Regulation of Metabolism on the MCAT

Imagine you are an assembly worker manufacturing cars. With your help, the machines make the process much quicker. Your job is to also regulate the number of cars being made. Without your help, the machines cannot stop or start assembling car parts together, resulting in an excess or not enough cars that meet consumer demands. 

In a similar manner to assembly line machines, enzymes act to increase the rate at which metabolism occurs; however, this must be regulated. These processes are regulated by metabolites to increase or decrease the activity of enzymes so that an adequate amount of product can be made to meet metabolic demands. 

Now that we have gone over an analogy of the regulation of metabolism, we can dive a little further into the key terms, definitions, and pathways that will be important for the MCAT

Let’s get started!

Regulation of Metabolism on the MCAT: What You Need to Know

The regulation of metabolism will show up in the Bio/Biochem section of the MCAT.

Introductory biochemistry accounts for 25% of the Biological and Biochemical Foundations of Living Systems section (Bio/Biochem) and 25% of the Chemical and Physical Foundations of Biological Systems section (Chem/Phys).

In this section, your understanding of negative and positive feedback mechanisms, which enzymes are regulated, and under what conditions will be fundamental to answering these questions.

Important Sub-Topics - Regulation of Metabolism

Allosteric and Hormonal Regulation of Carbohydrate Metabolism 

Enzymes of carbohydrate metabolism must be regulated through feedback pathways. Products that are produced downstream have the ability to modulate the activity of enzymes upstream. 

This is either completed through a positive feedback or negative feedback mechanism. The former involves a stimulation of an earlier step which promotes the production of a downstream product, while the latter involves the suppression of an earlier step which inhibits downstream products.

Feedback

There are several molecules and hormones that are of particular importance on the MCAT which participate in the feedback, allosteric regulation of enzymes in carbohydrate metabolism. 

For more in-depth content review on allosteric regulation of enzymes in carbohydrate metabolism, check out these detailed lesson notes created by top MCAT scorers. 

Important Definitions and Key Terms - Regulation of Metabolism 

Term

Definition

Allosteric regulation

When a regulatory molecule (either an activator or inhibitor) binds to an enzyme on a site that is not the active site.

Positive feedback loop

When the physiological system reinforces the changes that are occurring to increase the products of a reaction.

Negative feedback loop

When the physiological system inhibits the changes that are occurring to decrease the products of a reaction.

Additional FAQs - Regulation of Metabolism on the MCAT

What is the regulation of metabolism?

Regulation of metabolism is the modulation of enzyme activity, by hormones or metabolites of metabolism, to promote  or suppress product formation. This is required to prevent wasting energy and resources within the body, and to maintain homeostasis.

What are the four major mechanisms of metabolic regulation?

The four primary mechanisms of metabolic regulation are: 

1. Substrate availability
→ This is the concentration of substrate available. Increased substrate available may  
     activate enzymes required for their metabolism. 

2. Allosteric enzyme regulation 
→ When a regulatory molecule (either an activator or inhibitor) binds to an enzyme    
     on a site that is not the active site. 

3. Covalent enzyme modification 
→ Enzyme-catalyzed changes to an enzyme, which includes the addition or removal      
    of chemical groups of a synthesized protein.  

4. Regulation of enzyme synthesis 
→ Involves the activation or repression of gene transcription of specific enzymes.

What do I need to know about metabolic pathways on the MCAT?

Understanding the primary enzymes that get regulated, and under what conditions they get regulated (e.g. high ADP concentrations, low ATP concentrations, high pyruvate concentrations, etc.) are the most important aspects regarding the regulation of metabolic pathways.

How much of glycolysis do you need to know for the MCAT?

You should know the primary enzymes that get regulated (i.e. Hexokinase, Phosphofructokinase, and Pyruvate Kinase), their substrates and products, and under what conditions they are activated or repressed (i.e. does the steps require ATP, or produce ATP?). These enzymes are the highest yield. 

However, if you have the bandwidth, memorize all enzymes and products of glycolysis, this will only help you. There are some discrete questions that may test you on the products of other enzymes in glycolysis.

Additional Reading Links – Regulation of Metabolism on the MCAT

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