Digestion

Question 1

Definition of digestion

Answer 1

large molecules are being hydrolysed by enzymes into smaller molecules which can be absorbed across cell membranes

Question 2

what do the salivary glands do?

Answer 2

secrete salivary amylase = catalyses the hydrolysis of starch into maltose

Question 3

what does the oesophagus do?

Answer 3

moves food from mouth to stomach, thick muscular walls

Question 4

what does the stomach do?

Answer 4

inner layer = produces enzymes especially pepsins.

Other glands secrete mucus = prevents self digestion from HCL

Question 5

what does the pancreas do?

Answer 5

pancreatic juice: containing proteases, lipase and amylase

Question 6

what does the small intestine do? (ileum)

Answer 6

walls secrete enzymes. Has villi/microvilli for absorbing substances into bloodstream

Question 7

what does the large intestine do and what does the rectum do?

Answer 7

large: absorb H2O forms faeces
rectum: faeces are stored and periodically egested

Question 8

what is the difference between absorption and assimilation?

Answer 8

absorption: taking soluble molecules into the body
assimilation: incorporating absorbed molecules into body tissues

Question 9

what is the difference between physical and chemical breakdown?

Answer 9

physical: large food broken down physically i.e. by teeth or churning of stomach. Gives large SA
chemical: hydrolysis of large insoluble molecules by enzymes

Question 10

describe the process of carbohydrate digestion

Answer 10

1. saliva contains amylase = catalyses hydrolysis of starch to maltose
2. food in stomach, acidic = amylase denatures
3. food passed to ileum + mixed with pancreatic juice (pancreatic amylase) = continues hydrolysis of starch
4. in ileum, epithelial lining has maltase (a membrane bound disaccharidase)
5. glucose absorbed into epithelial cells with sodium via cotransporter (carrier) protein

Question 11

name 3 membrane bound disaccharidases

Answer 11

maltase, sucrase and lactase

Question 12

What maintains the pH7 in ileum

Answer 12

alkaline salts produced by pancreas

Question 13

name the enzyme which hydrolyses proteins, where it hydrolyses them and which part and the products

Answer 13

endopeptidase: stomach
- central peptide bonds broken
= product: polypeptides
+ inactive pepsinogen becomes active pepsin (endopeptidase) at low pH

Question 14

name the enzyme which hydrolyses polypeptides, where it hydrolyses them and which part and the products

Answer 14

exopeptidase: pancreatic juice
- terminal peptide bonds broken
= dipeptides

Question 15

name the enzyme which hydrolyses dipeptides, where it hydrolyses them and which part and the products

Answer 15

dipeptidase: membrane bound (cell surface)
- bonds between dipeptides
= amino acids

Question 16

What is the term called when bile salts spilt lipids into micelles and what does it achieve? (step 1 of lipid digestion)

Answer 16

emulsification: increase SA of lipids so hydrolysis of lipase is quicker

Question 17

what bonds are hydrolysed by pancreatic juice and where are they packaged? (step 2 of lipid digestion)

Answer 17

ester bonds broken = form monoglycerides and fatty acids and packaged in micelles

Question 18

when do micelles break down and release their contents before entering epithelial cell (in lumen) or in the epithelial cell? (step 3 of lipid digestion)

Answer 18

before

Question 19

How do monoglycerides + fatty acids move into epithelial cells and why this route? (step 5 of lipid digestion)

Answer 19

simple diffusion as they are nonpolar

Question 20

what happens at the endoplasmic reticulum (step 6 of lipid digestion) ?

Answer 20

monoglycerides and fatty acids recombined to make triglycerides

Question 21

what happens at the golgi apparatus? (step 7 of lipid digestion)

Answer 21

triglycerides associate with cholesterol + lipoproteins to form chylomicrons

Question 22

how do chylomicrons exit the epithelial cells? (step 8 of lipid digestion)

Answer 22

by exocytosis

Question 23

when chylomicrons exit the epithelial cells where do they enter? (step 9 of lipid digestion)

Answer 23

the lacteals (part of lymphatic capillaries) then into the blood

Question 24

how do fatty acids diffuse into cells from chylomicrons ? (step 10 of lipid digestion)

Answer 24

triglycerides in chylomicrons hydrolysed by enzyme in endothelial cells in capillaries

Question 25

what are fatty acids used for?

Answer 25

metabolic processes

Question 26

digestion of proteins = ?
digestion of carbohydrates =?
And both absorbed using = ?

Answer 26

= amino acids
= monosaccharides (glucose, fructose, galactose)
= facilitated diffusion and co-transport

Question 27

true or false: amino acids are NOT absorbed in the same way as glucose

Answer 27

false: they are absorbed in the same way

Question 28

when micelles break, what do they release? (step 4 lipid digestion)

Answer 28

monoglycerides + fatty acids