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Questions and Answers
Which of the following are dietary carbohydrates?
What is the major product of carbohydrate digestion?
Glucose
What are the two forms of glycogen storage in animals?
Muscle glycogen and liver glycogen
Cellulose is the main structural component of the rigid cell wall.
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What is the yield of energy when 1 g of carbohydrates is oxidized?
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What type of sugar is glucose categorized as?
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What are amino sugars derived from?
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Sialic acid is a family of compounds that contains ___ carbon atoms.
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What are the main types of dietary carbohydrates?
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Fiber can be broken down into sugar molecules.
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What is the major product of carbohydrate digestion?
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What role does glycogen play in the body?
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Which of the following is not a function of carbohydrates?
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What is cellulose primarily known for?
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What is the empirical formula for simple sugars?
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Match the type of sugar with the number of carbon atoms it contains:
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What are amino sugars commonly found in?
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What is the importance of sialic acid in the human body?
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Study Notes
Carbohydrates: An Overview
- Dietary carbohydrates include starch, sucrose, lactose, and indigestible fibers.
- Fiber is a type of carbohydrate that the body cannot digest.
- Most carbohydrates break down into sugar molecules called glucose, but fiber passes through the body undigested.
- The primary product of carbohydrate digestion is glucose, but some galactose and fructose are also produced.
- Glucose is a major fuel source oxidized by cells for energy.
- After a meal, glucose is converted to glycogen or triacylglycerol (TAG).
- Glucose is also converted into compounds like proteoglycans, glycoproteins, and glycolipids.
- Fructose and galactose are converted to intermediates in the pathways by which glucose is metabolized.
- Glycogen is the major storage form of carbohydrates in animals.
- The largest glycogen stores are found in muscle and liver.
- Muscle glycogen is used to generate ATP for muscle contraction.
- Liver glycogen is used to maintain blood glucose during fasting or exercise.
- The maintenance of blood glucose is a major function of the liver.
Carbohydrates are Essential for Life
- Carbohydrates are the staff of life for most organisms and the most abundant compound found in nature.
- Cellulose is the most abundant carbohydrate and is found in the woody structures and fibers of plants.
- Carbohydrates have two major biological functions:
-
Storage forms of fuel
- 1 gram of carbohydrate yields 4 kilocalories of energy when oxidized.
- Glucose is the major source of energy in our bodies.
- Starch is the chief storage form of carbohydrates in most plants.
- Glycogen is the chief storage form of carbohydrates in animals.
-
Structural elements
- Cellulose is the main structural component of the rigid cell wall in plants.
- Acid mucopolysaccharides and proteoglycans are important structural polysaccharides in animal tissue.
-
Storage forms of fuel
Other Functions of Carbohydrates
- Act as lubricants of skeletal joints
- Major components of the cell wall of bacteria
- Provide adhesion between cells.
- Confer biological specificity on the surface of animal cells.
Classification of Carbohydrates
- Carbohydrates can be classified based on the number of sugar units they contain.
-
Simple Sugars / Monosaccharides
- Contain a single polyhydroxyl aldehyde or ketone unit.
- Aldehydes: contain the group ---CHO, formed by the oxidation of alcohols.
- Ketones: Contain a carbonyl group attached to 2 carbon atoms.
- Monosaccharides cannot be hydrolyzed into a simpler form.
- They have the empirical formula of CnH
2n On. - They contain 2-10 carbon atoms.
- The names of sugars end with "ose."
Naming Simple Sugars
-
According to the number of carbon atoms (# of carbon atoms)
- Triose: contains 3 carbon atoms (glyceraldehyde).
- Tetrose: contains 4 carbon atoms (erythrose).
- Pentose: contains 5 carbon atoms (ribose).
- Hexose: contains 6 carbon atoms (glucose).
-
According to the functional group they contain
- Aldoses: contain the aldehyde group (mannose, galactose).
- Ketoses: contain the ketone group (fructose).
- Combinations of the 1st and 2nd methods: aldotriose, ketopentose.
-
According to the ring structure
- Furanose: 5-membered ring.
- Pyranose: 6-membered ring.
