Lactose (a sugar)
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| - | Lactose is a sugar found in milk and other foods. It is formed by a condensation reaction of the building blocks glucose and galactose. A large part of the human adult population is lactose intolerant. Because they are unable to efficiently digest lactose into its building blocks, lactose builds up and causes symptoms such as stomach pain. Lactose-intolerant individuals either have to limit lactose intake or take supplements to help digest it. | + | '''Lactose''' is a sugar found in milk and other foods. It is formed by a condensation reaction (also called dehydration synthesis) of the building blocks glucose and galactose. A large part of the human adult population is lactose intolerant. Because they are unable to efficiently digest lactose into its building blocks, lactose builds up and causes symptoms such as stomach pain. Lactose-intolerant individuals either have to limit lactose intake or take supplements to help digest it. |
This page assumes basic textbook knowledge of carbohydrate chemistry. For a refresher, see the relevant section in the first chapters of any college biology textbook, e.g. [https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_2e_(OpenStax)/01%3A_Unit_I-_The_Chemistry_of_Life/1.03%3A_Biological_Macromolecules/1.3.03%3A_Carbohydrates this one]. | This page assumes basic textbook knowledge of carbohydrate chemistry. For a refresher, see the relevant section in the first chapters of any college biology textbook, e.g. [https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_2e_(OpenStax)/01%3A_Unit_I-_The_Chemistry_of_Life/1.03%3A_Biological_Macromolecules/1.3.03%3A_Carbohydrates this one]. | ||
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Lactose is a sugar; like many other sugars (glucose, fructose, cellulose, amylose), it has a name ending in -ose. | Lactose is a sugar; like many other sugars (glucose, fructose, cellulose, amylose), it has a name ending in -ose. | ||
| - | Lactose (a disaccharide) is formed by a condensation reaction of glucose (a monosaccharide) and galactose (another monosaccharide). | + | Lactose (a disaccharide) is formed by a condensation reaction of glucose (a monosaccharide) and galactose (another monosaccharide). When lactose is hydrolyzed, it yields the building blocks glucose and galactose, see below. |
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| - | When lactose is hydrolyzed, it yields the building blocks glucose and galactose, see below. | + | |
[[Image:Lactase reaction.PNG|500px]] | [[Image:Lactase reaction.PNG|500px]] | ||
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==Function== | ==Function== | ||
| - | Lactose is one of the main sources of energy (calories) in human breast milk and milk from other animals. As hunter-gatherers, adult humans had no significant source of lactose in their diet, and no need for the ability to digest it. This has changed in societies that include dairy as significant part of their diet. Some adults produce sufficient quantities of the enzyme [[ | + | Lactose is one of the main sources of energy (calories) in human breast milk and milk from other animals. As hunter-gatherers, adult humans had no significant source of lactose in their diet, and no need for the ability to digest it. This has changed in societies that include dairy as significant part of their diet. Some adults produce sufficient quantities of the enzyme [[Lactase_%28a_protein%29|lactase]], enabling them to digest substantial amounts of lactose in their diets by hydrolyzing it, while others don't. |
== Quiz == | == Quiz == | ||
<quiz display=simple> | <quiz display=simple> | ||
| - | {What kind of biomolecules is | + | {What kind of biomolecules is lactose?} |
-A. Nucleic acid | -A. Nucleic acid | ||
+B. Carbohydrate | +B. Carbohydrate | ||
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-D. Lipid | -D. Lipid | ||
| - | {What kind of saccharide is | + | {What kind of saccharide is lactose?} |
-A. Monosaccharide. | -A. Monosaccharide. | ||
+B. Disaccharide. | +B. Disaccharide. | ||
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-D. Polysaccharide. | -D. Polysaccharide. | ||
| - | {What are the building blocks of | + | {What are the building blocks of lactose (more than one answer)} |
+A. Glucose | +A. Glucose | ||
-B. Fructose. | -B. Fructose. | ||
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-D. Threose. | -D. Threose. | ||
| - | {What kind of simple sugars are the building blocks of | + | {What kind of simple sugars are the building blocks of lactose?} |
-A. Tetroses. | -A. Tetroses. | ||
-B. Pentoses. | -B. Pentoses. | ||
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-D. Heptoses. | -D. Heptoses. | ||
| - | {What is the bond called that needs to be hydrolyzed to digest | + | {What is the bond called that needs to be hydrolyzed to digest lactose?} |
-A. Phophodiester bond. | -A. Phophodiester bond. | ||
-B. Peptide bond. | -B. Peptide bond. | ||
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-D. Hydrogen bond. | -D. Hydrogen bond. | ||
| - | {What enzyme is required to hydrolyze (digest) | + | {What enzyme is required to hydrolyze (digest) lactose?} |
-A. Polymerase. | -A. Polymerase. | ||
-B. Protease. | -B. Protease. | ||
Current revision
Lactose is a sugar found in milk and other foods. It is formed by a condensation reaction (also called dehydration synthesis) of the building blocks glucose and galactose. A large part of the human adult population is lactose intolerant. Because they are unable to efficiently digest lactose into its building blocks, lactose builds up and causes symptoms such as stomach pain. Lactose-intolerant individuals either have to limit lactose intake or take supplements to help digest it.
This page assumes basic textbook knowledge of carbohydrate chemistry. For a refresher, see the relevant section in the first chapters of any college biology textbook, e.g. this one.
Structure
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Function
Lactose is one of the main sources of energy (calories) in human breast milk and milk from other animals. As hunter-gatherers, adult humans had no significant source of lactose in their diet, and no need for the ability to digest it. This has changed in societies that include dairy as significant part of their diet. Some adults produce sufficient quantities of the enzyme lactase, enabling them to digest substantial amounts of lactose in their diets by hydrolyzing it, while others don't.
