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Carbohydrates on the MCAT: Things to Know

January 28, 2022
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Part 1: IntroPart 2: Carbohydrates on the MCATPart 3: Example Carbohydrate Questions on the MCATPart 4: FAQs About the MCATPart 5: Conclusion

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. This article is a guide to help study the theme of carbohydrates on the MCAT.

The point of the MCAT is to evaluate your understanding of sociocultural, biological, and psychological influences on behavior and social interactions, in accordance with how the human body processes emotion and stress.

MCAT is used by admissions officers as a predictor of your academic achievements in medical school. The MCAT helps you hone your skills in basic science, verbal reasoning, and writing ability. Your MCAT scores weigh very heavily on your application. In fact, some schools have minimum cut-off MCAT scores that applicants must reach in order to even be considered.

Some more information about the MCAT:

The test itself consists of four sections: 

This exam usually runs for 7.5 hours and explores chemical and biological reactions with regard to the questions. There are three foundational concepts that you must study in order to shape your answers to the questions given. They are:

  1. Foundational Concept 1 – Biomolecules with unique properties that determine how they contribute to the structure and function of cells, how they participate in the processes necessary to maintain life.
  2. Foundational Concept 2 – Highly-organized ensembles of molecules, cells, and organs interact to perform the functions of living organisms.
  3. Foundational Concept 3- Complex systems of tissues and organs that sense internal and external environments of multicellular organisms, and through integrated functioning, maintain a stable internal environment with a changing external environment.
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Carbohydrates on the MCAT

Carbohydrates, as you know, 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. 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. 

Monosaccharides are simple sugars, the most common being glucose. 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.

Disaccharides are sugar molecules composed of two monosaccharides. The bond between the two is called a glycosidic bond. Disaccharides are simple sugars and are classified into two groups: reducing sugars (can be a reducing agent) and non-reducing sugars (cannot act as a reducing agent) Non-reducing sugars – cannot act as a reducing agent. Disaccharides are water-soluble and colorless when put in water. Some have a sweet taste to them, others do not.

Polysaccharides are a carbohydrate made out of more than two monosaccharides linked by glycosidic bonds, creating a chain. They form via condensation polymerization and are insoluble in water. They lack a sweet taste, and almost all polysaccharides are non-reducing agents due to their complex structure.

Useful Reactions to Know

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. 

  1. Fischer and Haworth Projections

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.  

  1. Cyclization

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.

  1. Benedict’s reagent and Tollen’s reagent

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.

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Example Carbohydrate Questions on the MCAT

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.

Question #1

"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:
Pic_1
Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:
Pic_2
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.

Question #2

"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.

Question #3

"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.

FAQs About the MCAT

We've outlined several questions and answers below to help you increase your knowledge about Carbohydrates on the MCAT.

1. Which carbohydrates do I need to know?

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.

2. Which Sugars are going to be in the Carbohydrate section?

The general list is as follows:

These are said to be the structural sugars to help you figure out more complex formulas when writing the MCAT.

3. Are there any online resources to help me study?

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.

4. What would be the best time to take the MCAT?

To put it simply, the best time to take the exam is when you feel most ready. This varies from person to person, there is no specific ‘best’ time to take it. Just ask yourself: when do you want to get into medical school? Should you take the test more than once? Have you studied all the content on the exam?

Medical schools are able to see your scored exams, and there are limits on the number of times you can take the MCAT. Make appointments with a pre-health advisor to discuss the MCAT essentials.

5. Are there required courses or prerequisites I should take?

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.

6. How often can I take the MCAT?

As stated above, there are limits on how many times you can take the exam. Voiding and no-shows also count to your chances. You can be registered for one seat at a time, and here are the general intervals:

Conclusion

When applying to medical school, you should understand there is a set of principles to help students and staff alike that fairness and equity is represented in the professionalism throughout the medical school application process. Understanding these principles are important in your success in getting into medical school.

These protocols - known as ‘traffic rules’- are designed as guidelines for the types of professional communications expected of future medical and PhD students and medical school personnel. Members of the admissions community create these rules to help make sure all the applicants receive fair timing on notifications and the status of their medical school applications. They also help school programs ensure all their open positions are filled. These rules, however, do not overthrow the policies and timelines of individual medical schools.

The protocols are periodically reviewed by the AAMC’s Committee on Admissions and approved by the AAMC’s Council of Deans. This year, having reviewed the protocols, along with other aspects of the admissions process, they have identified opportunities to define high standards, ethical behavior, and professionalism in the application process for applicants and medical schools alike. Following the recommended protocols helps admissions policies and practices be applied equitably across the entire admissions process.

As a medical student, your actions during the application process are expected to be conducted in the spirit of professionalism and ethics seen in a physician. You are responsible for being honest throughout the entire process and you must understand how the enrollment process works for each school you apply to. Each school does have its own policies regarding admission and outline expectations and requirements. You must follow all specific deadlines and offer truthful, accurate information in your application. The American Medical College Application Service tool gives you a better idea of the seat availability of the medical school program of your choice. This also helps other applicants receive notification about the outcome of their applications to ensure medical schools will not have unfilled seats for their entering year. Every medical school is different, so you must be sure to review school-specific instructions, policies, and requirements when using this tool during the application process.

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.

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