3.3. Digestion and Absorption Flashcards
Define digestion
The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
Which enzymes are involved in the carbohydrate digestion and where are they found?
- Amylase in the mouth
- Maltase, sucrase, lactase in the membrane of the small intestine
What are the substrates and products of carbohydrate digestive enzymes?
- Amylase = starch into smaller polysaccharides
- Maltase = maltose into 2 x glucose
- Sucrase = sucrose into glucose and fructose
- Lactase = lactose into glucose and galactose
Where are lipids digested?
The small intestine
What needs to happen before lipids can be digested?
- They must be emulsified by bile salts produced by the liver
- This breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area
How are lipids digested?
Lipase hydrolyses the ester bond between monoglycerides and fatty acids
Which enzymes are involved in protein digestion and what is their role?
- Endopeptidases = hydrolyse between specific amino acids in the middle of a polypeptide
- Exopeptidases = hydrolyse between specific amino acids at the end of a polypeptide
- Dipeptidases - hydrolyse dipeptides into amino acids
How are certain molecules absorbed into the ileum despite a negative concentration gradient?
Through co-transport
Which molecules require co-transport?
Amino acids and monosaccharides
Explain how sodium ions are involved in co-transport
- Na+ ions are actively transported out of the cell into the lumen, creating a diffusion gradient
- Nutrients are then taken up into the cells along with Na+ ions
Why do fatty acids and monoglycerides not require co-transport?
The molecules are non-polar, meaning they can easily diffuse across the membrane of the epithelial cells
