Lecture 28 Flashcards
(37 cards)
How are amino acids consumed in the diet?
As proteins
What does protein digestion involve?
Hydrolysis of peptide bonds by different proteases / peptidases
What are the two types of peptidases?
Endopeptidase and exopeptidase
What do endopeptidases do?
Attack peptide bonds within the protein polymer
What do exopeptidase do?
Attack the last peptide bond near the end of the protein polymer
How do endopeptidases work?
Different endopeptidases act sequentially to produce smaller peptides each round
What is endopeptidase specificity determined by?
Adjacent amino acid side chain in the protein substrate
Where do carboxypeptidases cut?
Near the carboxyl-terminal residue
Where do aminopeptidases cut?
Near the amino-terminal residue
What are proteases produced as?
Zymogens
What are zymogens?
Inactive precursors to the peptidase / protease
Why are zymogens needed?
To prevent peptidase activity before reaching the GIT and breaking down the proteins within cells
How are zymogens activated?
Through cleavage of peptides from their structure
What are the two forms of zymogen activation?
Autolytic activation and catalytic activation
What is autolytic activation?
Change in chemical composition (e.g. pH) causing self activation (cleavage)
What is catalytic activation?
An active form acting as a catalyst to activate the inactive form
How are di- and tri-peptides absorbed into the SI?
By co-transport with H+ ions via a membrane transporter
How are amino acids absorbed into the SI?
Through an amino/Na+ cotransporter as amino acids are moving against their concentration gradient
What happens to absorbed di- and tri-peptides?
They are further digested into individual amino acids by cytoplasmic peptidases
How do amino acids enter the blood?
Through a facilitative transporter into the interstitial fluid and then to the blood
What are the different Na+ dependent carriers for amino acids across the SI?
Neutral AA, proline & hydroxyproline, acidic AA and basic AA & cysteine
What is deamination of amino acids?
The process of removing an amino group
What does deamination of amino acids generate?
A carbon skeleton and a free amino group
What can a carbon skeleton be used for?
Energy capture
