Digestion

Question 1

Describe the role of the enzymes of the digestive system in the complete breakdown of starch.

Answer 1

Amylase;(salivary/pancreatic)
(Starch) to maltose:
Maltase;(built into the membrane of the small intestine)
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond;

Question 2

Explain how the small intestine is adapted to its function in the absorption of the products of digestion.

Answer 2

Large surface area provided by villi / microvilli;
long / folds increase surface area / time for absorption;
thin epithelium;
short diffusion pathway;
capillary network absorbs amino acids / sugars;
lacteal for absorption of digested fats;
Maintains a steep concentration gradient
mitochondria supply ATP / energy for active transport;
carrier proteins (in membranes);

Question 3

Describe the processes involved in the absorption of the products of starch digestion.

Answer 3

Glucose moves in with sodium (into epithelial cell);
Via (carrier/channel) protein/symport;
Sodium removed (from epithelial cell) by active transport/sodium-
potassium pump;
Into blood;
Maintaining low concentration of sodium (in epithelial cell) /
maintaining sodium concentration gradient (between lumen
and epithelial cell);
Glucose moves into blood/out of the epithelial cell;
By (facilitated) diffusion;

Question 4

Describe and explain the roles of diffusion, facilitated diffusion and active transport in the absorption of digested food by the ileum.

Answer 4

Diffusion
movement along / down concentration gradient;
monoglycerides / micelles/fatty acids move into epithelial cells;
monoglycerides move from epithelium into blood;
chylomicrons move into lacteals / lymph;
Facilitated diffusion
Movement along / down concentration gradient;
reference to carrier / channel proteins;
monosaccharides or named / amino acids move into epithelial cells;
Active transport
movement against concentration gradient;
energy / ATP required;
reference to carrier proteins;
monosaccharide’s or named / amino acids moved into epithelial cells;
reference to co-diffusion e.g. glucose and NaCl;
monosaccharide’s or named / amino acids move into blood;

Question 5

Protein digestion

Answer 5

Begins in the stomach
Pepsin an endopeptidases hydrolyses peptide bonds within the polypeptide chain, breaking it into smaller chains (6-12 amino acids long), forms many ends 9starting points) for other proteases, exopeptidases.
Pepsin has an optimum pH around pH2-3
Pancreas produces other endopeptidases which continue protein digestion in the duodenum. Different endopeptidases have different peptide bonds that they target and so all proteins are hydrolysed to shorter chains. Different enzymes have different tertiary structures, and thus different active sites, and so bind with different substrates, the amino acids have different shapes due to the R groups

Exopeptidases in the small intestine hydrolyse the terminal peptide bonds releasing amino acids. There are aminopeptidases working from the N terminal end, and carboxypeptidases working from the C terminal end. Dipeptidases cut the dipeptides in half.

Exopeptidases and endopeptidases are can be bound to the membranes of the microvilli

Question 6

Digestion and absorption of fats

Answer 6

1Bile emulsifies triglycerides to smaller droplets;
2 provide large surface area for faster digestion;
3 Lipase (hydrolyses the ester bonds in triglycerides);
4 producing fatty acids and glycerol (monoglycerides)
5 Fatty acids and glycerol are; lipid soluble and pass through the membrane by simple diffusion
7 once inside the epithelial cells these components are recombined into triglycerides (at the SER)
8 Chylomicrons formed where the lipid is coated by proteins (occurs at the Golgi);
9 these then leave the epithelial cell (by exocytosis) and move into the lacteals