Chapter 4 - Enzymes and biological reactions Flashcards
What are the two types of metabolic reactions?
Anabolic reactions - building up molecules (E.g. protein synthesis).
Catabolic reactions - breaking molecules down.
What are metabolic pathways controlled by?
Enzymes,
What properties do enzymes show in a reaction?
- They speed up reaction.
- They’re not used up.
- They’re not changed.
- They have a high turn over rate.
- They decrease the required activation energy.
What structure does an enzyme have and what makes it soluble?
Tertiary structure folded into a spherical or globular shape. The hydrophilic R groups on the outside make it soluble.
What is the name of the site on the enzyme that has a specific 3D shape?
Active site
Where are the 3 main sites where enzymes act?
Extracellular - secreted from the cell by exocytosis.
Intracellular, in solution - act in solution inside cells.
Intracellular, membrane-bound - may be attached to membranes.
What is formed when an enzyme acts on a substrate?
An enzyme-substrate complex.
What is the basis of the lock-and-key model?
The unique shape of the active site means that an enzyme can only catalyse one type of reaction. (Enzyme specificity). The substrate is imagined fitting into the active site as a key fits into a lock. The shapes are specific to each other.
What is the basis of the induced fit model?
That the enzyme perhaps was flexible, not rigid and that the enzymes shape alters slightly to accommodate the substrate.
What is the activation energy of a reaction?
The minimum energy that must be put into a chemical system for a reaction to occur.
What are two ways of measuring the progress of an enzyme-catalysed reaction?
By measuring either the formation of product or the disappearance of substrate.
How can the shape of a graph showing an enzyme-catalysed reaction be explained?
- At first, there are many substrate molecules so many successful collisions if their is optimal conditions.
- ROR depends on no. of free active sites. Enzyme concentration is limiting factor.
- Further on, there is more product and so the substrate concentration becomes the limiting factor.
- All substrate used so line plateaus.
How will a change in temperature affect enzymes?
At low temperatures, the enzyme is inactive (reversible)
At optimum temp, enzymes have a lot of kinetic energy so the rate of reaction is at is fastest.
As you go above optimum, this energy begins to break the H bonds within, changing the 3D shape, denaturing it.
How will a change in pH affect enzymes?
Optimum pH -rate of reaction is highest.
Small changes to the optimum - Cause small reversible changes in structure and reduce activity
Extremes of pH - Denature enzymes. The charges on the aa side chains are affected by hydrogen/hydroxyl ions. It disrupts the ionic and hydrogen bonds maintaining the shape of the active site.
How do competitive inhibitors work?
They have a molecular shape complementary to the active site and similar to that of the substrate.
