lecture 23 - digestion of food molecules

Question 1

What are the 4 key macronutrients found in food?

Answer 1

Carbohydrate, protein, nucleic acids, fat

Question 2

What are the 3 main macronutrients that contribute to energy production in the body?

Answer 2

Carbohydrate, protein and fat

Question 3

In what form do carbohydrates contribute to energy production in the body?

Answer 3

Monosaccharides

Question 4

In what form do proteins contribute to energy production in the body?

Answer 4

Amino acids

Question 5

In what form do nucleic acids contribute to energy production in the body?

Answer 5

nucleotides

Question 6

In what form do fats contribute to energy production in the body?

Answer 6

Free fatty acids (FFA), monoacylglycerol (MAG), cholesterol

Question 7

What enzyme is used in the stomach for protein digestion?

Answer 7

Pepsin

Question 8

What type of enzyme is pepsin?

Answer 8

Protease

Question 9

What is the inactive precursor of the protease pepsin?

Answer 9

Pepsinogen

Question 10

What is the concentration of stomach acid secreted into the stomach?

Answer 10

0.1mol/L

Question 11

What is the function of stomach acid in terms of protein digestion?

Answer 11

Helps to denature proteins

Question 12

What are the 2 main phases of biochemical digestion?

Answer 12

Hydrolysis of bonds connecting monomer units in macromolecules, then the absorption of these hydrolysis products via the GI tract

Question 13

What bonds are broken in carbohydrate digestion?

Answer 13

Glycosidic bonds

Question 14

What bonds are broken in protein digestion?

Answer 14

Peptide bonds

Question 15

What bonds are broken in fat digestion?

Answer 15

Triacylglycerol ester bonds

Question 16

What are the 2 types of starch used by the body?

Answer 16

alpha-amylose, amylopectin

Question 17

What are the 3 types of carbohydrate taken in by the body for digestion?

Answer 17

Starch, simple sugars, fibre (cellulose)

Question 18

What are the main components of plant starch?

Answer 18

Amylopectin and amylose

Question 19

What is cellobiose?

Answer 19

A repeating disaccharide unit in cellulose that has Beta-1,4 bonds

Question 20

What is the stereoisomer of cellobiose?

Answer 20

Lactose

Question 21

What is the stereoisomer of lactose?

Answer 21

Cellobiose

Question 22

Why can mammals not hydrolyse the bonds in cellulose?

Answer 22

The bonds in cellobiose, which are the disaccharides that make up cellulose, have Beta 1,4 bonds, and mammals have no enzymes that hydrolyse this specific bond.

Question 23

What enzyme hydrolyses the bonds in lactose?

Answer 23

Lactase

Question 24

What is sucrose hydrolysed to?

Answer 24

Glucose and fructose

Question 25

What are the 2 enzymes that break down starch?

Answer 25

Salivary amylase and pancreatic amylase

Question 26

What is the structure of amylose?

Answer 26

A linear polymer of alpha-1,4 linked glucose units

Question 27

What is the structure of amylopectin?

Answer 27

A branched polymer of alpha-1,4 AND alpha-1,6 linked glucose units

Question 28

What foods typically contain glycogen as a starch source?

Answer 28

Liver and muscle

Question 29

How does hydrolysis of starch progress?

Answer 29

Repeated internal attack of alpha-1,4 glycosidic bonds all along the chain by amylase, yielding smaller and smaller oligosaccharides.

Question 30

What are the end products of the hydrolysis of starch?

Answer 30

Maltose and isomaltose - disaccharides

Question 31

Where does the final digestion of the products of amylase digestion occur?

Answer 31

At the brush border within the small intestine

Question 32

What enzymes are used at the brush border of the small intestine to digest disaccharides into monosaccharides?

Answer 32

Maltase, isomaltase, sucrase, lactase

Question 33

What is the key purpose of the digestion of dietary protein?

Answer 33

Supplying the body with amino acids, especially essential ones, to make body proteins

Question 34

What molecules does the digestion of dietary protein supply a source of nitrogen for?

Answer 34

Bases - purines and pyrimidines, and haem

Question 35

How are carbon skeletons from the digestion of dietary protein used as fuel?

Answer 35

Carbon skeletons used, while Nitrogen is converted to urea and then excreted in urine

Question 36

What are essential amino acids?

Answer 36

Amino acids that are essential for body function and protein synthesis, but cannot be directly synthesised by the body so must be obtained from the diet

Question 37

What is ‘Kwashiorkor’?

Answer 37

A condition resulting for a deficiency in dietary protein that causes osmotic imbalances in the GI system

Question 38

In what form are proteases secreted?

Answer 38

As inactive forms - zymogens/proenzymes

Question 39

How are proteases activated?

Answer 39

By the cleavage of peptides from their structure

Question 40

What is protease specificity determined by?

Answer 40

The adjacent amino acid side chains in the protein substrate impact on the specificity of binding and therefore the hydrolysis of the bond in the substrate.

Question 41

What are the 2 stages of protein digestion?

Answer 41

Endopeptidases attack peptide bonds within the protein, Exopeptidases attack peptide bonds at the end of the peptides.

Question 42

What are endopeptidases?

Answer 42

Enzymes that attack peptide bonds within a peptide during protein digestion

Question 43

What are exopeptidases?

Answer 43

Enzymes that attack peptide bonds at the end of peptides

Question 44

What are the 2 types of exopeptidase?

Answer 44

Aminopeptidase, Carboxypeptidase

Question 45

What is the function of aminopeptidase?

Answer 45

Attack peptide bonds at the amino-terminus of peptides

Question 46

What is the function of carboxypeptidase?

Answer 46

Attack peptide bonds at the carboxy-terminus of peptides

Question 47

What are the substrates of trypsin?

Answer 47

Polypeptides and chymotrypsinogen (is activated)

Question 48

What enzyme breaks the peptide bonds in dipeptides?

Answer 48

Dipeptidase

Question 49

What is pepsinogen activated to pepsin by?

Answer 49

Exposure to HCl at low pH in the stomach

Question 50

How is pepsinogen activated to pepsin in the stomach?

Answer 50

In the acidic environment, part of the protein unfolds, activating the pepsin protease and resulting in the hydrolysis of part of the protein sequence to generate stably activated pepsin.

Question 51

What is the order of proteases that break down protein, from large polypeptides to single amino acids and dipeptides/tripeptides?

Answer 51

Pepsin (stomach), trypsin (small intestine), chymotrypsin (small intestine), carboxypeptidases (small intestine), aminopeptidases (small intestine)

Question 52

What protein activates trypsinogen to trypsin?

Answer 52

Enterokinase (membrane bound in the small intestine)

Question 53

What protein activates chymotrypsinogen to chymotrypsin?

Answer 53

Trypsin