digestion and absorption (+enzymes)

Question 1

define digestion

Answer 1

Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
that are small enough be absorbed across cell membranes into blood

Question 2

what is the role of salivary glands in the digestive system?

Answer 2

release salivary amylase enzymes

Question 3

what is the role of the stomach in the digestive system?

Answer 3

produces HCL and protease enzymes. Also physically churns food

Question 4

what is the role of the teeth?

Answer 4

physically break food into smaller pieces and increase its surface area

Question 5

what is the role of the oesophagus?

Answer 5

carries food from the mouth to the stomach

Question 6

what is the role of the liver?

Answer 6

produces bile

Question 7

what is the role of pancreas?

Answer 7

Releases pancreatic juice onto food, as it exits the stomach, which contains proteases, lipases and carbohydrases.

Question 8

what is the role of gall blander?

Answer 8

stores/release bile into ileum

Question 9

what is the role of ileum?

Answer 9

Produces enzymes to digest food and absorbs products of food digestion into the blood

Question 10

what is the role of the large intestine?

Answer 10

absorbs water

Question 11

what are the 2 stages of digestion in a human?

Answer 11

-Physical breakdown by teeth or stomach churning
-Chemical digestion by enzymes

Question 12

what are the carbohydrase enzymes?

Answer 12

-Salivary Amylase +
Pancreatic Amylase (substrate: starch)
-Maltase (substrate: maltose)
-Sucrase (substrate: sucrose)
-Lactase (substrate: lactose)

Question 13

Give some examples of proteases involved in digestion

Answer 13

-Endopeptidase (substrate: protein)
-Exopeptidase(substrate: protein)
-Dipeptidase (substrate: dipeptides)

Question 14

what are the membranes bound enzymes?

Answer 14

-maltase
-sucrose
-lactase
-dipeptidases

Question 15

what is the function of salivary amylase and pancreatic amylase

Answer 15

• makes maltose
• in salivary glands, pancreas
  -acts in the mouth, ileum
  -alpha 1,4 and beta 1,6 glycosidic bonds are broken
  -the pancreatic amylase hydrolyse starch in the ileum that was not broken down in the mouth.

Question 16

what is the function of moltase?

Answer 16

-To break down maltose into 2 α-glucose molecules
-made in the ileum lining (stuck at the lining so it can be reused, if not it would be replenished which takes up a lot of energy)
-acts on the ileum
-a 1,4 glycosidic bonds are broken

Question 17

what is the function of sucrase?

Answer 17

-breaks down sucrose into a-glucose and fructose
-made in the ileum lining
-acts in the ileum

Question 18

what is the function of lactase?

Answer 18

-hydrolyse lactose into a-glucose and galactose
-made in the ileum lining
-acts in the ileum

Question 19

what is the function of endopeptidase?

Answer 19

-To hydrolyse the central peptide bonds in a large protein molecule to give smaller peptide molecules.
-made in the stomach and pancreas
-acts in the stomach and ileum
-peptide bonds are broken

Question 20

what is the function of exopeptidase?

Answer 20

-To hydrolyse the peptide bonds at the ends of peptide molecules, which releases amino acids and dipeptides
-made in the stomach and pancreas
-acts in the ileum and stomach
-peptide bonds broken

Question 21

What is the function of dipeptidases?

Answer 21

-hydrolyse dipeptides into amino acids
-made in the ileum lining
-acts in the ileum
-peptide bonds broken

Question 22

what is the function of lipase ?

Answer 22

-hydrolysis of ester bonds in a lipid molecule to form 2 fatty acids and a monoglyceride
-made in the ileum lining
-acts in the ileum

Question 23

What is meant by egestion?

Answer 23

The removal of faeces via the anus

Question 24

What is the function of bile salts?

Answer 24

To emulsify large lipid molecules into smaller lipid micelles. To increase the surface area that lipase can act on.

Question 25

How does physical breakdown aid digestion?

Answer 25

-Creates a larger surface area for enzymes to act on. -Makes food easier to ingest (swallow).

Question 26

Starch is not digested when food enters the stomach. Why?

Answer 26

The salivary amylase enzymes are denatured by the hydrochloric acid in the stomach.

Question 27

What is a membrane-bound disaccharidase?