Important Derivatives of Monosaccharides
-
Amino sugars
- Two amino sugars are widely distributed in plants and animals:
- Glucosamine: a product of the hydrolysis of chitin, which is the major polysaccharide of the shell of insects and crustaceans.
- Galactosamine: found in the characteristic polysaccharides of cartilage and chondroitin sulfates.
- Two amino sugars are widely distributed in plants and animals:
-
Sialic acid
- A family of compounds containing 9 carbon atoms that are acetylated derivatives of neuraminic acid.
- Found widely distributed in animal tissues and related forms are found to a lesser extent in other organisms.
- Humans have the highest sialic acid content in the brain, where they play an important role in neural transmission and ganglioside structure.
- Examples:
- N-acetylneuraminic acid: an important building block of the oligosaccharide chains found in glycoproteins and glycolipids of the cell coats and membranes of animal tissue.
-
N-acetylmuramic acid
- The major building block of the polysaccharide backbone of the bacterial cell wall.
Compound Sugars / Oligosaccharides
- Contain 2-10 units of monosaccharides.
-
Disaccharides
- The most abundant disaccharides are:
- Sucrose (composed of glucose and fructose)
- Lactose (composed of glucose and galactose)
- Maltose (composed of two glucose units)
- Maltose- is found in starchy foods like, bread, barley, and rice.
- Sucrose- is the most common disaccharide found in sugarcane, maple sap, and fruits.
- Lactose- is the major carbohydrate in milk and milk products.
- The most abundant disaccharides are:
-
Trisaccharides and tetrasaccharides
- Are less common than disaccharides but contain 3 and 4 sugar units, respectively.
Polysaccharides / Complex Sugars
- Contain a large number of monosaccharides.
- **Starch**
- The chief storage form of carbohydrates in plants.
- Polysaccharide composed of glucose units.
- Two types: Amylose and Amylopectin.
- Amylose is a linear polymer of glucose.
- Amylopectin is a branched polymer of glucose.
- **Glycogen**
- Highly branched polymer of glucose.
- The chief storage form of carbohydrates in animals.
- **Cellulose**
- Linear polymer of glucose.
- The main structural component of the rigid cell wall in plants.
- **Chitin**
- A linear polymer of N-acetylglucosamine.
- Found in the exoskeletons of insects and crustaceans.
- **Other polysaccharides**
- Heparin: Prevents blood clotting.
- Hyaluronic Acid: A component of connective tissue.
- Chondroitin Sulfate: A component of cartilage.
- **Mucopolysaccharides**
- Complex carbohydrates that contain amino sugars.
- Found in connective tissue, cartilage, and bone.
Digestion and Absorption of Carbohydrates
- Digestion starts in the mouth with salivary amylase.
- Absorption takes place in the small intestine.
- Dietary fibers are not digested but are important for digestive health and other functions.
- After digestion and absorption, glucose is transported to various tissues and cells to be used as energy.
Regulation of Blood Glucose Levels
- Insulin is a hormone that lowers blood glucose levels.
- Glucagon is a hormone that raises blood glucose levels.
- The liver plays a key role in regulating blood glucose levels by storing and releasing glycogen.
Carbohydrates and Health
-
Dietary fiber
- Helps maintain regular bowel movements.
- May reduce risk of heart disease, stroke, and diabetes.
- Plays a role in weight management.
-
Sugary drinks
- Linked to increased risk of obesity, type 2 diabetes, and cardiovascular disease.
-
Added sugars
- Contribute to weight gain and other health problems.
- It is recommended to limit added sugar intake.
Key Facts
- Monosaccharides: Single sugar units.
- Disaccharides: Two sugar units.
- Polysaccharides: Many sugar units.
- Glucose: Primary energy source for the body.
- Glycogen: Storage form of glucose in animals.
- Cellulose: Structural component of plants.
- Fiber: Indigestible carbohydrate.
- Insulin: Hormone that lowers blood glucose levels.
- Glucagon: Hormone that raises blood glucose levels.
Carbohydrate Overview
- Dietary carbohydrates include starch, sucrose, lactose and indigestible fibers.
- Fiber is a type of carbohydrate that the body cannot digest.
