Hubi 3003 (MUN) - Chapter 1 Defintions and Questions (Part 2)

What are the two sources of dietary protein?

- Exogenous sources

- Endogenous sources

What are some examples of exogenous protein sources?

- Animal proteins

- Plant products (vegetables, seeds, legumes)

What are some examples of endogenous protein sources?

- Mucosal cells

- Digestive enzymes

- Glycoproteins

Step 1 of Protein Digestion

In this step of digestion, gastric cells release the hormone gastrin, which enters the blood and causes the release of gastric juices.

Step 2 of Protein Digestion

In this step of digestion, hydrochloric acid in the gastric juice denatures proteins and converts pepsinogen to pepsin, which begins hydrolyzing peptide bonds.

Step 3 of Protein Digestion

In this step of digestion, partially digested proteins enter the small intestine, triggering the release of secretin and cholecystokinin.

Step 4 of Protein Digestion

In this step of digestion, secretin and cholecystokinin trigger the pancreas to release pro-enzymes and bicarbonate into the intestine. The bicarbonate neutralizes chyme.

Step 5 of Proteins Digestion

In this step of digestion, pancreatic proenzymes are converted into active enzymes in the small intestine. These enzymes digest polypeptides into tripeptides, dipeptides, and free amino acids.

Step 6 of Protein Digestion

In this step of digestion, intestinal enzymes in the lumen of the small intestine and within mucosal cells complete protein digestion.

Why doesn't pepsin destroy the stomach lining?

The stomach lining is lined by a layer of mucus. Mucus is composed of mucin and long chains of carbohydrates, which creates a neutral pH near the stomach lining. Pepsin can only hydrolyze peptide bonds at a low pH. So, since the lining of mucus makes the pH neutral near the stomach lining, it protects the epithelial lining of the stomach from being hydrolyzed by pepsin.

What is one of the major proenzymes involved in protein digestion?

Trypsinogen, which gets converted into its active form, Trypsin.

What are the multiple proenzyme targets of trypsin?

- Trypsinogen

- Chymotrypsinogen

- Procarboxypeptidase A and B

- Proelastase

Endopeptidase

A type of enzyme that cleaves peptide bonds within a protein chain

What are some examples of endopeptidases?

- Trypsin

- Chymotrypsin

- Elastase

- Collagenase

Exopeptidase

A type of enzyme that hydrolyses the peptide bonds at the end of proteins to remove single amino acids.

What is an example of an exopeptidase?

Carboxypeptidase

What is the function of carboxypeptidase A?

This type of carboxypeptidase cleaves off any neutral amino acids from a peptide chain.

What is the function of carboxypeptidase B?

This type of carboxypeptidase cleaves off any basic amino acids from a peptide chain.

What are some examples of brush border peptidases?

- Aminopeptidases

- Dipeptidylaminopeptidases

- Tripeptidases

What is the function of aminopeptidases?

These brush border peptides cleave N-terminal amino acids from oligopeptides.

What is the function of dipeptidylaminopeptidases?

These brush border peptides hydrolyze dipeptides.

What is the function of tripeptidases?

These brush border peptides are used for selecting specific amino acids to hydrolyze.

Amino acid transport is stimulated by ____ and ____

Insulin and Protein Synthesis

Step 1 of Amino Acid Transport

In this step, sodium binds to the amino acid transporter.

Step 2 of Amino Acid Transport

In this step, sodium binding increases the carrier protein's affinity for the amino acid, which then binds to the carrier.

Step 3 of Amino Acid Transport

In this step, a sodium-amino acid cotransporter is created.

Step 4 of Amino Acid Transport

In this step, a conformational change in the complex occurs, resulting in the delivery of sodium and amino acids into the intestinal cells' cytosol.

Step 5 of Amino Acid Transport

In this step, sodium is pumped out of the cell by a Na-K ATPase channel.

Km is affected by ____ and _____

Hydrocarbon mass and the charge of the amino acid side chain

As hydrocarbon mass ____, amino acid affinity and transport ____

Increase

Which has a faster rate of transport: neutral, basic, or acidic amino acids?

Neutral amino acids

Which has a faster rate of transport: essential amino acids or non-essential amino acids?

Essential amino acids

Which amino acids are absorbed the fastest?

- Methionine

- Leucine

- Isoleucine

- Valine

Peptide transport is _____ than free amino acid transport.

Faster