More exchange and transport systems: Digestion and absorption Flashcards
What is digestion
The process by which large biological molecules such as carbohydrates, lipids and proteins get hydrolysed into their smaller molecules
Why does digestion occur
It occurs so that large biological molecules can be broken down into nutrients, and absorbed into cell membranes - so it can be used for growth and repair
What digestive enzymes catalyses the breakdown of carbohydrates (and state what they catalyse the hydrolysis of)
- Amylase
- Membrane-bound disaccharidases
How many polysaccharides make up starch (and state the monomers of it)
- Its made of two polysaccharides chains
- Made of long chains of alpha glucose molecules
How does amylase work (what bonds do they catalyse the hydrolysis of) (what does it produce)
Amylase works by catalysing the glycosidic bonds in starch to produce maltose (a disaccharide)
Where is amylose produced
- The salivary glands - which releases it into the mouth
- The pancreas - which releases it into the small intestine
What are membrane-bound disaccharidases
They are enzymes attached to the cell membranes of epithelial cells lining the ileum- breaking down disaccharides into monosaccharides
How do membrane-bound disaccharidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)
Membrane-bound disaccharidases works by catalysing the hydrolysis of glycosidic bonds in disaccharides (maltose) to produce alpha glucose (a monosaccharide)
What digestive enzymes catalyses the breakdown of lipids
Lipase
What does lipase catalyse the hydrolysis reactions of (and what does it produce)
It catalyses the hydrolysis reactions of ester bonds in lipids - breaking them down into some monoglycerides, glycerol and fatty acids
What is emulsification
A process which large lipid globules are broken down into several small globules
What substance emulsifies lipids
Bile salts
Where are lipases mainly produced
The pancreas
Where are bile salts produced
The liver
Why is the emulsification of big lipid globules into micelles important
The formation of small droplets increases the surface area of lipids that available for the lipases to work on enabling faster hydrolysis
Describe the process of lipid digestion in order
- Lipids are coated in bile salts to create an emulsion
- Lipase hydrolyses lipids into glycerol and fatty acids (sometimes monoglycerides)
- Micelles are formed of the fatty acids, glycerol, monoglycerides and bile salts
- Micelles release the monoglycerides, fatty acids and glycerol and due to their non-polar nature (lipid soluble), they diffuse across the cell membrane
- Once in the epithelial cell, they are modified back into triglycerides inside the ER and Golgi body
How is the formation of micelles important (refer to the structure too)
They enable the lipid digestion products to be transported to the small intestinal surface for absorption
What are micelles
Water soluble vesicles formed of the fatty acids, glycerol, monoglycerides and bile salts
What are the two stages involved in the digestion of lipids
Physical digestion: emulsification & micelle formation
Chemical digestion: hydrolysis of ester bonds in lipids
What three digestive enzymes break down proteins
- Endopeptidase
- Exopeptidase
- Membrane-bound dipeptidases
How do membrane-bound dipeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)
They catalyse the hydrolysis of peptide bonds between dipeptides (two amino acids)
How do endopeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)
They catalyse the hydrolysis of peptide bonds between the amino acids in the middle of a polypeptide chain
How do exopeptidases work (what bonds do they catalyse the hydrolysis of) (what does it produce)
They catalyse the hydrolysis of peptide bonds between the amino acids at the end of a polypeptide chain
State the path of protein digestion
It starts in the stomach and ends in the ileum (in the small intestines)
Where are the products of digestion absorbed across
The ileum epithelium into the bloodstream
How is glucose and galactose absorbed into the ileum epithelium then into the bloodstream
Active transport with sodium ions via co-transporter proteins
How is fructose absorbed into ileum epithelium then into the bloodstream
They are absorbed by facilitated diffusion through another transporter protein than glucose + galactose
How are monoglycerides and fatty acids absorbed into the ileum epithelium then into the bloodstream
- Micelles help move these products towards the epithelium where they release the products allowing the products to be absorbed
- Monoglycerides and fatty acids are lipid-soluble, so can diffuse differently across the epithelial membrane
How are amino acids absorbed into the ileum epithelium then into the bloodstream
Active transport with sodium ions via co-transporter proteins
Describe the process of how amino acids and some monosaccharides (glucose and galactose) are absorbed
- Sodium ions are transported out of the epithelial cells in the ileum unto the blood using ATP - creating a concentration gradient as Na+ ion concentration decreases in the cell
- Na+ ions then diffuse from the lumen of the ileum into the epithelial cell down the concentration gradient alongside the products of digestion through co-transporter protein
- The products of digestion then moves out of the cell through down its concentration gradient facilitated diffusion through a channel protein
