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BIOC192 > Lecture 23: DIGESTION OF FOOD MOLECULES > Flashcards

Lecture 23: DIGESTION OF FOOD MOLECULES Flashcards

1
Q

What are the main macronutrients contributing to energy production in the body?

A

Carbohydrates, proteins and fats

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2
Q

What are carbohydrates hydrolysed to?

A

Monosacchrides

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3
Q

What are proteins hydrolysed to?

A

Amino acids

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4
Q

What are nucleic acids hydrolysed to?

A

Nucleotides

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5
Q

What is fat hydrolysed to?

A

FFA’s (free fatty acids), MAG (monoacylglycerol) and cholesterol

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6
Q

What is in the salivary glands?

A

Saliva (neutral pH) which contains mucous and amylase which starts the digestion of carbohydrates

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7
Q

What happens in the stomach?

A

Storing and mixing of food with gastric juices, slowly releases chyme into the intestine

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8
Q

What does the stomach secrete?

A

Acid from chief cells (0.1 M HCl) = denaturing, pepsinogen > pepsin > protein digestion and mucous layer (protective

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9
Q

What is the pH of the pancreas?

A

Slightly alkaline pH 7

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10
Q

What does the pancreas secrete?

A

Most of the digestive enzymes including, amylase, lipase, and several proteases

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11
Q

What happens in the liver?

A

Synthesis of bile salts/acids (stored in gall bladder) which is important for fat digestion

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12
Q

What happens in the small intestine?

A

The final phase of digestion and absorption

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13
Q

What is the first main phase of digestion?

A

Hydrolysis of bonds connecting monomer units in food macromolecules

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14
Q

What bonds are hydrolysed in carbohydrates?

A

Glycosidic bonds - starch > disaccharides

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15
Q

What bonds are hydrolysed in proteins?

A

Peptide bonds

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16
Q

What bonds are hydrolysed in fats?

A

Triacylglycerol ester bonds

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17
Q

What is the second phase of digestion?

A

Absorption of products from the gastrointestinal tract into the body

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18
Q

What % of energy intake do carbohydrates provide?

A

40-50%

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19
Q

What is in carbohydrates?

A

Starch, simple sugars and fibre

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20
Q

What is starch made of?

A

Amylose and amylopectin

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21
Q

What are some simple sugars?

A

Sucrose, lactose, fructose and glucose

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22
Q

What is fibre?

A

Cellulose which is indigestible by most mammals

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23
Q

What is the main component of plant starch?

A

Amylopectin

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24
Q

What is amylopectin made up of?

A

Polymers of up to 1 million glucose units

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25
Q

What is maltose present in?

A

Honey

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26
Q

What is the glycosidic linkage in maltose?

A

Alpha (1,4)

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27
Q

What is sucrose hydrolysed to?

A

Glucose and fructose

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28
Q

What are cellobiose and lactose?

A

Enantiomers of one another

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29
Q

Where can the functional group of monosaccharides be?

A

In either of two orientations

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30
Q

What is the convention for numbering carbon atoms?

A

Clockwise to the oxygen is C1

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31
Q

What is cellobiose?

A

A repeating disaccharide unit in cellulose

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32
Q

What do mammals not have?

A

An enzyme that can hydrolyse the beta (1,4) glycosidic bonds in cellulose

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33
Q

What is lactose present in?

A

Milk

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34
Q

What don’t some people have?

A

The lactase enzyme and are unable to hydrolyse lactose

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35
Q

What are the enzymes involved in carbohydrate digestion?

A

Salivary amylase, pancreatic amylase, maltase, lactase, sucrase and isomaltase

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36
Q

What is the source of salivary amylase?

A

Salivary glands

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37
Q

What is the substrate for salivary amylase?

A

Starch

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38
Q

Where is the site of action for salivary amylase?

A

Mouth

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39
Q

What is the source of pancreatic amylase?

A

Pancreas

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40
Q

What is the substrate for pancreatic amylase?

A

Starch

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41
Q

Where is the site of action of pancreatic amylase?

A

Small intestine

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42
Q

What is the source of maltase?

A

Small intestine

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43
Q

What is the substrate of maltase?

A

Maltose

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44
Q

What is the site of action of maltase?

A

Small intestine

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45
Q

what is the source of lactase?

A

Small intestine

46
Q

What is the substrate of lactase?

47
Q

What is the site of action of lactase?

A

Small intestine

48
Q

What is the source of sucrase?

A

Small intestine

49
Q

What is the substrate of sucrase?

50
Q

What is the site of action of sucrase?

A

Small intestine

51
Q

What is the source of isomaltase?

A

Small intestine

52
Q

What is the substrate of isomaltase?

A

Isomaltose

53
Q

What is the site of action of isomaltase?

A

Small intestine

54
Q

What is amylose?

A

A linear polymer of alpha 1,4 linked glucose units

55
Q

What is amylopectin?

A

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

56
Q

What does glycogen have. similar branched structure to?

A

Amylopectin

57
Q

What can glycogen be present in?

A

Consumed foods such as liver and muscle

58
Q

What is glycogen synthesised in?

A

Animals from glucose and stored in the liver an muscle, then broken down to glucose when required by the body

59
Q

What does the breakdown of glycogen stored in liver and muscle cels to glucose require?

