Melanie balances the world of physics with biology in Episode 10. We don’t want to break the Laws of Thermodynamics!
Melanie balances the world of physics with biology in Episode 10. We don’t want to break the Laws of Thermodynamics! (1:20). She then debunks the definition of an enzyme (3:00) while riding a rollercoaster. Don’t forget that enzymes are not used up during a reaction and are substrate and condition specific (4:00), Melanie describes a “toothpickase” hand example to dig deeper into environmental effects on enzyme function (4:55). She explains how other molecules may also compete for active site binding (5:40) in an inhibitory or regulatory way.
The Question of the Day (6:43) asks “ Which will cause a linear increase in reaction rate and why? Increasing substrate concentration? Or increasing enzyme concentration?
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Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap Enzymes and Energy
Lets Zoom out:
Unit 3 - Cellular Energetics
Topic - 3.1-3.4
Big idea - Energetics
Introduction: Metabolism is the totality of an organism's chemical reactions and is never at equilibrium. As living things, we require a constant input of energy to keep organization and complete cellular processes. A majority of your day is spent acquiring or using energy. Thanks to enzymes, you have an assist digesting that brown sugar pop tart from this morning and putting it to use.
Lets Zoom in:
We are momentarily entering the world of physics.
The first law of thermodynamics states that the energy of the universe is constant. Energy can be transferred and transformed, but it cannot be created or destroyed. The second law of thermodynamics states that during every energy transfer, some energy is unusable and is often lost as heat. Every energy transformation increases the entropy, or disorder, of the universe. Physicists can be so dramatic! But, what does this mean for biology?
OK - so if energy is being continually transferred and often lost as heat - why don’t living things run out of energy? Well, we can. A loss of energy flow or order results in death. But for the living, there is a constant requirement to take in more energy than is being used. We also need to maximize our efficiency during energy transfers (think chemical energy in the poptart used for mechanical energy of running). Living things monitor this transfer through sequential biological pathways where the product of one reaction step is often the reactant for the next.
Now that we can rest easy that we do not defy the world of physics - back to biology. In definition land, “Enzymes are biological catalysts that facilitate chemical reactions in cells by lowering the activation energy.” Yikes. It does you no good to learn a definition if there are words used in it that also need further defining. And then there you are, slowly falling down the rabbit hole of memorizing rather than understanding.
Imagine you are on a roller coaster, click -- click --- click up that first major hill. You get over the crest and plummet down the other side. The most exciting roller coasters transfer a ton of energy during the fall. This is much like chemical reactions. All molecules have energy stored in chemical bonds, with some having more energy than others. The reactants have to go up and over the hill during the formation of products. This hill is known as the activation energy. Once again: “Enzymes are biological catalysts that facilitate chemical reactions in cells by lowering the activation energy.” While less thrilling on a roller coaster, this is ideal for metabolism. Enzymes reduce how much energy is required for a chemical reaction to occur and thus, makes metabolism more efficient. Note that the difference in energy from reactants to products remains the same.
Enzymes are not used up in a reaction and are substrate and condition specific. Why? Enzymes are made of proteins - each having a unique structure for a specific function. Think back to our episode on biological molecules. Proteins are polymers made of amino acid monomers. These monomers differ in the chemistry of their R groups, which influences the manner in which the protein coils, bends and folds.
Consider the enzyme sucrase. It has a specific active site which fits the substrate sucrose, a disaccharide. This enzyme facilitates the catabolic reaction of sucrose with water into the monomers glucose and fructose. (as an aside, this is a common pattern for the enzyme to end in -ase and be named after the substrate it acts upon).
Enzymes function is influenced by environmental factors. Imagine your hand is an enzyme that needs to pick up and break flat toothpicks. Where would the active site be? Probably between your thumb and pointer finger. Under normal conditions, you are able to pick up and break toothpicks in half fairly easily. But what if you put an oven mitt over your hand? Or taped your fingers together? Or submerged your hand in ice water for a minute first? Or added round toothpicks to the pile? Enzyme rates are influenced by similar factors. They are influenced by pH, substrate concentration, temperature, and competitive molecules. In some instances, enzyme denaturation is reversible, allowing the enzyme to regain functioning. Enzymes can also be inhibited by the presence of other molecules such as poisons, pesticides, and antibiotics. If these molecules bind to an active site, they are classified as competitive inhibitors while those that bind elsewhere are called noncompetitive.
Enzyme function can be further regulated through cofactors (like magnesium) or coenzymes (like NAD+). These molecules cause confirmation changes to the active site. Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another. (Allo meaning other) An example of this is with feedback inhibition - where the end product of a metabolic pathway shuts down the pathway. Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed.
To recap….
All living things must acquire and transform energy for metabolism. These chemical reactions can be more efficient with the use of enzymes, which reduce the energy required to form products. Enzymes are made of proteins and can change shape under certain environmental conditions.
Today’s Question of the day is about reaction rate.
Question: Which will cause a linear increase in reaction rate and why? Increasing substrate concentration? Or increasing enzyme concentration?