Unit 3- Digestion =) Flashcards
Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (5)
- salivary & pancreatic amylase
- hydrolyse glycosidic bonds
- starch –> maltose
- maltase in small intestine
- maltose –> glucose
Explain the advantages of lipid droplet and micelle formation. (3)
- droplet- ↑ s.a. for lipase
- faster hydrolysis of lipids
- micelle- transport fatty acids & monoglycerides to membrane
Describe the process involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5)
- micelles contain bile salts + monoglycerides & fatty acids
- make f.a. ↑ soluble in water
- micelles transport f.a. to cell
- maintain ↑ conc. of f.a. to cell
- absorbed by diffusion
- triglyceride reformed (at RER)
- vesicles move to cell mem for exocytosis
The action of the sodium- potassium pump is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase. (2)
- hydrolysis of ATP (ADP+Pi) releases energy
- ✔️ ions to be moved against conc. gradient in a.t.
The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how. (2)
- maintains conc. gradient of Na+ from lumen of ileum into cell
- Na+ moves in by co-transport, bringing glucose w/ it
Describe the role of enzymes in the digestion of proteins in a mammal. (4)
- hydrolysis of peptide bond
- endopeptidase- middle of polypeptide–> shorter polypeptides + ↑ no. of ends
- exopeptidase- end of protein (remove terminal a.a.)–> dipeptides
- dipeptidase- dipeptides –> single a.a.
Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions.
Explain how. (3)
- Na+ from ileum cells into blood by a.t.
- maintains diffusion gradient for Na+ to enter cells from lumen
- glucose enters by co-transport w/ Na+ ions
Use your knowledge of lipid digestion to explain why concentration of fatty acids increased while that of triglycerides decreased at 75 minutes after meal was taken.
You should assume that no absorption had occurred. (3)
Triglyceride ↓ as:
1. lipase digests triglycerides
2. by hydrolysis
3. breaking the ester bonds between f.a. & glycerol
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction. (3)
- tertiary structure- specifically shaped a.s.
- only maltose can fit
- forms enzyme-substrate complex
The concentration of glucose in the blood rises after eating a meal containing carbohydrates.
The rise is slower if the carbohydrate is starch rather than sucrose.
Explain why. (3)
- starch digested into maltose
- maltose digested into glucose
- sucrose- single step, only 1 enzyme
Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. (2)
- endo hydrolyse internal peptide bonds
- ↑ s.a. / ends for exo to work on
Suggest how the golgi apparatus is involved in the absorption of lipids. (3)
- modifies triglycerides
- combines w/ proteins
- packaged for release
Describe and explain 2 features you would expect to find in a cell specialised for absorption. (2)
- folded mem –> ↑ s.a. for absorption
- ↑ no. of carrier proteins –> fast rate
- ↑ no. of mitochondria –> make ↑ ATP for a.t.
- ↑ mem-bound (digestive) enzymes –> maintains conc gradient ==> faster absorption
Describe the action of membrane-bound dipeptidases and explain their importance. (2)
- hydrolyse peptide bonds –> release a.a.
- a.a. can cross cell mem but dipeptides x
The action of endopeptidases and exopeptidases can increase the rate of protein digestion.
Descrobe how. (2)
- exo hydrolyse peptide bonds at ends of polypeptide + endo hydrolyse internal peptide bonds within polypeptide
- ↑ ends
