Lecture 14

Question 1

What are the functions of proteins?

Answer 1

• Building materials for growth and maintenance
• Enzymes
• Hormones
• Regulators of fluid balance
• Acid-base regulators
• Transporters
• Antibodies
• Source of energy

Question 2

What are the 24 specific organic compounds required?

Answer 2

9 essential amino acids
2 fatty acids
13 vitamins

Question 3

What are the 9 essential amino acids?

Answer 3

His, ile, leu, lys, met, phe, thr, trp, val

Question 4

Why are some amino acids non-essential?

Answer 4

Derived from other metabolic products

Question 5

What is the recommended intake of protein?

Answer 5

15-25% of total energy intake

0.84g/kg for males and 0.75g/kg for females

Question 6

What are the two factors that influence protein quality?

Answer 6

1) Digestibility: depends on source and other foods eaten with it. High for animal, less for plant.
2) Amino acid compositions: dietary protein must supply at least 9EAA plus enough N containing amino groups and energy for synthesis of others.

Question 7

What happens to protein in the mouth?

Answer 7

Chewing and crushing moisten protein-rich foods and mix them with saliva to be swallowed.

Question 8

What happens to protein in the stomach?

Answer 8

HCl uncoils and denatures protein strands and activates stomach enzymes (pepsinogen to pepsin):
Protein is broken down to smaller polypeptides by pepsin.

Question 9

What happens to polypeptides in the small intestines?

Answer 9

Polypeptides get broken down to tripeptides and dipeptides and amino acids by pancreatic endopeptidases (trypsin, chymotrypsin, elastase). Intestinal tripeptidases and dipeptidases hydrolyse peptides into amino acids that are absorbed.

Question 10

What happens to trypsinogen in the pancreas?

Answer 10

Inactive trypsinogen is converted to active trypsin by enteropeptidase

Question 11

What are the effects of trypsin?

Answer 11

• Inhibits trypsinogen synthesis
• Cleaves peptide bonds
• Converts pancreatic procarboxypeptidases to carboxypeptidases
• Converts chymotrypsinogen to chymotrypsin and elastase

Question 12

What exopeptidases are secreted in pancreatic juice?

Answer 12

Carboxypeptidase A and B

Question 13

What are the transporters of the small intestine that aid in transport of proteins?

Answer 13

• 3 Na+ linked amino acid transporters
• H+ linked peptide transporter (di and tripeptides)
• These symports are powered by an Na+/K+ antiport
• Small peptides are carried intact across the cell by transcytosis

Question 14

What percentage of protein digestion is complete when the jejunum is reached?

Answer 14

80%

Question 15

What is meant by nitrogen balance?

Answer 15

Nitrogen intake = rate of nitrogen expenditure

Question 16

What is nitrogen taken into the body largely as?

Answer 16

Amino acids

Question 17

What are the three states of N balance?

Answer 17

Negative, equilibrium, positive

Question 18

What is meant by negative nitrogen balance?

Answer 18

Net loss of N

Degradation exceeds synthesis

Question 19

What are the factors that can cause negative nitrogen balance?

Answer 19

• Decreased protein intake
• Starvation or reduced GI function
• Injury, trauma, surgical op
• Illness, infection or burns
• Some post-op conditions
• Many cancers
• Lactation

Question 20

How can negative N balance kill people?

Answer 20

Not enough protein to repair burns and other tissue damage

Question 21

What is meant positive nitrogen balance?

Answer 21

Net gain of N

Synthesis exceeds degradation

Question 22

What are the factors that can cause positive N balance?

Answer 22

• Increased protein intake
• Growth
• Pregnancy
• Recovery from illness or trauma

Question 23

How can an increase or decrease in protein intake be measured as?

Answer 23

Increase or decrease in protein intake causes a corresponding increase or decrease in oxidation and hence N losses

Question 24

What is the equation relating N and protein?

Answer 24

g N x 6.25 = g protein

Question 25

What are obligatory protein losses?

Answer 25

Even when no protein is consumed, there are obligatory urinary N losses of 3g N per day.

Question 26

What is the minimum intake of protein?

Answer 26

30-50 g of high quality protein needed to maintain N equilibrium

Question 27

What happens to amino acids in excess of the body’s requirements?

Answer 27

Cannot be readily stored so are deaminated to give ammonia and residual carbon skeletons. Ammonia is toxic so is carefully detoxified to urea.

Question 28

What are the compounds in which N is stored for excreted?

Answer 28

• Urea
• Uric acid
• Creatinine

Question 29

What happens to the carbon skeletons resulting from deamination of amino acids?

Answer 29

Either oxidised to produce energy or used in gluconeogenesis or lipogenesis

Question 30

What are the two protein deficiencies?

Answer 30

Kwashiokor and Marasmus

Question 31

What is Kwashiorkor?

Answer 31

Acute shortage of particularly protein. Calorie intake is usually adequate and obtained almost solely as carbs from starchy foods.

Question 32

What are the symptoms of Kwashiorkor?

Answer 32

• Some wasting in limbs
• Protruding belly (edema around liver)
• Some weight loss
• Enlarged fatty liver
• Loss of appetite
• Hair is sparse, thin, dry
• Skin lesions

Question 33

What is Marasmus?

Answer 33

Frank starvation, hunger and grossly inadequate diet. Also known as protein calorie malnutrition. Chronic condition.

Question 34

What are the symptoms of Marasmus?

Answer 34

• Severe chronic weight loss
• No detectable edema
• Difficult to refeed because no appetite
• Hair is sparse, thin, dry

Question 35

What is a primary cause of protein deficiency in non third-world countries?

Answer 35

Alcoholism