Which monomer units make up lactose

Both are disaccharides with different shapes and different properties. To answer this question, we'll need to have some background information on each of the sugars shown in the answer choices. A glycosidic bond between glucose and galactose will produce the disaccharide lactose, which is thus the correct answer.

Sucrose is a disaccharide composed of glucose and fructose. Maltose is also a disaccharide composed of two glucose molecules.

Moreover, fructose and xylose are monosaccharides. If you've found an issue with this question, please let us know. With the help of the community we can continue to improve our educational resources. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.

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Email address: Your name:. Example Question 1 : Identifying Disaccharides. Possible Answers: Sucrose. Correct answer: All of these are disaccharides. Explanation : Review the specific types of monosaccharides and glycosidic bonds that are involved in these disaccharides. Report an Error. Example Question 2 : Identifying Disaccharides. Maltose is a disaccharide composed of which two monosaccharides?

Explanation : Maltose, which is made up of two glucose monomers joined by an alpha-1,4 linkage, is the correct answer. Example Question 3 : Identifying Disaccharides. Possible Answers: None of these are found in fructose.

Correct answer: None of these are found in fructose. Explanation : Fructose is a monosaccharide; therefore, it is only made up of one type of carbohydrate. Example Question 4 : Identifying Disaccharides. Possible Answers: Both should be avoided. Correct answer: Neither needs to be avoided. Explanation : Lactose is a disaccharide that needs to be broken down to its monosaccharide components in the gut so that it can be absorbed.

Example Question 5 : Identifying Disaccharides. Lactose II. Galactose III. Possible Answers: II only. Correct answer: I and III. Figure 5. Glucose is distinguished by its structure: five carbons in the ring with one oxygen; CH 2 OH attached to a carbon; and OH and H groups attached to the other carbons. This sugar is known as blood sugar and is an immediate source of energy for cellular respiration.

Galactose is a sugar monomer in milk and yogurt. This is a sugar found in honey and fruits. We also have disaccharides as sugars in food. Disaccharides are dimers of the monomers we just discussed and are shown below.

One of the most common disaccharides is sucrose , which is common table sugar and is shown in Figure 5. It is a dimer of glucose and fructose. Another common sugar dimer is lactose. It is the major sugar in milk and a dimer of galactose and glucose see Figure 5. Maltose 5. It is a dimer made up of glucose and glucose. In the next section, we will discuss what starch and cellulose are composed of in order to see why maltose is a product of starch digestion.

All carbohydrate polymers are monomers that connect with what is called a glycosidic bond. For example, sucrose is a dimer of glucose and fructose. Figure 3. Five and six carbon monosaccharides exist in equilibrium between linear and ring forms.

Fructose and ribose also form rings, although they form five-membered rings as opposed to the six-membered ring of glucose. During this process, the hydroxyl group of one monosaccharide combines with the hydrogen of another monosaccharide, releasing a molecule of water and forming a covalent bond.

A covalent bond formed between a carbohydrate molecule and another molecule in this case, between two monosaccharides is known as a glycosidic bond Figure 4. Glycosidic bonds also called glycosidic linkages can be of the alpha or the beta type.

Figure 4. Sucrose is formed when a monomer of glucose and a monomer of fructose are joined in a dehydration reaction to form a glycosidic bond.

In the process, a water molecule is lost. By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group. In sucrose, a glycosidic linkage is formed between carbon 1 in glucose and carbon 2 in fructose.

Common disaccharides include lactose, maltose, and sucrose Figure 5. Lactose is a disaccharide consisting of the monomers glucose and galactose. It is found naturally in milk. Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose molecules. The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose. Figure 5. Common disaccharides include maltose grain sugar , lactose milk sugar , and sucrose table sugar.

The chain may be branched or unbranched, and it may contain different types of monosaccharides. The molecular weight may be , daltons or more depending on the number of monomers joined. Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of a mixture of amylose and amylopectin both polymers of glucose.

The starch in the seeds provides food for the embryo as it germinates and can also act as a source of food for humans and animals. The starch that is consumed by humans is broken down by enzymes, such as salivary amylases, into smaller molecules, such as maltose and glucose. The cells can then absorb the glucose. The numbers and refer to the carbon number of the two residues that have joined to form the bond. Figure 6. Amylose and amylopectin are two different forms of starch. Because of the way the subunits are joined, the glucose chains have a helical structure.

Glycogen not shown is similar in structure to amylopectin but more highly branched. Glycogen is the storage form of glucose in humans and other vertebrates and is made up of monomers of glucose.

Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells.