Lecture 17: Digestion Flashcards
Breakdown of carbs, proteins and lipid for digestion steps (2)
- Digestion: Large molecules are broken into smaller units via hydrolysis. Lipids- Fatty acids and Glycerol, Polusaccharides-Monosaccharides, Proteins-Amino acids
- Metabolism: Small molecules can be uptaken by cells and enter metabolic pathways to generate cellular energy
Mechanical digestion
Purely physical breakdown that does not change the chemical nature of the molecules
Chemical digestion
Enzymes break chemical bonds to produce smaller molecules
ex: Proteins-> amino acids
Absorption
Metabolites produced from digestion are absorbed into the bloodstream
Saliva contains
a-amylase to digest carbohydrates and lipase to digest lipids
*However, majority of digestion occurs later
Digestion in the stomach (2)
Condition+enzyme
- Acidic conditions (PH 1-2) causes protein denaturation (denatured proteins are better substrates for proteases)
- Protease pepsin is activated under low PH conditions and catalyzes protein degradation
Pepsin
Hydrolyzes denatured protein into shorter polypeptides
Proteases
Break peptide bonds with water to produce short peptides and amino acids
Pancreas role (2)
- Partially digested products in stomach triggers hormones that signals the pancreas to release:
1. sodium bicarbonate (NaHCO3) to neutralize PH as food travels from the stomach to the small intestines
2. Release host of enzymes into the small intestines to digest proteins, lipids and carbohydrates
Proteases are released as
zymogens to prevent them from digesting the pancreas
Inactivated form of enzyme to prevernt enzyme from digesting pancreatic tissue
Zymogens are activated by
proteolysis (Protein cleavage) from other proteases
Lipase
Lipids-> fatty acids and glycerol
Broken down products are
absorbed into the bloodstream and distributed to cells throughout the body
Pancreatic proteases and intestinal peptidases
degrade proteins to small peptides and amino acids
Carbohydrate digestion in the intestines (3):
Done by what+ how
- Done by a-amylase with degrades starch
- a-amylase cleaves a-1,4 bonds in starch but not a-1,6 bonds or terminal glucose residues (1,4 bonds)
- Disaccharide degradation by sucrase, lactase,matase
Lactase cleaves lactose into
Galactose and glucose
Maltase cleaves maltose into
glucose and glucose
Sucrase cleaves sucrose into
Glucose and fructose
Monosaccharides are taken up by
the intestinal cells and exported into the bloodstream
Ways of lipid digestion in the intestines (2):
- Gallbladder releases Bile salts into the small intestines
- Bile salts are amphipathic molecules that facilitate emulsification (combine two ingredients together which do not ordinarily mix easily).
- Lipase
Bile salts roles (2)
- Render triacygycerols more easily digestible by lipases
- Help package lipid degradation products into micelles
Emulsion
A mixture of lipid droplets and water
Lipase breaks down…
Triacyglycerol into fatty acids and monoacyglycerol (composed of a molecule of glycerol linked to a fatty acid via an ester bond)
Phospholipase
degrade cell membrane
Collagenase and hyaluronidase
Degrade connective tissues
