2.4 Enzymes Flashcards
What are enzymes
Biological catalysts
‘Biological’ because they function in living systems
‘Catalysts’ because they speed up the rate of chemical reactions without being used up or undergoing permanent change
What type of proteins are enzymes
globular proteins with complex tertiary structures
What do enzymes control
Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
Virtually every metabolic reaction within living organisms is catalysed by an enzyme
Enzymes are therefore essential for life to exist
How are enzymes produced
Protein synthesis inside cells
Intracellular enzymes
Are produced and function inside the cell
Extracellular enzymes
Secreted by cells ad catalyse reactions outside cells
Catalase
Intracellular enzymes
Converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues
Amylase
Extra cellular enzyme
Hydrolyses starch into simple sugars
What secrets amylase
Salivary glands and the pancreas
Where is starch digested
The mouth and small intestine
Trypsin
Extracellular digestive enzyme
Breaks down proteins into peptides and amino acids
What secretes trypsin
Pancreas and small intestine
Active site
where specific substrates bind forming an enzyme-substrate complex
What can change the shape of the active site
Heat or pH
Desaturation
Extremes of heat or pH can change the shape of the active site, preventing substrate binding
What must happen in order for reaction to occur
Substrates collide with enzymes active site and this must happen at correct orientation and speed
Enzymes specificity
The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
What is the shape of the active site determined by
complex tertiary structure of the protein that makes up the enzyme:
How does structure of proteins determine shape of active site
Proteins are formed from chains of amino acids held together by peptide bonds
The order of amino acids determines the shape of an enzyme
If the order is altered, the resulting three-dimensional shape changes
Enzyme-substrate complex
An enzyme-substrate complex forms when an enzyme and its substrate join together
How long is the enzyme-substrate complex formed for
only formed temporarily before the enzyme catalyses the reaction and the product(s) are released
Lock and key hypothesis
that both enzymes and substrates were rigid structures that locked into each other very precisely
Induced-fit hypothesis
The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme
Conformational changes
The slight change in shape in order for enzyme-substrate complex to be made
What does conformational change ensure
an ideal binding arrangement between the enzyme and substrate is achieved
Why does conformational changes happen
To maximise the ability of the enzyme to catalyse the reaction
Activation energy
the amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed
How do enzymes affect activation energy
Enzymes speed up chemical reactions because they reduce the stability of bonds in the reactants
What does the destabilisation of bonds lead to
Makes it more reactive
What would happen if without enzymes
extremely high temperatures or pressures would be needed to reach the activation energy for many biological reactions