Digestion and Absorption Flashcards
What enzyme are produced in the stomach?
Endopeptidases and exopeptidases
What enzyme are produced in the pancreas?
Pancreatic amylase, lipases and exopeptidases
What enzyme are produced in the ileum?
Membrane bound dipeptidases and disaccharidases
How is starch digested?
Salivary amylase hydrolyses glycosidic bonds in starch to produce maltose
In the stomach, salivary amylase denatures due to acidic pH
In the small intestines, pancreatic amylase continues to hydrolyse starch to maltose
Maltose is then hydrolysed to glucose by maltase enzymes in the membrane of epithelial cells in the small intestines
Why do epithelial cells have microvilli on the cell membrane?
Increase surface area for disaccharidases and dipeptidases
Describe the role of the enzymes of the digestive system in the complete breakdown of starch (3)
Salivary amylase hydrolyses the glycosidic bonds in starch to maltose
Pancreatic amylase continues to hydrolyse starch to maltose
Maltose is hydrolysed by maltase into glucose
Describe how glucose is absorbed from the ilium into the blood
Sodium ions are actively transported out of epithelial cell into the blood
This creates a concentration gradient of sodium ions
Cotransporter proteins have 2 binding sites complementary to Na+ and glucose. Only when both molecules bind will the molecules be moved across the membrane
Sodium ions and glucose enter by facilitated diffusion using co-transporter proteins
Sodium ions diffuse down its concentration gradient
Glucose moves into the cell against its concentration gradient
Glucose moves into the blood by facilitated diffusion
Why can only monosaccharides be transported across the epithelial cell membrane?
They are small enough and are complementary to the binding sites of specific carrier proteins that move specifically complementary monomers across the epithelial cell membrane
How are proteins digested?
Proteins are hydrolysed by proteases and this process begins in the stomach
Endopeptidases hydrolyses the peptide bonds within the polypeptide chain
This produces shorter polypeptide chains and increases surface area for the next enzyme. This makes digestion faster and more efficient
Exopeptidases hydrolyses the peptide bonds at the terminal ends of the protein, removing one amino acid at a time
Exopeptidases hydrolyse peptide bonds within in the polypeptide chain to produce amino acids and dipeptides
Dipeptidases hydrolyse dipeptides into amino acids
How are lipids digested and absorbed?
Lipid droplets are mixed with bile salts to form smaller droplets (emulsified)
This increases surface area for faster hydrolysis by lipase
Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides
Bile salts and fatty acids form micelles
Micelles make fatty acids soluble in water and bring them to the surface of the epithelial cell
Fatty acids enter the cell by simple diffusion
At the smooth endoplasmic reticulum, fatty acids and glycerol are recombined to form triglycerides
At the Golgi apparatus, triglycerides are modified, proteins are added to form lipoproteins (chylomicrons) and packaged into vesicles
Chylomicrons are transported into a lymph vessel by exocytosis.
Describe and explain two features you would expect to find in a cell specialised for absorption (2)
Microvilli so large surface area for absorption
Large number of co-transport proteins so fast rate of absorption
Large number of mitochondria so make more ATP by respiration OR to release energy for active transport
Membrane bound digestive enzymes so maintains concentration gradient for fast absorption
Describe the role of micelles in the absorption of fats into the cells lining the ileum (3)
Micelles include bile salts and fatty acids
Make the fatty acids more soluble in water
Bring fatty acid to cell/lining of the ileum
Maintain higher concentration of fatty acids to cell/lining of the ileum
Fatty acids absorbed by diffusion
What is the advantage in endopeptidases acting on proteins before exopeptidases do? (2)
Exopeptidases hydrolyse bonds at the ends of protein
molecules
Endopeptidases create more ends for exopeptidases to act on
