3B - More Exchange And Transport Systems Flashcards
What is digestion?
The process by which large food molecules are broken down into smaller molecules so that they can be absorbed into the from the gut into blood.
Why must digestion happen?
Large food molecules are too big to cross cell membranes, so they cannot be absorbed from the gut into the blood.
What type of reaction is digestion?
Usually hydrolysis.
What are carbohydrates broken down into in hydrolysis?
Disaccharides (and then monosaccharides)
What are fats broken down into in hydrolysis?
Fatty acids and monoglycerides
What are proteins broken down into in hydrolysis?
Amino acids
Why are there many different digestive enzymes?
Enzymes only work with a specific substrate and so different enzymes are needed to catalyse the breakdown of different food molecules.
Describe the digestion of starch in terms of products, bonds and enzymes.
- Starch broken down into maltose by amylase
- Glycosidic bond is hydrolysed
- Maltose broken down into two glucose molecules by maltase (a membrane-bound disaccharidase)
- Glycosidic bond is hydrolysed
Describe the digestion of carbohydrates in terms of products, bonds and enzymes.
STARCH
• Starch broken down into maltose by amylase
• Glycosidic bond is hydrolysed
DISACCHARIDES
• Disaccharides broken down into two monosaccharides by membrane-bound disaccharidases (e.g. sucrose by sucrase)
• Glycosidic bond is hydrolysed
What enzyme catalyses the breakdown of starch?
Amylase
Where is amylase produced and released?
- Salivary glands -> Released into mouth
* Pancreas -> Released into small intestine
What is the name for enzymes that catalyse the breakdown of disaccharides?
Membrane-bound disaccharidases
What are membrane-bound disaccharidases?
- Enzymes that are attached to the cell membranes of epithelial cells lining the ileum (small intestine).
- Break down disaccharides into monosaccharides.
Where are membrane-bound disaccharidases found?
Attached to the cell membranes of epithelial cells lining the ileum.
Describe the breakdown of maltose in terms of enzymes and products.
- Enzyme: Maltase
* Products: Glucose + Glucose
Describe the breakdown of sucrose in terms of enzymes and products.
- Enzyme: Sucrase
* Products: Glucose + Fructose
Describe the breakdown of lactose in terms of enzymes and products.
- Enzyme: Lactase
* Products: Glucose + Galactose
Describe the digestion of lipids in terms of products, bonds and enzymes (+ other substances).
- Bile salts emulsify lipid droplets to make smaller lipid droplets
- Lipids now broken down into monoglycerides and fatty acids by lipase
- Ester bond hydrolysed
- Monoglycerides and fatty acids stick with bile salts to form micelles
What enzyme catalyses the breakdown of lipids?
Lipase
Where is lipase produced and released?
• Pancreas -> Released into small intestine
What is a monoglyceride?
A glycerol molecule with one fatty acid attached.
Where are bile salts produced?
Liver
What do bile salts do and why?
- Emulsify lipids -> Several small lipid droplets have a bigger surface area than a single large droplet (for a given volume).
- This increases the SA for lipase to work on.
- Digestion happens faster.
Describe the digestion of proteins in terms of products, bonds and enzymes.
- Proteins are broken down into amino acids by proteases.
- Endopeptidases -> Hydrolyse peptide bonds within a protein.
- Exopeptidases -> Hydrolyse peptide bonds at the ends of a protein.