Peptides - covalent
bond links AA together. This is called a peptide bond - between the COOH of AA1
and the NH3 of AA2
di- = 2 AA linked together
peptide = usually 3 - 8 AA long
poly- = > 8 AA long
Function: dependent
on AA composition
Disulfide Bond: important for maintaining protein structure
Terminal Ends
Glycine = Amino terminal AA
Cysteine = Carboxyl terminal AA
Structure
1o =
the AA sequence of a protein
2o =
involves bonding with disulfide bonds
3o =
3-D shape - caused by:
1. Hydrophobic AA
(Neutral & Aromatic AA) go to inside
2. Hydrophilic AA
(Acid/Base) go to outside
¶ Protein function dependant on 3-D structure, 3-D
structure dependent on AA sequence, Þ AA determines function
Denature = irreversible unfolding of a protein
¯ 3-D structure Þ ¯
activity
Methods:
1. Heat
2. Chemical
3. ¯ pH
(HCl)
Protein
Digestion in the Monogastric
Goal: break
protein down to AA for absorption
Stomach
HCl =
parietal cells = ¯ pH Þ denature protein; activates pepsinogen to pepsin.
Pepsinogen = chief cells - proteolytic enzyme -
endopeptidase (cleaves peptide bond inside AA sequence).
Duodenum
Pancreatic enzymes - Trypsin & Chymotrypsin
(Endo) and Carboxypeptidase (Exo)
Duodenal enzymes (mucosal cells) - enterokinase amino
peptidase, dipeptidase
Once Endo- enzymes
cleave to poly-peptides, they "stop" and Exo starts.
¶ Enterkinase activates Trypsin
Absorption
Carrier system! There are at least 5. These
systems are specific for certain AA or types of AA (ie. Basic, Acidic) and are
used to get AA across the mucosal cell membrane.
If Basic is a carrier system, then both ARG and
LYS compete for absorption, so if a diet is high in ARG and LYS is adequate,
LYS may not be absorbed at a rate which is required, and although the diet
shows enough LYS, the body is not absorbing adequate amounts.