Lecture 21: Digestion and absorption of proteins and nucleic acids Flashcards
Why is adequate amounts of protein needed in the diet?
- Supplies amino acids with which our cell used to make body proteins
- Is a source of nitrogen for the biosynthesis of essential molecules e.g purines, pyrimidine and haem
- Carbon skeletons can be used as fuel
What is the role of gastrointestinal hormones in the regulation of digestive enzyme secretion?
Gastrointestinal hormones control the secretion of digestive enzymes
- ensure the digestive enzymes are only secreted when there is food to digest
e. g gastrin - stomach = stimulates secretion of gastric juices
e. g secretin - duodenum = stimulates the secretion of alkaline bile and pancreatic fluids
What are the essential amino acids?
Proteins that we CANNOT make
e.g leucine, lysine, valine etc
How are amino acids absorbed across the intestinal epithelium?
Amino acids are transported across the luminal membrane of intestinal epithelial cells by Na+ dependant pathways
Why are digestive enzymes secreted as inactive precursors?
How are they activated?
- Digestive enzymes are secreted as zymogens which protect tissues against ‘self digestion’
- Zymogens are activated in the stomach and small intestine by proteolytic cleavage
- Stomach and small intestine are protected against the action of the activated proteases by mucous
What are the two stages of protein digestion?
Endopeptidases: attacks peptide bonds WITHIN the peptide chain
e.g pepsine, trypsin and chymotrypsin
Exopeptidase: attack peptides bonds at END of peptide chain. There are two types”
- Aminopeptidases
- Carboxypeptidases
What are 3 diseases caused by malabsorption?
Kwashiokhor = inefficient protein in diet
Cystic fibrosis = CF patients have abnormally thick mucous secretions which block the movement of pancreatic enzymes
Coeliac disease = is an autoimmune disorder of the small intestine which disrupts the function of the intestinal mucosa
How are nucleic acids digested?
Nucleic acids such as DNA and RNA are hydrolysed in the stomach
- sugar phosphate backbone is cleaved by acid hydrolysis
Pancreatic nucleases hydrolyses fragmented DNA into nucleotides
Nucleotides are further broken down into nucleosides by phosphatase enzymes and are transported across the intestinal epithelia via a Na+ dependent transport system
What enzymes category are responsible for the hydrolyse of proteins?
PROTEASES which hydrolyse peptide bonds
e. g endopeptidases
e. g exopeptidases
Proteases are secreted in their inactive forms = zymogens and are activated by cleavage of peptides from their structure
