Lecture 13: Protein nutrition, digestion and absorption Flashcards
What is the role of proteins in the body?
Immune system Hormones Structural and mechanical Transport Fluid balance Acid-base balance Energy Channels and pumps Enzymes
Describe the constituents of a amino acid;
Side group (variable)
Acid group
Amino group
How many amino acids are there?
20 amino acids
9 of which are essential and must be obtained from foods i.e animal products, fish, soy products, quinoa
What sort of bonds to proteins have?
Peptide bonds
Di and tri-peptide
Whats important about protein folding?
Tertiary folding helps determine structure and function
Any variation in amino acids can change folding and thus function
i.e sickle cell anemia
Whats the RDI and AMDR of protein?
RDI; 0.84g/kg/day males and 0.75g/kg/day females
AMDR; 15-25% of energy intake
Whats the importance of protein quality?
Digestibility; Animal vs plant protein
Amino acid composition; limiting amino acid
That is if a food lacks one of the amino acids then this may limit how much of a protein can be made.
If someone is strict vegeterian or vegan, how can they ensure they get enough of the amino acids?
They can work out which foods are complementary for the amino acids and make sure they are getting all the essentials and not limiting
Prior to eating what can aide protein digestion?
Cooking
- Unfolds, denatures proteins
- Softens food
- Easier to chew and swallow
- Safer to eat
Describe steps 1-2 of protein digestion;
1) The mouth, Mechanical digestion, chewing and crushing
2) Saliva, lubricates foods
Describe how protein is digested in the stomach (step 3)
Acid activates pepsinogen to pepsin which breaks down large proteins into polypeptides and amino acids
Describe steps 4-5 of protein digestion
Polypeptides and amino acids enter the small intestine, the pancreas has released;
Trypsinogen
Chymotrpsinogen
Procarboxypepetidase
Enteropeptidase on the lumen surface of enterocytes activates trypsinogen-> trypsin (breaksdown peptide bonds, inhibits trypsinogen synthesis and converts;
Chymotrpsinogen -> chymotrypsin. (Breaks peptide bonds).
Procarboxypeptidase -> Carboxypeptidase. (Breaks apart peptide bonds at the carboyxl end)
Describe the further breakdown of polypeptides in the small intestine;
Luminal surface of enterocytes also contains enzymes;
- Amino peptidase
- Dipeptidase
- Tripeptidase
These all release AA which are absorbed by the SI
How are AA transported across the apical surface of the enterocytes?
Primary active transport with Na+ (ATP)
Secondary active transport with Na+ (gradient, not ATP)
Di/tri-peptides with Na+ secondary active transport.
How do AA and di/tri-peptides enter circulation from enterocytes?
Di/Tri-peptides are broken down to AA
AA then undergo facilitated diffusion via various transporters
Na/K ATPase create the gradient.
