3.3 Digestion And Absoption Flashcards
Explain what happens in digestion
● Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
●That are small enough be absorbed across cell membranes into blood
Describe the digestion of starch in mammals
● Amylase (produced by salivary glands / pancreas) hydrolyses starch to maltose
● Hydrolysis of glycosidic bond
● Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
Describe the digestion of disaccharides in mammals
● Membrane-bound disaccharidases hydrolyse disaccharides to 2 monosaccharides:
○ Maltase - maltose→ glucose + glucose
○ Sucrase - sucrose→ fructose + glucose
○ Lactase - lactose → galactose + glucose
● Hydrolysis of glycosidic bond
Describe the digestion of lipids in mammals, including action of bile salts
● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
● This increases surface area of lipids for increased / faster lipase activity
● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids
● Hydrolysis of ester bond
Describe the digestion of proteins by a mammal
● Endopeptidases- hydrolyse internal (peptide) bonds
within a polypeptide → smaller peptides
○ So more ends/ surface area for exopeptidases
● Exopeptidases-hydrolyse terminal(peptide) bonds at ends of polypeptide → single amino acids
● Membrane-bound dipeptidases-hydrolyse (peptide)
bond between a dipeptide → 2 aminoacids
● Hydrolysis of peptide bond
Suggest why membrane-bound enzymes are important in digestion
● Membrane-bound enzymes are located on cell membranes of epithelial cells lining ileum
● (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption
Describe the pathway for absorption of products of digestion in mammals
Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood
Describe the absorption of amino acids and monosaccharides in mammals
Co-transport:
1● Na+ actively transported from epithelial cells lining ileum to blood (by Na+/K+ pump)
● Establishing a concentration
gradient of Na+ (higher in
lumen than epithelial cell)
2 ● Na+ enters epithelial cell down its concentration gradient with monosaccharide or amino acid against its concentration gradient
● Via a co-transporter protein
3 ● Monosaccharide or amino acid moves down a concentration gradient into blood via facilitated diffusion
Describe the absorption of lipids by a mammal, including the role of micelles
● Bile salts combine with monoglycerides and fatty acids to form micelles
○ Micelles make monoglycerides and fatty acids (more) soluble in water
○ Micelles carry fatty acids and monoglycerides to cells lining the ileum ,where they break down to
release them
○ This maintains a high concentration of fatty acids and monoglycerides near cells lining the ileum
● Monoglycerides/ fatty acids are absorbed (into epithelial cell) by diffusion (as they’re lipid soluble)
● Triglycerides reformed in(epithelial) cells and
aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and fuse with it, releasing chylomicrons via exocytosis
○ Chylomicrons enter lymphatic vessels and eventually return to blood circulation
