Ch 4 Flashcards
Enzymes Definition
A class of proteins (exception – ribozymes are made of RNA) that serve as biological catalysts
What do enzymes do?
- Increase the rate of a reaction
- Are not changed by the reaction (so can be used again)
- Do not change the nature of the reaction – the reaction could have occurred without the enzyme, just much slower
- Lowers the activation energy of the reaction
What is activation energy?
the energy required for reactants to engage in a reaction (energy barrier we have to overcome)
• Most molecules lack the activation energy for a reaction.
- -> Adding heat increases the likelihood of are action occurring. This increases the rate of reactions, however, heat has some negative effects on cells.
- -> Catalysts help the reaction occur at lower temperatures.
Enzyme Activity
- structure dictates function
- characteristic 3D shape w/active sites
- reactants: substrates
- Measured by the rate at which substrate is converted to product
What are substrates?
fit into the active site like a key to a lock (“lock-and-key model”)
Induced-Fit Model
Sometimes the initial fit is not exact but will change as the substrate moves into the active site
Enzyme Nomenclature
- suffix: -ase
- first part of the name apply to the function
Phosphatases
remove phosphate groups
Synthetases/synthases
catalyze dehydration synthesis
Hydrolases
promote hydrolysis
Dehydrogenases
remove hydrogen atoms
Kinases
add phosphate groups
Isomerases
rearrange the atoms
Isoenzymes
-same name for enzymes w/same function in diff locations
molecules may be slightly different (in areas outside the active site) = isoenzyme
Enzyme activity influenced by….
- Temperature
- pH
- Cofactors and coenzymes
- Enzyme activation
- Substrate concentration
- Possible stimulatory or inhibitory effects of products on enzyme function
Enzymes and pH
- exhibit peak activity within a narrow pH range
- changes will result in enzyme conformational changes (like temp)
- Optimum pH reflects the pH of the fluid the enzyme is found in (ex. stomach vs. saliva vs. small intestine)
Coenzymes
organic molecules derived from water-soluble vitamins
- transport H/small molecules between enzymes
- larger
- required
Cofactors
help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding
- Cofactors are metal ions such as, Ca2+, Mg2+, Mn2+,Cu2+, Zn2+
- smaller, help form active site
Enzyme Activation
zymogen: inactive form of enzyme that is activated when needed (stored so don’t have to make again –> pepsinogen to pepsin)
-often requires additional enzymes to phosphorylate or
dephosphorylate the molecule
-inhibition can be controlled through turnover, by which enzymes are degraded
Substrate Concentration
- as substrate concentration increases, so will rate of enzyme saturation
- Adding more substrate will NOT increase the rate of the reaction
saturated
every enzyme in the solution is being used
Reversible Reactions
-enzyme can drive reaction in two different directions depending of concentration of substrate/product
the law of mass action
one side gets higher, the other reaction reverses
Metabolic Pathways
-reactions linked together in chains
-begin with an initial substrate and end with a final product,
–> w/many steps along the way
BRANCHED: where several products can be produced
