Digestion and absorbtion

Question 1

what enzymes are found in the salivary glands

Answer 1

salivary amylase

Question 2

what enzymes are found in the stomach

Answer 2

endopeptidases and exopeptidases

Question 3

what enzymes are found in the pancreas

Answer 3

pancreatic amylase, lipase and exopeptidases

Question 4

what enzymes are found in the ileum

Answer 4

membrane bound dipeptidases and disaccharidases

Question 5

what is assimilation

Answer 5

the process of absorption of vitamins, minerals, and other chemicals from food as part of the nutrition of an organism

Question 6

what is absorption

Answer 6

something passing through a membrane

Question 7

what is the function of the salivary glands

Answer 7

secretes salivary amylase (which hydrolyses starch to maltose)

Question 8

what is the function of the stomach

Answer 8

has gastric juice which is acidic which kills microorganism and contains exopeptidases which hydrolyses polypeptides to dipeptides

Question 9

what is the function of the pancreas

Answer 9

secretes pancreatic juice containing amylase, endopeptidases , exopeptidases and lipases.

Question 10

what is the role of the digestive system

Answer 10

hydrolyse large insoluble nutrients into small soluble molecules which are absorbed and assimilated

Question 11

what is the function of the small intestine (ileum)

Answer 11

• provides large surface area for the absorption of the products of digestion
• has maltase enzymes embedded on the epithelium cell membrane of the intestine

Question 12

Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (4)

Answer 12

1. Salivary / Pancreatic amylase hydrolyses starch into maltose
2. By hydrolysing glycosidic bonds
3. Maltose is hydrolysed into glucose
4. By maltase;

Question 13

why does the salivary amylase denature in the stomach

Answer 13

due to the high pH ionic bonds are broken changing the tertiary structure of enzyme

Question 14

why is an advantage of maltase being a membrane bound dissacharide

Answer 14

its within the membrane of epithelium cell so that glucose can be absorbed by membrane faster as there is short diffusion distance

Question 15

why can only monosaccharides be transported across the epithelial cell membrane

Answer 15

they are small enough and are complementary to the binding sites of specific carrier / channel proteins

Question 16

Describe how glucose is absorbed from the ilium into the blood [5]

Answer 16

1. Na+ are actively transported out of epithelial cell into the blood (by sodium potassium pump) with energy from hydrolysis of ATP
2. This creates a concentration gradient of Na+
3. Na+ and glucose enter by facilitated diffusion using (complementary) cotransporter proteins.
4. Na+ diffuse into the cell down its concentration gradient.
5. Glucose moves into the cell against its concentration gradient
6. Glucose moves into the blood by facilitated diffusion

Question 17

why can humans not hydrolyse cellulose

Answer 17

because they don’t produce cellulase

Question 18

Describe how amino acids are absorbed from the ilium into the blood [5]

Answer 18

1. Na+ (sodium ions) actively transported out of epithelial cell into the blood (by sodium potassium pump)
2. This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)
3. Na+ and amino acid are cotransported enter by facilitated diffusion
4. Na+ moves into the cell down its concentration gradient
5. Amino acids move into the cell against their concentration gradient / down an electrochemical gradient
6. Amino acids move into the blood by facilitated diffusion.

Question 19

describe protein digestion

Answer 19

1. Proteins are hydrolysed by enzymes called proteases in the stomach.
2. Endopeptidases hydrolyse the peptide bonds within the polypeptide chain.
3. This produces many shorter polypeptide chains and increases the surface area . This makes digestion faster and more efficient.
4. Exopeptidases hydrolyse the peptide bonds at the terminal ends of the protein, removing one amino acid at a time.
5. Exopeptidases are specific: one group are complementary to the terminal ends of the protein
6. The dipeptidases - enzymes embedded in the cell surface membrane of the epithelial cells hydrolyse dipeptides into amino acids which can now be absorbed by the ileum into the blood

Question 20

How do endopeptidases not denature in the stomach acid

Answer 20

This enzyme has acidic optimum pH

Question 21

why do lipids not need as much digestion

Answer 21

because they are not polymers

Question 22

why do you need micelles to transport fatty acids to surface to epithelial cell

Answer 22

because they are hydrophobic so they wouldnt normally move towards watery environment

Question 23

what is the function of lipases

Answer 23

hydrolyse lipids into glycerol, fatty acids and monoglycerides

Question 24

why do you need to emulsify fat droplets

Answer 24

to increase the surface area of the lipids so that the lipase enzymes are more effective

Question 25

describe the process of lipid digestion

Answer 25

1. Lipid droplets are mixed with bile salts to form smaller droplets (emulsified);
2. (Smaller droplets) increase surface area for faster hydrolysis by lipase;
3. Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides;
4. BILE SALTS, Glycerol and fatty acids form micelles;

Question 26

describe the process of lipid absorption

Answer 26

1. Micelles make Fatty acids soluble in water and bring FA’s to the surface of the epithelial cell membrane.
2. Fatty acids enter the epithelial cell by simple diffusion. (Micelles DO NOT cross the cell membrane)
3. At the S.E.R→Fatty acids, glycerol are recombined to form triglycerides.
4. At the golgi apparatus →Triglycerides are modified, proteins are added to form chylomicrons and packaged into vesicles. (Chylomicrons are water soluble and so can be carried in the blood.)
5. Chylomicrons are transported into a lymph vessel by exocytosis. They then enter the blood.