Answer 27

An enzyme that is part of the epithelial cell surface membranes of the ileum. They break down disaccharides.

Question 28

What is a gland?

Answer 28

An organ in the body that secretes substances such as enzymes or hormones.

Question 29

Describe the digestion of starch in mammals

Answer 29

● Amylase (produced by salivary glands / pancreas) hydrolyses starch to maltose ● Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose ● Hydrolysis of glycosidic bond

Question 30

Describe the digestion of lipids in mammals, including action of bile salts

Answer 30

● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets ● This increases surface area of lipids for increased / faster lipase activity ● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids ● Hydrolysis of ester bond

Question 31

Describe the digestion of proteins by a mammal

Answer 31

● Endopeptidases - hydrolyse internal (peptide) bonds within a polypeptide → smaller peptides ○ So more ends / surface area for exopeptidases ● Exopeptidases - hydrolyse terminal (peptide) bonds at ends of polypeptide → single amino acids ● Membrane-bound dipeptidases - hydrolyse (peptide) bond between a dipeptide → 2 amino acids ● Hydrolysis of peptide bond

Question 32

Suggest why membrane-bound enzymes are important in digestion

Answer 32

● Membrane-bound enzymes are located on cell membranes of epithelial cells lining ileum ● (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption

Question 33

what are micelles?

Answer 33

smaller emulsified lipid droplets associated with bile salts which creates a larger surface area for faster lipase action

Question 34

what are the advantages of micelle formation?

Answer 34

1. droplets increase surface area (for lipase/enzyme action) 2. so faster hydrolysis/digestion of triglycerides/lipids 3.micelles carry fatty acids and glycerol through membrane to internal epithelial cell

Question 35

exo and edopeptidases are required for protein hydrolysis - name another enzyme needed to complete protein hydrolysis

Answer 35

dipeptidases

Question 36

Why does the action of exo and endopeptidases result in more efficient hydrolysis?

Answer 36

endopeptidases create more ends or increase in surface area (for exopeptidases);

Question 37

Describe the action of membrane dipeptidases

Answer 37

-Hydrolyse peptide bond to release amino acids (dipeptides cannot cross the cell membrane)

Question 38

Describe the pathway for absorption of products of digestion in mammals

Answer 38

Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood

Question 39

Describe the absorption of monosaccharides in mammals

Answer 39

1. sodium removed from epithelial cell by active transport via sodium potassium carrier protein 2. into the blood 3. maintaining a low concentration of sodium in the cell 4. glucose moves into the sodium 5. via a co-transporter carrier protein 6.glucose moves into the blood 7. by facilitated diffusion

Question 40

Describe the absorption of amino acids in mammals

Answer 40

1. sodium removed from epithelial cell by active transport via sodium potassium carrier protein 2. into the blood 3. maintaining a low concentration of sodium in the cell 4. amino acid moves into the sodium 5. via a co-transporter carrier protein 6. amino acid moves into the blood 7. by facilitated diffusion

Question 41

Describe the absorption of lipids by a mammal, including the role of micelles

Answer 41

● Bile salts combine with monoglycerides and fatty acids to form micelles ○ Micelles make monoglycerides and fatty acids (more) soluble in water ○ Micelles carry fatty acids and monoglycerides to cells lining the ileum, where they break down to release them ○ This maintains a high concentration of fatty acids and monoglycerides near cells lining the ileum ● Monoglycerides / fatty acids are absorbed (into epithelial cell) by diffusion (as they’re lipid soluble) ● Triglycerides reformed in (epithelial) cells and aggregate into globules ● Globules coated with proteins forming chylomicrons which are then packaged into vesicles ● Vesicles move to cell membrane and fuse with it, releasing chylomicrons via exocytosis ○ Chylomicrons enter lymphatic vessels and eventually return to blood circulation

Question 42

describe the structures of capillaries and how it aids function

Answer 42

1. walls are folded into villi- increase the S.A for faster absorption 2. walls are 1 cell thick- short diffusion distance so faster absorption 3. epithelial cells have microvilli - increase in S.A for faster absorption 4. many capillaries- rich blood supply maintains diffusion gradient 5. muscle in villi- maintain diffusion gradient by moving contents of lumen