Biology: Digestion

Question 1

Digestion

Answer 1

During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.

Question 2

Carbohydrates in Digestion

Answer 2

Digestion in mammals of carbohydrates by amylases and membrane-bound disaccharidases.

Question 3

Lipid in Digestion

Answer 3

Digestion in mammals of lipids by lipase, including the action of bile salts.

Question 4

Protein in Digestion

Answer 4

Digestion in mammals of proteins by endopeptidases, exopeptidases and membrane-bound dipeptidases

Question 5

Co-transport

Answer 5

Co-transport mechanisms for the absolution of amino acids and of monosaccharides by cells lining the ileum of mammals

Question 6

Endopeptidases

Answer 6

Catalysis hydrolysis reactions that break petite bonds in the middle of the polypeptide chain to produce smaller polypeptide chains

Question 7

Exopeptidases

Answer 7

Catalysing hydrolysis reaction that break down peptide bond at the ends of the chains into depedites and some amino acids

Question 8

Dipeptidases

Answer 8

Catalysing hydrolysis reaction that breaks down peptide bond between two amino acids.

Question 9

Starch Digestion

Answer 9

Starch is large and insoluble and is digested in the mouth and small intestine to produce small, soluble molecules that can be absorbed into the blood.

salivary amylase is made in the salivary gland and secreted into the mouth. This salivary amylase catalysis the hydrolysis reaction that break glycosidic bonds connecting glucose units in starch. It does this by forming and enzyme substrate complex and lowering the activation energy. When starch binds to the active site of amylase, the active site changes shape to fit the substrate and this puts a pressure of the glycosidic bond make it easier to break. The product of the breakdown is maltose. Starch Digestion into maltose also occurs in the small intestine as pancreatic amylase made in the pancreas is sacred in the small intestine

In the cell membrane of the small intestine epithelial calls is the enzyme maltase (intrinsic protein). This maltase catalyses the hydrolysis reaction that breaks the glycosidic bond between the glucose units in maltose.
This produces small, soluble glucose units that can then be absorbed into the blood.

Question 10

The absolution of Glucose using Sodium Co-transport

Answer 10

Sodium ions are actively transported out of the ileum epithelial cells into the blood using a carrier protein in the membrane. This transport requires the hydrolysis of ATP to provide the energy to move the sodium ions against the convention gradient. The removal of sodium ions from the epithelial cell establishes a concentration gradient for the movement of sodium ions into the cell from the small intestine lumen. The sodium ions move into the cell via facilitated diffusion. This does not require energy, but com[e,teary shaped carrier proteins are required. This carrier protein has 2 receptor sites. One receptor site is complementary to sodium ions and the second receptor is complementary to Glucose. Both glucose and sodium ions need to bind to the carrier protein for transport to occur. The co-transport of glucose with the sodium ions enables glucose to be transported into the epithelial cell against the concentration gradient. The glucose then moves into the blood via facilitated diffusion using a carrier protein with a complementary shaped receptor site.

Question 11

Lipid digestion and absorption

Answer 11

1. Triglyceride / lips digestion take solace in the small intestine
2. Bile made in the liver and stored in the fall bladder is released into the duodenum
3. The bile is Aline and it neutralises the stomach acid to produce the optimum pH for lipase to act.
4. Truckers are non-polar and therefore insole so form large lips globules with a small surface area to volume ratio
5. Bile contains bile salts and these have hydrophobic tails and negatively charged hydrophilic heads.
6. Mechanical digestion in the stomach breaks down the large fat problems into smaller one and the bile salts attach to the droplets with their hydrophobic tails within the droplet and their hydrophilic heads on the outside associating with water.
7. The negative charge of the bile salt heads replies droplets form each other, so they do not re-join.
8. This emulsification gives the droplets with large surface to volume ratios.
9. There is more surface for lipase to act on and so there is a faster hydrolysis of the triglycerides.
   10l. The lipase catalysis the hydrolysis reaction that breaks the ester bond
10. To produce 2 fatty acids and a Monoglyceride (3 fatty acids and 1 glycerol)
11. The fatty acids and monoglyceride / glycerol interact with bile salts to form micelles.
12. Bile salts give greater solubility and the micelle holds as high concentration of fatty acids and monoglycerides that they transport to the surface of the ileum epithelial cell.
13. Here the micelles break down and fatty acids and monoglycerides / glycerol diffuse into the epithelial cells. There was a a higher concentration of fatty acids and monoglycerides in the micelle than within the cell and they are lipid soluble, so they move through the bilayer via simple diffusion.
14. They move into the smooth ER where concession reaction take place to form a triglycerides.
15. The triglycerides are transported to the golgi body via vesicles and within the Golgi body are modified by being combined with proteins and cholesterol to form chylomicrons.
16. Vesicle scomating the chylomicrons from and move to the surface of the small intestine epithelial cell where they fuse with the membrane, realign the chylomicrons via exocytosis.
17. The chylomicrons enter the lacteal of a villi and are transported through the lymphatic system
18. The lymphatic system drains into the subclavian vein located in the neck, so the tryclides enter the blood at this point.