Ch. 4 Enzymes and Energy Flashcards
What are enzymes?
Class of proteins that serve as biological catalysts
What is the enzyme exception?
Ribozymes are made of RNA
What do enzymes do?
Increase rate of reaction
Not changed by reaction (can be used again)
Do not change nature of reaction - reaction could have occurred w/o enzyme, just much slower
Lowers activation energy of reaction
What is activation energy?
Energy required for reactants to engage in a reaction
–a barrier we have to overcome
Most molecules ____ the activation energy for a reaction.
Lack
Adding ____ increases the likelihood of a reaction occurring.
Heat
–increases rate of reaction, yet has some negative effects on cells.
____ help the reaction occur at lower temperatures.
Catalysts
Why do we have enzymes?
Because heat isn’t a great option in physiology to speed up a reaction
The function of an enzyme is dictated by its ____.
Structure
Describe the shape of enzymes.
Characteristic 3D shape or conformation, has pockets that serve as active sites in the enzyme
Enzyme reactants are called ____.
Substrates
Lock-and-key model
Substrates fit into the active site like a key to a lock
Induced-fit model
The initial fit is not always exact, but will change as the substrate moves into the active site
All enzymes end with the suffix ____.
-ase
Phosphatase?
Remove phosphate groups
Synthetase and Synthase?
Catalyze dehydration synthesis
Hydrolase?
Promote hydrolysis
Dehydrogenase?
Removes hydrogen atoms
Kinase?
Add phosphate groups
Isomerase?
Rearrange the atoms
Does an enzyme that does the same job in two different organs have the same name?
Yes
–names are given to enzymes based on function
What are isoenzymes?
Molecules that may be slightly different (in areas outside the active site)
How is enzyme activity measured?
By the rate at which substrate is converted to product
What influences enzyme activity?
- Temperature (heat makes reaction occur faster)
- pH (different enzymes activate at different pH levels)
- Cofactors and coenzymes
- Enzyme activation
- Substrate concentration (adding more substrate = reaction occurs faster)
- Possible stimulatory or inhibitory effects of products on enzyme function
Most enzymes work really well at what temperature?
37ºC (our core body temperature)
Enzymes exhibit peak activity within a ____ pH range.
Narrow
pH changes will result in what?
Enzyme conformational changes
True or False: Optimum pH reflects the pH of the fluid the enzyme is found in.
True
What are coenzymes?
Organic molecules derived from water-soluble vitamins
Larger molecules, many enzymes require these to function properly
What do coenzymes transport?
Hydrogen atoms and other small molecules between enzymes
What are cofactors?
Help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding.
Much smaller than coenzymes
What types of ions are cofactors?
Metal ions such as Ca2+, Mg2+, Mn2+, Cu2+, Zn2+
Can cofactors bind at different sites?
Yes
What is zymogen?
Enzymes, particularly of the digestive system, are often produced in an inactive form called a Zymogen that is activated when needed
Make enzymes, store them, release when needed
–ex: pepsinogen –> pepsin
Enzyme inhibition can be controlled through what?
Turnover, by which enzymes are degraded
Enzyme activation often requires ____ ____ to phosphorylate or dephosphorylate the molecule.
Additional enzymes
As the substrate concentration ____, so will the rate of the reaction until the enzyme becomes ____.
Increases; saturated
What is meant by saturated?
Every enzyme in the solution is being used
Will adding more substrate (in already saturated enzymes) increase the rate of the reaction?
No, if it’s saturated (all enzymes are being used), the reaction can’t increase
Reversible Reactions
Sometimes a single enzyme can drive a reaction in two directions, depending on the concentration of substrate/product
When one side gets higher, the other reaction reverses; the law of mass action
–wants to be in equilibrium
What are metabolic pathways?
Reactions linked together in a chain (or web)
–begin with an initial substrate and end with a final product, with many enzymatic steps along the way
Coupling a bunch of reactions together = metabolic pathway
Are few metabolic pathways branched or linear?
Few are linear
Most include branches where several products can be produced
End product inhibition
Branch points are often inhibited by a form of negative feedback in which one of the final products inhibits the branch point enzyme
Allosteric Inhibition
The product binds to the enzyme at a location away from the active site and changes the 3D conformation of the enzyme
–influencing activity, but influencing it away from the active site (still gives us structural changes)
End product in inhibition keeps the final product from ____.
Accumulating
Endergonic Reactions
Chemical reactions that require an input of energy
Products contain more free energy than the reactants (trap some energy in products)
ex: glucose –> glycogen (synthesis reaction)…stored energy in our cells
Exergonic Reactions
Releasing energy
Chemical reactions that produce energy. Products will have less free energy than the reactants.
Energy is used to make ATP for use in other endergonic reactions in the body.
ex: breaking glucose down into CO2 and water produces energy
Coupled Reactions
Energy from the environment (food) is broken down in exergonic reactions to drive the endergonic reactions in our bodies.
Energy must be stored in a usable form, ATP
Use exergonic reactions to drive endergonic reactions
