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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
What is maltose present in?
Honey
26
What is the glycosidic linkage in maltose?
Alpha (1,4)
27
What is sucrose hydrolysed to?
Glucose and fructose
28
What are cellobiose and lactose?
Enantiomers of one another
29
Where can the functional group of monosaccharides be?
In either of two orientations
30
What is the convention for numbering carbon atoms?
Clockwise to the oxygen is C1
31
What is cellobiose?
A repeating disaccharide unit in cellulose
32
What do mammals not have?
An enzyme that can hydrolyse the beta (1,4) glycosidic bonds in cellulose
33
What is lactose present in?
Milk
34
What don't some people have?
The lactase enzyme and are unable to hydrolyse lactose
35
What are the enzymes involved in carbohydrate digestion?
Salivary amylase, pancreatic amylase, maltase, lactase, sucrase and isomaltase
36
What is the source of salivary amylase?
Salivary glands
37
What is the substrate for salivary amylase?
Starch
38
Where is the site of action for salivary amylase?
Mouth
39
What is the source of pancreatic amylase?
Pancreas
40
What is the substrate for pancreatic amylase?
Starch
41
Where is the site of action of pancreatic amylase?
Small intestine
42
What is the source of maltase?
Small intestine
43
What is the substrate of maltase?
Maltose
44
What is the site of action of maltase?
Small intestine
45
what is the source of lactase?
Small intestine
46
What is the substrate of lactase?
Lactose
47
What is the site of action of lactase?
Small intestine
48
What is the source of sucrase?
Small intestine
49
What is the substrate of sucrase?
Sucrose
50
What is the site of action of sucrase?
Small intestine
51
What is the source of isomaltase?
Small intestine
52
What is the substrate of isomaltase?
Isomaltose
53
What is the site of action of isomaltase?
Small intestine
54
What is amylose?
A linear polymer of alpha 1,4 linked glucose units
55
What is amylopectin?
A branched polymer of alpha 1,4 and alpha 1,6 linked glucose units
56
What does glycogen have. similar branched structure to?
Amylopectin
57
What can glycogen be present in?
Consumed foods such as liver and muscle
58
What is glycogen synthesised in?
Animals from glucose and stored in the liver an muscle, then broken down to glucose when required by the body
59
What does the breakdown of glycogen stored in liver and muscle cels to glucose require?
A debranching enzyme
60
What does amylase do?
Hydrolyses alpha 1,4 glycosidic bonds
61
What happens in starch digestion?
Repeated internal attack yielding smaller and smaller oligosaccharides producing maltose/isomaltose disaccharides as end products
62
What is maltose broken down into?
2 glucose units form the linear parts of amylopectin
63
What is isomaltose broken down into?
2 glucose units from the branched parts of amylopectin
64
What is sucrose broken down into?
Fructose and glucose
65
What is lactase broken down into?
Galactose and glucose
66
What happens with the monosaccharides?
They are absorbed into the body
67
What is a lactose intolerance?
Lactase enzyme deficiency (genetic basis)
68
What does lactose intolerance cause?
Bloating, flatulence (wind) and diarrhoea due to fermentation of lactose by intestinal bacteria
69
What does people with lactose intolerance need to do?
Avoid lactose in diet
70
What does digestion of dietary protein supply?
Amino acids to make body proteins and essential amino acids which the body can't synthesize
71
What are dietary proteins a source of?
Nitrogen for purines, pyrimidines and haem
72
What can carbon skeletons be used as?
Fuel (N converted to urea and excreted as urine)
73
What are the essential amino acids?
Leucine, lysine, threonine, tryptophan, isoleucine, methionine, phenylalanine and valine (found in grains
74
What is kwashiorkor the result of?
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
What else happens because of kwashiorkor?
The level of albumin in the blood is low affecting colloidal osmotic (oncodic) pressure and also transport of molecules (hormones, drugs)
76
What does protein digestion involve?
Hydrolysis of peptide bonds
77
What is protein digestion performed by?
Several different proteases
78
How are proteases secreted?
As inactive forms (zymogens or proenzymes)
79
How are all proteases activated?
By cleavage of peptides from their strutcure
80
What is protease specificity determined by?
Adjacent amino acid side chains (to the left)
81
What side chains are adjacent to bonds cleaved by pepsin?
Aromatic (Phe, Tyr)
82
What side chains are adjacent to bonds cleaved by trypsin?
Positively charged (Lys, Arg)
83
What side chains are adjacent to bonds cleaved by chymotrypsin?
Aromatic (Phe, Tyr)
84
What is the first stage of protein digestion?
Endopeptidases attack peptide bonds within the protein (peptide) polymer
85
What are examples of endopeptidases?
Pepsin, trypsin and chymotrypsin
86
What is the second stage of protein digestion?
Exopeptidases attack peptide bonds at the end of the protein (peptide) polymer
87
What are examples of exopeptidase?
Aminopeptidases (from N terminus) and carboxypeptidases (from C terminus)
88
What enzymes are involved in protein digestion?
Pepsin, trypsin, chymotrypsin, carboxypeptidase, aminopeptidase anf dipeptidase
89
What is the source of pepsin?
Stomach mucous
90
What is the substrate of pepsin?
Proteins, pepsinogen
91
What is the site of action of pepsin?
Stomach
92
What is the source of trypsin?
Pancreas
93
What is the substrate of trypsin?
Polypeptides, chymotripsinogen
94
What is the site of action of trypsin?
Small intestine
95
What is the source of chymotrypsin?
Pancreas
96
What is the substrate of chymotrypsin?
Polypeptides
97
What is the site of action of chymotrypsin?
Small intestine
98
What is the source of carboxypeptidase?
Pancreas
99
What is the substrate of caboxypeptidase?
Polypeptides
100
What is the site of action of carboxypeptidase?
Small intestine
101
What is the source of amino peptidase?
Small intestine
102
What is the substrate of amino peptidase?
Polypeptides
103
What is the site of action of amino peptidases?
Small intestine
104
What is the source of dipeptidases?
Small intestine
105
What is the substrate of dipeptidases?
Dipeptides
106
What is the site of action of dipeptidases?
Small intestine
107
When is pepsinogen activated to pepsin?
Following exposure to HCl in the stomach
108
What does the acidic environment of the stomach cause?
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
What hydrolyses trypsinogen to trypsin?
A membrane bound enterokinase
110
What hydrolyses chymotrypsinogen to chymotrypsin?
Trypsin
111
What is procarboxypeptidase hydrolysed to?
Carboxypeptidase

BIOC192 (38 decks)

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