Digestion + absorption

Question 1

What must the enzymes involved in digestion be?

Answer 1

Different for each large molecule/polymer (specific substrate) to catalyse the hydrolysis of these large molecules

Question 2

What happens in digestion?

Answer 2

Large molecules such as polymers and triglycerides are broken down (hydrolysed) into smaller molecules that can cross membranes for cell processes

Question 3

What enzyme catalyses the breakdown of starch?

Answer 3

Amylase

Question 4

Where is amylase produced?

Answer 4

Salivary glands + release into mouth
Pancreas + released into the duodenum (top of ileum)

Question 5

How does amylase work?

Answer 5

Catalyses the hydrolysis of glycosidic bonds in amylose to produce the disaccharide MALTOSE

Question 6

What breaks down the disaccharides produced from the hydrolysis of carbohydrate by amylase?

Answer 6

Enzymes called disaccharidases which are bound to membranes of epithelial cells lining ileum

Question 7

What do membrane bound disacchaidases do?

Answer 7

Catalyse the hydrolysis of disaccharide by breaking glycosidic bond to form 2 monosaccharides

Question 8

How are monosaccharides glucose and galactose absorbed into the blood?

Answer 8

Across epithelial cell membranes lining ileum via co transport using a co transporter protein
Then into capillary

Question 9

Cotransport summary

Answer 9

Na+ ions are actively pumped out of ileum cells into blood by Na+K+ATPase protein pump so a concentration gradient of Na+ ions are established
Co transporter protein facilitates the diffusion of Na+ ions into epithelial cells down conc gradient which pulls glucose and galactose into cells against conc gradient
Glucose and galactose passively diffuse out by facilitated diffusion into blood

Question 10

How is fructose absorbed into the blood?

Answer 10

Absorbed by facilitated diffusion using a carrier protein

Question 11

What happens to amylase in the stomach?

Answer 11

Acidic pH denatures this enzyme so the hydrolysis continues in the more neutral duodenum (thanks to bile)

Question 12

What enzyme catalyses the hydrolysis of triglyceride?

Answer 12

Lipase

Question 13

Where is lipase produced?

Answer 13

In the pancreas and secreted into the duodenum

Question 14

What helps the hydrolysis of triglycerides?

Answer 14

Bile salts produced in liver, stored in gallbladder and released into duodenum

Question 15

What do bile salts do?

Answer 15

Emulsify lipid droplets that are large into small lipid droplets with a larger surface area thus increases surface area for lipase to work on: increases rate if hydrolysis

Question 16

Bile salts + large lipid droplet

Answer 16

= small lipid droplets with attached bile salts

Question 17

Lipase digestion of small lipid droplets with attached bile salts

Answer 17

hydrolysed into into micelles:
Ester bonds broken in triglycerides to form monoglycerides (1 glycerol + 1 fatty acid) or just fatty acids which are attached to bile salts

Question 18

Micelles

Answer 18

A monoglyceride or fatty acid(s) attached to bile salts

Question 19

What is the point in micelles?

Answer 19

Help with the absorption of these lipids into the lacteal vessel

Question 20

What do micelles do?

Answer 20

Move the monoglyceride and fatty acids towards the epithelium cells of the ileum because they make these products water soluble
Then release them to membrane of epithelial cells

Question 21

How are fatty acids and monoglycerides absorbed into the ileum’s epithelial cells?

Answer 21

By simple diffusion across epithelial cell membrane

Question 22

Where are the monoglycerides/ triglycerides taken to within epithelial cells?

Answer 22

In vesicles to the smooth endoplasmic reticulum to process and reform triglycerides

Question 23

Where are the reformed triglycerides (from sER) taken?

Answer 23

To Golgi to be modified into chylomicron along with proteins synthesised from rER and a mono layer of phospholipids

Question 24

Where are chylomicrons taken?

Answer 24

Enclosed into another vehicle then secreted by exocytosis into lacteal vessel to be drained into blood

Question 25

What enzyme catalyses the hydrolysis of proteins?

Answer 25

Peptidases enzymes

Question 26

What do peptidases do?

Answer 26

Catalyse the hydrolysis of peptide chains to form amino acids by breaking peptide bonds

Question 27

Different types of peptidases?

Answer 27

Endopeptidases Exopeptidases (including dipeptidases)

Question 28

Endopeptidases

Answer 28

ENdopeptidases act to hydrolyse peptide bonds withINthe chain INside the polypeptide to form shorter chain polypeptides with more terminal ends

Question 29

Exopeptidases

Answer 29

Enzymes which act to hydrolyse peptide bonds at the end of the polypeptide chain to form dipeptides

Question 30

Dipeptidase

Answer 30

A type of Exopeptidase which works specifically on the peptide bond between a dipeptide to separate 2 amino acids bonds

Question 31

Membrane bound dipeptidase

Answer 31

Located in cell surface membrane of epithelial cells to release amino acids

Question 32

Benefit of Endopeptidases

Answer 32

Produce multiple shorter chain polypeptides to allow for more exopeptidases to hydrolyse more terminal peptide bonds thus release amino acids at a faster rate

Question 33

How are amino acids absorbed into the blood stream?

Answer 33

From the lumen of the ileum through epithelial cells by cotransport

Question 34

Why are some enzymes membrane bound???

Answer 34

So the enzymes wont be carried away from the substrate and lost in faeces

Question 35

Why arent all enzymes membrane bound??

Answer 35

So the enzyme and substrate can mix in the lumen and actually form enzyme substrate complexes = faster rate of hydrolysis

Question 36

Lactase

Answer 36

Catalyses hydrolysis of glycosidic bond in lactose To produce glucose and galactose

Question 37

Sucrase

Answer 37

Catalyses hydrolysis of glycosidic bond in sucrose To produce glucose and fructose