Biochemistry : Identifying Biochemical Molecules

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #2 : Identifying Disaccharides

Lactose intolerance is a very common disorder, which involves a decrease in the function of the enzyme lactase. Which of the following should be avoided in a patient with lactose intolerance?

Possible Answers:

Neither needs to be avoided

Galactose

Both should be avoided

Glucose

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). Lactose is made up of galactose and glucose monosaccharide units. An enzyme called lactase, found on the intestinal walls, is used to break down lactose to galactose and glucose. A person with lactose intolerance lacks lactase and, therefore, cannot break down lactose to its components. This leads to malabsorption of lactose. However, there is no problem with galactose and glucose absorption. This means that a patient with lactose intolerance can still digest galactose and glucose if given separately.

Example Question #1 : Identifying Disaccharides

Hypoglycemia is a disorder that signifies low levels of glucose in the blood. In some cases of hypoglycemia, glucose levels can be brought back to normal via consumption of sugars. What sugar(s) can be administered to a patient with hypoglycemia?

I. Lactose

II. Galactose

III. Sucrose

Possible Answers:

I and III

I only

II only

I and II

Correct answer:

I and III

Explanation:

As the question states, hypoglycemia is characterized by low levels of glucose in the blood. To bring the glucose levels back to normal, one can ingest foods that contain high amounts of glucose. To solve this question we need to decide which of the stated options can be broken down to glucose. Lactose is a disaccharide that is made up of glucose and galactose. An enzyme, called lactase, breaks down lactose to its components, which can then be absorbed by the intestinal cells; therefore, ingesting glucose will increase glucose levels in the blood. Similarly, sucrose is a disaccharide made up of fructose and glucose; therefore, ingesting sucrose will also increase glucose levels in the blood.

Galactose is a monosaccharide and, therefore, cannot be broken down to any further. It is absorbed as galactose by the intestinal cells. This will not increase the concentration of glucose in the blood.

Example Question #2 : Identifying Disaccharides

Which reducing sugar(s) is/are formed from two glucose molecules connected by a 1 to 4 linkage?

Possible Answers:

Cellobiose

More than one of these

Maltose

Sucrose

Lactose

Correct answer:

More than one of these

Explanation:

Maltose, made from the breakdown of starch, contains a 1 to 4 alpha linkage, and cellobiose, made from the breakdown of cellulose, contains a 1 to 4 beta linkage. Both are disaccharides with different shapes and different properties.

Example Question #1 : Identifying Disaccharides

Which of the following sugars is composed of glucose and galactose?

Possible Answers:

Maltose

Sucrose

Fructose

Lactose

Xylose

Correct answer:

Lactose

Explanation:

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.

Example Question #1 : Identifying Nitrogenous Bases And Derivatives

Whichof the following is formed from hypoxanthine attached to ribose?

Possible Answers:

Inosine

Guanosine

Pseudouridine

Dihydrouridine

Correct answer:

Inosine

Explanation:

The minor base (modified base) inosine is essential for translation and commonly found in tRNA wobble base pairing.

Example Question #51 : Identifying Biochemical Molecules

What is the name of the pictured fatty acid? 

Arachidonic acid

Possible Answers:

Linoleic acid

Eicosapentaenoic acid

Palmitoleic acid

Oleic acid

Arachidonic acid

Correct answer:

Arachidonic acid

Explanation:

The pictured structure represents arachidonic acid due to the 20-carbon carboxylic acid chain with characteristic unsaturated (double) bonds after carbons 5, 8, 11, and 14.

Example Question #52 : Identifying Biochemical Molecules

Identify the common name of the fatty acid shown here.

Real oleic acid

Possible Answers:

Linoleic acid

Palmitic ccid

Arachidonic acid

Oleic acid

Myristic acid

Correct answer:

Oleic acid

Explanation:

Oleic acid is a fatty acid consisting of 18 carbon molecules and a single unsaturated (double) bond after carbon 9, as pictured.

Example Question #1 : Identifying Specific Lipid Structures

What hormone does this structure represent?

Cholesterol

Possible Answers:

Cholesterol

Luteinizing hormone

Estrogen

Progesterone

Testosterone

Correct answer:

Cholesterol

Explanation:

The structure represents cholesterol. The hydroxyl group attached to the terminal cyclohexane and the 6-carbon chain on the opposite end are easily recognizable substituents.

Example Question #1 : Identifying Specific Lipid Structures

Organic peanut butter contains both saturated and unsaturated fats.

What is the difference between saturated and unsaturated fats?

Possible Answers:

Unsaturated fats contain double bonds and saturated fat do not

Unsaturated fats are lipids and saturated fats are carbohydrates

Unsaturated fats do not contain glycogen and saturated fats do

Unsaturated fats do not contain cholesterol and saturated fats do

Correct answer:

Unsaturated fats contain double bonds and saturated fat do not

Explanation:

Unsaturated fats are said do be unsaturated because of their lack of saturation with hydrogen atoms, due to carbon's ability to make four bonds, and one or more carbons in the hydrocarbon tail of an unsaturated fatty acid contains a double bond to another carbon. Both unsaturated and saturated fats are lipids, but neither contain cholesterol nor glycogen.

Example Question #3 : Identifying Specific Lipid Structures

Which of the following associations about lipids is false?

Possible Answers:

Triacylglycerols - no hydrophobic fatty acid tails

Steroid - multiple rings

Isoprene - five-carbon atoms

Glycolipids - hydrophobic fatty acid tails

Phospholipid - hydrophobic fatty acid tail

Correct answer:

Triacylglycerols - no hydrophobic fatty acid tails

Explanation:

Triacylglycerols, like phospholipids and glycolipids, have long, hydrophobic, fatty acid tails. Steroids are characterized by their ABCD ring structure. Isoprene, the building block of steroids and polyisoprenoids, has five carbon atoms.

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