Human Biochemistry Enzymes
Characteristics of Enzymes Enzymes are proteins which catalyze biological chemical reactions In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzymes converts them into different molecules, called the products They are very specific due to their 3D tertiary and quaternary structure They can speed up a reaction by up to 10 7 times ie) Catalase breaks up hydrogen peroxide into hydrogen and oxygen
Inorganic Catalysts vs. Enzymes Inorganic Enzymes Example MnO2 H2O2 H2 + O2 Catalase H2O2 H2 + O2 Speed Slower Faster Temperature Wide range Mild, specific conditions needed Specificity Low High
How do Enzymes work? http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032270&showselfstudytree=true
Enzyme Action & Sucrase Enzyme sucrase breaks down a molecule of sucrose into glucose and fructose http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032271&showselfstudytree=true
Enzyme Specificity Enzymes are specific for one particular reaction or group of related reactions. Lactose Triglycerides Amylose Protein (milk sugar) (lipid) (starch) Lactase Lipase Amylase Protease
Lock & Key Model Key words: Enzyme, Substrate, Active Site, Enzyme-Substrate complex, Lock & key model, Induced fit model
Induced Fit Model
What is the difference?
How does an enzyme affect activation energy? Activation energy the amount of energy needed to trigger the reaction Without reaching the activation energy, reactions can't take place Enzymes catalyze this process by providing a reaction pathway which is lower in the amount of energy required to activate the reaction. Enzymes do NOT change the activation energy
Activation Energy
Activation Energy The amount of activation energy that is required is considerably less when enzyme is present
Factors Affecting Enzymes Temperature Substrate concentration ph Enzyme concentration Heavy Metal Ions
Temperature Normally Temperature increases the rate of reaction In the case of enzymes, there is an optimal temperature in which it operates Too far out of that range and the enzyme does not function optimally Enzyme is said to be denatured no longer a catalyst
Temperature
ph Changes in ph can disrupt bonds and 3D shape of the enzyme Enzyme is said to be denatured no longer a catalyst
ph
Heavy Metal Ions The presence of heavy-metal ions can permanently alter the tertiary structure of an enzyme. Heavy metals such as Ag +, Hg 2+, Pb 2+ have strong affinities for SH groups and replace the hydrogen atoms in these groups. As the SH group is part of the side chain of the amino acid cysteine, it is present in many enzymes, which may then be affected by heavy metals.
Substrate Concentration As [substrate] increases, so does reaction rate More substrate means more frequent collisions with enzyme Reaction rate will plateau when all the active sites are filled with substrate
Enzyme Concentration As [enzyme] increases, so does reaction rate More enzymes means more frequent collisions with substrate Reaction rate will plateau when all the active sites are filled with substrate; substrate becomes the limiting factor
What happens when an enzyme fails? TAY-SACHS DISEASE Hexosaminidase is the enzyme necessary to break down the fats in the brain and blood Lack of Hexosaminidase results in build up of fats in the brain This disease is inherited genetically FABRY DISEASE α-galactosidase is an enzyme that works in lysosomes to break down proteins, fats, nucleic acids & sugars A defect in the gene prevents the enzyme from folding properly and it cannot carry out its usual function The build up of Gb3 (its main substrate) causes damage to tissues and organs
Competitive & Non- Competitive Inhibition
Competitive Inhibition
Allosteric Inhibition
Kinetics of Enzymes Enzymes must be in contact with the substrate in order to function: 3 rate constants describe the interaction: k1 - enzyme and substrate turning into the enzymesubstrate complex k2 - the enzyme-substrate complex releases the substrate and enzyme k3 - the enzyme-substrate complex releases the product and the enzyme
Steady State The concentration of enzymes is usually tiny so we can assume that the [substrate] is much larger This means that the enzyme should always be functioning and the [ES] should be near constant
The Michaelis constant (Km) is equal to the substrate concentration at half the maximum rate of the enzyme Small Km indicates a HIGH affinity for the substrate; Vmax will be reached quickly Large Km indicates a LOW affinity for the substrate
Steady State
Try it!