Overview
What bond links two amino acids together?
Peptide bond
Where is enterokinase secreted from?
Brush border (the microvilli)
Where does most protein ABSORPTION take place?
Duodenum and jejunum
What is located on the basolateral membrane that initiates free AA absorption?
Na/K pump
What is the form in which the majority of proteins are absorbed into the cell? (Not the bloodstream)
Small peptides
(Mostly di and tripeptides)
Where does protein digestion begin, and what enzyme is responsible?
Begins in the stomach with pepsin
The pancreas produces protein zymogens that are responsible for what percentage of protein digestion?
50%
What can happen if you absorb a whole protein?
When is a time in your or an animal's life when absorbing whole protein is essential?
Allergic reaction
Neonate (Colostrum)
What process, discussed previously, is similar to free AA absorption?
Monosaccharide absorption
When these small peptides are absorbed into the cell what hydrolyzes them into amino acids?
Cytosolic peptidases
Where are zymogens created and stored? Why are they stored as zymogens?
Pancreas
Zymogen is the inactive version of the enzyme. If stored as the active form, it would break down the cell creating and storing it.
What are the three zymogens that the pancreas synthesizes and secretes?
Trypsinogen
Chymotrypsinogen
Procarboxypeptidase
What are the two fates of proteins once broken down(digested)?
1. Most (99%) absorbed into bloodstream
2. Remain in the enterocyte to be used for the synthesis of new cells and enzymes
What type of transport is free amino acid absorption? Why?
Active
Na/K pump requires ATP
What molecule is driving this gradient-driven transport?
Hydrogen
Explain the difference between an endopeptidases and an exopeptidases.
Endopeptidases: Enzyme that breaks peptide bonds on the internal portion of an amino acid chain. (NOT next to the N and C terminus)
Exopeptidases: Enzyme that breaks peptide bonds on the end of an amino acid chain (Next to the N and C terminus)
Fill in the blanks in this statement.
Duodenum recognizes _______ and secretes ____ which stimulates the pancreas to secrete protein digesting enzymes in their _____ state.
Proteins
CCK
inactive
Absorption of small peptides is generated via an H+ gradient and requires pH in the lumen to ______ than the pH within the enterocyte.
Lower
Can free amino acids be absorbed into the blood?
YES
Name two ways free amino acids are absorbed via the basolateral membrane.
Diffusion and Na-independent carriers (facilitated)
Explain the process of denaturing.
Process where protein uncoils and loses its shape. Therefore, it loses its ability to function.
List the enzymes repsonsible for the activation of the following pancreatic zymogens.
1. Trypsinogen --> Trypsin
2. Chymotrypsinogen --> Chymotrypsin
3. Procarboxypeptidase --> Carboxypeptidase
1. Enterokinase (Enteropeptidase) and Trypsin
2. Trypsin
3. Trypsin
Are free amino acids and small peptides absorbed the same way? Are both absorbed into the bloodstream?
NO and NO
ONLY free amino acids are absorbed into the blood.
(We will discuss differences in transport.)
Draw free amino acid absorption process on the board.
see notes
Draw small peptide absorption on the board.
see notes