Enzymes Flashcards
Define enzymes
Enzymes are biological catalysts that are mostly made up of protein. They speed up the rate of a chemical reaction, while remaining chemically unchanged at the end of the reaction.
When does enzyme ≠ protein?
Ribozymes, made of nucleic acids
How do enzymes work?
Enzymes work by lowering the activation energy of chemical reactions by providing an alternate pathway for the reaction, speeding up the rate of reaction.
A small amounts of enzymes are required since they remain chemically unchanged and can be reused to catalyse more reactions
What does activation energy refer to, and how does lowering it help?
Activation energy refers to the amount of energy required to break the existing bonds between the reactant molecules and begin the reaction.
By lowering it, a larger fraction of reactant molecules can react at any given time, speeding up the rate of reaction
What are anabolic and catabolic reactions?
Anabolic: simple to complex
Catabolic: complex to simple
What does the metabolism of an organism mean?
The sum of all the chemical (anabolic and catabolic) reactions occurring within the organism
What are substrates and what is the relationship between enzyme and substrate?
Substrates are the reactants of the reaction.
Since enzymes have a specific 3D conformation (proteins) of the active site, they are only complementary in shape to some substrates.
When the substrate fits to the active site o an enzyme, an enzyme-substrate complex formed. The catalytic action of the enzyme converts the substrate into products
What is the active site of an enzyme?
The active site is region of an enzyme where substrate molecules bind and undergo a chemical reaction.
What is the lock and key hypothesis?
The enzyme is the lock, the substrate is the key.
The active site on enzymes is where the substrate molecules can fit.
The conformation of the active site is complementary to the shape of the substrate, so only the specific molecules are able to fit into the active site.
One type of enzyme can catalyse only one type of chemical reaction, as it is only able to bind to one type of substrate.
What is the induced fit hypothesis? (More accepted)
When the conformation of the active site is not exactly complementary to the shape of the substrate.
When the substrate binds to the active site of the enzyme and causes a change in the conformation of the active site, known as induced fit.
The substrate plays a role in the final shape of the enzyme, and that the enzyme molecule and its active site is slightly flexible.
Describe what happens during an enzyme catalysed reaction
When effective collisions occur, the substrate binds to the complementary active site of the enzyme, forming the enzyme-substrate complex. The substrate is converted into products, while the enzyme remains chemically unchanged at the end of the reaction.
(The proximity and orientation of the substrates in the active site of the enzymes play a part in both hypothesis)
Describing effect of temperature on activity of an enzyme
At low temperatures the enzyme activity is low. As temperatures increase towards the optimal temperature of __, the rate of reaction increases. At temperatures above __ to __, the rate of reaction drops.
Explaining temperature on the activity of an enzyme
At low temperatures, the enzyme is inactive. The enzyme and substrate molecules possess low kinetic energy due to the low temperatures. Thus the chances of forming an enzyme-substrate complex are low, due to the low number of effective collisions between the enzyme and substrate.
As the temperature increases towards the optimal temperature, the rate of reaction increases. This is because the enzyme and substrate molecules have higher kinetic energy at higher temperatures, increasing the chances of forming an enzyme-substrate complex due to the increased number of effective collisions between enzyme and substrate.
At the optimal temperature __, the rate of reaction is the highest.
At temperatures above the optimal temperature, the rate of reaction decreases because enzyme molecules permanently denature and lose their 3D conformation of its active site, so substrates are no longer complementary to the active site and can no longer fit, so the reaction cannot proceed and the rate of reaction decreases.
The effect of pH on the activity of an enzyme
At pHs close to pH 0 and pH __, the activity of the enzyme is low but increases, and decreases from pH __ to pH __
At the extreme pHs of pH __ and __, the enzyme is permanently denatured, losing its 3D conformation of its active site and substrates can no longer fit into the active site, and the reaction can no longer proceed, so the rate of reaction is low.
At pHs that deviate from the optimal pH, the ions in the solution district the bonds that help an enzyme maintain its 3D shape, resulting in the loss of the shape of its active site.
When there is an excess of what, what is the ROR?
An excess of substrate means ROR is directly proportional to enzyme concentration (linear graph)
An excess of enzymes means the increase on substrate increases ROR only till the saturation point, where it levels out
