Lecture 14

Question 1

What are the roles of proteins?

Answer 1

1. Building material.
2. Hormones.
3. Enzymes - digestive.
4. Immune function.
5. Fluid balance.
6. Transporters.
7. Antibodies.
8. Source of energy.

Question 2

What are proteins made of?

Answer 2

Amino acids: nonessential amino acids and essential amino acids.

There is a: acid group, amino group, alpha hydrogen and side group (R group).

Question 3

What are the 9 essential amino acids?

Answer 3

1. Histidine (his)
2. Isoleucine (ile)
3. Leucine (leu)
4. Lysine (lys)
5. Methionine (met)
6. Phenylalanine (phe)
7. Threonine (thr)
8. Tryptophan (trp)
9. Valine (val)

Question 4

What are essential amino acids?

Answer 4

Amino acids that we cannot make in our body or derive from other metabolic products; thus we have to get them from our diet.

Question 5

What are proteins?

Answer 5

Polypeptide - amino acids in a long chain.

Question 6

What happens when sequencing of proteins goes wrong in Haemoglobin molecules?

Answer 6

We get sickle-cell anaemia. This is where the blood cells become sickle-shaped. Reduction in the capacity for red blood cells to carry oxygen around their body.

Question 7

What is the RDI for protein?

Answer 7

Total = 12-25% of energy intake.

Male = 0.84g/kg/day
Female = 0.75g/kg/day

Question 8

What is protein quality?

Answer 8

High quality proteins.
Digestibility - animals vs plants.
Amino acid composition - limiting amino acid.

Question 9

Describe digestion of protein in the mouth?

Answer 9

Chewing and crushing moisten the protein-rich foods mixed with saliva.

Question 10

Describe digestion of protein in the stomach?

Answer 10

HCl denatures protein strands and it activates pepsinogen (pepsinogen
-> pepsin). Pepsin and HCl then turn protein into smaller polypeptides.

Question 11

Describe digestion of protein in the SI?

Answer 11

When the pancreas secretes enzymes in the precursor form: endopeptidases (trypsin, chymotrypsin and elastase).

Polypeptides -> (endopeptidases) tripeptides, dipeptides and amino acids.

SI produces enzymes that chop the peptides into smaller amino acids.

Peptides -> (tripeptidases, dipeptidases, aminopeptidases) amino acids.

Question 12

What is the key step in digestion of proteins?

Answer 12

Membrane-bound enteropeptidase converting inactive trypsinogen to trypsin. This will then allow trypsin to stop production of trypsinogen and to allow the enteropeptidase to activate other proteases. Thus allowing for further breakdown of polypeptides.

Question 13

Describe absorption of proteins?

Answer 13

There are 3 Na+ linked amino-acid transporters and H+ linked peptide transporters that transport only di and tripeptides. These are powered by Na+/K+ anti porters. The amino acids enter the blood by facilitated diffusion carriers and by diffusion.

Question 14

What happens to amino acids once taken up by the liver?

Answer 14

We are constantly turning over protein. The amount of enzymes secreted into digestive system, is reabsorbed back into the body. The amino acids -> nitrogen pool -> tissue protein. The bi-products are:

NH3 (ammonia), Urea. Don’t want the bi-products in our body.

Question 15

Describe nitrogen balance?

Answer 15

The amount of protein we consume we excrete. Very little faecal loss of nitrogen, majority excreted via the urine.

Question 16

Why is Nitrogen balance important?

Answer 16

Conditions where people go into positive or negative nitrogen balance.

Question 17

How do you calculate nitrogen balance?

Answer 17

Nitrogen intake = nitrogen expenditure.

g Nitrogen x 6.25 = 1g protein.

Question 18

What are factors that cause negative nitrogen balance?

Answer 18

1. Decreased protein intake (over the short-term).
2. Starvation or reduced gastrointestinal function.
3. Injury, trauma or surgical operation.
4. Illness or infection or burns (up to 70g/d).
5. Some post-operative conditions.
6. Many cancers.
7. Lactation.

Question 19

What are factors that cause positive nitrogen balance?

Answer 19

1. Increased protein intake (over short term).
2. Growth.
3. Pregnancy.
4. Recovery from illness or trauma.

Question 20

What is the percentage of total deaths of children under the age of 5 in the world associated with malnutrition?

Answer 20

35%.

Question 21

What is the cause of Marasmus?

Answer 21

Severe deprivation or impaired absorption of protein, energy, vitamins and minerals.

Question 22

What are the symptoms of marasmus?

Answer 22

1. Severe weight loss.
2. Severe muscle wasting, with no body fat.
3. Growth:

Question 23

What causes Kwashiorkor?

Answer 23

Inadequate protein intake or more commonly infections.

Question 24

What is the incidence age of Kwashiorkor?

Answer 24

Older infants and young children (1-3yr).

Question 25

What are the symptoms of Kwashiorkor?

Answer 25

1. Some weight loss.
2. Some muscle wasting, with retention of some body fat.
3. Growth: 60-80% weight-for-age
4. Edema.
5. Enlarged fatty liver.
6. Apathy, misery, irritability, sadness.
7. Loss of appetite.
8. Hair is dry and brittle; easily pulled out; changes colour; becomes straight.
9. Skin develops lesions.