Enzymes Flashcards
What are enzymes?
Enzymes are protein molecules made by cells that act as biological catalysts and increase the rate of a chemical reaction by up to 10^12 times.
What is a catalyst?
A chemical that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction. It provides an alternate pathway with a lower activation energy.
What is the role of enzymes?
They affect both the structure and function within cells, tissues and organs…
… by speeding up reactions that would otherwise require high temps, pressure, reactant concentrations, extreme pHs.
Why are enzymes useful as biological catalysts?
They are more specific than chemical catalysts - they do not produce unwanted by-products and rarely make mistakes.
Cells which make / use enzymes can regulate their production and activity to fit the organism’s needs.
What is meant by the Vmax?
Enzymes can only increase rates of reaction up to a certain point - Vmax.
What are the two reactions enzymes can catalyse?
- anabolic (structure)
- catabolic (function)
What are anabolic reactions?
Enzymes form biological molecules that make up living tissues.
What are catabolic reactions?
Enzymes break down biological molecules - providing organisms with energy and building materials.
What is the difference between intracellular and extracellular enzymes?
- intracellular - enzymes that catalyse reactions within cells
- extracellular - enzymes that catalyse reactions outside of cells - secreted from cells
Where are intracellular enzymes found?
- free in solution (e.g. cytosol, mitochondrial matrix, stroma)
- fixed in place (on cell surface membrane / inner membranes)
What is meant by a metabolic pathway?
A series of consecutive reactions, with the use of specific enzymes.
Reactants, intermediates and products are known as metabolites.
What is an intracellular enzyme example?
Catalase - works inside cells to catalyse the breakdown of hydrogen peroxide (metabolic waste product).
Catalase consists of four polypeptide chains and a haem group with iron.
What are the examples of extracellular enzymes?
Amylase:
- produced in salivary glands, pancreas and small intestine. It acts in the mouth to digest starch to the disaccharide maltose.
Trypsin:
- made in the pancreas. Acts in the lumen of the small intestine and digests proteins by hydrolysing peptide bonds.
How do fungi, bacteria and yeast work as extracellular enzymes?
They secrete enzymes into their environment so large nutrient molecules can be digested extracellularly and absorbed.
How is an enzyme’s active site determined?
Active sites determine the enzyme’s specificity.
- consists of 6-10 amino acids - active site features and complementary substrate are determined by the R groups of these amino acids.
What is meant by enzyme-substrate complex?
The complex that forms in the active site after the reaction is complete, before the product(s) leave.
What is meant by activation energy and how do enzymes affect it?
The minimum amount of energy required for a reaction to start.
Enzymes reduce the amount of energy needed so reactions can often happen at lower temperatures - speeding up the rate of reaction.
How do enzymes work in anabolic and catabolic reactions?
- anabolic - substrates held close together, reducing repulsion and allowing them to bond more easily
- catabolic - fitting substrate into active site puts strain on the bonds, making them easier to break.
What is meant by the lock and key hypothesis?
An enzyme’s active site is complementary in shape to the substrate.
What are the issues with the lock and key hypothesis?
- does not fully explain how enzyme / substrate molecules are able to collide successfully
- collisions are random - meaning it would be difficult for the two molecules to bind in the correct way
What is the induced fit hypothesis?
When the substrate molecule fits into the active site, the active site changes shape slightly to mould itself around the substrate molecule.
- on binding, subtle R group changes provide a more precise conformation that exactly fits the substrate.
