Lesson 13/14 - enzymes Flashcards
what are enzymes?
- Enzymes are globular proteins that are catalysts
- A catalyst is a molecule that speeds up a chemical reaction (increases the rate) but remains unchanged/isn’t used up at the end of a reaction
- They’re called “biological catalysts” because they are made by living cells (all proteins)
what does the term metabolism refer to?
all the reactions of the body
what are the 2 types of metabolism (reaction of the body)
- Anabolic reactions: Building up molecules – e.g. protein synthesis (energy absorbed)
- Catabolic reactions: Breaking molecules down – e.g. digestion (energy released)
what are anabolic and catabolic reactions controlled by?
enzymes
what happens in the enzyme controlled reaction where sucrose breaks down?
water is absorbed, and glucose and fructose are produced
what are the substrates and products in the enzyme controlled reaction where sucrose breaks down?
sucrose is the substrate, glucose and fructose are the products
what happens in the enzyme controlled reaction of the condensation of glucose and fructose.
water is released, sucrose is produced
what are the key points of an enzyme?
- Globular protein (made by cells)
- Speeds up a reaction
- Is not used up
- Is not changed by the reaction
- Can be used repeatedly – therefore effective in small amounts
- Have a high turn-over (They catalyse many reactions per second)
what are the substrates and products in the enzyme controlled reaction where sucrose is produced?
glucose and fructose are the substrates, sucrose is the product
what happens during an enzyme substrate complex?
- An enzyme acts on its substrate (with which it makes temporary bonds at the active site) forming an enzyme-substrate complex
- When the reaction is complete the products are released leaving the enzyme unchanged and the enzyme ready to receive another substrate molecule
substrate definition
The specific reactant molecule
active site definition
Place on enzyme where substrate binds (fits). Correct, complementary shape for substrate molecule
catalyst definition
A molecule that speeds up a chemical reaction but remains unchanged at the end of a reaction
enzyme definition
Globular proteins that are catalysts (made by living cells)
enzyme substrate complex definition
Intermediate structure formed during an enzyme-catalysed reaction in which the substrate and enzyme bind temporarily
explain the specificity of enzymes
Each enzyme will only catalyse 1 specific reaction. Because the enzyme has a specific 3D tertiary structure, resulting in the active site having a specific shape. Therefore, the active site is only complementary to and will bind to 1 substrate to form an enzyme-substrate complex.
maltose is hydrolysed by the enzyme maltase. explain why maltase catalyses only his reaction. (3)
- the active site has a specific shape/tertiary structure/active site’ that is complementary to substrate/maltose
- only maltose can bind/fit
- to form an enzyme substrate complex
where are enzymes made?
like other proteins, inside cells
can enzymes act inside or outside of cells?
both
what are the terms for both sites of enzyme action?
Intracellular (inside cells)
Extracellular (secreted from cells)
How are enzymes secreted from cells?
by exocytosis
Example of a process enzymes would be needed for?
Digestion – e.g. amylase, made and secreted by cells in the salivary glands
what are the 2 models/theoris of enzyme action?
- The lock and key model (earlier model)
- The induced fit model (current model)
which model for enzyme action proposes that enzymes are flexible structures?
the induced fit model
Explain how enzymes use induced fit to catalyse/speed up a reaction
- Before the reaction, the active site is NOT complementary to the substrate
- As the substrate binds, the active site changes shape to better fit/become complementary to the substrate forming an enzyme-substrate complex
- This stresses/distorts the bonds in the substrate - causing the reaction to occur and the products to be released
Explain why the induced fit model is a better explanation of enzyme action than the lock and key model
- The lock and key model suggests that the active site of the enzyme is a rigid structure and that the substrate is an exact fit to the active site (1 mark)
- The induced fit model matches current observations that the active site changes shape slightly upon binding of the substrate to become a more exact fit which then allows the reaction to proceed
what is meant by the Collision theory?
In order for a reaction to take place, a substrate and enzyme must collide with each other.
Both enzyme and substrate molecules are in constant motion and collide naturally.
What important factor may affect the rate at which enzyme and substrate collide and therefore react?
Temperature - usually increases the rate.
In most living systems, temperatures above 40 degrees C cause irreversible damage to proteins (they denature)
For an enzyme to catalyse a reaction, it must…
- Come into physical contact with a substrate(s)
- The substrate must be complementary to the active site
- They must collide with enough energy and with a suitable orientation
= SUCCESSFUL COLLISION!
what is the activation energy?
the minimum amount of energy required to activate a reaction.
The minimum energy required for molecules to react (breaking existing bonds/making new ones)
How do enzymes actually speed up the rate of reactions?
They lower the activation energy of a reaction
Explain how the active site of an enzyme causes a high rate of reaction (3)
lowers activation energy
induced fit causes active site (enzyme) to change shape
so enzyme -substrate complex causes bonds to form/break
explain what determines the shape of an enzyme and how this is essential for its function
- Enzymes are proteins
- The primary structure of any protein is a particular sequence of amino acids
- The elements in the amino acid R groups determine the bonds the amino acids make with each other
- These are hydrogen bonds, disulphide bridges and ionic bonds and they hold the enzyme in its tertiary structure
- The shape of the enzyme (its tertiary structure) is very important as it determines the shape of the enzyme’s active site (where the substrate binds)
- Enzymes are specific for their substrates
- If the shape of the active site is not complementary the substrate and enzyme will not bind (and no reaction will take place – no product will be made)
- The protein chain folds into a spherical or globular shape with hydrophilic R groups on the outside of the molecule (making enzymes water soluble) – reactions take place in solution
