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BIOC192 2022 > lecture 23 - digestion of food molecules > Flashcards

lecture 23 - digestion of food molecules Flashcards

1
Q

What are the 4 key macronutrients found in food?

A

Carbohydrate, protein, nucleic acids, fat

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2
Q

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

A

Carbohydrate, protein and fat

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3
Q

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

A

Monosaccharides

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4
Q

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

A

Amino acids

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5
Q

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

A

nucleotides

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6
Q

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

A

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

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7
Q

What enzyme is used in the stomach for protein digestion?

A

Pepsin

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8
Q

What type of enzyme is pepsin?

A

Protease

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9
Q

What is the inactive precursor of the protease pepsin?

A

Pepsinogen

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10
Q

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

A

0.1mol/L

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11
Q

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

A

Helps to denature proteins

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12
Q

What are the 2 main phases of biochemical digestion?

A

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

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13
Q

What bonds are broken in carbohydrate digestion?

A

Glycosidic bonds

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14
Q

What bonds are broken in protein digestion?

A

Peptide bonds

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15
Q

What bonds are broken in fat digestion?

A

Triacylglycerol ester bonds

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16
Q

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

A

alpha-amylose, amylopectin

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17
Q

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

A

Starch, simple sugars, fibre (cellulose)

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18
Q

What are the main components of plant starch?

A

Amylopectin and amylose

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19
Q

What is cellobiose?

A

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

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20
Q

What is the stereoisomer of cellobiose?

A

Lactose

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21
Q

What is the stereoisomer of lactose?

A

Cellobiose

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22
Q

Why can mammals not hydrolyse the bonds in cellulose?

A

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.

23
Q

What enzyme hydrolyses the bonds in lactose?

A

Lactase

24
Q

What is sucrose hydrolysed to?

A

Glucose and fructose

25
Q

What are the 2 enzymes that break down starch?

A

Salivary amylase and pancreatic amylase

26
Q

What is the structure of amylose?

A

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

27
Q

What is the structure of amylopectin?

A

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

28
Q

What foods typically contain glycogen as a starch source?

A

Liver and muscle

29
Q

How does hydrolysis of starch progress?

A

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

30
Q

What are the end products of the hydrolysis of starch?

A

Maltose and isomaltose - disaccharides

31
Q

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

A

At the brush border within the small intestine

32
Q

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

A

Maltase, isomaltase, sucrase, lactase

33
Q

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

A

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

34
Q

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

A

Bases - purines and pyrimidines, and haem

35
Q

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

A

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

36
Q

What are essential amino acids?

A

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

37
Q

What is ‘Kwashiorkor’?

A

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

38
Q

In what form are proteases secreted?

A

As inactive forms - zymogens/proenzymes

39
Q

How are proteases activated?

A

By the cleavage of peptides from their structure

40
Q

What is protease specificity determined by?

A

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.

41
Q

What are the 2 stages of protein digestion?

A

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

42
Q

What are endopeptidases?

A

Enzymes that attack peptide bonds within a peptide during protein digestion

43
Q

What are exopeptidases?

A

Enzymes that attack peptide bonds at the end of peptides

44
Q

What are the 2 types of exopeptidase?

A

Aminopeptidase, Carboxypeptidase

45
Q

What is the function of aminopeptidase?

A

Attack peptide bonds at the amino-terminus of peptides

46
Q

What is the function of carboxypeptidase?

A

Attack peptide bonds at the carboxy-terminus of peptides

47
Q

What are the substrates of trypsin?

A

Polypeptides and chymotrypsinogen (is activated)

48
Q

What enzyme breaks the peptide bonds in dipeptides?

A

Dipeptidase

49
Q

What is pepsinogen activated to pepsin by?

A

Exposure to HCl at low pH in the stomach

50
Q

How is pepsinogen activated to pepsin in the stomach?

A

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.

51
Q

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

A

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

52
Q

What protein activates trypsinogen to trypsin?

A

Enterokinase (membrane bound in the small intestine)

53
Q

What protein activates chymotrypsinogen to chymotrypsin?

A

Trypsin

BIOC192 2022 (37 decks)

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