Enzymes

What are enzymes? Special proteins that coordinate the cell’s activities Important: 1)All enzymes are proteins 2)All proteins are NOT enzymes

Enzymes are Catalysts Catalysts: speed up chemical reactions but do not change as a result of the reaction ***Enzymes do not change the amount of product that is formed in a reaction

What are catalysts used for? 1)Used in industrial processes to reduce heat or pressure requirements 2)Used in living organisms –Reactions must occur at body temp and atmospheric pressure (LOW)‏ 3)Without catalysts reactions would be too slow 4)Needed to sustain life

How do enzymes work? Each chemical reaction requires a specific enzyme Enzymes must be made of something that can take many different shapes Proteins and their 4 levels of structure work well

How do enzymes work? 1)Enzymes act upon a substance called a substrate 2) The enzyme has an indent in it called the active site where the substrate can fit into, kind of like a lock and a key

How do enzymes work? Substrate fits into active site and interacts with exposed amino acids by ionic or hydrogen bonding Forms enzyme-substrate complex

The Lock and Key Model

Induced Fit Model

Summary of How enzymes work 1)Substrate ( reactant) fits into the active site of the enzyme 2)The enzyme breaks/forms bonds and releases the products 3)The enzyme can then be used again with another substrate

How do enzymes speed up a chemical reaction? Enzymes decrease the amount of energy required to start a reaction. The energy required to start a reaction is the activation energy

How enzymes speed up chemical reactions Enzymes work by lowering the activation energy –This is done by the enzyme-substrate complex –This complex has lower activation energy –Makes the reaction proceed quicker and easier

Factors that affect the activity of an enzyme 1)Temperature 2)pH 3)Amount of an enzyme 4)Amount of substrate ( like the reactant part of the chemical equation) 5)Inhibitors

Temperature –Increase temperature --> Increase movement of molecules –More collisions between substrate and enzyme –More successful conversions –Moving higher than optimum temp reduces activity Enzyme is made of protein High temperatures can denature the enzyme –Tertiary structure is changed –3D structure of enzyme changes too much for substrate to fit –Most enzymes in the human body have an optimum temperature around 40 C

pH –A change of pH means a change in H+ ions in surrounding –Affects the bonding of R-groups –Affects the shape of the enzyme –Most human enzymes have optimum at 7 (neutral)‏ –Stomach enzymes (pepsin) have optimum at 2 –Liver enzymes arginase has optimum at 10

Enzyme concentration –Enzymes are not used up during reactions –Can work effectively at low concentrations –Usually substrate molecules are in excess –Reaction rate is limited by enzyme concentration –Increased concentration --> increased reaction rate

Substrate concentration –If substrate concentration is low some enzyme sites empty –Rate of reaction will be lower –If substrate conc. is then increased --> rate increases –This increase continues until substrate is in excess Enzyme active sites are saturated with substrate

Inhibitors Inhibitors are chemicals which reduce the rate of enzyme catalyzed reactions –Alter the shape of the active site directly or indirectly 1)Non-reversible bind permanently disabling enzyme –Permanent change of tertiary structure (break disulfide bond)‏ –Always non-competitive 2)Reversible inhibitors bind temporarily to enzyme –Competitive inhibitors Similar shape to substrate and fit into active site Prevents substrate from entering enzyme –Non-competitive inhibitors Bind to other parts of the enzyme altering shape of enzyme Active site no longer fits substrate

Inhibitors