1.7 Enzyme action Flashcards
What type of proteins are enzymes
Globular proteins that act as catalysts
What are catalysts
Alter the rate of a chemical reaction without undergoing permanent changes themselves
They can be reused repeatedly so are therefore effective in small amounts
Do enzymes make reactions happen?
No, they simply speed up reactions that already occur
Reaction eg:
Sucrose + water–> Glucose + fructose
What conditions must be satisfied for reactions like this to take place naturally
. The sucrose and water molecules must combine with a sufficient amount of energy to alter the arrangement of their atoms to form glucose and fructose
. The free energy of the products must be less than that of the substrates
. There must be an initial amount of energy for the reaction to start (activation energy)
How do enzymes work
There is an activation energy (eg a hill or barrier) which must initially be overcome before the reaction can proceed.
Enzymes lower this activation energy
So reactions can take place at lower temperatures than normal.
Why are enzymes good in the body
Enzymes enable some metabolic processes to occur rapidly at the human body temperature of 37 degrees, which is relatively low in terms of chemical reactions.
Without enzymes these reactions would proceed too slowly to sustain life
Describe the structure of enzymes
. Globular proteins
. Have a specific 3D shape that is a result of their sequence of amino acids (primary protein structure)
Describe the structure of the active site of enzymes
. They have a specific functional region (active site) which is made up of a relatively small number of amino acids.
. The site forms a small depression in the larger enzyme molecule.
. The enzyme acts on a substrate molecule, which fits into the depression forming an enzyme -substrate complex
The substrate molecule is held to the active site by bonds that temporarily form between certain Amino acids of the active site, and groups on the substrate
What holds the substrate and active site together
The substrate molecule is held to the active site by bonds that temporarily form between certain Amino acids of the active site, and groups on the substrate
What is the induced fit model of enzyme action
. The active site forms as the enzyme and substrate interact
. The proximity of the substrate ( a change in environment of the enzyme) leads to a change in the enzyme that forms the functional active site
So the enzyme is flexible and can mould itself around the substrate, despite it having a certain general shape ( but this alters when in the presence of a substrate).
Then the product molecules are released and the active site is free to accept another pair of substrate molecules, and resumes its original shape
How do enzymes lower the activation energy of a substrate
The enzyme changes shape to mould itself around the substrate.
This puts a strain on the substrate molecule, which can distort particular bonds and consequently lowers the activation energy needed to break the bond.
Describe the lock and key model of enzyme action
. Enzymes work the same way as a key activates a lock
.The substrate will only fit the active site of one particular enzyme
. Shape of substrate fits exactly into the active site of the enzyme
Limitations of the lock and key model
. Enzymes are considered to be a rigid structure
However scientists found that other molecules can bind to enzymes at sites other than the active site , which suggests the enzymes shape is being altered by the binding molecule