A

A debranching enzyme

60
Q

What does amylase do?

A

Hydrolyses alpha 1,4 glycosidic bonds

61
Q

What happens in starch digestion?

A

Repeated internal attack yielding smaller and smaller oligosaccharides producing maltose/isomaltose disaccharides as end products

62
Q

What is maltose broken down into?

A

2 glucose units form the linear parts of amylopectin

63
Q

What is isomaltose broken down into?

A

2 glucose units from the branched parts of amylopectin

64
Q

What is sucrose broken down into?

A

Fructose and glucose

65
Q

What is lactase broken down into?

A

Galactose and glucose

66
Q

What happens with the monosaccharides?

A

They are absorbed into the body

67
Q

What is a lactose intolerance?

A

Lactase enzyme deficiency (genetic basis)

68
Q

What does lactose intolerance cause?

A

Bloating, flatulence (wind) and diarrhoea due to fermentation of lactose by intestinal bacteria

69
Q

What does people with lactose intolerance need to do?

A

Avoid lactose in diet

70
Q

What does digestion of dietary protein supply?

A

Amino acids to make body proteins and essential amino acids which the body can’t synthesize

71
Q

What are dietary proteins a source of?

A

Nitrogen for purines, pyrimidines and haem

72
Q

What can carbon skeletons be used as?

A

Fuel (N converted to urea and excreted as urine)

73
Q

What are the essential amino acids?

A

Leucine, lysine, threonine, tryptophan, isoleucine, methionine, phenylalanine and valine (found in grains

74
Q

What is kwashiorkor the result of?

A

Deficiency of dietary protein which causes an osmotic imbalance in the gastrointestinal system, causing the abdomen to swell (oedema) due to retention of water

75
Q

What else happens because of kwashiorkor?

A

The level of albumin in the blood is low affecting colloidal osmotic (oncodic) pressure and also transport of molecules (hormones, drugs)

76
Q

What does protein digestion involve?

A

Hydrolysis of peptide bonds

77
Q

What is protein digestion performed by?

A

Several different proteases

78
Q

How are proteases secreted?

A

As inactive forms (zymogens or proenzymes)

79
Q

How are all proteases activated?

A

By cleavage of peptides from their strutcure

80
Q

What is protease specificity determined by?

A

Adjacent amino acid side chains (to the left)

81
Q

What side chains are adjacent to bonds cleaved by pepsin?

A

Aromatic (Phe, Tyr)

82
Q

What side chains are adjacent to bonds cleaved by trypsin?

A

Positively charged (Lys, Arg)

83
Q

What side chains are adjacent to bonds cleaved by chymotrypsin?

A

Aromatic (Phe, Tyr)

84
Q

What is the first stage of protein digestion?

A

Endopeptidases attack peptide bonds within the protein (peptide) polymer

85
Q

What are examples of endopeptidases?

A

Pepsin, trypsin and chymotrypsin

86
Q

What is the second stage of protein digestion?

A

Exopeptidases attack peptide bonds at the end of the protein (peptide) polymer

87
Q

What are examples of exopeptidase?

A

Aminopeptidases (from N terminus) and carboxypeptidases (from C terminus)

88
Q

What enzymes are involved in protein digestion?

A

Pepsin, trypsin, chymotrypsin, carboxypeptidase, aminopeptidase anf dipeptidase

89
Q

What is the source of pepsin?

A

Stomach mucous

90
Q

What is the substrate of pepsin?

A

Proteins, pepsinogen

91
Q

What is the site of action of pepsin?

92
Q

What is the source of trypsin?

93
Q

What is the substrate of trypsin?

A

Polypeptides, chymotripsinogen

94
Q

What is the site of action of trypsin?

A

Small intestine

95
Q

What is the source of chymotrypsin?

96
Q

What is the substrate of chymotrypsin?

A

Polypeptides

97
Q

What is the site of action of chymotrypsin?

A

Small intestine

98
Q

What is the source of carboxypeptidase?

99
Q

What is the substrate of caboxypeptidase?

A

Polypeptides

100
Q

What is the site of action of carboxypeptidase?

A

Small intestine

101
Q

What is the source of amino peptidase?

A

Small intestine

102
Q

What is the substrate of amino peptidase?

A

Polypeptides

103
Q

What is the site of action of amino peptidases?

A

Small intestine

104
Q

What is the source of dipeptidases?

A

Small intestine

105
Q

What is the substrate of dipeptidases?

A

Dipeptides

106
Q

What is the site of action of dipeptidases?

A

Small intestine

107
Q

When is pepsinogen activated to pepsin?

A

Following exposure to HCl in the stomach

108
Q

What does the acidic environment of the stomach cause?

A

Pepsinogen protein to unfold, which activates the pepsin protease and results in hydrolysis of part of the pepsinogen protein sequence to generate stably active leptin protease (produces more pepsin)

109
Q

What hydrolyses trypsinogen to trypsin?

A

A membrane bound enterokinase

110
Q

What hydrolyses chymotrypsinogen to chymotrypsin?

111
Q

What is procarboxypeptidase hydrolysed to?

A

Carboxypeptidase

BIOC192 (38 decks)

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