Carbohydrates + Nucleic Acids Flashcards
(21 cards)
Where does digestion of carbohydrates begin?
In the mouth
- salivary amylase
Digestion pathway of carbohydrates
Polysaccharides –> Oligosaccharide –> Disaccharide –> Monosaccharide
Role of salivary amylase
Break down starch into maltose
Role of pancreatic amylase
- in the small intestine
Breaks down polysaccharides into disaccharides, and eventually into monosaccharides
What are brush border enzymes?
Enzymes found on the apical surface of enterocytes
- they convert disaccharides to monosaccharides
What happens to monosaccharides inside enterocytes?
they exit into the bloodstream via GLUT2 transporter found on the basolateral membrane
Transporters for monosaccharide absorption into enterocytes
SGLT1 (glucose/galactose)
GLUT5 (fructose)
What are enterocytes?
Simple columnar epithelial cells lining inner surface of intestines
- intestinal cells
What is lactase deficiency?
Inability to digest lactose due to low lactase enzyme levels
2 main types of lactase deficiency
Primary
- genetic, age
Secondary
- due to GI disease
Function of sodium-glucose linked transporter 1 (SGLT1)
Responsible for absorbing glucose & galactose from the intestinal lumen into enterocytes
- Secondary active transport
- works by using sodium gradient created by Na⁺/K⁺ ATPase pump
Main causes of carbohydrate malabsorption
- Damage to lining of small intestine
- inflammatory bowel diseases
- celiac disease
- infections - Enzyme deficiencies
- lactase
- sucrase
Symptoms of carbohydrate malabsorption
bloating
flatulence (pété)
diarrhoea
abdominal cramps
How carbohydrate malabsorption cause diarrhoea?
Undigested carbohydrate draw water into intestines, increasing the osmotic load, leading to diarrhoea
End products of nucleic acid digestion
Nitrogenous bases
- adenine, guanine, cytosine, thymine
Pentose sugars
- ribose, deoxyribose
Phosphate ions
Where does nucleic acid digestion primarily occur?
In the small intestine
- pancreatic enzymes, intestinal enzymes
How are pentose sugars absorbed?
Passive simple diffusion across intestinal lining (villi epithelium)
How are phosphates absorbed?
Paracellular absorption
- through tight junctions between intestinal cells
Transcellular absorption
- active transport across intestinal membrane (main transporter is Na⁺-dependent phosphate transporter)
Why don’t nucleic acid malabsorption cause disease?
The body can effectively recycle the end products ;
End products can be reused to build new nucleic acids
Where does absorption of monosaccharides occur?
In the small intestine, primarily in jejunum
Digestive enzymes in pancreatic juice
Amylase
Protease (e.g. trypsin, chymotrypsin)
Lipase
Nuclease
