12.8 digestion and absorbtion Flashcards
Polypeptides & proteins are hydrolysed into amino acids by
proteases.
Carbohydrates are hydrolysed into simple sugars by
carbohydrases.
Fats are hydrolysed into glycerol, fatty acids and monoglycerides , by
lipases
Salivary glands enzyme?
Salivary Amylase
Enzyme in Stomach
Endopeptidases (e.g. Pepsin) & Exopeptidases
Enzymes in the pancreas
Pancreatic Amylase, Lipases & Exopeptidases
Enzymes in illeum
Membrane bound Dipeptidases & Dissacharidases
Describe the breakdown of starch
- Food enters the mouth and is broken up by teeth (mechanical digestion), then mixed with saliva.
- Salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion).
- In the stomach this salivary amylase is denatured due to acidic pH
- In the small intestine, pancreatic amylase continues to hydrolyse the starch to maltose.
- Maltose is then hydrolysed to glucose by maltase enzymes in the membrane of the epithelial cells. The glucose can then be absorbed.
- In mammals, cellulose is NOT hydrolysed, as the enzyme cellulase is not produced.
Amylase location and product of reaction
- Synthesised and secreted from Salivary Glands and Pancrea
-Starch to Maltose
Maltase location and product of reaction
within membrane of epithelium cell membrane of ileum
Maltose to Glucose
Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (4)
Salivary / Pancreatic amylase hydrolyses starch into maltose;
By hydrolysing glycosidic bonds;
Maltose is hydrolysed into glucose;
By maltase;
Describe how glucose is absorbed from the ilium into the blood [5]
Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump);
This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
(Cotransporter proteins have 2 binding sites complementary to Na+ and glucose. Only when both molecules bind will the molecules be moved across the membrane)
Na+ and glucose enter by facilitated diffusion using (complementary) cotransporter proteins.
Na+ diffuse into the cell down its concentration gradient.
Glucose moves into the cell against its concentration gradient / down an electrochemical gradient
Glucose moves into the blood by facilitated diffusion
Monosaccharides (glucose, fructose, and galactose) are absorbed by…
facilitated diffusion and CO-TRANSPORT using SPECIFIC carrier proteins (due to their specific shaped binding sites).
Describe how amino acids are absorbed from the ilium into the blood [5]
Na+ (sodium ions) actively transported out of epithelial cell into the blood (by sodium potassium pump);
This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell);
Na+ and amino acid enter by facilitated diffusion;
Na+ moves into the cell down its concentration gradient;
Amino acids move into the cell against their concentration gradient / down an electrochemical gradient;
Amino acids move into the blood by facilitated diffusion.
Lipid digestion
Lipid droplets are mixed with bile salts to form smaller droplets (emulsified);
(Smaller droplets) increase surface area for faster hydrolysis by lipase;
Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides;
BILE SALTS, Glycerol and fatty acids form micelles;
Micelles make Fatty acids soluble in water and bring FA’s to the surface of the epithelial cell membrane.
Fatty acids enter the epithelial cell by simple diffusion. (Micelles DO NOT cross the cell membrane)
At the S.E.R→Fatty acids, glycerol are recombined to form triglycerides.
At the golgi apparatus →Triglycerides are modified, proteins are added to form lipoproteins (called chylomicrons) and packaged into vesicles. (Chylomicrons are water soluble and so can be carried in the blood.)
Chylomicrons are transported into a lymph vessel by exocytosis. They then enter the blood.
