.

Question 10

Function of arginine?

Answer 10

precursor of NO and creatine

Question 11

Function of lysine ?

Answer 11

lysine residue interacts with glutamine when factor x111a converts low tensile fibrin polymer into a high tensile strength clot.

Question 12

Functions of glutamine?

Answer 12

1. ) substrate for protein synthesis
2. ) contols acid base balance
3. ) Substrate for hepatic ureagenesis
4. ) Substrate for hepatic gluconeogenesis
5. ) Fuel for intestinal enterocytes
6. ) Ammonia scavenger
7. ) Substrate for citrulline and arginine synthesis
8. ) Nitrogen donor
9. )Nitrogen transport
10. ) Stimulates glycogen syntheses
11. ) Arginine NO metabolism

Question 13

What are the determinants of the nutritional quality of protein?

Answer 13

1. ) content of indispensable AAs

2. ) extent to which the indispensable AAs are available to host metabolism

Question 14

What are the classes of protein?

Answer 14

1st class - animal proteins

2nd class - plant proteins

Question 15

How do we measure the quality of proteins?

Answer 15

PDCAAS - based on the profile of AAs and digestibility of the protein.

Question 16

PDCAAS of different foods (Egg, milk, beef/chicken/fish, gelatin, soybean, kidney beans, whole wheat bread)?

Answer 16

Egg - 1
Milk - 1
Beef/fish/poultry - 0.82-0.92
gelatin - 0.08 - totally deficient in tryptophan and deficient in isoleucine, threonine

soybean - 1
kidney beans - 0.68 - deficient in methionine but rich in lysine
whole weat bread - 0.40 - deficient in lysine but rich in methionine

Question 17

What if nitrogen intake is more than excretion or the oppsoite?

Answer 17

more than excretion - tissue gorwth and total body protein increases

less than excretion - total body protein decreases

Question 18

how much protein lost in fracture of femur, muscle wound, 35 % burns, gastrectomy, typhoid fever?

Answer 18

fracture of femur - 900 g
muscle wound - 1350-1900 g
35 % burns - 1400-1650 g
gastrectomy - 645-850 g
typhoid fever - 685 g

Question 19

What are the body requirements for protein?

Answer 19

usually 0.8g per kg for adults and for athletes 1 g /kg

children - 2g per kg per day

Question 20

whatis kwashiorkor?

Answer 20

Pure protein deficiency in children

Question 21

what is maramus?

Answer 21

energy deficiency where there is a reduced number of T lymphocytes and so there are defects in the generation of phagocytic cells and production of immunoglobulins. Many die from secondary infectin rather than starvation.

Question 22

Where does the most common protein energy malabsorption occur in the USA?

Answer 22

In hospitals after a response to infection, trauma or surgery. There is accelerated rate of lipolysis, proteolysis and gluconeogenesis. The net result is that there is low serum albumin or decreased cellular immunity.

Question 23

What can increased protein intake result in?

Answer 23

increased protein breakdown products like urea. Since there is more urea it has to be eliminated by the kidneys. So high protein diets increase water loss and can cause problems if the kidneys cannot concentrate urine.

Question 24

What is the problem with taking supplements of one kind of amino acid like arginine?

Answer 24

They all use the same transport systems so when one amino acid is taken up, another amino acid will have its absorption slowed down. This is a problem for people who use supplements like arginine. Where it shares the transport system with lysine and it upsets the AA balance in the body.

Question 25

What can cause a protein allergy?

Answer 25

When a protein in the diet is absorbed without being fully digested.

Question 26

What are the essential amino acids?

Answer 26

9 of them

1. ) Histidine
2. ) Esoleucine
3. ) Leucine
4. ) Lysine
5. ) Methionine
6. ) Phenylalanine
7. ) Threonine
8. ) Tryptophan
9. ) Valine

In infants arginine is also essential

Question 27

What are the essential precursors and for what essential amino acids?

Answer 27

Cysteine - methionine (precursor)

Tyrosine - phenylalanine (precursor)

Question 28

What are the non essential amino acids?

Answer 28

Alanine
Aspartate
Glutamate

Question 29

What are the semi-essential amino acids?

Answer 29

Arginine
Asparagine
Glutamine 
Glycine 
Proline
Serine 

Alaine comes from pyruvate
Aspartate from oxaloacetate
Glutamate from alpha-KG