- Most carbohydrates are broken down into sugar molecules called glucose.
- Fiber passes through the body undigested.
- Glucose is the major fuel source for cells and is oxidized for energy.
- After a meal, glucose is converted to glycogen or TAG (triacylglycerol).
- Glucose is also converted to compounds like proteoglycans, glycoprotein, and glycolipids.
- Fructose and Galactose are converted to intermediates in pathways that metabolize glucose.
- Glycogen is the major storage form of carbohydrates in animals.
- The largest glycogen stores are in muscle and liver.
- Muscle glycogen is used to generate ATP for muscle contraction.
- Liver glycogen is used to maintain blood glucose during fasting or exercise.
- The maintenance of blood glucose is a major function of the liver.
Carbohydrate Functions
- Carbohydrates are the staff of life for most organisms and the most abundant compound found in nature.
- Cellulose is the most abundant carbohydrate and is found in the woody structures and fibers of plants.
- Carbohydrates have two major biological functions:
-
Storage forms of fuel:
- 1 gram of carbohydrate oxidized yields 4 kilocalories of energy.
- Glucose is the major source of energy in the body.
- Starch is the chief storage form of carbohydrates in most plants.
- Glycogen is the chief storage form of carbohydrates in animals.
-
Structural elements:
- Cellulose is the main structural component of the rigid cell wall.
- Acid mucopolysaccharides and proteoglycans are important structural polysaccharides in animal tissues.
-
Storage forms of fuel:
Other Carbohydrate Functions
- Act as lubricants of skeletal joints.
- Major components of the cell wall of bacteria.
- Provide adhesion between cells.
- Confer biological specificity on the surface of animal cells.
Carbohydrate Classification
- Carbohydrates are classified according to the number of sugar units they contain.
Simple Sugars / Monosaccharides
- Contain a single polyhydroxyl aldehyde or ketone unit.
- Aldehydes contain the group ---CHO, formed by the oxidation of alcohols.
- Ketones contain a carbonyl group attached to two carbon atoms.
- Cannot be hydrolyzed into a simpler form.
- Have an empirical formula of CnH
2n On. - Contain 2-10 carbon atoms.
- Sugar names end in "ose".
Naming Monosaccharides
- According to the number of carbon atoms:
- Triose - 3 carbon atoms (glyceraldehyde)
- Tetrose - 4 carbon atoms (erythrose)
- Pentose - 5 carbon atoms (ribose)
- Hexose - 6 carbon atoms (glucose)
- According to the functional group:
- Aldoses - contain the aldehyde group (mannose, Galactose)
- Ketoses - contain the ketone group (fructose)
- Combination of the above methods: aldotriose, ketopentose.
- According to the ring structure:
- Furanose - 5 membered ring.
- Pyranose - 6 membered ring.
Important Monosaccharide Derivatives
Amino Sugars
- Glucosamine - product of hydrolysis of chitin (the major polysaccharide of insect and crustacean shells).
- Galactosamine - found in characteristic polysaccharides of cartilage and chondroitin sulfates.
Sialic Acid
- A family of compounds that contains 9 carbon atoms and are acetylated derivatives of neuraminic acid.
- Found widely distributed in animal tissues and related forms are found in other organisms like micro-algae, bacteria, and archaea.
- The brain has the highest sialic acid content.
- Important role in neural transmission and ganglioside structure.
- N-acetylneuraminic acid - important building block of the oligosaccharide chains found in glycoprotein and glycolipids of the cell coats and membranes of animal tissues.
N-acetylmuramic Acid
- Major building block of the polysaccharide backbone of the bacterial cell wall.
Compound Sugars / Oligosaccharides
- Consist of 2-10 monosaccharide units linked by glycosidic bonds.
- Can be hydrolyzed in the presence of acids or enzymes into their constituent monosaccharide units.
- Common examples: Disaccharides (2 units) - sucrose, lactose, maltose.
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Description
This quiz covers the essential aspects of dietary carbohydrates, including their types such as starch, sucrose, and fiber. Learn about the digestion process, the role of glucose as a key energy source, and the storage of carbohydrates in the body. Test your understanding of how carbohydrates function and their importance in nutrition.
