Reviewed by:
Former Chief Resident in Anesthesiology, Weill Cornell Medicine, & Admissions Officer, Columbia University
Reviewed: 10/12/23
Read on below to learn what you need to know about carbohydrates on the MCAT and review example MCAT Carbohydrate questions and answers.
The Medical College Admissions Test (MCAT) is an entrance exam for prospective medical students in North America. It is a computer-based test that centers on physical and biological sciences, verbal reasoning, and writing skills. Hundreds of prospective medical school students take the test annually, seeking admission into medical school.
At Inspira Advantage, our job is to break down the medical school admissions process into manageable steps - including the MCAT! Though it may seem intimidating, our experts have compiled important information on each section of the MCAT to ensure you have all the study materials necessary to get prepared for test day.
This article is a guide to help study the theme of carbohydrates on the MCAT, which appear on many of the questions in the Biological and Biochemical Foundations of Living Systems section. We’ll cover common reactions on the MCAT you need to know, sample carbohydrates questions on the MCAT, and answer some of the most frequently asked questions on the subject.
Let’s get started!
Carbohydrates are biological components made of carbon, hydrogen, and oxygen and are broken down in chains by your digestive enzymes in order to fuel your body with appropriate nutrients. In this section, we cover the types of carbohydrates and the common sugars on the MCAT you need to know.
Carbohydrates come in three types: monosaccharides, disaccharides, and polysaccharides. When learning about carbohydrates, the MCAT will ask about each class of carbohydrates and the essential role they play in humans and other living organisms.
These classes of sugars are categorized as “reducing” and “non reducing.”A reducing sugar acts as a reducing agent, which is identifiable through the presence of free anomeric carbon, meaning that it has a glycosidic bond. A non-reducing sugar lacks the free anomeric carbon.
Let’s break down the three types of carbohydrates:
Simple sugars are known as monosaccharides, with glucose being the most common. They come in typically three to seven carbon atoms. All are considered reducing sugars.
Regardless of form, monosaccharides share a common chemical makeup: one part carbon atom, two parts hydrogen atoms, and one part oxygen atom. Disaccharides and Polysaccharides’ chemical makeup differs from these.
Comprising two monosaccharides, disaccharides are sugar molecules that are connected by a glycosidic bond. These simple sugars can be categorized into two groups, namely reducing sugars (able to act as reducing agents) and non-reducing sugars (incapable of acting as reducing agents).
When dissolved in water, disaccharides are colorless and water-soluble. While some disaccharides have a sweet taste, others are not sweet.
Polysaccharides are carbohydrates that consist of chains of more than two monosaccharides linked together by glycosidic bonds. They are formed through condensation polymerization and are not soluble in water. Polysaccharides do not have a sweet taste, and due to their complex structure, nearly all of them are non-reducing agents.
Here are some common carbohydrate reactions that can show up on the MCAT. These formulas can be applied to many equations when covering the topic of carbohydrates on the exam.
Carbohydrates can be represented in many forms. With the Fischer projection, it depicts a two-dimensional representation of a molecule that gives three-dimensional data. In a diagram, horizontal lines can be seen as ‘wedges’ that go outwards. The vertical lines are seen as ‘dashes’ – where the functional groups are going inwards.
The Haworth projection is a cyclic shape of sugar, where the carbon has two bonds to oxygen. These are seen as the standard depiction in organic chemistry for carbohydrate illustrations. The Haworth projection causes thicker bonds between carbon atoms and represents those closest to the observer.
When cyclic sugars are formed through intramolecular reactions (reactions between two functional groups of the same molecule), sugars known as aldoses form a hemiacetal. When a ketose only has a ketone group and no other further oxidized group, their cyclization forms a hemiketal.
When dissolved in solution, most sugars have spontaneous cyclization, also known as mutarotation. This allows many sugars to be found in various combinations and linear forms.
These two reagents are commonly used to detect the presence of reducing sugars. They react with reducing functional groups in their own unique ways: Benedict’s reacts with aldoses to form a red copper-like substance, while Tollen’s reacts with aldehydes to form a silver, mirror-like substance.
Below are some sample questions (along with answers and explanations) to help you understand how to approach the exam questions, figure out the proper formula, and the reasoning aspects of it as well.
"Drain cleaners are a common household staple used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominantly of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.
A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:
Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:
In contrast to the proteins in Reactions 1 and 2, the body uses carbohydrates __________."
Possible Answers:
to store energy for use over many days
to function as a secondary energy source after fatty acids have been oxidized
to dissolve nonpolar solutes in blood
to store energy for immediate use
to create structural elements of cells
Correct answer:
to store energy for immediate use
Explanation:
Carbohydrates are the energy currency of cells. They are burned first before fats and proteins in order to generate that energy. Proteins, on the other hand, are usually the functional biomolecules, fulfilling structural and enzymatic roles.
"Which of the following accurately describes glucose?"
Possible Answers:
Aldopentose
Ketopentose
Ketohexose
Aldohexose
Correct answer:
Aldohexose
Explanation: Glucose consists of six carbons. When not in its ring form, there is an aldehyde at the end of the molecule, thus making glucose an example of an aldohexose.
"Which of the following carbohydrates is created in animals, but not in plants?"
Possible Answers:
Amylose
Glycogen
Cellulose
Starch
Correct answer:
Glycogen
Explanation: Glucose stored in animal cells are known as glycogen. Plants store glucose as either starch or cellulose. Amylose is a specialized component of starch and plays a pivotal role in plant energy storage. Plants do not form glycogen in the same way that humans cannot form or break down cellulose.
Here are our answers to some frequently asked questions about carbohydrates on the MCAT.
The top classes of carbohydrates you must know are mono-, di, and poly-saccharides for the MCAT. A good tip would be to create a flow chart and break each class down into their reactions, their components, and some examples of them. For instance, disaccharides include maltose, lactose, and sucrose.
The general list of sugars on the MCAT is as follows:
These are said to be the structural sugars to help you figure out more complex formulas when writing the MCAT.
Yes. There are different online websites that can cater to your study plan, as well as offering different teaching techniques and accommodations for those seeking it. The resources are always available, ranging from the Khan Academy to Youtube.
Memorizing disaccharides for the MCAT can be challenging, but there are a few techniques that can help make the process easier. Creating flashcards, using mnemonic devices, and studying practice problems are all excellent ways to study. Remember, it's important to understand the concepts behind the disaccharides and how they are formed rather than just memorizing them.
All of the MCAT content is usually covered in introductory courses at many post-secondary institutions. Introductory biology, chemistry, organic chemistry, physics, and the like are usually taught in the first semester during the first years. If you are unsure about it, talk with a pre-med advisor about helpful courses that can aid in meeting your educational goals.
While studying for the MCAT, you should get familiar with the following monosaccharides:
In addition to knowing the structures of these monosaccharides, you’ll also need to understand their functions and roles in various metabolic processes.
The MCAT test has concepts that deal with natural, social, and behavioral sciences. Critical analysis and reasoning skills are essential for one to pass it and get into medical school. This article can help shed light on where to start when answering for carbohydrates and make studying a bit more organized and easier.
When studying biochemistry on the MCAT, make sure to focus on fully understanding each concept rather than focusing solely on memorization. The questions on the MCAT will be challenging, but will ultimately be manageable if you have a firm grasp of the material on each section.
Good luck!
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