Digestion and Absorption Flashcards
What occurs during digestion?
- During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.
What 2 enzymes are carbohydrates hydrolysed by in digestion?
- Amylases.
- Membrane-bound disaccharides.
Where is amylase produced? What is its function?
- Produced by pancreas and salivary glands.
- Hydrolyses starch into maltose.
Where does the digestion of carbohydrates start and end?
- Starts in mouth.
- Continues in duodenum.
- Completed in the ileum.
What are the 3 different enzymes that proteins can be hydrolysed by?
- Endopeptidases
- Exopeptidases
- Membrane- bound dipeptidases.
What do endopeptidases enzymes do?
- Endopeptidases hydrolyse peptide bonds between amino acids in the middle of the polymer chain.
What do exopeptidases enzymes do?
- Exopeptidases enzymes hydrolyse peptide bonds between amino acids at the end of a polymer chain.
What do membrane-bound dipeptidases enzymes do?
- Membrane-bound dipeptidases enzymes hydrolyse peptide bond between two amino acids (ie. hydrolyse peptide bond in dipeptides.)
Where does protein digestion start and where does it end?
- Starts in stomach.
- Continues in duodenum.
- Completed in ileum.
What 2 things are lipids digested by?
- Lipase enzyme.
- Action of bile salts.
Where is lipase produced? What does it actually do to hydrolyse lipids?
- Produced in pancreas.
- Hydrolyses (the 3) ester bonds in triglycerides to form fatty acids, monoglycerides.
Where are bile salts produced and what do they do?
- Produced in liver.
- Emulsify lipids, increase surface area for lipase to act on.
- Form micelles
What are the two stages involved in digestion of lipids?
- Physical digestion stage –> emulsification/ micelle formation.
- Chemical digestion stage –> lipase.
Advantage of micelles
- Many small droplets (micelles) provides a larger surface area to enable the faster hydrolysis action by lipase.
What are micelles (ie. what are they formed of?) What is the role of micelles in the absorption of lipids?
- Micelles are water-soluble vesicles formed of fatty acids, monoglycerides and bile salts.
- Micelles will carry fatty acids, glycerol, monoglycerides to cells lining the ileum.
- Will release fatty acids, glycerol, monoglycerides for absorption.
By what method of transport are amino acids and monosaccharides absorbed by the cells lining the ileum of mammals?
- Co-transport
Why are glucose and amino acids absorbed by co-transport by the cells lining the ileum of mammals?
- There needs to be higher concentration of glucose/ amino acids in lumen compared to epithelial cells BUT USUALLY, there is a higher concentration of glucose/ amino acids in epithelial cells.
- This is why co-transport (type of active transport ) is needed.
What happens when micelles come close to the cells lining the ileum of mammals (the ileum epithelial cells?)
- Because fatty acids/ monoglycerides are non-polar, there will simply diffuse across the cell-surface membrane of ileum epithelial cells to enter the cell.
- Once in the ileum epithelial cell, modified back into triglycerides in endoplasmic reticilum/ golgi apparatus.
What are the 5 steps for the co- transport of glucose/ amino acids and sodium ions from the ileum to the blood within the capillary?
1.) Sodium ions are transported out of the epithelial cell into the blood (within the capillary) by active transport by a carrier protein.
2.) This creates a sodium ion concentration gradient.
3.) Sodium ions diffuse from the lumen (down concentration gradient) into epithelial cell by facilitated diffusion.
4.) Protein sodium ions diffuse through is co- transporter protein. So when sodium diffuses, glucose can also attach to the protein and be transported into epithelial cell against its concentration gradient.
5.) Glucose will then move by facilitated diffusion from the epithelial cell to the blood (within capillary. )
True or False
Co-transport of amino acids doesn’t involve sodium ions, it involves glucose + amino acids.
- Co-transport of amino acids involves amino acids + sodium ions, doesn’t involve glucose at all!
Describe the processes involved in the absorption and transport of digested lipid molecules from ileum into lymph vessels.
2020 Paper 2 AS
MS ANSWER - LEARN WORD FOR WORD!
- Micelles contain bile salts/ fatty acids/ monoglycerides.
- Carry fatty acids/ monoglycerides to cells lining ileum.
- Fatty acids absorbed by diffusion INTO the cells.
- Triglycerides are formed in cells.
- Triglycerides are modified in golgi where they are combined with proteins.
- Vesicles move to cell- membrane/ exocytosis.
Why does having endo/ exopeptidases increase the rate of digestion/ hydrolysis of protein?
- Endopeptidases creates more ends.
- For Exopeptidases to act on.
(2 marks)
Why do endo/ exopeptidases work at different points in polypeptide chain?
- Have different shaped active sites.
- So, different enzyme-substrate complexes form.
(Past Paper Q)
How is the golgi involved in absorption of lipids?
- Golgi will modify triglycerides by combining them with proteins.
