Lecture 14 Flashcards
What are the functions of proteins?
- Building materials for growth and maintenance
- Enzymes
- Hormones
- Regulators of fluid balance
- Acid-base regulators
- Transporters
- Antibodies
- Source of energy
What are the 24 specific organic compounds required?
9 essential amino acids
2 fatty acids
13 vitamins
What are the 9 essential amino acids?
His, ile, leu, lys, met, phe, thr, trp, val
Why are some amino acids non-essential?
Derived from other metabolic products
What is the recommended intake of protein?
15-25% of total energy intake
0.84g/kg for males and 0.75g/kg for females
What are the two factors that influence protein quality?
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.
What happens to protein in the mouth?
Chewing and crushing moisten protein-rich foods and mix them with saliva to be swallowed.
What happens to protein in the stomach?
HCl uncoils and denatures protein strands and activates stomach enzymes (pepsinogen to pepsin):
Protein is broken down to smaller polypeptides by pepsin.
What happens to polypeptides in the small intestines?
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.
What happens to trypsinogen in the pancreas?
Inactive trypsinogen is converted to active trypsin by enteropeptidase
What are the effects of trypsin?
- Inhibits trypsinogen synthesis
- Cleaves peptide bonds
- Converts pancreatic procarboxypeptidases to carboxypeptidases
- Converts chymotrypsinogen to chymotrypsin and elastase
What exopeptidases are secreted in pancreatic juice?
Carboxypeptidase A and B
What are the transporters of the small intestine that aid in transport of proteins?
- 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
What percentage of protein digestion is complete when the jejunum is reached?
80%
What is meant by nitrogen balance?
Nitrogen intake = rate of nitrogen expenditure
What is nitrogen taken into the body largely as?
Amino acids
What are the three states of N balance?
Negative, equilibrium, positive
What is meant by negative nitrogen balance?
Net loss of N
Degradation exceeds synthesis
What are the factors that can cause negative nitrogen balance?
- Decreased protein intake
- Starvation or reduced GI function
- Injury, trauma, surgical op
- Illness, infection or burns
- Some post-op conditions
- Many cancers
- Lactation
How can negative N balance kill people?
Not enough protein to repair burns and other tissue damage
What is meant positive nitrogen balance?
Net gain of N
Synthesis exceeds degradation
What are the factors that can cause positive N balance?
- Increased protein intake
- Growth
- Pregnancy
- Recovery from illness or trauma
How can an increase or decrease in protein intake be measured as?
Increase or decrease in protein intake causes a corresponding increase or decrease in oxidation and hence N losses
What is the equation relating N and protein?
g N x 6.25 = g protein
What are obligatory protein losses?
Even when no protein is consumed, there are obligatory urinary N losses of 3g N per day.
What is the minimum intake of protein?
30-50 g of high quality protein needed to maintain N equilibrium
What happens to amino acids in excess of the body’s requirements?
Cannot be readily stored so are deaminated to give ammonia and residual carbon skeletons. Ammonia is toxic so is carefully detoxified to urea.
What are the compounds in which N is stored for excreted?
- Urea
- Uric acid
- Creatinine
What happens to the carbon skeletons resulting from deamination of amino acids?
Either oxidised to produce energy or used in gluconeogenesis or lipogenesis
What are the two protein deficiencies?
Kwashiokor and Marasmus
What is Kwashiorkor?
Acute shortage of particularly protein. Calorie intake is usually adequate and obtained almost solely as carbs from starchy foods.
What are the symptoms of Kwashiorkor?
- 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
What is Marasmus?
Frank starvation, hunger and grossly inadequate diet. Also known as protein calorie malnutrition. Chronic condition.
What are the symptoms of Marasmus?
- Severe chronic weight loss
- No detectable edema
- Difficult to refeed because no appetite
- Hair is sparse, thin, dry
What is a primary cause of protein deficiency in non third-world countries?
Alcoholism
